BIOLOGICALLY-BASED TECHNOLOGIES FOR MANAGEMENT OF CROP INSECT PESTS IN LOCAL AND AREAWIDE PROGRAMS
Location: Insect Behavior and Biocontrol Research Unit
Title: Host suitability affects odor association in Cotesia marginiventris: implications in generalist parasitoid host-finding
Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 6, 2012
Publication Date: March 22, 2012
Citation: Harris, C.M., Ruberson, J.R., Meagher Jr, R.L., Tumlinson, J.H. 2012. Host suitability affects odor association in Cotesia marginiventris: implications in generalist parasitoid host-finding. Journal of Chemical Ecology. 38(4):340-347.
Interpretive Summary: Many parasitic wasps in the family Braconidae are important natural enemies against caterpillar pests that attack agricultural crops such as corn, forage grasses, turf, peanuts, and cotton in the southeastern, eastern and central United States. These wasps can even provide a level of control in cropping systems that are intensively managed. However, basic information such as how female wasps find their caterpillar hosts is not very well known. Scientists at The Pennsylvania State University, the University of Georgia, and at the USDA-ARS ,Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, conducted laboratory experiments using the wasp Cotesia marginiventris to search and find different caterpillar species. Results suggested that female wasps can learn and associate egg-laying behavior with different caterpillar hosts, and that these positive experiences are important in searching for new caterpillars. This research expands our knowledge of an important natural enemy against pests in agricultural crops.
Insect herbivores often induce plant volatile compounds that can attract natural enemies. Cotesia marginiventris (Hymenoptera: Braconidae) is a generalist parasitoid wasp of noctuid caterpillars and is highly attracted to Spodoptera exigua-induced plant volatiles. The plasticity of C. marginiventris associative learning to volatile blends of various stimuli, such as host presence, has also been shown, but little is known about how this generalist parasitoid distinguishes between host species of varying suitability. S. exigua is an excellent host that yields high parasitoid emergence, while Trichoplusia ni serves as a sub-optimal host species due to high pre-imaginal wasp mortality, and we have found that S. exigua and T. ni induce different volatile blends while feeding on cotton. Here, wind tunnel flight assays were used to determine the importance of differentially induced volatiles in host-finding by C. marginiventris. We found that, while this generalist parasitoid wasp can distinguish between the two discrete volatile blends when presented concurrently, a positive oviposition experience on the preferred host species (S. exigua) is more important than host-specific volatile cues in eliciting flight behavior towards plants damaged by either host species. Furthermore, wasps with oviposition experience on both host species did not exhibit a deterioration in positive flight behavior, suggesting that oviposition in the sub-optimal host species (T. ni) does not cause aversive odor association.