(/irj ^^ (it).

Col

INSECTS

AFFECTING

SUGARBEETS

GROWN FOR

SEED

AGRICULTURE HANDBOOK NO. 253

AGRICULTURAL RESEARCH SERVICE

UNITED STATES DEPARTMENT OF AGRICULTURE
Contents

Page

Foliage feeders 2

Lepidopterous larvae 2

Grasshoppers and crickets 11

Blapstinus beetles 11

Spider mites 12

Southern garden leafhopper 14

False chinch bug 14

Aphids 15

Seed feeders 21

Lygus bugs 21

Stink bugs 23

Virus vectors 25

Beet leafhopper and curly top. 25

Aphids and yellows viruses 27

Literature cited 28

Washington, D.C. Issued December 1963

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C, 20402 - Price 15 cents
INSECTS AFFECTING SUGARBEETS

GROWN FOR SEED

By OBIN A. HILLS, entomologist. Entomology Research Division,

Agricultural Research Service

Sugarbeets grown for seed are

subject to attack by various insects

from the time the crop is planted in

the late summer until the seed is

harvested the following June or

July. These pests include (1) foliage feeders, chewing insects, and

sucking insects; (2) insects that

feed directly on the developing

seed; and (3) vectors of various

virus diseases. Without control,

chewing insects often ruin stands

soon after emergence of the plants,

and sucking insects may so lower

the vitality of the plants that little

or no seed is produced.

Studies were undertaken by the

Bureau of Entomology and Plant

Quarantine ^ in 1938 at its Phoenix,

Ari¿., laboratory to determine what

insects were occurring in the beetfields and what effect they were

havmg on the plants and on the

seed produced. Surveys were conducted in the beetfields from the

time the plants first emerged in the

fall until the seeds were harvested

the following spring. The seasonal

occurrence of all insects as well as

their relative abundance was recorded.

The damage of chewing insects

was obvious, but the effect of sucking insects on the beet seed crop required special study. In these

studies the various species were confined separately on seed spikes in

field cages. Lygus bugs were soon

Now Entomology Research Division,

Agricultural Research Service.

identified as a major pest, and their

abundance in various fields was correlated with losses in seed yield and

viability. The effect on the beet

seed crop of virus vectors such as

the beet leafhopper, which transmits curly top, and aphids, wliich

transmit the yellow virus, was determined. The effectiveness of insecticides against the various insects as well as the most effective

time of application was studied in

small plots and later in large-scale

farmer-cooperative plots.

The purpose of this publication

is primarily to assist growers and

others to identify the more economically important insects that occur

in fields of sugarbeets grown for

seed and to become familiar with

the relationship of these insects to

the production of sugarbeet seed.

Some of the insects found in the

fields are of little or no econornic

importance ; others feed on pest insects and are beneficial.

The nature and amount of damage done by the various insects and

the need for control remain relatively constant. However, because

of the development of resistance in

insects to insecticides and the continual improvement of insecticides,

recommendations are subject to

change. Therefore, the mention of

insecticides in this handbook should

not be interpreted as a recommendation for their use. The latest insectide recommendations are given

in the current issue of Agriculture

Handbook 120, Insecticide Recom1
AGR. HANDBOOK 2 53, U.S. DEPT. OF AGRICULTURE

mendations of the Entomology Research Division for the Control of

Insects Attacking Crops and Livestock.

The production of sugarbeet seed

in the United States is a comparatively new industry. Prior to

World War I practically all sugarbeet seed used in the United States

was imported from Europe, where

it was grown by the biennial method. By this method the seed was

planted in the spring and the roots

were harvested m the fall and held

over the winter in clamps, or pit

silos. In the spring the roots were

removed from the clamp and

planted in the field. With the resumption of growth, seed stalks developed and produced seed for harvest the following fall.

In an attempt to establish a beet

sugar industry in New Mexico, trial

plantings of sugarbeets were made

by the New Mexico Agricultural

Experiment Station at State College, N. _Mex., in the early 1900's.

These trials were unsuccessful. In

the 1920's through a cooperative

agreement with the U.S. Department of Agriculture, trial plantings

of sugarbeets for sugar were agam

made. These were primarily timeof-planting experiments. Beets

were planted on the 1st and 15th of

every month throughout the year.

From these trial plantings it was

discovered that sugarbeets planted

in the early fall not only successfully overwintered but produced a

crop of seed the following spring or

early summer.

Further tests were conducted to

develop an adequate fertilizer program as well as to determine the

proper planting dates, the best seeding rates, row width, and spacing

of plants in the row. Eesults of

these experiments placed the annual method of beet seed production on a sound footing and were

basic to an industry in the United

States that now supplies all the

sugarbeet seed used in this country.

The first commercial plantings of

sugaibeets for seed by the annual

method were made near Las Cruces,

N. Mex., in 1927. Other areas

proved to be better suited for the

crop than New Mexico, and by 1962

beet seed was produced in Arizona,

California, Nevada, Utah, and

Oregon.

The insects attacking the beet

seed crop are described in this handbook under the following headings:

Foliage Feeders, Seed Feeders, and

Virus Vectors.

FOLIAGE FEEDERS

Lepidopterous Larvae

The most severe damage caused

by lepidopterous larvae is to the

young beet plants as they emerge

in the fall. Unless the fields are

watched closely, the stands may be

ruined in the early stage of development and replanting will be necessary (fig. 1).

The three most important species

attacking the sugarbeet crop are the

beet armyworm {SpodojHera exigua (Hübner)), the yellow-striped

armyworm {Prodenia omithogalli

Guenée), and the garden webworm

{Loxostege siinilalh (Guenée)).

Also several of the cutworms are

sometimes of economic importance.

Both the eggs and larvae of all these

species are attacked by small parasitic wasps, but usually they are inadequate and chemical control is

often necessary.

Beet Armyworm and YellowStriped Armyworm

Moths of the beet armyworm are

grayish brown with light-gray

markings on the forewings (fig. 2).
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED

FiGTJBE 1.—Sugarbeet seedlings damaged by lepidopterous larvae. (XI.)

There is a characteristic light-gray

spot about halfway back and toward the outer margin of each forewmg. They have a wingspread of

about 1 inch, and when at rest they

are five-eighths to three-fourths

inch long. Moths of the yellowstriped armyworm are somewhat

darker and have distinctive lightgray markings on the forewings

(fig. 3). They are a little larger

than the beet armyworm, with a

wingspread of about I14 to 11/2

inches, and when at rest they are

three-fourths to seven-eighths inch

long.

The hindwings of both species are

white with a dark band near the

outer edge. Both of these armyworm moths are nocturnal but readily fly in daylight if disturbed.

They deposit large masses of eggs

on small plants almost as soon as

they emerge. The egg masses are

covered with scales from the body

of the moth (fig. 4). This distinguishes them from other eggs. The

individual eggs are approximately

0.50 mm. in diameter. They hatch

in a few days into light-green larvae with dark heads.
AGR. HANDBOOK 253, U.S. DEPT. OF AGRICULTURE

TC-7454

FIGURE 2.—Moth of the beet armyworm

(Spodoptera exigua). (X 3.)

In the early stages of development these two species of

armyworms are very similar in appearance. Their feeding habits and

damage to the plants are also similar. The larvae, or small worms,

remain in grou^js, spinning protective webs. Often they will tie

leaves together with webbing to

form a protective cell for the group.

At this stage the worms feed only

on the surface of the leaves causing

skeletonizing. "Wlien about threeeighths inch long, they spread out

over the plants and consume entire

leaves.

The full-grown beet armyworms

are a little over 1 inch long (fig. 5).

They are pale olive to dark green

above and yellowish green beneath.

TC-7495

FIGURE 3.—Moth of the yellow-striped

armyworm (Prodenia ornithogalli).

(X 2},.)

TC-745J

FIGURE 4.—Armyworm egg mass: A,

Eggs covered with moth scales as they

normally occur; B, scales removed to

show eggs. (X 8.)
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED

_^r-''^^^^!^^1B.

y ?

TC-7466

FiGUHE 5.—Full-grown beet armyworm

{Spodoptera exigua). (X 2.)

These two colors meet at a narrow

pale-yellow line along each side.

In the more highly colored specimens there is sometimes a second

narrow pale-yellow line above this

stripe. There may also be a pale

line or stripe along the sides below

the dividing line of the two colors.

There is a distinctive black spot on

each side of the second thoracic segment, which has the second pair of

legs. This is sometimes difficult to

see in the darker specimens, but it

is characteristic of the beet armyworm.

The full-grown yellow-striped

armyworms are about li/^ inches

long with a conspicuous yellow

stripe along each side of the back

and a white or light-yellow stripe

on each side (fig. 6). Several

narrow light-colored lines between

these stripes give the appearance of

a broad multicolored stripe along

the sides. A broad dark stripe below this stripe in some specimens

with a broad pinkish stripe below

that gives the appearance of three

broad stripes along the sides. The

colors vary considerably.

In some individuals the back between the yellow stripes is velvety

black; on others it is gray and may

take on a pink cast. In some specimens there is a pair of black spots

on the back of each body segment

just inside the yellow stripes. These

are sometimes in the shape of a triangle. Usually there is a conspicuous velvety black spot on each side

of the first abdominal segment. In

the lighter colored specimens a pink

median stripe often occurs on the

back, and they may also be pink beTC—7467

FIGURE 6.—Full-grown yellow-striped

armyworms (Prodenia ornithogalh).

(X IV3.)

low the stripe on the sides. All are

olive green on the underside.

The half-grown larvae are usually not so highly colored. Most

of them are light to dark olive green

on the back with a dark shadowhke

median stripe. They have the same

yellow stripes along each side as the

full-grown larvae.

Garden Webworm

Moths of the garden webworm

have a wingspread of about seveneighths inch, and when at rest they

are about one-half inch long (fig.

7). They are light brown with

shadings and irregular markings of

light and dark gray on the forewings.

The flattened cream-colored eggs

are usually placed on the underside

of the leaves of young plants m

small masses overlapping like fish

scales or shingles (fig. 8). They

are covered with a transparent

plasticlike coating.
AGR. HANDBOOK 253, U.S. DEPT. OF AGRICULTURE

TC-7458

FIGURE 7.—Moth of the garden webworm

{Loxosiege similalis). (X 4^-)

The larvae are more damaging

than the larvae of either of the

armyworms because they feed in

the terminal bud; thus, a comparatively small amount of feeding will

kill the plants. Newly hatched garden webworm larvae are pale yellowish green with small black spots

over the entire body. As the larvae

grow, the spots become more conspicuous (fig. 9).

The full-grown larvae are about

three-fourths inch long and pale

green with two white lines down the

back. There are six black spots on

each body segment. Three are located on each side of the dorsal

white lines and are arranged in a

triangle. Wh&n the larvae are disturbed, they have a characteristic

backward wiggle. The larger larvae often spin a silken tunnel from

the feeding site to the base of the

plant. This tunnel may lead to a

silk-lined cell beneath a clod. The

larvae feed mostly at night and

spend much of the time within this

tube. This habit makes them more

TC-7459

FIGURE 8.—Eggs of the garden webworm

(Loxostege similalis) on the underside

of a beet cotyledon. (X 16.)

TC-746(I

FIGURE 9.—Full-grown garden webwornis

{Loxostege similalis). (X 3.)
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED

FIGURE 10.—Moth of the granulate cutworm (fe&ia sw6<erranea). (X 2.)

difficult to kill with insecticides

than other species that feed in the

open.

Cutworms

_ Cutworms are also a problem at

times during the fall. Several species may attack sugarbeets. All cutworm moths are nocturnal. They

Jave dusty-gray heavy bodies.

Ihey have a wingspread of U/^ to

¿ inches and are % to 1 inch long

when at rest.

. The most common species infesting the seed beetfields in the Southwest IS the granulate cutworm (Feim subterránea (Fabricius)) (fig.

10). Moths of this species lay their

eggs in groups of usually not more

than 6 to 18 eggs ( fig. 11 ). They are

off white, about 0.67 mm. in diameter, and ribbed, with a purple spot

on the top and an irregular purple

band around this spot. As the

young larva matures within the &gg,

It becomes darker. Most of the eggs

are laid on the underside of the

leaves. Often the moths are attracted to small weeds in the beet693-392 O—63 2

TC-7462 and TC-7463

FIGURE 11.—Eggs of the granulate cutworm {Feliia subterránea) on the underside of a sugarbeet cotyledon {A) and

of a small careless weed {B). ( X 9 and

X 4.)

field, and more eggs may be laid on

these than on the beets.

Damage to the young plants by

the small cutworms is similar to

that by the small armyworms.

Larger cutworms often cut off the

plants at the soil surface, as the

name implies. They feed mostly at

night and hide under clods in the

daytime. Full-grown cutworms are

about 11/2 inches long, varying from

light gray to dark browmish gray,

sometimes with darker markings.

If disturbed, the worms curl up

tightly and may remain inactive for

several minutes (fig. 12).

t...
8 AGR. HANDBOOK 2 53, U.S. DEPT. OF AGRICULTURE

TC-7464

FIGURE 12.—Full-grown granulate cutworm (Feltia subterránea). (X 3.)

Salt-Marsh Caterpillar

The salt-marsh caterpillar {Estigmene ocrea (Drury)) is often a

problem in the fall, especially where

seed beets are grown near cotton.

The eggs are deposited in large

numbers on cotton leaves. The larvae feed in cotton until they are

nearly full grown and then move

out in hordes, feeding on almost

anything as they move. Aluminum-foil barriers around the beetfields will prevent injury from the

migrating caterpillars. A foil strip

about 7 inches wide is set upright

in the ground so that about 5 inches

protrudes above the soil surface.

Post holes dug against the barrier

about every 20 feet will trap the

caterpillars as they travel along the

foil.

At rest, the moths of the saltmarsh caterpillar appear white,

with small black spots scattered

over the wings (fig. 13). In this

position they are about 1 inch long.

If the wings are spread, they reveal

an orange body with black bands.

The hindwings of the female are

white, whereas those of the male are

orange. The wingspread is usually

a little over 2 inches. The eggs are

spherical, pearly white, and about

0.80 mm. in diameter. They are

laid in large masses (fig. 14).

Newly hatched caterpillars are

dark and covered with long black

hairs. They feed for a time close

to the old egg mass and then disperse. The full-grown caterpillarf

are about 2 inches long and are cov

rC-7274A

FIGURE 13.—Moth of the salt-marsh

caterpillar {Esligmene aerea). (X 2.)

TC-74eä

FIGURE 14.—Egg mass of the salt-marsh

caterpillar {Estigmene aerea) on a small

leaf of a beet seed stalk. (X 2}i)
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED 9

iiGUHE 15. Salt-marsh caterpillar {Estigmene aerea) on the remains of a cotton leaf.

(X m.)

ered with black and rust-colored

nairs from which they get the name

woolly bear (fig. 15). Partially

grown larvae are sometimes more

gray.

Occasionally the eggs will be laid

on the leaves of larger beet plants

iate .in the fall or in the spring on

small leaves on the seed stalks, but

ine young caterpillars soon disperse

and little damage is caused. Usually the only control necessary is the

aluminum-foil barrier to prevent

the larger caterpillars from entering the beetfield as they migrate

from cotton.

Celery Leaf Tier

Lan^ae of the celery leaf tier

iydea ntbigalis {Guenée)) sometimes become numerous in seed

beetfields in the spring and may do

some damage by defoliating the

plants. The moths are difficult to

distinguish from those of the garden webworm. They are light

brown with darker markings on the

forewings (fig. 16). They have a

wingspread of about seven-eighths

inch and when at rest are approximately one-half inch long. Tliey

have a distinct snout, and in the

resting position they appear triangular in outline. The eggs and Qgg

masses are similar to those of the

garden webworm (fig. 8).

The full-grown larvae are about

three-fourths inch long and pale

green or yellow green with a dark

median line down the back and a

white line on either side of the dark

line (fig. 17). The body is sparsely

co^'ered with very fine hairs, barely

visible to the unaided eye. When

ii&¿
10 AGE. HANDBOOK 2 53, U.S. DEPT. OF AGRICULTURE

The mature larvae pupate on the

leaves within these silken cells and

the moths emerge in a few days.

Platynota stultana

Another species of moth, Platynota stultana Walsingham, sometimes infests seed beets both in the

fall and in the spring. The moth is

slightly smaller than the celery leaf

tier and is darker brown (fig. 18).

TC-7468

FIGURE 16.—Moth of the celery leaf tier

{Udea rubigalis). (X 5.)

the larvae are disturbed, they have

a rapid backward wiggle similar to

that of the garden webworm. They

are web spinners and form protective cells by tying leaves together.

TC-7467

FIGURE 17.—Larvae of the celery leaf

tier {Udea rubigalis). (X 2}i.)

TC-746a

FIGURE 18.—Moth of Platynota stultana.

(X 5.)

It has a distinct snout similar to

that of the moths of the garden

webworm and celery leaf tier, but it

does not have the same triangular

outline when at rest. In this position the outer edges of the foreAvings are nearly parallel for about

two-thirds the length of the body

and the anterior one-third slopes

sharply toward the head.

The eggs of Platynota are similar

to those of the garden webworm

and the celery leaf tier in that they

are flat and laid in masses overlapping like fish scales or shingles

(fig. 19). They are covered with a

transparent plastic coating as are

the eggs of the other two species,
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED 11

FIGURE 19.—Egg mass of Platynota

stullana. (X 16.)

but they are green. Usually the

masses are larger and flatter than

those of the garden webworm or

celery leaf tier. The mass is usually

about one-eighth inch across and

one-fourth inch long and contains

30 to 40 eggs. However, it may

sometimes be longer and contain

over 200 eggs. The individual eggs

are approximately 0.50 mm. across.

Ihe extreme flatness and green

color make them very hard to see.

They may be laid on either surface

of the beet leaf or on nearby weeds.

The habits of the larvae are similar to those of the celery leaf tier

and garden webworm. The Platynota larvae are about three-fourths

inch long when full grown and vary

from light green to olive green

(fig. 20). There is a dark line

down the middle of the back. A

row of white dorsal spots on each

body segment forms a dotted line

on each side of the dark median

line.

Usually control is not required,

but occasionally Platynota may become numerous enough to require

insecticide treatment. However,

large numbers of moths are sometimes produced that move to other

crops, particularly cotton. The larvae of Platynota have also caused

considerable damage to cantaloup

by tunneling into the rind.

Grasshoppers and Crickets

Grasshoppers and crickets are not

often a problem in sugarbeets

grown for seed, but they do occasionally occur in newly planted

fields and can under these conditions do considerable damage to the

young plants.

Grasshoppers sometimes become

numerous in weedy fence rows and

ditchbanks adjacent io newly

planted beetfields. Johnsongrass is

especially attractive to these insects. Such areas should be cleaned

up before planting.

Blapstinus Beetles

Small darkling ground beetles

{Blapstinus spp.) sometimes attack

beet seedlings soon after the plants

emerge. Ordinarily they feed on

decaying organic matter, and therefore fields most susceptible to attack are those planted to beets before residues of the previous crop

are completely decomposed. These

beetles are dark brown or nearly

black and about one-fourth inch

long (fig. 21 ). They occur not only

around bits of decaying organic

matter but also under nearby clods.

Control is not often necessary, but

occasionally it may be desirable.
12 AGR. HANDBOOK 2 5 3, U.S. DEPT. OF AGRICULTURE

FIGURE 20.—Larvae of Platynota stuUana. (X 5}í-)

TC-7470

Spider Mites

Two species of mites of the genus

Tetranyclius occur in the seed beets

in southern Arizona—T. desertorum Banks and telarius (L.).

Other species may occur m the seed

beet growing areas of California,

Utah, and Oregon. These species

are not easily distinguished, but

this is not important, since they

cause the same damage and are controlled in the same manner. These

mites, sometimes called red spiders,

feed on the foHage or seed spikes of

sugarbeets at any time of the year,

but they do not ordinarily become

numerous enough to damage the

crop until warm w^eather in the

spring. They may be anywhere in

the field, but they are often more

numerous near the edge and especially along a dusty road.

They are ovoid, vary from pale

green to red, and usually have large

dark spots on each side, w^hich can

be seen with a hand lens (fig. 22).

The adult females are about onehalf mm. long; the males are

slightly smaller. The eggs are

spherical, about 0.14 mm. in diameter, and almost transparent when

first deposited. They become reddish before they hatch into sixlegged larvae, which are only a little larger than the egg itself. After

the first molt, eight-legged nymphs

appear. Both larvae and nymphs

resemble the adult, except they are

smaller and pale green. All species
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED 13

TC-7471

FIGURE 21.—Darkling ground beetle

{Blapstinus spp.). (X 10.)

spin webs. As populations increase,

webbing becomes more noticeable.

Often spider mites are held in

clieck by predators, primarily the

minute pirate bug {Oyñus tristiGolor (White)). Before chemical

control is started, these predators

and mite populations should be

watched. If Orius is sufficiently

TC-747Í

FIGURE 23.—Minute pirate bug {Orius

tristicolor). (X 25.)

numerous, mite populations will

gradually decline.

The Orius adults are about three

thirty-seconds inch long (fig. 23).

The forewings are black and white

and are held flat over the back. The

nymphs are orange and ovoid (fig.

2Í). Both adults and nymphs feed

on adults, nymphs, and eggs of

spider mites and are also predaceous on thrips and eggs of other

insects.

Mites feed by sucking plant juices

and thereby devitalize the plants

/

FIGURE 22.—Spider mite

sp.). (X 40.)

TC—7273

{Tetranychus FIGURE 24.—Nymphs of the minute

pirate bug {Orius tristicolor). (X 15.)
14 AGR. HANDBOOK 253, U.S. DEPT. OF AGRICULTURE

TC-747E

FIGURE 25.—Adult of the southern

garden leafhopper (Empoasca solana).

(X 18.)

and reduce the seed yield. If they

are present in the field, reproduction begins with warm spring

weather. If they are not held in

check by predators, they may become so numerous as to completely

web over the seed stalks. Such an

infestation will greatly reduce the

seed yield, but there is no evidence

that mites affect the viability of the

seed. Timing of insecticide applications is important in mite control.

Populations should be watched. If

noticeable increases occur in the absence of predators, miticide treatment is indicated.

Southern Garden Leafhopper

The southern garden leafhopper

{Empoasca solana DeLong) is

often the most numerous insect in

seed beetfields in the winter and

early spring, particularly in the

Southwest. The adults are light

green, slender, and approximately

one-eighth inch long (fig. 25). The

nymphs resemble the adults in general form and color. The nymphs

are usually found on the underside

of leaves and have a habit of moving across the leaf with a "crablike"

motion when disturbed. When the

adults are disturbed, they fly

readily.

This insect has sucking mouth

parts and ordinarily is of little economic importance. However, experiments by Hills et al. {15) '

showed that when excessively large

numbers were allowed to breed

during the winter in field cages,

seed yield was reduced, but the

germination of the seed was unaffected.

False Chinch Bug

The false chinch bug {Nysim

ericae (Schilling)) is a true bug

and therefore has suckmg mouth

parts. It is dark gray and a little

over one-eighth inch long (fig. 26).

' Italic numbei-s in parentheses refer to

Literature Cited, p. 28.

. TC-74'6

FIGURE 26.—False chinch bug {.Nysius

ericae). (X 16.)
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED 15

The wings are plaited over the back

^yhen at rest. These bugs normally

breed on weeds, either within the

cultivated area or in adjacent uncultivated lands. Mustards are

among the favored host plants.

Only occasionally are these insects of economic importance to the

beet seed grower. Results of fieldcage tests (8) showed that 500 false

chinch bug adults per plant from

bloom to harvest dicl not reduce the

yield or viability of the seed. However, from field observations it is

shown that these insects are highly

gregarious and may occur in large

numbers in comparatively small

areas. Under these conditions

plants on wliich they congregate

may become so desiccated that they

appear burned. If this occurs on

the seed stalks when the seeds are

maturing, little or no seed will be

set.

The big-eyed bug (Geocoris sp.)

commonly occurs in seed beetfields

and is sometimes confused with the

false chinch bug. It is about the

same size and color as the false

chinch bug, but it can easily be distinguished by its stubby antennae

and large prominent eyes from

which it gets its name (fig. 27).

Geocoris is predatory on other insects and is therefore beneficial.

Aphids

The green peach aphid {Myzus

pérsicas (Sulzer) ) (figs. 28 and 29)

is the most numerous aphid attacking sugarbeets growm for seed, although in some of the southern

California areas the bean aphid

{Aphis fahae Scopoli) also occurs

in considerable numbers. The principal damage caused by aphids is

the transmission of harmful viruses.

The direct effect of their feeding is

devitalization of the plants. They

dp not reduce seed viability, but if

TC—7471

FIGURE 27.—Big-eyed bug {Geocoris sp.).

(X 14.)

sufficiently numerous they will reduce seed yield {8).

Aphids have many natural enemies, which will often hold populations at a low level or sometimes almost eliminate them from the field.

However, the buildup of parasitic

and predaceous insects is sometimes

slow. Since the aphids are vectors

of harmful viruses, the grower cannot usually afford to wait. However, he can take advantage of

assistance from these insects by

choosing an insecticide effective

against the aphid, but less harmful

to the beneficial insects.

Lady beetles are among the most

effective natural enemies of aphids.

The convergent lady beetle {Hippodamla convergens Guérin-Méneville) is one of the most numerous

species occurring in the seed beetfields. The beetles move into aphidinfested fields, feed on aphids, and

deposit eggs on the plants (fig. 30).

The eggs are spindle shaped, about
16 AGR. HANDBOOK 253, U.S. DEPT. OF AGRICULTURE

TC-7478

FiGUEE 28.—A colony of green peach aphids (Myzus persicae) on the back of a sugarbeet leaf. (X 5.)
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED 17

The stalk is hairlike and approximately 5 mm. long. The eggs hatch

into larvae similar in form to those

of the lady beetle, but they are

slightly more slender and less

highly colored. They are about

three-eighths inch long when fully

grown and brownish gray ; they are

covered with short, spiny hairs.

They have mandibles resembling

ice tongs with which they seize

their prey (fig. 35).

Unlike the lady beetle larvae,

these insects do not completely consume the aphids. The mandibles

are hollow tubes through which

they extract the body fluids of their

prey. For this reason they destroy

more aphids in a given length of

time than do larvae of the lady

beetles.

TC-T478

FIGURE 29.—Winged green peach aphid

(Myzus persicae). (X 10.)

one-sixteenth inch long, and pale

yellow. They are laid on the leaves

or stems in clusters. These hatch

into alligatorlike larvae. Larvae of

the more common species are black

or bluish gray with orange markings (fig. 31).

Both adults and larvae feed voraciously on aphids. In the absence

of aphids, the adults will maintain

themselves in the fields on pollen.

The full-grown larvae reach a

length of nearly one-half inch and

then attach themselves to stems or

leaves, where they pupate (fig. 32).

Lacewings {Chrysopa spp.) are

also important predators of aphids.

The adults of the more common

species are very delicate. They

are about five-eighths inch long

with four membranous light-green

wings (fig. 33). The eggs may be

laid singly or in groups on slender

stalks (fig. 34). They are elongateovoid, approximately 1.0 mm. long,

0.40 mm. wide, and pale green.

TC-7480

FIGURE 30.—Adult of the convergent lady

beetle (Hippodamia canvergens) and

eggs on a beet seed spikelet. (X 5.)
18 AGR. HANDBOOK 2 53, U.S. DEPT. OF AGRICULTURE

FIGURE 31.-

beetle

(X 7.)

TC-7481

-Larva of the convergent lady

{Hippodamia convergens).

Larvae of syrphid flies are also

predaceous on aphids. The adult

flies resemble wild bees, except that

they have only one pair of wings.

The eggs are deposited on aphidinfested foliage, and the maggots

feed on the aphids.

There are also several very small

wasplike insects that are true parasites, depositing eggs directly within the bodies of the aphids. The

larvae then feed on the aphid internally and finally pupate within

the body and emerge through a circular opening in the abdomen.

These parasitized aphid bodies can

easily be distinguished by their

swollen appearance, brown color,

and the emergence hole of the wasp

(fig. 36).

Fungus diseases may also attack

aphids and under certain conditions

majy' completely eliminate an infestation. First, dead aphid bodies

appear among the colonies, and

soon the whole colony may become

infected. Sometimes the dead

bodies may be covered with a typical fungus growth, or they may

simply appear as mummies.

TC-7482

FIGURE 32.—Pupae of the convergent

lady beetle {Hippodamia convergens) on

a beet leaf. (X 3.)
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED 19

TC-7483

FIGURE 33.—Green lacewing (Chrysopa

spp.). (X 4.)

TC-74S4

FIGURE 34.—Egg of the green lacewing

{Chrysopa spp.) on a beet leaf.

(X 16.)
20 AGR. HANDBOOK 2 5 3, U.S. DEPT. OF AGRICULTURE

TC—7608 and TC-7B07

FIGURE 36.—Parasitization of the green

peach aphid {Myzus persicae) : Ä,

Parasitized aphid with parasitic wasps;

B, aphid bodies from which adult parasites have emerged. ( X 9 and X 5.)

TC—7485

FIGURE 35.—Larva of the green lacewing

(Chrysopa spp.) with an aphid.

(X 12.)
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED

SEED FEEDERS

21

Studies in field cages (8) of all

potential seed-feeding insects found

in the beetfields showed that insects

of the genus Lygus and several species of stink bugs were the primary

cause for the production of nonviable seed and were also responsible for lower yields. Since lygus

bugs were found to be the most

numerous of the seed feeders, more

detailed studies (9) were made with

single specimens of males, females,

and nymphs of the various species

in cages on seed spikelets to determine the comparative amount of

damage attributable to each.

Lygus Bugs

At least three species of Lygus

occur throughout the areas where

sugarbeet seed is grown. These are

Z. hesperus Eaiight, lineolaris

(Palisot de Beauvois), and elisus

Van Duzee. Occasionally other

species may occur in the more northern areas, but they have not been

found in significant numbers.

The adults average about onefourth inch in length and oneeighth inch in width. L. hesperus

is slightly larger than the other

two species and elisus smaller. L.

hesperus is angular with whiplike

antennae about two-thirds the

length of the body (fig. 37). It

varies from yellowish green to reddish brown. L. lineolaris varies

from green to brownish, often having distinctive yellow spots on the

outside edge and toward the rear of

the forewings. L. elisus is usually

pale green. All have a prominent

triangular plate in the center of

the body at the base of the forewings.

The nymphs resemble the adults

in form (fig. 38) but are usually

pale green, although the larger

nymphs of liesperus or lineolaris

""v^

TC-748e

FIGURE 37.—Adult of Lygus hesperus.

(X 8.)

TC-7481

FIGURE 38.—Nymph of Lygus hesperus.

(X 8.)
22 AGR. HANDBOOK 2 53, U.S. DEPT. OF AGRICULTURE

may have a brownish cast. To the

casual observer the smaller nymphs

may slightly resemble aphids, except for the prominent antennae

and their rapid movement. The

very small nymphs appear to be all

legs and antennae. Lygus adults

can easily be seen on the seed heads,

but because of their color and size

the nymphs are very inconspicuous

and can easily oe overlooked.

Their presence is best detected with

a muslin swe«p net, or for cursory

examination the stalks may be

shaken over a piece of white paper

or a card.

In the southern areas hesferus

and lineolarù are the predominant

species. In northern California

and in Oregon elisus predominates.

All three species feed on the developing seed, causing the embryos

to collapse and resulting in hollow,

lightweight seed balls (fig. 39).

This damage shows up primarily

in a reduced percentage of germinating seed balls and also in reduced yield, since many of the

lightweight seed balls are discarded

in the recleaning process.

^

.^

^

TC-7488

FIGURE 39.—Dissected multigerm seed

balls of sugarbeet: Upper row damaged

by lygus bugs has only shriveled germs;

lower row has healthy well-filled seed

balls. (X 3.)

L. hesperus and lineolaris cause

slightly more damage than does

elbiibs, and the females and nymphs

of all three species destroy more

seed per insect than do the males.

Usually the Lygus population is

predominantly nymphs at the time

the crop is susceptible to injury by

these insects and, therefore, control

is ordinarily directed against the

nymphs.

Lygus females are attracted to

the seed beetfields soon after seedstalk development has started in the

spring. They deposit eggs within

the tissues of the growing tips of

the seed stalks while the stalks are

still vegetative, and by the time

flowering starts the first brood of

nymphs begins to appear.

Sweep-net collections throughout

the season in the Salt Eiver Valley

of Arizona indicated that one

Lygus per sweep of a 14:-inch insect

net at the peak of populations on

developing seed will cause a measurable reduction in the percentage

of germinating seed. These collections further showed that 20

Lygus females per 100 sweeps in

the fields when seed stalks are

vegetative (usually April 1-15 in

the Salt River Valley) are sufficient

to produce a damaging population

of nymphs by the time the plants

begin to flower. Since very few

males occur in the beetfields early

in the season, a count of total adults

at this time is sufficiently accurate.

The Lygus species damage only

the soft newly formed seed. Although the insects may be present

earlier, experiments by Hills and

Taylor {16) showed that little or

no damage occurred until soft seed

was present. However, since some

soft seed is present soon after

blooming starts, it is recommended

that the first insecticide applications be made in the early bloom

stage if there are as many as one
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED 23

Lygus per sweep of a 14-iiich insect

net.

Before the development of DDT,

Lygus control was difficult. Dusting sulfur or pyrethrum extractimpregnated sulfur dust gave partial control. However, the first

field trials with DDT in 1944 and

1945 showed remarkable results

{13). For several years good control of Lygus was obtained with

DDT, resulting in increased germination and yield of seed {4)

{20). By 1953 some growers reported poor results with DDT, and

field-plot tests in 1954 {18) showed

that DDT was not so effective as it

had been in 1944 and 1945. Therefore, since 1954 it has been necessary to use other insecticides either

alone or in combination with DDT,

and rarely can satisfactory results

be obtained with one application.

This change in the effectiveness of

DDT is attributed to the development of resistance in Lygus to this

insecticide.

Stink Bugs

Three species of stink bugs commonly infest fields of seed beets—

the Say stink bug {Chlorochroa

sayi Stal), the red-shouldered plant

bug {Thyanta pallido virens spinosa Euckes), and the brown stink

bug {Euschistv^ servus impictiventris Stal). The small plant bug

{Thyanta irevis Van Duzee) and

the conchuela {Chlorochroa ligata

(Say)) may sometimes also occur.

The general appearance of these

pugs is similar. Each has a prominent pronotum, or plate directly

behind the head, and a scutellum, or

triangular plate in the center of

the back. The anterior of the insect is angular with a distinct head

and prominent four-jointed antennae. The posterior is rounded and

the wings are plaited on either side

of the scutellum. The forewings

FIGURE 40.—Say stink bug {Chlorochroa

sayi). (X 4.)

are thickened and heavy except for

the membranous tips. The hindwings are entirely membranous.

The Say stink bug is the most

common species found in the seed

beetfields (fig. 40). These insects

vary slightly in size but will average about one-half inch in length

and about five-sixteenths inch in

width. The overall color varies

from bright green to olive green

flecked with white. Sometimes

there is an orange band around the

lateral edges of the abdomen.

The red-shouldered plant bug is

slightly smaller than the Say stink

bug, averaging about three-eighths

inch in length and one-fourth inch

in width (fig. 41). It varies from

bright green to light greenish

brown. The pronotum has points

on either side, which are sometimes

reddish, or the posterior edge of the

pronotum may be reddish, from

which it gets the name red-shouldered plant bug.

The brown stink bug is slightly

larger than the Say stink bug,

averaging about nine-sixteenths
24 AGR. HANDBOOK 253, U.S. DEPT. OF AGRICULTURE

TC-7490

FIGURE 41.—Red-shouldered plant bug

(Thyanla pallido virens spinosa).

(X 5.)

inch in length and three-eighths

inch in width (fig. 42). It varies

from light brown or tan to dark

brown. It is more angular than

the Say stink bug and has a prominent point on either side of the

pronotum.

The small plant bug is, as the

name implies, much smaller than

the other species (fig. 43). It is

only about one-fourth inch long and

three-sixteenths inch wide. The

general shape is the same as that of

the Say stink bug and it varies from

green to light brown.

The conchuela is very closely related to the Say stink bug and resernbles this species except for color.

It is dark, almost black, with a red

band around the edge of the abdomen and a red dot on the back at

the tip of the scutellum.

Studies in field cages (9) showed

that, on an average, one Say stink

bug adult confined on a seed spikelet during seed formation caused

206 nonviable seed balls per season

as compared to 86 nonviable seed

balls for one Lygus female or

nymph. Cage studies (<?) also

showed that the red-shouldered

plant bug caused equally as much

damage as Lygus but not so much

as the Say stink bug. Later studies

by Hills and McKinney {ñ)

showed that the brown stink bug

could cause almost as much damage

as the Say stink bug, and further

studies by Hills and Taylor (Í7)

showed that the Say stink bug could

drastically reduce the yield of

nearly mature seed and could cause

some damage to seed after the

stalks were cut and in the windrow.

These insects not only caused nonviable seed balls but also killed some

of the embryos in other seed balls

and thus reduced the number of

sprouts per viable ball.

No data are available on the comparative damage that may be

caused by the small plant bug, but

it has occasionally been noted as numerous in seed beets and appeared

to be feeding on the nearly mature

seed as do other stink bugs.

TC-7481

FIGURE 42.—Brown stink bug {Euschistus servus impictiventris). (X 3.)
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED 25

_ TC-7492

FIGURE 43.—Small plant bug {Thyanta

hrevis). (X 7>i.)

Although all the stink bugs

tested have caused as much or more

damage to sugarbeet seed than does

Lygus, they are not considered as

important economically as Lygus

because of their erratic occurrence.

Several years may pass with so few

stink bugs that they are of little

concern to the beet seed grower.

However, these insects are migratory and can suddenly appear in

fields near harvest with drastic results. Usually they will appear on

the edge of the fields first and can

be detected if the fields are closely

watched.

During the middle of warm days

stink bugs will seek shade and go

down deeper into the plants, where

they are difficult to detect. They

can best be observed during the

early-morning hours, when they

will be up on the sunny side of the

spikelets. Sweep-net collections do

not give an accurate estimate of the

numbers present, since these bugs

have a habit of dropping to the

ground at the least disturbance.

The best way to detect stink bugs is

to carefully examine the fields during the early-morning hours. If

stink bugs are readily observed, insecticides should be applied.

VIRUS VECTORS

At least three important virus

diseases affect sugarbeets grown for

seed. These are curly top, transmitted by the beet leafhopper (Circulifer tenellus (Baker)), and beet

yellows and beet western yellows,

both of which are transmitted by

aphids.

Beet Leafhopper and Curly

Top

The beet seed producing areas of

Arizona, New Mexico, California,

Utah, and Nevada are subject to infestation by the beet leafhopper and

damage by curly top disease. The

beet leafhopper is a slender insect,

approximately one-eighth inch

long, varying from gray to greenish yellow (fig. 44). When disturbed, it will usually take off for a

short flight with a hop. The

nymphs resemble the adults in general form (fig. 45). Very young

nymphs are a pale yellowish green,

but m later stages they have darkbrown or red markings. In the

full-grown nymphs, developing

wings, or wing pads, can be seen.

Most of the individuals th.^t feed

on the beet seed crop develop in surrounding desert areas and migrate

to the beetfields. In general there

are two movements, one in the fall

and one in the spring. The magnitude of the movement is dependent

on the abundance of breeding host

plants. During the winter and

spring the insects breed on winter

annual plants in the desert and

move to the cultivated areas with
26 AGR. HANDBOOK 2 53, U.S. DEPT. OF AGRICULTURE

.;•- Experiments by Hills et al. (11)

showed that infestations of curly

top-infective beet leafhoppers on

seed beets in the spring are of little

concern, even on curly top-susceptible beets. On the contrary, migrations of beet leafhoppers in the fall,

when the beets are small, can be

disastrous, even to curly top-resistant varieties. An average beet

leafhopper population of 50 per

100-foot row on small beets in the

fall indicates a need for insecticide

treatment.

Beet leafhopper populations cannot be accurately counted without a

counting cage (7). They are very

active and will jump and fly from

the plants before they can be

counted if observations are attempted without this equipment.

Experience has shown that the

sweep net is of little value in estimating beet leafhopper populations. The activity of these insects

varies so greatly with temperature,

wind movement, and time of day

that sweep-net collections are unreliable. .

Field tests by Hills et al. [W

from 19M to 1947 showed that

DDT in a spray or dust was effective against the beet leafhopper.

TC-7493

FIGURE 44.—Beet leafhopper {Circulifer

tenellus). (X 25.)

brood maturity or with the drying

of the host plants. During the summer there are other annual plants

in the desert on which the insects

breed and from which they move to

the cultivated areas in the late summer or fall. The magnitude of leafhopper infestations in the seed beets

is, therefore, indirectly dependent

on winter and summer rains, which

help to germinate and maintain

these desert plants.

In addition to the influx of leafhoppers from desert areas, there

are always some leafhoppers that

develop on weeds within the cultivated areas. These insects are especially important economically,

not only because of their nearness

to the cultivated crops but also because a higher percentage of them

are likely to be carrying the curly

top virus.

TC-74e4

FIGURE 45.—Nymph of the beet leafhopper {Circulifer tenellus). (X ¿^1
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED 27

Observations in 1961 indicated that

this insecticide was still effective

against this insect. Experiments

by Hills et al. {19) in 1959 showed

that leafhoppers can be controlled

up to the four-leaf stage by seed or

soil treatment with phorate or Disyston.'

Aphids and Yellows Viruses

Beet yellows, widely known as

virus yellows, was first recognized

in sugarbeets in the United States

in 1951 [3), but it was not reported

in sugarbeets grown for seed until

1955 {1). The green peach aphid

is the most important vector of the

yellows virus in seed beets. Bennett (i) showed that other aphids

are capable of transmitting this virus. However, the green peach

aphid is not only an eíBcient vector but widely distributed and is

numerous in seed beetfields everywhere that the crop is grown. This

insect also has a wide variety of

breeding host plants, which increases the possibility of its carrying the virus from alternate hosts

to sugarbeets.

The work of Bennett and McFarlane {2) showed that yellows from

early-spring infection reduced the

yield of beet seed 43 to 70 percent.

Later infections resulted in reductions of 19 to 21 percent. There was

also a reduction in seed size but not

in germination. In 1958 field-plot

tests by Hills et al. [10) showed an

average decrease in seed yield of

35 percent where an infestation of

yellows-infective green peach aphids occurred on November 20. Infestations on February 21, March

26, April 8, and April 21 resulted

'Mention of proprietary products

does not constitute their endorsement by

the U.S. Department of Agriculture.

in yield reductions of 27, 18, 14,

and 7 percent, respectively. These

experiments demonstrated the need

for early and thorough aphid control.

In 1960 Duffus (5) discovered a

virus disease of sugarbeets, which

he named radish yellows. Later he

called it beet western yellows {6).

Symptoms are similar to those of

beet yellows, although the virus is

unrelated. Field tests by Duffus

{6) showed that western yellows

reduced tonnage and sucrose content in sugarbeets the same as beet

yellows. The two viruses together

reduced beet tonnage more than

either one alone, but the reductions

were not more than additive.

Field experiments by Hills et al.

{11) showed that beet western yellows and beet yellows both reduced

the yield of beet seed and that a

mixture of the two viruses reduced

the yield more than either one

alone. In these experiments beet

western yellows reduced yields 13

percent and beet yellows 17 percent,

whereas a combination of the two

viruses reduced yields 36 percent.

Neither of the viruses affected the

germination of the seed.

Studies by Bennett {1) and Sylvester {21) showed that the beet

yellows virus is semipersistent.

After acquiring the virus, most of

the aphids lose the ability to transmit it in 24 hours, although a few

may retain the virus for as long as

72 hours. On ih& other hand, Duffus (5) showed that the western

yellows virus is persistent in the

aphid. Once the insect acquires the

virus, it can transmit western yellows the rest of its life. In all probability, therefore, a beetfield some

distance from the virus source

would be more likely to become infected with beet western yellows

than beet yellows.
28 AGR. HANDBOOK 25 3, U.S. DEPT. OF AGRICULTURE

LITERATURE CITED

(1) BENNETT, C. W.

1960. SUGAR BEET YELLOWS DISEASE IN THE UNITED STATES. U.S DeDt ACT

Tech. Bui. 1218, 63 pp. '

(2) and MOFABLANE, J. S.

1959. EFFECT OF THE VIEU8 YELLOWS ON SUGAB BEET SEED PEODTJCTION. US

Agr. Res. Serv., Plant Dis. Rptr. 43: 1188-1190.

(3) CooNS, G. H.

1952. VIRUS YELLOWS OP BEET IN THE UNITED STATES. U.S. BuT. Plant Indus.,

Soils, and Agr. Engin., Plant Dis. Rptr. 36: 356-363.

(4) DOXTATOR, C. W.

1948. THE EFFECT OF LYQU8 CONTROL ON THE PRODUCTION OF EUTE SEED. Amer.

Soc. Sugar Beet Technol. Proe. 5: 499-501.

(5) DUFFUS, J. E.

1960. RADISH YELLOWS, A DISEASE OF RADISH, SUGAB BEET, AND OTHEE CEOPS.

Phytopathology 50: 389-394.

(6)

1961. ECONOMIC SIGNIFICANCE OF BEET WESTERN YELLOWS (RADISH YELLOWS)

ON SUGAB BEET. Phytopathology 51: 605-607.

(7) HILLS, O. A.

1933. A NETW MBH-HOD FOR COLLECTING SAMPLES OF INSECT POPULATIONS. JOUT.

Econ. Ent. 26: 906-910, illus.

ISOLATION-CAGE STUDIES OF CERTAIN HEMIPTER0U8 AND HOM0PTEE0TT8

INSECTS ON SUGAR BEETS GROWN FOE SEED. JoUT. EcOn. Ent. 34 : 756-760,

illus.

COMPARATIVE ABILITY OF SEVERAL SPECIES OF LYQUS AND THE SAY STINKBUG TO DAMAGE SUGAB BEETS GEOWN FOR SEED. JoUr. AgT. RcS. 67:

389-394.

BENNETT, C. W., JEWELL, H. K., and others.

EFFECT OF VIRUS YELLOWS ON YIELD AND QUALITY OF SUGAB BEET SEED.

Jour. Econ. Ent. 53: 162-164.

CouDRiET, D. L., JEWELL, H. K., and others.

EFFECT or THREE IN8E0T-BOBNE VIRUS DIBEASES ON SUGAB BEET SEED PRODUCTION. Jour. Econ. Ent. 56 : 690-693, illus.

and McKiNNEY, K. B.

DAMAGE BY EUSCHISTUS IMPICTIVENTBIS AND CHLOROCHBOA 8AYI TO SUGAB

BEETS GROWN FOB SEED. Jour. Econ. Ent. 39: 335-337.

McKiNNEY, K. B., and PEAY, W. E.

1946. LYGUS CONTROL IN SUGAR BEETS GROWN FOR SEED. Amer. Soc. Sugar Beet

Technol. Proc. 4: 298-318, illus.

MAST, A. A., and WOOD, R. C.

FIELD INSECTICIDE TESTS AGAINST THE BEET LEAFHOPPER IN SUGAB BEETS

GROWN FOR SEED. Amer. Soc. of Sugar Beet Technol. Proc. 5:480-486.

RoMNEY, V. E., and MCKINNEY, K. B.

EFFECT OF EMPOASCA SOLANA ON SUGARBEETS GROWN FOR SEED. JOUr.

Econ. Ent. 37: 698-702, illus.

and TAYLOR, B. A.

LYGUS DAMAGE TO SUGAR BEET SEED IN VARIOUS STAGES OF DEVELOPMENT.

Amer. Soc. Sugar Beet Technol. Proc. 6: 481-487, illus.

and TAYLOR. E. A.

EFFECT OF THE SAY STINK BUG ON MATURING SUGAB BEET SEED. Amer.

Soc. Sugar Beet Technol. Proc. 6: 488-490, illus.

TAYLOR, B. A., and "VALCABCE, A. C.

RESISTANCE OP LYGUS BUGS TO DDT ON SUGAB BEETS GEOWN FOR SEED.

Jour. Econ. Ent. 49: 94.

VALCARCE, A. C, JEWELL, H. K., and COUDRIET, D. C.

1960. BEBT LEAFHOPPER CONTROL IN SUGAR BEETS BY SEED OB SOIL TREATMENT.

Amer. Soc. Sugar Beet Technol. Jour. 11: 15-24.

1941.

(9)

1943.

(10)

1960.

(11)

1963.

(12)

1946.

(13)

1946.

(14) -

1948.

(15)

1944.

(16)

1950.

(17) -

1950.

(18)

(19) -

1956.
INSECTS AFFECTING SUGARBEETS GROWN FOR SEED 29

(20) MoREOW, W. B., WOOD, R. C, and MAST, A. A.

1948. PROGRESS REPORT ON THE COMMERCIAL CONTROL OF LTGUS ON THE SU6AB

BEET SEED CROP IN ARIZONA AND NEW MEXICO. Amer. Soc. Sugar Bect

Technol. Proc. 5: 493-498.

(21) SYLVESTER, E. S.

1956. BEET YELLOWS VIRUS TRANSMISSION BY THE GREEN PEACH APHID. Jour.

Econ. Eut. 49; 789-800.

U.S. GOVERNMENT PRINTING OFFICE: 1983 O—«93-392