Chemical interaction between the larva of a dipteran parasitoid and its coleopteran host: A case of exploitation of the communication system during the searching behaviour?

Abstract

The robber fly Mallophora ruficauda is one of the principal apicultural pests in the Pampas region of Argentina. As adults, the flies prey on honey bees and other insects; while, as larvae, they parasitize scarab beetle larvae. Females of M. ruficauda lay eggs away from the host in tall grasses. After being dispersed by the wind, larvae drop to the ground, where they dig in search of their hosts. It is known that second instar larvae of M. ruficauda exhibit active host searching behaviour towards its preferred host, third instar larva of Cyclocephala signaticollis, using host-related chemical cues. Furthermore, previous works show that these chemical cues are produced in the posterior body half of hosts. However, the precise anatomical origin of these cues and whether they mediate any behaviour of C. signaticollis larvae remains yet unknown. In order to determine the precise origin of the chemical cue, we carried out olfactometer assays with different stimuli of extracts of the posterior C. signaticollis body half. Additionally, we tested whether C. signaticollis is attracted to any of the same extracts as in the previous experiments. We found that both second instar of M. ruficauda and third instar of C. signaticollis are attracted to extracts of the fermentation chamber (proctodeum). This is the first report of attraction of conspecific larvae in scarab beetles. We discuss a possible case of system communication exploitation in an immature parasitoid-host system.

Host specificity in the host-seeking larva of the dipteran parasitoidMallophora ruficaudaand the influence of age on parasitism decisions

“…As in previous works, M. ruficauda shows a high preference for parasitizing C. signaticollis and detects its chemical cues originating in the posterior half of the host's body (Castelo & Lazzari, 2004;Groba & Castelo, 2012). However, our work suggests that orientation to potential hosts of the genus Cyclocephala can show some flexibility depending on the nature of the cue detected by the parasitoid and its age, and this behaviour is modulated by the different chemical cues released by the potentials hosts.…”

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

“…Although we were unable to determine the exact role of microorganisms in the C. signaticollis larvae' behaviour, our results showed that presence of gut's microorganisms is decisive in individual's orientation toward conspecific's stimuli. This evidence as well as aggregation in field and the previous behavioural experiments in the laboratory (Castelo & Capurro, 2000;Castelo & Corley, 2010;Groba & Castelo, 2012), indicate a probable communication system between immature individuals of C. signaticollis by means of microorganisms' semiochemicals. Several surveys have determined that microorganisms produce pheromones involved in aggregation behaviour and mate's searching.…”

Behavioural plasticity induced by intraspecific competition in host orientation in a parasitoid

“…This species is an endemic robber fly of Argentina, particularly of the Pampas region inhabiting open grasslands near bee farms (Castelo, 2003). Once moulted to the second instar, the parasitoid larva orientates to the host guided by chemical cues arising from the hosts' fermentation chamber (Castelo & Lazzari, 2004;Groba & Castelo, 2012). Mallophora ruficauda has a high preference for parasitising the third-instar larvae of Cyclocephala signaticollis Burmeister (Coleoptera: Scarabaeidae) in the field (Castelo & Capurro, 2000;Castelo, 2003;Castelo & Corley, 2010).…”

“…Parasitoid larvae are dispersed by the wind, they bury themselves once they reach the soil and, after moulting to the second instar, actively locate and parasitise hosts. Once moulted to the second instar, the parasitoid larva orientates to the host guided by chemical cues arising from the hosts' fermentation chamber (Castelo & Lazzari, 2004;Groba & Castelo, 2012). As eggs are placed on tall grasses away from the host and the wind is the main agent of dispersion, the number of larvae on any given portion of soil is very variable.…”