SO-269

1981

A Phloem Sandwich Unit for Observing Bark Beetles,

Associated Predators, and Parasites’ .

Donald N. Kim, and Mitchel C. Miller

SUMMARY

This paper describes a phloem sandwich that

allows observation of parent beetles, their brood,

and associates within the inner bark, and permits

observation of predator and parasite behavior on the

bark surface. The construction of the unit permits

the introduction of multiple pairs of beetles into a

single sandwich.

Additional keywords: Bark beetle rearing,

Scolytidae.

The behavior of bark and engraver beetles in their

galleries has traditionally been studied using an

“observation plate” or “phloem sandwich.” Originally,

this device consisted of a thin, flat section of inner

bark placed between two plates of glass held together by elastic bands (Bedard 1933). Moist cotton

packed between the two plates prevented dessica-

- tion of the bark. Kaston and Riggs (1937) ensured

the inner bark’s intimate contact with the glass, a

necessity for successful brood development, by using

tightly bolted wooden clamps. Reid (1958, 1962)

and Yu and Tsao (1967) used similar devices with

friction tape binders to study the behavior of Den-

‘The work herein reported was funded in part by the U.S. Department of Agriculture’s Expanded Southern Pine Beetle Research

and Applications Program.

drocfonus ponderosae Hopk. and D. frontalis Zimm.

Hopping (1961) used Lucite plastic sandwiches

sealed with adhesive tape to study Ips spp. Whereas

with the earlier sandwiches beetles had to be

- introduced at one end of the unit,. Hopping’s design

permitted them to be introduced through a hole

in the center of the face plate: The beetles could

thus excavate galleries in any direction. Nagel and

Fitzgerald (1975) used this type of sandwich to study

behavior and prey consumption of Medetera aldrichi

Wheeler. Unfortunately, adult bark beetles can etch

acrylic plastic and bore through it, making observation difficult. Bushing (1967) improved the design

by rep)acing the lower glass with a plywood base to

hold the inner bark between the glass and wooden

base by means of U-shaped metal clamps. The unit

was sealed by filling the space between the wooden

base and glass with paraffin, and beetles were introduced through a hole drilled in the center of the base.

A disadvantage of all these designs is that they do

not allow beetles or associates access to the outer

bark surface. Many parent bark beetles construct

air holes, which probably control humidity in their

galleries (Melnikova 1964, Gaumer and Gara 1967).

The phloem sandwich constructed by Beanlands

(1966) from a plastic petri dish and a mason jar ring

provided an air space above the outer bark surface

into which the beetles could void their boring dust.

Southern Forest Experiment Station/T-10210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma, Tennessee, Eastern Texas.

1
,H

Figure 1 -Open bark surface phloem sandwich. A = 4.76-mm bolt, B = plastic uppersurface with one introduction

and two ventilation holes, C = plastic spacer blocks;-one with entrance shaft, D = aluminum foil,

E = inner bark, F = glass lower surface, G = U-clamp, H = 4.76-mm wingnut.

However, the upper portion of this sandwich had

no holes to allow gas exchange between the unit

and ambient air.

To facilitate studies of the insect and mite predatars and parasites of scolytid beetles, investigators

at the Southern Forest Experiment Station devised

a phloem sandwich unit incorporating the best

features of previous designs. This unit (fig. 1) consists Of a plate glass lower surface (0.64X15.24X

19.05 cm), a bark phloem section (14.60X18.42 cm

planed to uniform thickness), and a plastic top plate

(0.64X1 5.24X22.80 cm). Edges of the bark section

are sealed with paraffin. Plastic spacers (0.64X2.54X

15.24 cm on sides and 0.64x3.81 xl 5.24 cm on ends)

are glued to the outer edges of the top plate to keep

it from touching the bark surface. To discourage

beetles from tunnelling into the plastic spacers,

their lower surfaces are laminated with household

aluminum foil using double-sided carpet tape. Four

or more Plastic spacers (0.64x0.64x2.54 cm), glued

uniformly around the center of the top plate’s inner

side, exert pressure in the center to prevent warping

of the bark section and its loss of contact with the

lower glass surface. The unit is held together with

clamps made of 16-gauge steel shelf standards.

The top plate has two 2.54-cm screened ventilation holes. Moisture can escape from the unit

through functional vent holes constructed by beetles.

Large predators and parasitoids can be introduced

through the 1.27~cm access hole located between

the screened ventilation holes. This opening can

be plugged following introductions. Adult beetles,

phoretid associates, and small parasitoids are introduced through a hole slightly larger than the.

diameter of the beetle. The hole is drilled at an

angle of less than 45O in one or more of the short

spacers, making multiple introductions possible.

Franklin (1967) found that a hole drilled in the bark

at less than’45O facilitated southern pine beetle

penetration. Pairs of southern pine beetles placed

D0na’d N. Kinn and Mitchel C. Miller are Entomologists, Southern Forest Experiment Station, Forest Service-USDA, Pinevitre* Louisiana 7 1360.

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in the entrance shaft have penetrated the bark of

sandwiches in less than 30.minutes. Forced attacks

of adult southern pine beetles can be facilitated

by screwing similar entrance blocks to wood slabs

or bolts.

Ips beetles have completed normal development

in this sandwich, but success with the southern pine

beetle has been limited. The phloem unit sho:Jld

remain usable for 5 to 6 weeks, providing intimate

contact of the inner bark and the lower glass

plate is achieved and maintained. Each unit costs

approximately $4 and, barring accident, should be

reusable indefinitely.

LITERATURE CITED

Beanlands, G. E.

1966. A laboratory-rearil?g method for observirlg

adult bark beetles and their developing broodls.

Can. Entomol. 98:412.-414.

Bedard, W. D.

1933. The number of larv;al instars and the appro>:imate length of the larvzrl stadia of Dendroctoncls 8

pseudotsugae Hopk., with a method for their

determination in relatilon to other bark beetle:;. ;

J. Econ. Entomol. 26:l 128-l 134.

Bushing, R. W.

1967. Parasites of the western pine beetle, Den- j

droctonus brevicomis. Le Conte (Coleoptera: ,

Scoiytidae), with partic:ular reference to Roptro- 1

cerus xylophagorum (Ratzeburg) (Hymenop- j

tera: Torymidae). Ph.Cr. dissertation, Univ. Calif., \

Berkeley. 120 p. 1

/

Franklin. R. T.

1967. ‘A technique for studying the insect Parasites of Dena’roctonus frontalis and other bark

beetles (Coleoptera: Scolytidae). J. Ga. Entomol. Sot. 2:153-44.

Gaumer, G. C:, and R. I. Gara.

1967. Effects of phloem temperature and moisture content on development of the southern

pine beetle. Contrib. Boyce Thompson Inst.

23:373-377.

Hopping, G. R.

1961. Techniques for rearing Ips De Geer(ColeoPtera: ScolytiQaef. Can. Entomol. 93:1(X0-1063.

Kaston, B. J., ancl D. S. Riggs.

1937. Studies on the larvae of the native elm

bark’beetle. ,). Econ. Entomol. 30:98-l 08.

Melnikova, N. I.

1964. Biologic;21 significance of the air hole:5 in egg

tunnels of Scolytus ratzeburgi Jans. (Coleootera:

Ipidae). Entcrmol. Rev. (Transl. Entomol. Ob‘ozr,)

43( 1): 16-23.

Nagel, W. P, and T, D. F;‘tzgerald.

1975. Medetera a/drict,:ii larval feeding behaviorand prey consumption ,(Dipt.: Dolichopodidat?){ <.

Entomophaga 20:121-12’7. ..

Reid, R. W.

1958. The behavior of the mc?untain pine beetle,

Dendroctonus montjco/ae f-,(opk., during mating, egg laying and gallery c onstruction. Can.

Entomol. 90:505-509.

Reid, R. W.

1962. Biology of the mountain pint ? beetle, Dendroctonus monticolae Hopkins, in the East

Kootenay region of British Columbi,‘a. II. Behavior in the host, fecundity and intern, al changes

.in the female. Can. Entomol. 94:605+ 813.

Yu, C. C., and C. H. Tsao.

1967. Gallery construction and sexual b ehavior

in the southern pine beetle, Den&o‘ :tonfJs

frontalis Zimm. (Coleoptera: Scofytidae). , 1. Ga.

Entomol. Sot. 2:95-98.

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