Oviposition behavior of Aphelinus asychis (Hymenoptera: Aphelinidae) and Aphidius matricariae (Hymenoptera: Aphidiidae) and defense behavior of their host Diuraphis noxia (Homoptera: Aphididae)

Laboratory experiments were done to determine whether differences in attack behavior of Aphelinus asychis Walker and Aphidius matricariae Haliday and defense by their host Diuraphis noxia (Mordvilko) could explain higher parasitism by A. asychis in the field. Attack behavior differed strongly between the 2 parasitoid species: A. asychis took 4 times longer to oviposit in individual hosts than A. matricariae, and A. matricariae parasitized 6 times more hosts per unit time. These differences may have arisen in part because A. asychis appears to assess host quality with its ovipositor after insertion and A. matricariae appears to assess host quality by antennal palpation before ovipositor insertion. Although adult A. asychis uses some hosts for nutrition rather than oviposition and A. matricariae does not, A. matricariae still killed more hosts pet unit time than A. asychis. Although some D. noxia defended themselves when attacked, aphid defense did not reduce parasitism by either wasp species. Thus, neither difference in the efficacy of aphid defense nor difference in oviposition behavior can explain greater parasitism by A. asychis in the field.