MOVEMENT AND RESPONSE TO SEMIOCHEMICALS BY PARASITOIDS OF PLATHYPENA-SCABRA (LEPIDOPTERA, NOCTUIDAE)

On legumes, Plathypena scabra (F.), are parasitized by Cotesia margini ventris (Cresson), Diolcogaster facetosa Ashmead, and Aleiodes nolopha nae (Ashmead); these primary parasitoids are hyperparasitized by Mesoc horus discitergus (Say). D, facetosa and A. nolophanae are host-specia lists and C. marginiventris and M. discitergus are host-generalists. I n the first experiment, we tested the hypothesis that the specialists are more vagile than the generalists by placing trap plots consisting of either the native tick-trefoil, Desmodium paniculatum L., or soybea n, Glycine max (L.) Merrill, between and within legume fields. D. face tosa parasitism of P. scabra placed in trap plots outside legume field s was high, while parasitism by C. marginiventris was low in those plo ts. This result suggested higher vagility of the host-specialist compa red with the host-generalist. In addition, tick-trefoil and soybean pl ots were equally apparent to both parasitoid species. In the second ex periment, we tested the hypothesis that generalist parasitoids respond to a broader range of volatiles than specialist parasitoids. The flig ht response of the four parasitoid species to volatiles was measured i n a flight funnel in no-choice assays. The 2 test odors used were gree n leaf volatiles released from soybeans damaged mechanically, and the plant-host complex that included soybeans fed upon by P. scabra larvae and P. scabra larvae plus associated kairomones. All 4 parasitoid spe cies initiated upwind flight to green leaf volatiles, but the host-spe cialist, A. nolophanae, responded more strongly to the plant-host comp lex than to green leaf volatiles. Some upwind flights in the absence o f volatile release were observed, but they were too few to explain the response of the parasitoids to green leaf volatiles or the plant-host complex.