Submitted to: Insect Neurochemistry and Neurophysiology Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 1997
Publication Date: N/A
Technical Abstract: Euplectrus comstockii, is an ectoparasitic, gregarious, eulophid wasp which parasitizes the larval stage of several important lepidopteran pests. Parasitization of both natural and unnatural hosts prevents molting in the instar parasitized. Here we report the effect of wasp venom on the European corn borer (unnatural host), an important pest of corn and other vegetables. An extract prepared from venom glands of adult E.comstockii, when injected into O. nubilalis 5th instars, inhibited growth, development and molting of the injected larvae. The observed effect was dose and age dependent. When 3rd, 4th and 5th instar O. nubilalis were envenomated by adult wasps, the larvae also were developmentally arrested and failed to undergo a molt. However, 3rd and 4th instars underwent apolysis (separation of the epidermis from the old cuticle) and produced new cuticle. Fifth instars did not. A premolt hemolymph ecdysteroid peak was not observed in these experimental 5th instars, but injections of 20-hydroxyecdysone induced apolysis and new cuticle formation. Envenomated 4th instars exhibited a premolt hemolymph ecdysteroid peak. HPLC/RIA revealed that 20-hydroxyecdysone was present in the hemolymph of these pharate 5th instars. Our results support the view that the mode of action of the venom depends upon the instar parasitized.