## CENTRAL VALLEY JOINT VENTURE

T EC HN ICA L 

## G UIDE T O 

## B ES T 

## M ANA GEME NT 

## P R ACT ICES FOR



## M OSQ U IT O 

## C ONT R OL IN 

## M A NAGED 

## W ETLA NDS



### Dean C. Kwasny 1 

### , Mike Wolder 2 

### , and Craig R. Isola 2

Ph ot o: Ji m Pi ckeri n g, BLM

1 Califo r n i a D e p a rtm e n t o f Fish an d G a m e , Lan d s an d Facilities Bran ch

, 181 2 N i n t h Street , Sacram en to

, CA

95 8 14

2 U

. S. Fish an d W i l d life Serv ice, Sacram en to N a tio n a l W ild l i fe Refu g e Com p lex

, 7 5 2 C o u n ty R o ad 99W

, W illow s , CA 95 988



### June 2004

### T ABLE OF 

### C ONTENTS



### Page

A C K N O W L E D G E M E N T S

... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . . . . . i i i

LIST OF TABLES.......................................................................... iv

LIST OF FI GURES......................................................................... iv

INTRODUCTION......

... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . . . 1

MANAGED W ETLAND DE S C R I P T I O N

... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . 3

WETLAND HABITAT MANAGEMENT.............................................. 4

Seasonal Wetland s.................................................................. 4

Se m i -perm a nent and Perm anent W e t l ands...................................... 5

MOSQUITO BIOLOGY................................................................... 6

Floodwater Mosquitoes............................................................ 6

Ochlerotatus melanimon

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Standing Water Mo squitoes........................................................ 6

Culex tarsa lis

... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . . . 6

Culex erythrothorax

... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . 7

Anopheles freeborni

... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . 7

MOSQUITO ABUNDANCE IN WETLAND HABITATS........................... 9

MONITORI NG MOSQUITO POPULATIONS........................................ 10

Imm a ture Stages.................................................................... 10

Adult Stages......................................................................... 10

BEST MANAGEMENT PRACTICES................................................... 11

Water Managem e nt Practices ........................................... 11

Vegetation Managem e nt Practices.

...................................... 17

Wetland Infrastructu re Maintenance.................................... 21

Wetland Restoration an d Enhancement Featu r es

..................... 23

Biological Controls........................................................ 26

COORDINATION W I TH MOSQUI TO AND VECT OR C ONTR O L

DISTRICTS.................................................................................. 28

REFERENCES AND LI TERATURE CITED.......................................... 31

A P P E N D I C E S

... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . 3 4

ii

### A CKNO WLEDGEMEN T S



### This techn i cal guide was prepared by the Central Valley Joint Venture’s

Mosquito Working Group, which includes repr es entatives f r o m the Calif ornia W a terf owl

Association, California Departm e nt of Fish and Ga m e , California Departm e nt of Health

Services, Ce ntra l Valley Joint Ventu r e, Ducks Unlim ited, Mos quito and V ector Contro l

Association of California, Natural Resources Conservati on S e rvice, Suisun Resource

Conservation District, U

. C. Davis, U.S. Fish and W ildlife Service, and W ildlife

Conservation Board.

We are extrem ely grateful to the m a n y individuals and groups that provided

inform ation on the m o sq uito Best Managem e nt Practices for the guide. Through the

practical ap plications of these practices and continuing experim e ntation, creative

solutions are being found to help reduce m o squito conflicts while providing quality

wetland habitat in the Central Valley. Although m u ch of this inform ation can be found in

other pub lis hed litera tur e , the f o cus of this guide is on techniques from th e first hand

experience of wetland managers and mosquito ab atem ent tech nician s who spend m u ch of

their tim e working in we tland hab ita ts.

This guide would not have been po ssible witho u t the en cou r agem ent and

partnership of the Mosquito and Vector C ontrol Association of Calif ornia. This

docum ent exem plif ies their comm itm ent to Inte grated Pes t Managem e nt f o r m o squitoes

and will be updated as addition a l inf o rm ation becom e s available on hab i tat-based

practices for m o squito control.

The following individuals provided co mments on the document: Donald Blake,

To m Blankinship, Dave Brown, Rob e rt Ca priola, Jim Camy, Steve Chapp e ll, Steve

Cordes, Craig Downs, Cl iff Feldheim, Dave Feliz, Alan Forkey, Jessica Groves, Mike

Higgins, Joe Hobbs, Rob Holbrook, Allan Inm a n, Gale Jirik, Sa m Johnson, Vicki

Kram er, Sharon Lawler, Greg Mensik, Ron Mc Bride, Marco Metzger, Harold Novick,

Peter Perrine, Fritz Reid, Loren Ruport, Cha dd Santerre, John Schulte, Jam e sina Scott,

Dave Sm ith, John Stroh, Joel Trum bo, Mike W o mack, and W illiam W a lton.

Special than ks to the s t af f at the Cent ral Valley Joint Venture, including Rob

Holbrook, Ruth Ostroff, and Bob Shaffer for their technical support.

Docu m e nt printed by U.S. Bureau of Reclam ation.

iii

### L IS T OF 

### T ABLES



### P a g e

Table 1. Water Managem e nt Practices to Reduce Mosquito Production in

Managed Wetland s.......................................................... 14

Table 2. Vegetation Managem e nt Prac tices to Reduce Mosquito Production

in Managed Wetlands....................................................... 20

Table 3. Wetland Infrastructure Maintenanc e Activitie s to Reduce

Mosquito Production in Managed Wetland s.......

...................... 22

Table 4. Wetland Restoration and Enhancement Featu r es to Reduce

Mosquito Production in Managed Wetland s............................. 24

Table 5. Biological Controls......................................................... 27

Table 6. Suggested Coordination Ac tivities B e tween W e tland Managers

and Mosquito and Vecto r Control Districts (MVCDs)................. 30

L IS T OF 

### F IG URES



### P a g e

Figure 1. Chronology of W e tland Loss in California.............................. 3

Figure 2. Watergrass ( Echinochloa crusgalli ) and W e tland Irrigation......... 4

Figure 3. Se m i -perm a nent W e tland.................................................. 5

Figure 4. Seasonal Wetland F l ooding and Potential Tim e Periods for

Significant Mosquito Production......................................... 9

Figure 5. Rapid Flood ing.............................................................. 12

Figure 6. Vegetation Mowing......................................................... 17

Figure 7. Vegetation Disking and Dense Bermuda Grass ( Cynodon

dactylon )..................................................................... 18

Figure 8. Faulty W a ter Control S t ructure........................................... 21

Figure 9. Wetland Swale............................................................... 23

iv

### I NTRO DUC TION



### Public attitudes about w e tla nds have greatly changed in the last few decades.

Historically, wetlands w e re regarded as im pedi ments to econo m i c progress and

“reclaim ed” for agricu ltu ral produ ction and ot her commercial uses. Today, wetlands are

valued for their habitat for fish and wildlif e, recreational opportunities, and the benefits

they provide in term s of fl ood control, water filtration, and ground water recharge.

There is g r eater awareness of the sig n ifican ce of the loss of over 95% of the Central

Valley’s historic wetlands, and a public desire to restore, protect, and m a nage these

habita ts (Ce n tra l Valley Habitat Join t Venture 19 90).

W ith m o re public inte res t in r e sto r a tion, protection, and m a na gem e nt of wetland

habitats, conservation projects have increased from a few s m a l l

, sit e -specifi c effort s t o

larger, coop erative prog ram s . Partnerships h a ve been forged between res ource agen cies,

conservation groups, and private citizens to help further wetland restoration and

protection g o als. Several lands cape s cale restoration plans have been developed

throughout California. However, as Ca lifornia becom e s m o r e urbanized and

developm ent encro aches into his t or ic ally rura l are a s, conf lic ts can ar ise f r o m public

health concerns about m o squito production in wetlands, rice fields, or other rural sources.

To address these concerns as they relate to wetla nds, this tec hnical gu ide has been

developed to provide infor m ation on habitat m a nagem e nt strategies to reduce m o sq uito

production in m a naged wetlands, and to f acilitate greater cooperation among wetland

habitat m a n g ers and Mosquito and V ector C ontrol Districts (MVCDs). T h e term , “Best

Managem e nt Practices (BMPs)” is used to de scribe habitat managem e nt strategies that

are generally defined as a practice o r com b in ation of practices determ ined to be an

effective and practical m eans for reducing m o s quito populations , production rates, or the

tim ing of ha tch. These BMPs focus on e xploitin g the eco log i cal relationships am ong

mosquitoes, their preda t o r s, and the w e tland habitats they use for breeding. In m a ny

cases, th ese practices are also beneficial to the general m a nagem e nt of wetlands and the

wildlife they support.

The BMPs identif ied in this guide are also an es se ntia l com p onent of Integ r ated

Pest Managem e nt (IPM) for m o squi toes, wh ich incorporates knowledge of m o squito

biology and the use of effective treatm ents to control m o squitoes while posing the least

risk to people and the environm ent. IPM em ploy s a variety of m o squito control m e thods

that include habitat m a n a gem e nt, biological co n t rol agents, and pesticid e applicatio n.

Ideally, BMPs can be used to lower the produc tion of m o squitoes and reduce the need for

chem ical treatm ent without significantly di srupting the ecological character, habitat

function, or wildlife us e of m a naged wetlands.

The CVJV h a s prepared this guide to pr esent a full range of BMP options specific

to m a naged wetlands. T h e BMPs have been iden tif ied f r om the scien tif ic litera t ure, a s

well as f r om practica l ap plica tions b y we tland managers and MVCDs. The extent of

their use m a y be lim ited by cost and personnel co nstraints, physical lim itations of certain

wetlands, or specif i c hab ita t and wild lif e m a nagem e nt goals. In som e instances, poten tia l

disadvantages need to be weighed before im plem entation of BMPs. BMPs to achiev e

mosquito control should not gr ea tly d i srupt the e c o logica l cha r acter or h a b ita t function of

the wetland site. Not all BMPs can be ef f

ectively im plem ented in eve r y wetland

environm ent. Som e initial inve stig ation will b e r e quired of wetland m a nagers, in

1

### cooperation with MVCDs, to iden tify those BMPs m o st applicab le to an individual site.

Prior to the implem entation of BMPs, c onsultation should be conducted w ith MVCDs

and appropriate resource agencies to determ ine th e suitability of BMPs, and to ensure

com p liance with State a nd Federal wetland regulations and conservation easem ents.

The inf o rm ation in this g u ide is appli cable to m a naged wetlan d s in the Ce ntra l

Valley of California, includi ng the Sacram ento and San Joaquin Valleys, and the DeltaSuisun regio n . It is inten d ed to be a r e f e re nce for wetland s t ewards inclu d ing: th e private

wetland owner or caretaker, Refuge or W ildlife Area m a nag e r, wetland biologist, or

mosquito an d vector con t rol techn i cian, a nd should be useful when m a king habitatrelated decisions to reduce m o squito produc tion. The guide is intended to be as

com p rehensive as possible and describe BMPs based on the best available inform ation.

As addition a l m onitoring and research is conducted, BMPs may be refined, new BMPs

m a y be developed, and p r ior i ties f o r use will b e d e term ined.

Additional copies of this technical gu ide can be o b tained by contacting th e

Central Valley Joint Venture office at (916) 414-6460.

2

### M ANAG ED 

### W ET LAN D 

### D ESC R IP TIO N



### There are few wetland ecosystem s in North America that have been m o re heavily

modified than those in C a lifornia. Massi ve flood control, water storage, and water

conveyance projects have altered the na tural hydrology that once supported over four

m illion acre s of wetlands in the Cen t ral Valley ( C entral Va lley Habita t J o int Ventu r e

1990). Today, m o st of t h e rem a ining five percent of historic wetlands in the Central

Valley require intensive m a nage m e nt , including “artificial” fl ooding. It is now the task

of wetland m a nagers to em ulate natural hydrology and recreate a dynam i c and productive

wetland system through varied flooding regim e s and periodic vege tation control.

Managed wetlands are typi cally flooded using delivered canal water, water

diverted from rivers or sloughs , or deep well pumping. W it hout the application of water,

most m a naged wetlands would rem a in dry or experience only periodic flooding in the

wettest of years. As a result, m a naged wetla nds have levees, water con t ro l stru ctu r es, and

other f eatu r e s that allow f o r rela tive l y inte nsive m a nage m e nt , m o st notably the tim ing,

depth, and duration of flooding. This infr astructure allows for habitat m a nagem e nt

practices to prom ote a variety of benefits to m a ny species of wild life (v egetation for

food and cover, adequate water quality, breedin g and resting sites )

. This capability can

also lend itself to m a nag e m e nt practices that discourage m o s quito production.

The BMPs in this docum ent were developed for use in m a naged wetlands, and are

not applicable to wetland habitats w h ere natural hydrology is stil l intact and hu m a n

intervention is m i ni m a l or nonexistent. Som e exa m ples of we tland habitats where these

BMPs are n o t applicable includ e vernal poo ls, tidal wetlands , natural seeps, and

rivers/stream s and their associated wa ter bodies (oxbow lakes, sloughs, etc.).



### C h r onol ogy of W e t l a nd Los s i n C a l i f or ni a

0 500, 000 1, 000, 000 1, 500, 000 2, 000, 000 2, 500, 000 3, 000, 000 3, 500, 000 4, 000, 000 4, 500, 000 5, 000, 000

18 50 1 875 190 0 1 925 195 0 1 9 7 5 2 0 0 0Wetland Acres

Fi gure 1. C h r o n o l o gy o f w e tl and l o ss i n C a l i f or ni a

. I n fo rm ati on base d on dat a p r o v i d ed i n t h e

Conce p t Pl a n f o r W a t e r f o wl W i nt eri n g Ha b i t a t Preser vat i o n (US F W S 19 78 ) a n d CV HJ V

Im pl em ent a ti on Pl a n (1 9 9 0 )

.



### 3

### W ET LAN D 

### H ABITA T 

### M ANAG EM EN T



### In the Central Valley, managed wetla nds are described by three m a in floo ding

regim e s; seasonal, sem i -perm a nent, and perm anent (Sm ith et al. 1995). These flooding

regim e s are distinguished by the tim i ng and duration tha t water is p r esen t on the land.

Seasonal Wetlands

Seasonal wetlands are by far the m o st abundant wetland habitat in the Central

Valley, com p rising about 85-95% of all m a nage d wetlands (C entra l Valle y Habitat Joint

Venture 1990). They are initially flooded between August and October, rem a in flood ed

throughout the winter, and are drawn down in the spring, between March and May.

Spring draw -down concentrates invertebrates in receding wetlands to prov ide forage for

m i gratory waterfowl and shorebirds and exposes mudflats that germ inate important seed

producing plants called “moist-soil” plants . Following draw- down, m o st seasonal

wetlands rem a in dry for the summ er . Seasonal wetlands are the m o st diverse and

productive type of m a naged wetland. They typically have the greatest diversity of

vegetation and water depths, num be r of speci es (both plant and anim al), and abundance

of m i gratory birds and other wetland-depe ndent w ildlife on an annual basis.

Depending on location, conditions, or habi tat objectives, seasonal wetlands m a y

require irrigation one to two m onths follo wing draw-down to bring m o ist-soil plants,

such as swamp tim othy (Heleochloa schenoides) , watergrass (Echinochloa crusgalli) , or

sm artweed (Polygonum lapathifolium )

, to m a turity and enhance their production of seed

for waterfowl and other wildlife (Naylor 2002) . Irrigation may also be employed as a

m e thod to control undesirable plant species, such as cocklebur (Ducks Unlim ited 1995a).

Depending on the spring weather conditions, typ e of m o ist-s o il vege tatio n that is

being encouraged, or the need to discourag e certain species, irrigation cou l d occur Figure 2

. Watergrass ( Echinochl o a crus galli )

and Wetl and Irri ga ti on

. We t l a nds a r e oft e n

i rri gat e d t o g r o w see d pr o duci n g pl a n t s , s u c h as

w a terg rass, to meet th e en ergetic requ irem e n ts

of

m i grat ory w a t e rfo wl a n d t o re duce cr op

d e pred atio n b y attractin g w a t e rfo w l t o w e tlan d

areas. Pho t os: Cen t ral V a lley Jo in t V e n t u r e



### 4

### anytim e from May through July, and could vary in both number and duration. Following

irrigation, when soils dry sufficiently to support heavy equipm ent, vegetation

m a nage m e nt (disking and m o wing) is conduc ted to lim it the exte nt of undesirable

vegetation and prom ote the growth of m o ist-soil plants.

Additional infor m ation on seasonal wetland m a nagem e nt can be found in A Guide

to Wetland Habitat Management in the Central Valley (Sm ith et al. 1995) and

Management of Seasonally Flood ed Impoundments for Wildlife (Fredrickson and Taylor

1982).

Semi-permanent and Permanent Wetlands

Se m i -perm a nent and perm anent wetlands com p rise only 5-15% of the total

m a naged we tlands in the Central Valley (C entral Valley Habitat Joint Venture 1990).

Se m i -perm a nent wetlands are typically flooded from October through m i d-July and

perm anent wetlands are flooded year-round. Th ese habitat types are often characterized

by a com b in ation of open water, em ergent vegetation (e.g., cattails ( Typha spp.), tules

( Scirpus acutus ), and other bulrushes), and submerge nt aquatic vegetation (e.g., horned

(Zannichellia palustris) and sago pondweed ( Potamogeton pectinatus )). T h ey provide

habita t im portan t to r e sid e nt wild lif e, a nd provide breeding and m o lting ha bita ts f o r

waterfowl at a tim e of year when m o st seasonal wetlands are dry (Ducks Unlim ited

1995b). Sem i -per m a nent wetlands are dr awn down after the br eeding season, and

m easures such as disking, m o wing, or bur ning are comm onl y used to m a nage vegetation

growth. Per m anent wetlands are typically drawn down every three to five years to

recycle nutrients and increase productivity and, in som e cas es, control undesirable fish

populations (e.g. carp). Sim ilar to other m a naged wetland types, undesirable vegetation

in perm anent wetlands is t ypically controlled through di sking, m o wing, or burning.

Figure 3

. Sem i

permanent Wetlands.

Sem i -perm a nent

wet l a nd s pr ovi de

critical h a b itat for

resid e n t w ild life at a

tim e of year when

m o st seasonal

w e tlan d s are dry.

Ph ot o: Jac k Sp arks

, CDFG



### 5

### M OSQUITO 

### B IO LOGY



### Mosquitoes are dip t eran insects with a quatic immature s t ages and an aerial adult

stage. They have four aq uatic larv al s t ages (i nstars) plus an aquatic pup al s t age. The adult

em erges from the pupal stage on to th e surface of the water, expands its w i ngs, harden s its

exoskeleton, and flies off. Depending on s easonal and environ m ental conditions and the

particular mosquito species involved, it generall y takes from three to 12 days for a m o squito

to com p lete its life from developed egg to early adult stage. In general, as am bient

tem p erature increases, the num ber of days requi red fro m hatching to em ergence as an adult

decreases. Although som e sp ecies of m o squitoes (e.g., Cule x tarsalis ), are capable of long

f lights f r om the aqua tic h a bita t, the m o squito prob lem created by a wetland will gene rally be

proportional to the distance from co ncentrations of hu m a n a nd do m e stic anim al populations.

There are four prim ary species of m o squitoes ( Ochlerotatus melanimon, Culex

tarsalis, Culex erythrothorax, Anopheles freeborni ) that can be produced in m a naged

wetlands and surrounding agricultura l lands that have been the s ubjects of control efforts by

MVCDs in the Centra l Valley. The s e f our speci es can be categorized by life history traits

into two distinct groups (floodwater mos quitoes and standing water m o sq uitoes).

Floodw a ter Mosquitoe s ( Ochlerotatus melanimon )

The life cycle of the floodwater m o s quito begins with flooding of ground that has

undergone a dry period. The summe r dry cycle in seasonal or sem i -permanent wetlands fits

the criteria f o r this species’ habitat needs. Once flooded, e ggs that were laid during the

previous dry cycle hatch, pupate, and em erge as adults. Research conducted in Merced

County foun d that Ochleratatus melanimon developed f r om f

i rst in sta r la r v ae to adu lt stage

in eight to nine days in s easonal wetlands during the last half of Septem be r (Mortenson

1963). Gravid fe m a les then return to lay their eggs singly on drying soil, in leaf litter, in

cracks in the soil, or at th e base s of grasses and other plants in areas that h a ve been flo oded

previously. Each fe m a le lays approxim ately 150 eggs per ovarian cycle. These eggs are

very drought resistant, allowing them to survive during the summer.

Floodwater mosquitoes are often the m o st abundant m o squito produced by m a naged

seasonal wetlands, especially during su mm er i rrig a tions and/o r f a ll f l oodin g. Relativ e to

other species, adult females are agg r essive a nd f eed prim arily on m a mmals. During the day,

f

e m a les will bite if distu r bed or if a host pr esents itself, but generally biting and swarm i ng

activities peak at dawn or dusk. Floodwater m o squitoes h a ve been iden tified as a p r im ary

nuisance species and as seconda ry or “bridge” vectors for Ca lifornia encephalitis virus and

western equ i ne encephalitis, and are considered m oderately effective as vectors of W e st Nile

virus.

Standing Water Mosquitoes ( Culex tarsalis, Culex erythrothorax, Ano p heles freeborni)

Culex tarsa lis

Peak num be rs of Cx. tarsalis occur in the Central Va lley during the summ er.

Fem a les lay their eggs o n the water s u rface in bu nches called rafts. Each raft contains

around 100-150 eggs, hatching about 24 hours after be ing laid. The imm a t u re stages can be

6

### found in almost any source of water except tr eeholes. During the summ e r , developm ent

fro m egg to adult takes about seven to nine da ys. Peak populations o ccur in late June or

early July, but can continue into late summer. Adults can emerge continuously throughout

the summ er and fall in areas that hav e been fl ooded for an extended period of tim e, us ually

for m o re than 2-3 weeks (i.e. ricefields, poorly drained pastures, sem i -perm a nent/perm a nent

wetlands, seasonal wetlands flooded in August, se wer treatm e nt plants, and dairy farm s).

Biting and s w arm i ng activities a r e ty pically at dawn or dusk. Adults spend daylight

hours restin g in secluded places su ch as anim al burrows. Culex ta rsalis prim arily bite birds,

but will b ite hum a ns, livestock, and o t her m a mma ls if the oppo rtunity presents itself. In

California, this species co mm only fe eds on song birds in spring and early summer, and

switches to m a mmalian f eeding in la te summ er and f a ll. This change in f eeding hab i ts f r om

birds to m a mmals, co mbined with large populati ons and the ability to travel long distances,

ma k e s Cx. t a rsalis a potent vector of som e o f California’s arboviruses. C u lex ta rsalis is

considered the prim ary vector for western eq uine encephalom y elitis virus (WEE) to hum ans

and equines, and St. Louis encephalitis virus (SL E ) to hum an s. Culex tars alis has been

identified as a prim ary vector of W e st Nile v i rus in the weste r n United Sta t es.

Culex erythrothorax

.

These m o squitoes p r efer to deposit their egg rafts am id very thick aquatic vegetation

in ponds and in the m a rgins of lakes. The larv ae can be difficult to sam p le because they are

extrem ely se nsitiv e to d i s t urbanc es (e. g . vibra tions f r om the collec t or ’s f ootsteps o r dip p er),

tend to rem a in subm erged longer than other m o squito species after being disturbed, and

prefer to stay am id the stem s of vege tation wh ere collection can be problem atic. This larval

habitat can also be difficult to treat w ith la rvicides because th e water is deep, creating a

much greater volum e to surface area ratio than co mmonly encountered for Cx. tarsalis. In

addition, the thick veg e tation can p r otect th e water surface from liquid formulations of

larv icides. Fish are no t always effective at controlling this s p ecies b ecau se they are v i sual

predators and cannot find the larvae am ong thic k growth of plants. Unlike m o st other Culex

species, some individuals of Cx. erythrothorax bite (feed) during the day. Fortunately, this

species do es not m i grate far (generally less th an 1 m ile) f r om the larv al ha bita t. It is a m a jor

pest where wetlands with deep water and a quatic vegetation occur near hum a n activity.

Culex erythrothorax is highly susceptible to WNV infec tion and m a y act as a bridge vector

of this virus in California (Goddard et al . 2002).

Anopheles freeborni

Anopheles freeborni a l so occurs in th e Centra l Va lley and is nu m e rous during the

summer, peaking in late July or Aug u st. Ricefields, and sem i -perm a nent and perm anent

wetlands are the prim ary production areas for th is species, although the immature stages are

also found in ditches, seepages, and sloughs. Fe m a les lay th eir eggs sing ly on the su rface of

the water where they hatch approxim ately 24 hour s later. On the average, it takes about 9-

12 days for An. freeborni to develop fro m egg to adult. Like Cx. tarsalis , this spe c ie s can

produce a continuous supply of newly em erged adults under the right habitat conditions.

Adults rest during the day a nd bite and swarm d u ring dusk. In autum n , fem a les enter a

physiological state called diapause, during wh ich reproduction is suspended and activity is

7

### dim i nished. They over- winter un til January, Fe b r uary, or Ma rch when th ey com e out of

diapause and seek blood m eals on warm days . After obtaining a blood meal, m a ny fe m a les

resum e their over-wintering state until April or May when they begin laying eggs once

more. The f e m a les will readily bite hum a ns and lives tock. T h is spec ies c a n be a vec t or of

m a laria in th e western U n ited States. Malar i a wa s a m a jor public he alth p r oblem in

California through the early 1900s. A co m b inati on of case detection and mosquito control

reduced tran sm ission to very low lev e ls by th e 1920s. Three m a jor outbreaks in the last 40

years have served as reminders that th e introduction of the m a laria parasite ( Plasmodium

falc iparum and P. vivax ), com b ined with presen ce of the Anopheles m o squito vectors, can

result in tran sm ission.

8

### M OSQUITO 

### A BU NDA NC E IN 

### W ETL AND 

### H ABITA T S



### Mosquito abundance reaches its peak during the flood-up of seasonal wetlands

during late su mm er and early fall (Figure 4). Because hundreds of acres of seasonal

wetlands are flooded per week, there can be a constant influx of new m o s quito cohorts,

resulting in a large sustained population of m o sq uitoes over the flood-up period. As each

wetland floods, floodwater m o squitoes ( Oc. melanimon ) can be produced initially (on

average within seven to ten days), followed by Cx. tarsalis af ter app r oxim a tely two weeks

of inundation. There is a second smaller and m u ch shorter-lived peak that is often observed

during the spring/summer irrigation of seasonal wetlands. T h is involves less acreage and is

not sustained since the irrigations are usually completed in seven to ten days. The irrigated

wetlands then revert back to a dr y period until flood- up in th e f a ll.



### J F M A M J J A S O N D

Mo n t h M o squ i t o p r oduct i on

po t e nt i a l 

### Irri g a ti o n s Fa l l Fl o o d -u p A c r e s of Fl o ode d M a na ge d S e a s on a l W e t l a n d

Figure 4

. Seas on al wetl and floodin g and p o te nti a l ti me periods for signific an t mosq uito pr oducti on

.



### Se m i -perm a nent and perm anent wetlands can produce An. freeborni and Cx. tarsalis

, but because of their lim ited acreage, stable water levels, and abundance of m o squito

predators (fish, dragonflies, and other predat ory invertebrates) th ey are typically not

considered “problem ” production areas requiri ng additional control m easures. However,

they can still be m a naged to m i ni m i ze m o s quito populations by properly m a naging water

and vegetation (Sacram ento Nati onal W ildlife Refuge Co m p l e x 2000). If water levels are

allowed to fluctuate, these wetlands can produ ce f l oodwater m o squitoes that m a y becom e a

concern.

9

### M ONITORING 

### M OSQUITO 

### P OPULA T IONS



### MVCDs determ ine m o s q uito abundance in wetlands using a variety of sam p ling

techniques. Potential breeding sites and su rrounding areas are sam p led to assess m o squito

populations and determ i n e the need for control e fforts. Treatm e nt thresholds are typically

determ ined based on m o nitoring both aquatic and aerial life stages of m o squitoes.

Immatur e Stages (aqu atic)

Larvae and / or pupae are typically s a mple d using a “dipper”, which is a 14-ounce

white cup attached to a long wooden or m e tal ha ndle. The dipper is used to determ ine the

rela tive d e ns ity of larv ae by taking s t a ndard sam p les of water f r om a potential m o squito

source. The contents are exam ined, recording m o squito num bers and species, resulting in a

“num ber per dip” index. Sa m p ling immature lif e stages of mosquitoes serves to identify

significant production sites and can help determ ine the potential need for treatm e nt. This is

done based on the quantity and speci es of larvae found (per dip), identification of the larval

instar stage, nu m b er of d a ys required for th e larvae to pupate and em erge, and proxim ity to

urban areas. Monitoring larval m o sq uito produ ction through o ut a wetlan d can help identify

problem areas where certain BMPs can be em ployed to reduce future production.

When aquatic vegetation is abundant, som e species of m o squitoes are difficult to

sam p le in their imm a ture stage. La r v al traps have been developed, but they are not widely

used. Column sa m p ling devices have been used successfully by quickly inserting a wide

pipe in to the substra t e an d then exhau s tive l y sam p ling th e water with in.

Adult Stage (flying)

The relative abundance of adult m o sq uitoes is estim a ted using light traps, carbon

dioxide-baited traps, or landing counts, depe nding on the individual MVCD’s protocol.

Traps are hu ng from trees, buildin gs, or special s t ands and us ually rem a in in the s a m e place

throughout the season and fro m year to year. L i ght trap contents are collected weekly

during the mosquito season. The total num ber of adult fem a les, by species, is divided by the

num b er of nights th e trap was activ ated, and th e index value is reported as adult fem a les per

trap night.

W ith landing counts, an observer stands with in the sam p le site and faces away from

the wind and counts the nu m b er of mosquitoes that land on his pant legs over a period of

one m i nute. The count is divided by two for a “leg count” index. This procedure is usually

done early in the m o rning or at dusk when te m p e r atures are cool and m o s quitoes are most

activ e and is repeated th ree or four tim es per site.

10

### B ES T 

### M ANA GEM E N T 

### P R ACTIC ES



### The BMPs in this docu m ent are habita t-bas e d s t ra tegie s tha t can be im plem ented

when needed for m o squito control in m a naged wetlands. These strategies represent a range

of practices that wetland m a nagers can incorp orate into existing habitat managem e nt plans

or in the design of new wetland restoration or en hancem ent projects. Id eally, BMPs can be

used to decrease the production of mosquitoes an d reduce the need for ch em ical treatm ent

without significantly disrupting th e ecological character, habitat function, or wildlife use in

m a naged we tlands. It should be reco gnized th at BMPs function as a first line of defense in

deterring m o squito production and can be used in com b ination with othe r Integ r a t ed Pest

Managem e nt (IPM) tools such as, biologica l con t rols, la rvic ides (Append ix A), and

adulticides (Appendix B) when necessary.

In m a ny cases, BMPs overlap with co mm onl y used habitat managem e nt practices to

conserve water and m a nage wetland vegetation for wildlife (Batzer and Resh 1992a, Batzer

and Resh 1992b, Resh and Schlossb erg 1996). No t all BMP s will be app r opriate for a given

wetland location or set of circum stances. Ther efore, habitat managers are encouraged to

work closely with both their local MVCD and ag ency biologists to select BMPs based on

their poten tial effectiven ess for regio n al or s ite sp ecific cond itions, and habitat m a nag e m e nt

strategies. The im ple m entation of BMPs w ill likely be lim ited by cost and personnel

constraints, potential impacts on wetland habitat, and wildlife response to these m easures.

In the follo wing section

, BMPs have been classified into fiv e catego r ies. These

categories are not listed in order of impor tance and m a y be used in com b ination.

• Water Managem e nt Practices

• Vegetation Managem e nt Practices

• Wetland Infrastructure Maintenance

• Wetland Restoration and Enhancement Features

• Biological Controls

Following each category is a table su mmarizing th e BMPs that outlines strateg i es, m o squito

control objectives, advantages, and di sadvantages (Tables 1 through 6).

Water Man agement Practices

Water m a na gem e nt is one of the wetl and m a nage r’s greatest tools for reducing

mosquito populations (T able 1). However, it re q u ires that water is readily available, o f

sufficient qu antity and q u ality, and that the c onv eyance inf r a s truc ture is a d equate to p e rm it

rapid flooding or drainage. In som e instances , circum stances outside the control of wetland

m a nagers may lim it the ability to implem ent wa ter m a nagement BMPs. Such circum stances

m a y include when agriculture drain water or delivered water is available for flooding,

lim ited water quantity or poor water quality, and undersized water delivery or drainage

inf r astru c tu r e . In m a naged wetlands where th es e lim itations a r e not an iss u e, the f o llo wing

water m a nagem e nt practices should be considered.

Timing of F l ooding : The tim ing of wetland floodi ng can greatly influence

mosquito production (Fanara and Mulla 1974, Ba tzer and Resh 1992a). Delayed flooding

m a y reduce mosquito production by shifting floo ding schedules later in the year, when

11

### tem p eratures are cooler and m o squito producti on is less of a problem . Delayed flooding

should be considered for wetlands with histor ic m o squito problem s and those in close

proxim ity to urban areas. However, delayed flooding m eans that less wetland habitat is

available for wildlife during tim es of the year such as August and September when wetlands

are particularly lim ited. Delayed flooding m a y also have limited app lic a b ility f o r so m e

properties th at ar e requ ir ed to tak e water on a “when available” schedu le and have little

control over the tim i ng o f flooding. Delayed flooding m a y b e especially difficult for State

and Federal areas that are obligated to provide “early” habitat to reduce crop depredation by

waterf owl.

Given the lim ited feasibility of delayed flooding on som e pro p erties, phased flooding

of wetlands m a y be useful to allow habitat m a nagers to provide som e level of early flooded

habitat while delaying flooding on a portion of a property. P h ased flooding involves

flooding habitat throughout the fall and winter in proportion to wildlife need and takes into

consideration other wetland habitat that m a y be available in surrounding areas.

For wetlands that are floode d early (August - early Septem ber) or in close proxim ity

to urban areas, the use of vegetation and wate r m a nagem e nt BMPs should be a high priority

(Tables 1 and 2).

BMPs: Delayed or phased fall flooding, Ea rly fall flood-up planning (see Table 1 for

additional explanation)

Speed of Wetland Flooding : As a general rule, the faster water can be applied

during fall flooding and s p ring/summer irrig a tion, the fewer g e nerations o f m o squitoes will

be hatched. Slow feather-edge flooding, a lthough beneficial to fo raging waterbirds, can

produce m u ltiple, stagg e red hatches of floodwater m o squitoes and, if treatm e nt is necessary,

often requires MVCDs to visit wetlands over a nu m b er of days for contro l activities (Garcia

and Des Rochers 1983). Such an intensive tr eatm ent effort is expensive and results in

additional disturbance to wildlife.

BMPs: Rapid fall flooding, Rapid irrigat ion (see Table 1 for additional explanation)

Fi gure 5. Rapi d

Flooding. Rapid

fl o odi ng sh o u l d be

u s ed to red u ce th e

p o t en tial for

m u l tip le h a tches of

m o squitoes ca use d

by sl o w feat he r-e dge

fl o odi ng

. Ph ot o:

USF W S



### Water Control : Once wetlands have been flooded, it is im portant for wetland

m a nagers to ensure that pond elevations do not fluctuate except during planned draw-down

or periods of low m o squito pro duction (i.e. winter m onths). Fl uctuating water leve ls te nd to

12

### expose wetland edges to drying and provide suit able habitat for floodwater m o squitoes to

lay eggs (Garcia and Des Rochers 1983). W h en water levels are subsequ e ntly rais ed, a new

cohort of mosquitoes m a y be hatched. W a ter levels should be m a intained by checking water

levels frequently, and adding water to offset any losses. A constant m a intenance flow of

water will also help m a intain s t eady wate r levels, im prove wa ter quality, and reduce

stagnation.

If possible, wetlands can be flooded to deeper water depths during the fall and

allowed to recede durin g the cooler winter m onths to provid e shallow water d e pths f o r

foraging waterbirds. Deeper water depths (24 inches) at initial flooding have been shown to

significan tly reduce m o squito dens ities at Grizzly Island W ildlife Area (B atzer and Resh

1992a, b).

When flooding wetlands, water sources cont aining m o squito predators should be

used to he lp coloniz e wetlands with p r edac ious in sects o r m o squitof i sh th a t are p a ssiv e ly

transpo r ted by water fro m upstream locati ons (C ollins and Resh 1989). Predator

populations can be m a intained in perm anent wa terways used to flood seasonal wetlands. In

the Suisun Marsh, where water is readily available for floodi ng, seasonal wetlands are often

initially flooded, and if mosquitoes becom e abu ndant, water levels are drawn down to

concentrate mosquito larvae in ditches for biol ogical con t rol, larvic ide trea tm ent, or to

drown larvae through turbulen t water m ove m e nt (Chappell pers. comm ). Following this

action, wetlands are immediately re-flooded.

BMPs: Maintain stab le water lev e ls, Circ ulate water, Use de ep initial flo oding,

Subsurface irrigate, Utilize water sources with mosquito predators for flooding, Flood and

drain wetland (see Table 1 for additional explanation)

Frequency and Duration of Irrigation : Spring and summer irrigation is a comm on

wetland m a nagem e nt practice used to increase seed production and biom a ss of m o ist-soil

plants (Naylor 2002), an d reduce co mpetition fro m undesirable plan ts in seasonal wetlands.

The need to irrigate seasonal wetlands s hould be assessed closely by wetland m a nage rs.

During years with above averag e spring precip itation, irrigatio ns m a y not be necessary to

m a xi m i ze moist-soil plant production. W h en po ssible, m a nagers should shorten the duration

of irrigation to 4 to 10 days to reduce the likelihood of hatc hing floodwater m o squitoes and

elim inate th e possibility of creating h a bita t f o r standing water mosquitoes. However, shorter

irrigations m a y not always be f easible, espe cia l ly when gro w ing m o re water in tens ive plan ts

such as watergrass and sm artweed, or when conducting flooding to control undesirable plant

species. In the case of weed control, plants should be m o nitored and water held only long

enough to elim inate weeds. The necessary tim ing can be determ ined wh en weeds have

turned black or have disintegrated. F i nall y, following wetland irrigations, water should be

drawn down into waterways containing m o squito predato r s th at can con s u m e any mosquito

larvae which m a y have hatched.

BMPs: Reduce number of irrigations, Use rapi d irrigation, Draw down a nd irrigate

in early spring, Irriga te prior to fie ld comple tely drying, Drain irriga tion water into d i tches

or other water sources w ith mosquito predat ors, Use subsurface irrigation (see Table 1 for

additional explanation)

13Table 1. Water Management Practices to reduce mosquito production in managed wetlands.Best ManagementPracticeStrategiesMosquitoControl ObjectiveAdvantagesDisadvantagesDelayed or phasedfallfloodingDelay flooding ofsomewetlandunitsuntil later in the fall.Delayfloodingunits with greatesthistorical mosquitoproductionand/orthose closest tourbanareas.To delayinitiation offloodwatermosquito productionin seasonalwetlandsbyreducingthe amountof mosquitohabitat availableduringoptimalbreedingconditions (warmsummer/earlyfall weather).Reduce the timeavailable for standingwatermosquito productionin seasonalwetlands.Depending onflooddate,canreducethe needoramount ofadditional treatment. Delayedfloodingcanprovide “new”foodresourcesforwildlife later intheseason when wetlandsare finallyflooded.Reducesthe amount ofhabitatfor earlyfall migrants andotherwetland-dependent species,andmay increasepotential forwaterfowl depredation onagricultural crops(especiallyrice).Floodingis oftendictatedby water availability orcontractualdates fordelivery.Delayedfloodingmaystillproducemosquitoes inwarmyears. Privatehunting clubscan’tlease blinds that aren’t flooded.Early fall flood-upplanningApply BMPs towetlandsidentified for early flooding.Tothe extentpossible, areastargetedfor earlyfall floodingshouldnotbenearurban centers and shouldnot havea historyofheavymosquitoproduction.To reducethe earlyseasonproduction ofmosquitoes ortoreduce their encroachment onurban areas.Allows for theprovision ofearlyfloodedhabitat while minimizingmosquito productionandconflicts withurban areas.Someadditional effortrequiredto monitor andidentify suitableareas.Requiresthe extensiveuseof BMPs to ensure mosquitoesare not produced.Rapid fall floodingFloodwetlandunit asfast aspossible. Coordinatefloodingwithneighbors or waterdistricttomaximize flood-uprate.To minimize number ofmosquitocohorts hatchingonagiven area.Reducesthe need formultipletreatments neededbysynchronizing larvaldevelopment andadultemergence.Inturn, reduceswildlife disturbance byMVCDs.Requires coordination& abilitytofloodquickly. Reducesslow,feather-edgefloodingthat isheavily utilizedby waterbirds.Rapid irrigation4-10dayirrigation (fromtimewater enters the pond tocompletedraw-down).Shorten irrigationperiodtoreduce time available formosquitoes (especiallyCulextarsalisandAnopheles freeborni)to complete lifecycle.Provides somelevel ofwetlandirrigationwhile reducing thetimeavailable for mosquitoes tocomplete lifecycle.Requires ability to rapidly flood& drain wetland.Iffloodingisusedfor weedcontrol,rapidirrigation may notbefeasible.Table 1. Water Management Practices to reduce mosquito production in managed wetlands, ContinuedBest ManagementPracticeStrategiesMosquitoControl ObjectiveAdvantagesDisadvantagesMaintain stable waterlevel (summerand earlyfall flooding)Ensureconstantflowofwaterintopond to reduce waterfluctuation duetoevaporation,transpiration,outflow, andseepage.Toreduce conditionsforadditional floodwater mosquitoproduction insummer and fall.Provides astable wetlandenvironment forbreedingwildlifeduring springandsummer. Discouragesundesiredexcessivevegetative growthwhich could alsobecomeadditional mosquito breedingsubstrate.Requires regular monitoringandadjustmentstowater controlstructures.Maybedifficult ifwater availability is intermittentorunreliable.Reducesmudflathabitat that is attractive toshorebirdsandwaterfowl.Water circulationProvide a constant flowofwaterequal todischargeat drainstructure.To keepwater freshandmovingto deter stagnant conditionsformosquito production; reduceswater level fluctuationandpotential productionoffloodwater mosquitoes.Discourageswarmwaterconditions associated with avianbotulismoutbreaks.Requires landownertopurchaseadditional “maintenance”water.May bedifficult if wateravailability is intermittent orunreliable.Deep initial flooding(18-24”)Flood wetlandasdeepaspossible at initial flood-up.To reduce shallow waterhabitatformosquitobreeding. Mayprovide moreopen waterbyover-toppingvegetation,therebyfacilitatingmosquitopredation orwind action that drowns larvae.Potentially slows mosquitodevelopment byeliminatingwarm,shallow water habitat.Requires additionalwater andinfrastructureadequate toflooddeeply. Reduces shallowwaterforaginghabitat for shorebirdsand waterfowl.Utilize water sourceswith mosquitopredators for floodingwetlandsFlood wetlandswith watersourcescontaining mosquitofishorother invertebratepredators.Waterfrompermanent pondscanbeusedtopassively introducemosquito predators.Toinoculate newly floodedwetlands with mosquitopredators.Mayestablish mosquito predatorsfaster than natural colonization.Requires source ofwaterwithalready established mosquitopredators.Notapplicable towetlandsflooded with wellwater.Drain irrigation waterinto ditches or otherwater bodies withabundant mosquitopredatorsDrain irrigationwater intolocations withmosquitopredators asopposedto adjacentseasonal wetland ordryfields.To reducethe amount oflarvaethroughnaturalpredation andminimize the number of adultsthat emerge.Alreadya common wetlandmanagement practice.Must haveditchorwater bodywith establishedpredatorpopulationavailable to acceptdrain water.Flood &drainwetlandFlood wetlandandhatchlarvaeinpond.Drain wetlandtoborrowor other ditch wherelarvae canbe easily treated,drowned inmovingwater,orconsumed bypredators.Immediately reflood wetland.Hatches mosquito larvae andmoves themto a smaller areafortreatment before they can emergeas adults.Can eliminate or reducetheneedfor additionalmosquito controlefforts.Additional costto purchase waterto re-floodwetland.Timing iscritical. Requires monitoringandis labor intensive.Table 1. Water Management Practices to reduce mosquito production in managed wetlands, ContinuedBest ManagementPracticeStrategiesMosquitoControl ObjectiveAdvantagesDisadvantagesReducenumber ofirrigationsEvaluatenecessity of irrigation,especially multipleirrigations,based onspringhabitatconditions andplant growth.Eliminate irrigationswhenfeasible.To eliminate unneededadditionalirrigations whichcould providepotential habitat for mosquitoes.Reduces potential needforadditional mosquito control.Saveswaterand manpower costs.Discouragesexcessivegrowthofundesirable vegetation (i.e.jointandbermudagrass)Mayreduce seedproductionorplantbiomass with less irrigation.Early springdrawdownandirrigationDraw-downwetland in lateMarchor earlyApril.Irrigate inlate April or early May whenweather is cooler andmosquitoesare lessof aproblem.To reduce needforirrigation inJune, July, and August,whenpotential for mosquito productionwouldbehigher.Wetlandirrigation canbeaccomplished withoutcreatingpotential mosquitoproblems.May allow moist-soilplants totake advantage ofnaturalrainfallduringthe spring.Reduces shallowwetland habitatformigratory shorebirds andwaterfowl inApril and May,duringamajormigrationperiod.Newlygerminated wetland plantsmay be impactedby coldweatherconditions. May stimulategerminationand growthofundesirable wetland plants.Don’tlet fieldcompletely dry andcrack between springdraw-down andirrigationIrrigate wetland beforesoilcompletely dries.Toeliminate necessarydryingperiodforfloodwater mosquitoto lay eggs.May reduce mosquitoesproducedfromirrigationRequires closemonitoringofsoilmoisture to correctly timeirrigation.SubsurfaceirrigationMaintainhigh ground waterlevels bykeepingboat channelsor deepswalespermanentlyflooded.To reduceamount ofirrigationwaterduringmosquito breedingseason.Reduceneedforsurfaceirrigationwhile maintaining soilmoisture to promotemoist-soilplant production.Requires deep swales orboatchannelstobe effective.Requiresadditionalpipes in channelsforequipment access. Maynotproduce intended irrigationresultif water table isnaturally low.Requiresthat water bemaintained longerthan normalinswales.May promote unwantedvegetationgrowth inswalesorpromoteirrigation ofnon-targetplants inwetland.

### Vegetation Management Practices

Wetland m a nagers com m only use vegeta tion co ntrol to alter plant sp ecie s

com position and abundance to influence wildlife us e (Sm ith et al. 1995). As the vegetative

community in a wetland changes through tim e, unde sirable species inevitably encroach into

wetland hab ita ts. Som e species m a y be relativ ely benign, while others m a y be problem atic,

reducing habitat diversity or crowding out plan ts im portant as wildlif e f o r a ge or cove r

. Vegetation is also an important habitat re quirem ent for m o squ itoes and can im prove

mosquito survivorship by providing refuge from predators (Walton and Mulla 1989) and

abundant food resources for larvae. Vegetation can also increase m o squito developmental

rates by raising water temperatures (Collins and Resh 1989). To m a nage the vegetative

community to benef it wildlif e, wetlan d m a na gers use a num be r of techniques, including

mowing, burning, disking, and grazing. Thes e habitat m a nagem e nt practices can be used

alone or in co m b ination and can also be used to reduce m o sq uito production (Table 2).

Any m a nagem e nt action that a lte rs th e com position of wetland vegeta tion m a y create

either benefits or detrim e n ts to wildlif e. Th e decision to conduct such operations should be

determ ined by the m a nagem e nt objectives of an individual habitat m a nager. Site specific

characteristics, habitat m a nagem e nt objectives, co st, and recreational use (e.g., hunter

access ) all h a ve to be carefully considered in v e g e tation m a nagem e nt plans. Typically, any

vegeta tion c ontrol m easure will resu lt in the sho r t-term loss of cover f o r wildlif e. Su ch

com p ro m i se s have to be weighed in term s of th e long-term benefits they provide for wildlife

resources versus the ancillary benefits they prov ide f o r m o squito con t rol.

Mow i ng : Mowing is co mm only used to create open water habitat for shorebirds and

waterfowl prior to flooding seasonal wetlands . Mowing to create open water provides

opportunities for the biological c ontrol of m o squitoes and enha nces the effectiveness of

pesticides by allowing greater saturation of m o sq uito habitats. Experim e ntal m o wing of

approxim a tely 50% of a wetland has been show n to reduce the density of mosquitoes and

concentrate their dis t rib u tion while increas ing de nsities of in verteb rates that are cons um ed

by waterfowl (Batzer and Resh 1992a). Sim ilarly, Garcia and Des Rochers (1984) found

Fi gure 6. Ve g e ta tion

Mow i n g

. Mo w i n g

can be use d to create

ope n wat e r ha b i t a t

and re duce m o squit o

d e nsities. If mo squ ito

co n t ro l is n ecessary,

m o wi ng ca n

conce n trate

m o squi t o es a n d

enha nce pest i c i d e

appl i cat i o n by

allo w i ng b e tter

penet r at i o n o f

veget a t i o n. P h ot o:

Jack Spa r ks, C D FG



### 17

### that seasonal wetlands mowed with a 50% plan t-cover ratio enhanced wind action that

moved m o s quito larvae to wetland edges where treat m e nt efforts could then be concentrated.

The benefits of m o wing, unlik e burning or disking, tend to be short term and require

that the practice be im plem ented on an annua l basis. Mowing m a y also leave residual

m a tter that, when flooded, provides habita t for mosquitoes (Brown pers. comm ).

Burning : Controlled bu rning, where and when feasib le, can effectively control

vegeta tion. Burning, esp ecia lly when imm e diately f o llowed with disking

, can of f

e r multip le

year con t rol of m o squitoes, reduces vegetation used by m o sq uitoes f o r br eeding ac tiv ities,

and also directly results in the kill of mosqu ito eg gs due to high tem p eratures asso ciated

with fire (Resh and Schlo ssberg 1996, W h ittle et al. 1993). Burning releas es nutrients stored

in plant m a terials and m a kes them available to benefit plant and invertebrate production

during the following flooding cycle. However, due to liability issue s , dif f i culty with

perm itting, a i r qua lity, an d the coord i nation that must take place with m u ltip le agen cies prio r

to its im plem entation, burning has lim ited applic ability f o r Centra l Valle y wetlands,

especially th ose on private land s.

Disk ing : Disking is com m only used by habitat managers to reduce dense stands of

em ergent or undesirable vegetation, and provide favorable co nditions f o r the es tablish m ent

of

m o ist-soil plants cons um ed by wa terfowl. Disking, unlike mowing, tends to change the

vegetation co m position of a wetland and provide s a m o re perm anent m e a n s of controlling

vegetation. Disking has also been shown to significantly re duce densities of m o squitoes

over m u ltiple years, incr ease th e den s ities of m a croinver t eb ra tes im portan t in th e die t s of

waterfowl, and encourag e the replacem ent of less desirable vegetation by moist-soil plants

(Resh and Schlossberg 1996). The benefit of disking can often be enhanced by first

mowing or burning vegetation targe t e d for control.

Haying and Graz ing : Agricultural practices su ch as haying and grazing m a y also

be useful to control wetland ve geta tion. However, little inf o r m ation is availab l e on th eir

ef

f

ectivenes s as m o squito contro l m e asures. Hay i ng, while f u nctiona lly s i m ilar to m o wing,

m a y provide the sam e mosquito control benefi ts. Haying has the poten tial added benefit of

rem oving cut plan t m a terial that m a y decay a nd n e gativ ely affect water qu ality, thereb y

increasing mosquito production (Brown, pers. co mm ). Ho wever, haying rem oves valuable Figure 7

. Ve g e ta ti on Di s k i n g and De nse B ermud a Gr ass ( Cyno do n da ctylo n ). De nse s t ands o f berm uda

grass are known to ha rbor m o squit o es (Ga r cia and Des R o c h ers 1 9 83 ). Be rm uda g r ass al so t e nds t o l i m it

habi t a t di ver s i t y i n seas onal w e t l a nds a n d i s t a rget e d f o r c o n t rol by wet l a n d m a nager usi n g di s k i n g. Ph ot o :

J a c k S p ar ks

, CD FG an d US FW S



### 18

### seed resources consum e d by wildlife and interru p t s the cycle of nutrient releas e back into

wetland environm ents. In addition, haying ha s lim ited applic ability in m o st wetland

environm ents because of the relative rem o te ness of wetlands from agricultural operations,

difficulty of running haying equipm e n t in unlevel ed wetland terrain, and low palatability of

wetland veg e tation as liv estock f o rag e

. Grazing is frequently used to reduce plan t biom a ss in wetlands and provide short

grass and open water habitats for shorebirds and w a terfowl. However, grazing anim als

require sources of water for drinking and often irrigated grasslands for forage. W a ter used

to m eet thes e needs m a y provide add ition a l hab i tats f o r m o squitoes. Fur t herm ore, grazing

anim als can crea te wallo ws or depres sions in m o ist wetland te rrain tha t tr a p water and crea te

additional m i crohab ita ts f o r m o squitoes (Brown, pers. comm.). Addition a l res ear ch n eeds to

be conducted to determ ine the usefulness of grazing as a m o s quito reduction tool.

19Table 2. Vegetation managementpractices to reduce mosquito production in managed wetlands.Best ManagementPracticeStrategiesMosquitoControl ObjectiveAdvantagesDisadvantagesMowingMow undesirableorovergrownvegetation that serves asmosquito breedingsubstratepriorto flooding.To reduce standingvegetationthat mosquitoescan use for egglaying and larval development.To createopen water habitat thatallowsmosquito predators (fish,invertebrates,birds)better accessto larvae and potentiallymorewaveactiontodrown mosquitolarvae.Improveswildlife habitat byproviding open-water.Effects are largely temporary,somust beconductedannually.Overusecould be detrimentaltosomespecies ofwildlife and nontarget invertebrates. Mowedvegetation may floatprovidingmosquito habitatanddecompositionmay affect waterquality.BurningControlled burnofundesirableorovergrownvegetation that mayprovide mosquitobreedingsubstrate.See mowing. Can alsokillmosquito eggs.See mowing.Requiresburnpermit. Liabilityconcerns.Mostlandowners arenot adequatelypreparedtoconduct a controlled burn.Special consideration shouldbetaken aroundplastic pipesorwater controlstructures. Overusecould be detrimentaltosomespeciesof wildlife andnon-targetinvertebrates.DiskingDiscundesirable orovergrownvegetation that mayprovidemosquito breedingsubstrate.See mowing.See mowing.Canprovidelonger-termcontrol ofundesirable vegetation byitselfor in conjunction with othermanagement practices.Creates walkingproblemsforhunters.Overuse could bedetrimental to somespecies ofwildlife and non-targetinvertebrates.HayingMowand bale undesirable orovergrownvegetation that mayprovide mosquitobreedingsubstrate.Seemowing. Also removesvegetation after cutting.Dual benefits ofimprovinghabitat and reducing mosquitobreedingsubstrate. Removal ofmowed vegetationfurtherdecreasesmosquito breedingsubstrate andmay improvewaterquality.Overusecould be detrimentaltosomespecies ofwildlife and nontarget invertebrates. Removesseed that winteringwaterfowlforageon. Expensive.Oftendifficult tofindsomeone tobaleandhaul plant material.Selective GrazingSummer-Fall grazing.Shortduration,highintensitygrazing.To reduce standingvegetationthat provides habitat formosquitoes.Relatively inexpensive.Irrigation forgrass and/orlivestock watering mayexacerbate mosquitoproduction.Livestock tendtoforageonplants that produceseedforwaterfowl.Livestock maydamage leveesorditches.

### Wetland In frastruc tur e Maintena nce

Wetland infrastructure is the foundation for habitat m a nage m e nt. A properly

functioning water delivery and drainage system

, well m a intained levee s , corre ctly op erating

water control structures, and efficient pu m p s are key to avoiding the unnecessary production

of m o squitoes through simple neglect (Table 3). Tim e and money invested in these

proactive maintenance activities will reduce m o squito production and help landowners avoid

additional costs of controlling m o squitoes a nd unwanted vegetation when fall flooding or

irrigating wetlands.

Levee and Water Control Structu re Inspectio n and Repair : Levees and water

control structures should be inspected on an annual basis to identify problem areas that m a y

inadvertently leak water and produce m o squitoes . This includes identifying weak spots or

rodent dam a ge in levees that m a y seep wa ter during flooding. W a ter control structures

should be water-tight and properly s ealed to prevent seep ag e.

Ditch and Sw ale Cleaning : Vegetation in wate r delive r y ditches and swales can be

problem atic by creating habitat for mosquitoes or by sim p ly im peding the flow of wa ter that

facilitates rapid flooding or drainage. Typi cal m a intenan ce ac tivitie s of water d e liv ery and

drainage ditches include the use of herbicid es or periodic dredging to remove problem

vegetation that inhibits water flow. Ditches a nd swales should be cut to grade to prevent the

uninten tional trapping of water. Likewise, silt th at accum u lates in front of outlet structures

should be removed so it does not trap water in drainage swales.

Fi gure 8. Faulty W a ter

Contr o l Struc t ure.

D e fectiv e w a ter co n t ro l

structures should be

replace d with s t ructures

th at can b e com p le tely

sealed to preve n t wate r

seepa g e. Phot o: USFWS



### Pump Tests and Repair : If wetland m a nagers use pum ps fo r flooding, periodic

pu m p testing should be conducted to m a ke sure pu m p s are operating at optim u m e ffi ciency.

This will en sure tha t pu mps are pro v iding m a ximum output, and will f a c ilitate rap i d

flooding.

21Table 3. Wetland infrastructure maintenance activities used to reduce mosquito production in managed wetlands.Best ManagementPracticeStrategiesMosquitoControl ObjectiveAdvantagesDisadvantagesLevee Inspection&RepairWalk or drivelevees,flagproblemspots, repairas needed.Consider design elements toimprove integrity of levee (seelevee designinTable4).To reducemosquitohabitat/production causedbyseepage intoadjacentfieldsordry ponds.Allowsforearlyidentification ofproblemspots.Helps conservewaterandreduces growth ofunwantedvegetation.Requires annualmonitoringandfunding for repairs.Water ControlStructure Inspection,Repair, &CleaningInspect structures and repairorreplace as needed.Remove siltand vegetationbuild-up infrontofstructures. Adequatelyclose,boardor mud-upcontrols.To reducemosquitohabitat/production causedbyseepage intoadjacentpondsordrainage ditches. Remove siltblockages thatmaytrap waterandimpede drainage.Enhanceswater managementcapabilities and limits unwantedvegetation orstandingwater.Requires annualmonitoringandfunding for cleaningorrepair.Ditch CleaningPeriodically remove silt orvegetationfromditches tomaintain efficient waterdeliveryand drainage.Toallow for rapidflooding/drainage &reducevegetation substrate forbreedingmosquitoes.Enhanceswater managementcapabilities and limits unwantedvegetation orstandingwater.Requires funding for ditchcleaning.Excessive vegetationremoval onditchbanks can resultin negative impacts to nestingbirds andotherwildlife.Pump Tests &RepairTest pumpefficiency and makeany necessaryrepairs tomaximize output.Couldidentifyoutput problemsand if corrected, allow managersto flood morerapidly.Maypromote faster irrigationand flood-upif outputcan beimproved.Requirespumptest. Maybecostly to repair or replacepump/well.

### Wetland Restoration and Enha ncement Features

All well p l a nned wetlan d resto r ation and e nhancem ent projects begin with an initial

survey and design phase. It is during this pha se that landowners and restoration biologists

have the opportunity to discuss design feat ures w ith MVCDs and incorpo r ate BMPs to

reduce m o squito production. Tim e spent at the design stage can save thousands of dollars in

annual operation and m a inten a nce costs and prevents prob lem s resulting from poor water

m a nage m e nt and unintended m o squito produc tion. W e tland design typically focuses on

aspects of water control that prom ote vegetation b e neficial to wildlife, con s erve water, and

allow f o r pe riodic vegetation con t ro l. In turn, wa ter con t ro l is also an im portan t m o squito

BMP (Sacram ento-Yolo Mosquito and Vector C ontrol District 1995, Contra Costa Mosquito

and Vector Control District 2001).

Wetland design features to reduce mosquito production : Wetland design features

that reduce mosquito production include indepe ndent flooding and drainage capabilities of

wetland units, size considerations in the design of wetland units to facilitate rapid flooding,

and the incorporation of design features that promote habitats for m o squito predators and

allow thos e predato r s access to m o squitoes (Table 4). W a ter delivery ditches, water control

struc t ures, a nd levees sh ould be des i gned and bu ilt to spec if ication s tha t prevent win d and

water erosio n, provide equipm ent access for m a intenance activities, and reduce dam a ge

caused by b u rrowing an im als (Table 4). These d e sign f eatu r es will f a c ilitate o t her m o squito

BMPs such as water and vegetation m a nage m e nt practices, in frastructure m a intenance, and

natural m o s quito predation.

BMPs: Independent water management , Adequately sized water control

structu r es, S w ale construction, Wetland size con s ideration, Ditch design , Levee design &

compaction, Deep channels or basins constr ucted in seasonal wetlands, Permanent water

reservo i r th at floods into seasonal wetlands (fo r addition a l explanation see Table 4)

Figure 9. Wetl and

Swale. Swales can

be desi g n e d i n t o

r e stor atio n or

enha ncem ent

projects to

facilitate rap i d

fl o odi ng an d

rem ove st an di n g

water d u rin g s p ri ng

dra w

- d ow n. P h ot o:

Chad d Sant er r e

, CW A



### 23Table 4. Wetland restoration and enhancement featuresto reduce mosquito production in managed wetlands.Best ManagementPracticeStrategiesMosquitoControl ObjectiveAdvantagesDisadvantagesIndependent watermanagementTo the extentpossible,designwetland projects to includeindependent inlets and outlets foreach wetland unit.Toreduce theneed to movewater throughmultiple wetlandunitswhenfloodingorirrigatingtarget areas.This can reducethenumber ofmosquitoesproducedper floodevent.Creates wetlandunits that arehydrologicallydistinct fromoneanotherallowingfordiversewetlandmanagement.May require additionalwatercontrol structures andditches tobe constructedand maintained.Increasesrestoration costs andcomplexityofmanagement.Adequately sized watercontrol structuresIncrease sizeand numberofwatercontrol structures.Wheninstalling, set topropergrade toallowfor complete draw-down.To improve ability to implementrapid flooding/irrigation BMPs(Table 1).See rapid flooding/irrigationBMPs (Table1).Increasedsizeand numberofwatercontrol structures willincreaserestoration costs andmanagement complexity.Swale construction(sloped from intake todrain)Construct orenhance swales sothey are sloped frominlet tooutlet andallow the majority ofthe wetlandtobedrawndown.To improve ability to implementrapid flooding/irrigation BMPs(Table1). Creates a means tomove water throughwetlandswithoutflooding entire wetlandbasin. Reduces mosquitohabitatbyallowingisolated sectionsofhabitat to drain. Providesmosquito predators withaccessto all portionsof wetland.See rapid floodingandirrigationBMPs (Table1). Provideshabitatdiversityandenhancescapabilities to implementmoistsoil management. Provides amore cost-effective andwildlifefriendly alternative to laserleveling tocreate drainage.See rapid floodingandirrigationBMPs (Table1). Reducesstanding waterin spring that isoften usedbyforagingwaterbirds. May result inadditional expense tocreateswales.Shallow swales must beperiodically re-cut if siltdeposition or denseemergentvegetation is aproblem.Couldbea deep water hazardinhuntingareas.Wetland sizeconsiderationsInstall cross-levees tofacilitatemore rapidirrigationandfloodup(Table1).Build“underwater”levees that isolate irrigationwaterduringthe spring,but canbe overtoppedduringfallandwinterflooding.To improve ability to implementrapid flooding/irrigation BMPs(Table 1).Assistswith faster flooding anddrainage. Cross levees(checks)can provideloafing habitatforwaterfowl andshorebirds.Additional levees may result indecreasedwildlife use anddiversity. Expensive.Requiresadditional levee maintenanceandwater controlstructures.Ditch design(2:1slopes&minimum4foot bottom)**consider 3:1 slopeorgreater todiscourageburrowinganimaldamage andpotentialseepageproblemsConstruct orimprove ditchestoquality standard thatpreventsunwanted vegetationgrowthorunnecessary seepage.Reduceslikelihoodofvegetationgrowingalongditch banks.Excessive vegetationslows waterflow, traps silt, and canbeusedas substratefor mosquito eggs.Improveswater flowanddecreasesmaintenanceofvegetation that grows along canalbanks.Mayrequirere-designingsomedeliveryditches to meet specificdesigncriteria.Could affecthabitat for wildlife species suchas giant gartersnakes.Steeperslopesmayerode morequicklyand createdahazard for hunters.Table 4. Wetland restoration and enhancement features to reduce mosquito production in managedwetlands, ContinuedBest ManagementPracticeStrategiesMosquitoControl ObjectiveAdvantagesDisadvantagesLevee design&compaction (>3:1slopes&>80%compaction)**consider5:1slopeorgreater inareas proneto over-landfloodingand leveeerosion.Constructorimprove leveestoquality standard that ensuresstability andprevents unwantedseepage.Toreduce mosquito habitatcausedby seepage intoadjacentfieldsordryponds.Properly constructed leveesprevent seepage fromerosionorrodent damage, andreduceneedfor annual maintenance.Additionalexpense torepair orbuild levees on existingproperties.Deepchannelsorbasins constructed inseasonal wetlandsExcavatedeepchannels orbasinsto maintain permanent waterareas (> 2.5feetdeep) withinaportion of seasonal wetlands.Provides year-roundhabitat formosquito predators whichcaninoculate seasonal wetlands whenthey are irrigatedor flooded.Toreduce mosquito larvaethroughpredation.Provideson-site sourceofmosquitofishandothermosquitopredators toseasonal wetlands.Increases overallhabitatdiversity.Expensive to excavateandmaintain permanentwater.Potential problemswith emergentvegetation.Maybe adeepwaterhazard inhunting areas.Permanent waterreservoir that floodsinto seasonalwetlandsMaintain separate permanentwaterreservoir that conveyswater toseasonal wetlands.Provides year-roundhabitat formosquito predators whichcaninoculate seasonal wetlands whenthey are irrigatedor flooded.Toreduce mosquito larvaethroughpredation.Provideson-site sourceofmosquitofishandothermosquitopredators toseasonal wetlands.Increases overallhabitatdiversity.Additionalexpense toconstructreservoirthat feeds watertoseasonal wetlandsand expensiveto maintain permanent water.

### Biological Controls

Naturally occurring predators, such as fish , dragonflies, aquatic m acroinvertebrates,

and certain bird and bats, can c ontribute to the reduction of mos quitoes (Table 5 ) . However,

it often takes tim e before predator populations becom e established and have an effect on

mosquito numbers, because m o squitoes freque ntly exploit ephem e ral habitats and have

relatively short lifecycles. Ce rtain predator populations can be supplem ented, for example,

through the stocking of mosquitofish ( Gambusia affin is ), bu t in m o st ins t ances a hab ita t

m a nager’s best strategy is to m a intain natura l predator populations on- site. For biological

controls to be effective, wetland m a nagers ne ed to create an environm ent that is both

conducive to m a intain in g predato r p opulati ons and providin g predato r s with access to

mosquito prey.

Encourage on-site predator populations : Managem e nt practices have been

developed that incorporate perm ane n t wate r within seasonal wetlands to “inoculate”

newly flooded habitats with an on-site predat or source. This can be acco m p lished by

m a intaining perm anent water in swales and deep borrow ditches, or by flooding wetlands

with water f r om nearby perm anent wetlands. P e rm anent water sou r ce s will need to be

m a intained when season al wetlands are dry, if wild populations of m o squ itofish are to be

sustain e d on -site. Such “dry season ” predator reservoirs should be 18 inches or greater in

depth to reduce predation of m o squitofish by herons and egrets (Collins and Resh 1989).

Dry season reservoirs should be interconnected to seasonal we tlands through swales or

ditche s to a l low m o squitof i sh to seek hab itat as seasonal wetlands are drawn down an d,

conversely, to allow m o s quitofish to disperse through seasonal wetlands as they are reflooded in the fall.

It is critical to the su cces s of biological control to lim it the use, when possible, of

broad spectru m insecticides that not only kill m o squitoes, bu t also e lim inate the i r na tur a l

predators. Control program s that co m b ine bi ological controls with ch em ical insecticides

often result in suboptim al results because the predators take longer to recover from

insecticide induced m o rtality than m o s quito populations (Walton et al. 1990).

Provide predator acces s to mosquitoes : The extent of wetland vegetation m a y lim it

predator access to m o squitoes (W alton and Mu lla 1989, Collins and Resh 1989). W e t l ands

with significantly dense vegetation provide an abundance of hiding places for m o squitoes

and can lim i t aquatic predator dispersion. Vegetation m a nagem e nt BMPs can be used to

reduce dense stands of cattail, tules, or other em e r gent ve getation and provide predators

access to m o squito prey. Isolated bas i ns that do n o t interconn ect to the main water bo dy of

a wetland will also lim it an aquatic p r edato r’s access to m o squito prey. To encourage

mosquito predation, wetland swales can be cons tructed to connect isolated basin with deep

water areas containing aquatic m o squito predators.

26Table 5. Biological ControlsBest ManagementPracticeStrategiesMosquitoControl ObjectiveAdvantagesDisadvantagesEncourage or stockMosquitofish(Gambusiaaffinis)Stockmanagedwetlandswithmosquitofishorencouragehabitats fornaturalizedpopulations.Utilize watersources with mosquitofish topassivelytransport predatorstonewlyflooded habitats.To supplement mosquitopredatorpopulation.Provides anon-chemical controlof mosquito larvae.Mosquitofish areoften available freeofcharge tolandowners fromtheirlocal district.May reducenon-targetpopulationsofinvertebratesorother mosquitopredators.Notappropriate for vernalpoolhabitats. Maynegatively impactsensitive species.Encourage invertebratepredatorsMaintain permanentor semipermanent water wheremosquitopredators candevelop andbemaintained.Discourage useofbroad spectrumpesticides.Toreduce mosquitopopulationsthroughpredation.Providesbiological control ofmosquito larvae and adults.None.Encourage swallowcolonies and otherinsectivorous birdsDonot discourage nestingswallows.Toreduce mosquitopopulationsthroughpredation.Providesbiological control ofadult mosquitoes.Guano.The valueofinsectivorous birdshas notbeenadequately quantified.Encourage BatsEncouragebatcolonies (e.g.build batboxes)Toreduce mosquitopopulationsthroughpredation.Providesbiological control ofadult mosquitoes.Potential(or perceived potential)for transmissionofrabies. Thevalueofinsectivorousbatshasnotbeenadequatelyquantified.

### C OORDINATION W I TH 

### M OSQUITO AND 

### V EC TOR 

### C ONTRO L 

### D IST R I C TS



### The responsibilities of MVCDs and wetland m a nagers have som e inherent conflicts.

MVCDs hav e a responsibility to reduce vector s that m a y transm it disease to hum ans o r

cause a significant nuisance. W e tland m a nagers have a re spo n sibility to m a intain and

enhance wetlands; a public trus t resource that provides ha bitat for m i gratory birds,

threatened and endangered species, and help s to reduce depredation from waterfowl on

agricu ltu ral lands. Public resou r ce agencies are increasingly being asked to provide

wetland habitat to m eet the recreational dem a nds of hunters, anglers, bird watchers,

photographers, and hikers. W e tland m a nagers recognize that mosquito production m a y be a

by-product of wetland m a nage m e nt and in som e cases m a y contribute to problem s requiring

mosquito control. However, in order fo r both MVCDs and wetland habitat m a nagers to

accom p lish their ob jectiv es, cooperation and coordination is essential.

MVCDs and wetland m a nagers have a histor y of conflict going b ack over 30 years in

the Central Valley (Lusk 1979). Such conflic t was largely the result of MVCDs being

perce i ved as rely ing sole ly on the us e of chem ical pesticides f o r contro l ac tivitie s and

concerns regarding the potential effects on wildlife and food-chain resources such as

invertebrates. However, MVCD use of Integr ated Pest Managem e nt (IPM) has helped to

address this concern by employing a variety of control m e thods that include habitat

m a nage m e nt , biological control, and the use of more target-specific pe sticide products. The

increasing costs of pesticides and concerns over pesticide res i stan ce have also spurred a

more holistic approach to m o squito m a nage m e nt

. The success of IPM depends on cooperation and sharing inform ation on habitat and

water m a nagem e nt schedules, collaborating on the identification of problem areas,

monitoring the effectiveness of BMPs, an d coordinating on wetland restoration and

enhancem ent projects (T able 6).

Coordinate habitat management and flooding schedules : By providing advanced

inform ation regarding habitat and water m a na gem e nt schedules, wetland m a nagers enable

MVCDs to m a ke sugge stions regarding BMPs , schedule m onitoring efforts, and, if

necessary, control m o squitoes as efficiently as po ssible. In re turn, MVCDs can provid e

landowners with useful input and feedback on how to reduce mosquito production and

potentially reduce their abatem ent costs.

Identify pr oblem area s for mosqu i to production and target imp l eme n tation of

BMPs : Coordination is also required on the part of MVCDs to id en tif y the highes t p r ior ity

wetlands for the im plementation of BMPs. For exam ple, Garcia and Des Rochers (19 83)

found that Ochlerotatus melanimon larvae were largely res t ricted to specific areas in a few

fields on Gray Lodge Wildlife Area. As a result, lim ited resources could be focused on

these prob lem areas.

Coordinate w e tland ha bitat restor ation and enhancement project design : Prior

to enhancem ent or restoration projects, MVCD s s hould be consulted to determ ine if design

features to reduce m o sq uitoes can be inco rporated. By involving MVCDs early in the

process, problem s associated with design feat ures or poor engineeri ng that m a y encourage

mosquito production can be avoided.

Coordinate Pest Control Activities : To f acilitate the tim e ly and ef f

ectiv e use of

pesticides in wetland areas, MVCDs shoul d inform wetland m a nagers about proposed

pesticide ap plica tions. T h is can be a ccom p lis hed by providing a brief, annual plan that

28

### identifies the pesticide products, approxim a te us e rates and application m e thods that m a y be

used during the year. Whenever possible, MVC D s should also provide wetland m a nagers

with information about the specific locations where pesticide products will be used. An

annual sum m a ry report of pesticide use should be provided to the wetland m a nager after the

conclusion of the application season.

Coordinate monitoring activities : Determ ining the success o f BMPs will be larg ely

based on the m onitoring of m o squito production following their im plem en tation. This effort

will r e quir e wetland m a nagers to wo rk dire ct ly with MVCDs to f aci lita te monitoring and

will a l so pro v ide an opp ortunity f o r wetland m a nagers to f a m iliarize the m selves with the

m e thods used for m onitoring and thresholds for treatm e nt. The m onitoring process will

provide va lu able inf o rm ation to ref i n e BMPs and determ ine their f u tur e p r ior ity f o r us e.

Ultim ately, this proce ss will prov ide a uni que op portunity to develop and use new

techniques to reduce m o squito production in m a n a ged wetlands.

29Table 6. Suggested coordination activities between wetlandmanagers and Mosquito and Vector ControlDistricts (MVCD).Best ManagementPracticeStrategiesMosquitoControl ObjectiveAdvantagesDisadvantagesHabitat managementand flooding schedulecoordinationConsult withMVCDson agencysponsored habitatmanagementplansonprivate lands (i.e.Presley Program). Consult withDistricts on thetiming ofwetlandfloodingonpubliclands – urgeprivate landownerstodothesame.Allows MVCDs theopportunitytoprovideinput onhabitatmanagement andrecommendBMPs toreduce mosquitoes.Reduces potential conflictsbetween MVCDs, landowners,and agencies/NGOs whenmanagingorfloodingwetlands.Provides information exchange.Requires a commitment of timefromMVCDs,landowners, andagencies/NGOs to meet andcoordinate activities.Identify problemareasfor mosquitoproductionandtargetfor implementationofBMPsIdentify problemlocations formosquitoproduction with localMVCDs andworktoimplementmosquito BMPs.Identifypotential cost-share opportunitiesto implementBMPs.Worktoreduce mosquitoproduction throughBMPsonproperties thatare mostproblematic.Allows limited resourcesfromMVCDs and agencies/NGO’s tobe targeted towardsproblemareas.Providesopportunities formonitoring the effectivenessofBMPs.NoneWetland HabitatRestoration andenhancement projectdesign&coordinationConsult with local MVCDsonthedesignof restorationandenhancement projects.To determinewhere features todiscourage mosquitoproductioncanbe incorporated intowetlandhabitat restoration andenhancement projectswherefeasible.Reduces potential conflictsbetween MVCDs, landowners,and agencies/NGOs whenrestoringor enhancingwetlands.Provides apriori consultationforMVCDs onwetland projects.Requires someflexibility fromMVCDs, landowners, andagencies/NGOs when designingprojects. BMPs will likelyincrease theproject cost.Coordinate PestControl ActivitiesWorkwith local MVCDs tounderstandpesticidesusedformosquito treatment, and theircosts and environmental impacts.To assure the use of mosquitocontrol agentswith the greatestefficacy and environmentalsafety.Reduces potential conflictsbetween districts,landowners,and agencies/NGOsregardingpesticidesused for mosquitotreatment.May require additionalcoordination effort fromMVCDs, landowners, andagencies/NGOs.Coordinate MonitoringActivitiesFacilitate monitoringmosquitopopulations oflarval and adultstagesbeforeand afterimplementation ofBMPs.Determinethe effectiveness ofBMPs torefineandprioritizetheir futureuse.Provides a means toevaluateanddocument effectivenessof BMPs.Requires timeand resourcestoaccomplish.

### REFERENCES AND LITERATURE CITED

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31

### Garcia, R. and B. Des Rochers. 1984. Studies on the biology and ecology of m o squitoes in

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. K. Re isen, and T. W. Scott. 2002. Vector com p etence of

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33

### Appendix A. Co m p arison of potential m o squito larvicides used in m a naged wetland

environm ents. Inform ation provided by the Pestic ides Investigation Unit of the Departm e nt

of Fish and Ga m e

.

Pesticide Surfa ce O il Surfa ce Film Metho p r ene D i m i l i n B a c i l l u s

thuringiensis

israelensis (Bti) Ba cillus

sphaericus (Bs )

Trade Name Gol d en

Bear Oil A g n i qu e MMF A lto sid D i milin 2 5 W V ectob ac

Teknar

Aq ua bac Vectolex

Mo de of

Acti on Suf f o cat i o n S u f f o cat i o n G r owt h

regu lato r Ch itin inh i b itor S to m ach p o i son Sto m ach p o ison

Toxi c o l o gi cal

Impac t s 1 :

Fish & Fr ogs U nkn own U nkn own L o w Pr a c t i c a l l y n o n

t oxi c Practically n o n

to x i c Practically n o n

t oxi c

Toxi c o l o gi cal

Impac t s 1 :

Birds Low; at col d

te m p eratures

may im pact

yo un g

w a terfow l U nkn own V e r y l o w Pr actically n o n

t oxi c Practically n o n

to x i c Practically n o n

t oxi c

Pote nti a l Imp a cts

t o in v e rt e b ra te

for a ge b a se

fo r wildlife 2 Mo d e rate to

h i gh ; bro a d

spectrum

com pou nd M ode rat e

t o hi gh;

br oa d s p ect r u m

com pou nd Proba b ly

lo w ; fairly

nar r o w

spectrum M ode rat e

t o hi gh;

br oa d s p ect r u m

com pou nd Som e species

of

m i dge l a rva e

subfam ily

Ch irono m in ae;

p o t en tially

o t h e r p r im it iv e

diptera n la rvae Proba b ly

lo w ; fairly

narr o w

spectrum

com p ound

Com m ent s Petrole u m

d i stillate;

ap p lied ov er

surface of

wat e r; m a y be

ef

f ectiv e fo r 2-3

day s Reduces wate r

surface te nsion Ju ven ile

ho rm one

mi mic;

effective on

later stag e

m o sq u ito es

(instars 3

- 4) N a t u r a l l y

occurri ng

soil bacteri u m ;

m o st effective

on early stage

larvae (insta rs

1

- 3 ) ;effectiv e

fo r onl y 1- 2

d a ys; no t

effectiv e in

w a ter w ith h i gh

or ga ni c co nt en t Can be ef fect i v e

fo r week s; use d

p r im arily fo r

Culex spp. in

w a ter w ith h i gh

or ga ni c co nt en t ;

not e ffecti v e on

all species of

m o sq u ito

1 Actual hazard is de pe nde nt on e x pos u re , as well as toxicity.

2 Very di ffi c u l t t o assess

. De p e nde nt on n u m e ro us fact o r s s u ch as t h e t o t a l area t r e a t e d, f r e que ncy of t r e a tm ent

, and seas on of t r eatm e nt.



### 34

### Appendix B. Co m p arison of potential m o squito adulticides used in m a naged wetland

environm ents. Inform ation provided by the Pestic ides Investigation Unit of the Departm e nt

of Fish and Ga m e

.

Ma la thion Nal e d P y r e t h r i n P e r m e t h r i n Resmethrin Sumithrin

Trade Name Fy fan o n T r u m pet

Di b r om Pyr a non e

Pyroci de A q u a Reslin

Bio m ist

Perm anone Scou rg e A n v i l

Mo de of

Acti on Cent ral ne r v o u s

syste m (CNS)

i nhi bi t o r CNS i n hi bi t o r Cont act C o n t act C o n t act S y st em i c

Toxi c o l o gi cal

Impac t s 1 : Fis h

and Fr ogs V a riab le; so m e

fish s p ecies a r e

hi g h l y

su scep tib le,

as are m a ny

am phi bi an s Mo d e rately to

hi g h l y t oxi c Hi g h l y t oxi c Hi g h l y t oxi c Hi g h l y t oxi c M a y be l e ss

t oxi c t o s o m e

aquatic s p ecies

th an o t h e r

pyreth rins

Toxi c o l o gi cal

Impac t s 1 : Birds Mo d e rately

t oxi c Mo d e rately to

hi g h l y t oxi c Mo d e rately

t oxi c Practically n o n

t oxi c Practically n o n

to x i c Practically n o n

t oxi c

Pote nti a l Imp a cts

t o in v e rt e b ra te

for a ge b a se

fo r wildlife 2 Mo d e rate to

h i gh ly to x i c;

br oa d s p ect r u m

in secticid e Mo d e rate to

hi g h l y t oxi c;

br oa d s p ect r u m

in secticid e Mo d e rate to

hi g h l y t oxi c;

br oa d s p ect r u m

in secticid e Mo d e rate to

hi g h l y t oxi c;

br oa d s p ect r u m

in secticid e Mo d e rate to

hi g h l y t oxi c;

br oa d s p ect r u m

in secticid e Mo d e rate to

h i gh ly to x i c;

br oa d s p ect r u m

in secticid e

Com m ent s Or ga no p hos

phat e

in secticid e Or ga no p h os phat e

in secticid e Botanical

p e sticid e Sy nt het i c

py reth rin Sy nt het i c

py reth rin Sy nt het i c

pyreth rin

1 Actual hazard is de pe nde nt on e x pos u re , as well as toxicity.

2 Very di ffi c u l t t o assess

. De p e nde nt on n u m e ro us fact o r s s u ch as t h e t o t a l area t r e a t e d, f r e que ncy of t r e a tm ent

, and seas on of t r eatm e nt.



### 35