Defensive behaviors of the Oriental armywormMythimna separatain response to different parasitoid species (Hymenoptera: Braconidae)

Abstract

This study examined defensive behaviors ofMythimna separata(Lepidoptera: Noctuidae) larvae varying in body size in response to two parasitoids varying in oviposition behavior;Microplitis mediatorfemales sting the host with the ovipositor after climbing onto it whileMeteorus pulchricornisfemales make the sting by standing at a close distance from the host.Mythimna separatalarvae exhibited evasive (escaping and dropping) and aggressive (thrashing) behaviors to defend themselves against parasitoidsM. mediatorandM. pulchricornis. Escaping and dropping did not change in probability with host body size or parasitoid species. Thrashing did not vary in frequency with host body size, yet performed more frequently in response toM. mediatorthan toM. pulchricornis. Parasitoid handling time and stinging likelihood varied depending not only on host body size but also on parasitoid species. Parasitoid handling time increased with host thrashing frequency, similar in slope for both parasitoids yet on a higher intercept forM. mediatorthan forM. pulchricornis. Handling time decreased with host size forM. pulchricornisbut not forM. mediator. The likelihood of realizing an ovipositor sting decreased with thrashing frequency of both small and large hosts forM. pulchricornis, while this was true only for large hosts forM. mediator. Our results suggest that the thrashing behavior ofM. separatalarvae has a defensive effect on parasitism, depending on host body size and parasitoid species with different oviposition behaviors.