Host gut microorganisms’ cues mediate orientation behaviour in the larva of the parasitoidMallophora ruficauda

Abstract

AbstractThe robber flyMallophora ruficaudais one of the most important apicultural pests in the Pampas region of Argentina. This species is a parasitoid of scarab beetle larvae. Females lay eggs away from the host, and the larvae perform active search behaviour towardCyclocephala signaticollisthird instar larvae, parasitoid's preferred host. This behaviour is mediated by host-related chemical cues produced in hosts’ fermentation chamber. Also,C. signaticollislarvae are attracted to fermentation chamber extracts. As scarab larvae have microbe-rich fermentation chamber, it has been suggested that microorganisms could be involved in the production of these semiochemicals. The aims of this work were first to ascertain the presence of microorganisms in the fermentation chamber ofC. signaticollislarvae and second to determine the role of microorganisms in the orientation response of parasitoid and host larvae. We found that microorganisms-freeC. signaticollislarvae showed deterioration in their development and did not produce the attractive semiochemicals. Therefore, we isolated fermentation chamber microorganisms of host larvae by means of different cultures media, and then, assayed different microorganisms’ stimuli by binary choice tests. We were able to isolate microorganisms and determine thatM. ruficaudalarvae are attracted to semiochemicals from protein degradation in the fermentation chamber. However,C. signaticollislarvae were not attracted to any semiochemicals associated with microorganisms’ activity in the fermentation chamber. Although we were unable to elucidate the exact role of gut microorganisms in host behaviour, we discuss their relevance in parasitoid host-seeking behaviour and host conspecific interaction inM. ruficauda–C. signaticollissystem.