Monday, December 10, 2007 - 8:53 AM

Electroantennogram and behavioral responses of Pteromalus cerealellae (Ashmead) (Hymenoptera: Pteromalidae) to odor stimuli associated with its host, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae)

Ebenezer O. Onagbola, and Henry Y. Fadamiro, Auburn University, Department of Entomology & Plant Pathology, 301, Funchess Hall, Auburn University, Auburn, AL

Pteromalus cerealellae is an ectoparasitoid of larvae of the bruchid, Callosobruchus maculatus (Fab.) (Coleoptera: Chrysomelidae), which live endophytically in cowpea seeds. The role of host-related semiochemicals in host location behavior of this parasitoid was investigated using electroantennogram (EAG), behavioral (olfactometer), and analytical (gas chromatography) techniques. Responses of mated and unmated female P. cerealellae were tested to a variety of host-related chemical stimuli including hexane extracts of uninfested cowpea seeds, (bruchid)-infested cowpea seeds, bruchid larvae (whole body or WB), larval frass, adult female bruchids (WB), and adult male bruchids (WB). All of the tested stimuli elicited significant EAG response in unmated and mated female P. cerealellae. Results from Y-tube olfactometer bioassays demonstrated significant response of mated female P. cerealellae to extracts of uninfested cowpea seeds, infested cowpea seeds, adult female bruchids, bruchid larvae, and larval frass, but no significant response was elicited by the extract of adult male bruchids. Pair-wise comparisons of the four most attractive stimuli (uninfested seeds, infested seeds, bruchid larvae, and larval frass) in a four-way olfactometer showed preference of mated female P. cerealellae for the extract of uninfested cowpea seeds compared to larval frass. No significant differences were recorded between other paired treatments. Gas chromatographic (GC) analyses of the chemical profiles of the various tested stimuli revealed quantitative and qualitative differences in chemical composition, which may explain the observed greater parasitoid response to cowpea seed extracts. These results suggest that female P. cerealellae may be using chemical stimuli associated with the habitat of its host (cowpea seeds) rather than host-specific kairomones, as long range host location cues.

Species 1: Hymenoptera Pteromalidae Pteromalus cerealellae (parasitic wasp)