I COLLEGE OF AGRICULTURE COOPERATIVE EXTENSION SERVICE WASHINGTON STATE UNIVERSITY

PULLMAN, WASHINGTON 99163

May, 1966 E. Mo 2631

ENEMIES OF THE ALFALFA LEAFCUTTING BEE AND THEIR (X)NTROL by Carl Johansen and Jack Eves Associate Entomologist and Experimental Aide Department of Entomology

One of the major pollinators of alfalfa grown for seed in the state of Washington, the alfalfa leafcutting bee (), has been increasingly killed by parasites and nest destroyers during the past 3 years. Seventeen of these pests have been identified to date. The most numerous parasite is the small wasp, Monodontomerus obscurus . It is shiny blue-green and only 1/8 to 1/6 inch long. A carpet , glabrum, is currently the most abundant nest destroyer. It is oval, dull black with three faint lines of white bristles across the wing covers, and 1/10 to 1/7 inch long.

Control

Control of the parasites and nest destroyers of the alfalfa leafcutting bee is largely a matter of good management practices. Since all parasite adults complete emergence at least t wo days before the ma le leafcutters begin to emerge, they can be readily destroyed in an incubation room. Pests such as Trogoderma remain active in the bee nests , feeding and reproducing through­ out the year. A more complex system of sanitary measures is required to keep them below damaging population levels. Helpful practices are classified as: (1) cleanup, (2) cold storage , ( 3) nest renovation, and (4) use of poison baits.

Cleanup -- To trap the parasites emerging in your leafcutting bee incubation room, simply place a pan of water beneath a light bul b. The parasites are strongly attracted to light and then drop into the water. When parasites are actively emerging , the traps should be emptied and the contents destroyed daily in order to ensure effectiveness. If there are windows in the room, the parasites can be collected with a vacuum cleaner and destroyed each day.

Bee nest structures should be mounted on pins or spikes, providing about a half-inch clearance from the wal l s of your field shelters. Debris such as leaf cuttings, po llen, and old cell materials will not accumulate to provide food for carpet and other nest destroyers.

EXTENSION WORK IN AGRICULTURE AND HOME ECO OMICS I COOPERATION WITH U.S. DEPARTMENT OF AGRICULTURE E. M. 2631 -Page 2

Gordon Hobbs , Canada Department of Agriculture 9 Lethbridge, advocates the use of grooved boards for leafcutting bee nests . This recommendation has considerable merit because the bees can be more effectively managed and protected from their enemies with this type of shel ter. The component boards are separated after bee re- nesting is comp l ete and the individual cells peeled from the grooves. Such cells can be examined and those con­ taining defective or parasitized bee larvae removed and destroyed during the winter months.

Cold Storage - - Carpet beetles and other nest dest royers are active at low temperat ures and can cause considerable damage at 50° F. Leafcutter nests stored in open or unheat ed buildings can be severel y damaged by these pests. Stora~e of nest structures at 35 - 38°F. will s t op t his activity during the 7 - 9 1/2 months the bees are i nactive (time depe ndent upon locality and whether one or two bee generations per se ason are bei ng ut i lized.) Some alfalfa seed growers rent commercial cold storage space for this purpose.

Nes t Renovation -- Ol d leafcutter nest bl ocks cont aining nest destroyers can be pl aced in a box-type containe r which i s light-tight except for one or more small openings. These may be pl aced i n the f i e l d between bee shelters. The bees will emerge and fly out, while many of t he c arpe t beetles tend to remain with the ol d material . If the bees move back i nt o the box, attach a metal s c reen cone about 5 inches in diameter at t he bas e and wi t h a ha l f-inch open ing a t the tip over the exit hol e. This f o rms a on e~way passage and the bees will soon f l y off to a fie l d sheltero

After most of the bees have emerged , the old 9 infes ted nest material can he burned. However 7 if you wish to s ave drilled wo od bl ocks , simpl y heat them to 150° F. for several hours. Lar ge quantities mi ght be t reat ed in a com­ mercial lumber kiln.

Poison Baits -~ We tested a modification of t he "Tr ogo t rap" ( developed by F. L. Blanc , California State Department of Agricu l t ure for use in khapra beetle detection) against carpet beetl es i n l eafcutter ne s t s . Traps are prepared from 4" x 4" pieces of open- face corrugated c ardboard. The bait is a mixture of two parts canned dog food and one pa rt powdered mil k by volume to which is added enough 50% DDT wettabl e powde r t o provide a 1% bait (e . g. two grams of DDT per 98 grams of t he dog f oo d~il k mixtu re ) . A putty knife is used to smear the bait int o the co r rugations, leaving about a one­ inch wide c l ean area border ( see Figure 1). A 4 9 ~ x 4u piece of heavy wrapping paper is gl ued over the bait-smeared c ar dboard. The finished trap is attracti ve to both beetles and ma ture l a r vae of Tr ogode nna and the l eaf­ cutting bee will not contact the DDT bai t i f c a rdboard wi th corrugations 1/8 inch or less in diameter is used. E. M. 2631 - Page 3

Figure 1. Construction of Trogotrap (Courtesy of Plant Pest Control Div., USll\)

DDT-treated Trogotraps provided good control of Trogoderma in our experiments. Longer strips of cardboard with the open ends of the corrugations facing out­ wards may be prepared to fit under leafcutting bee nest blocks in field shelters or stacks of nests in storage.

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