Ontogeny of a chemical cue in a parasitoid dipteran.

CRESPO. J.E.; GALLARDO, G.L.; CABRERA, G.M.; CASTELO, M.K.

Colonia

Congreso; 1st Meeting of the Latin American Association of Chemical Ecology; 2010

Alaeq

The robber fly Mallophora ruficauda is an ectoparasitoid of scarab beetle larvae. As adultsthey prey on honey bees, while as larvae they parasite mainly third-instar larva ofCyclocephala signaticollis. Females of M. ruficauda lay eggs away from the host on tallgrasses. After being dispersed by the wind, larvae drop to the ground and search for theirhosts. The hosts are readily available during summer time, but they are not fully grownwhen the parasitoid larva appears. It is known that second-instar larvae of M. ruficaudaexhibit active host searching behaviour towards their host, but it is unknown if they canorientate to the first two host instars odours. The aims of this work were to characterize thechemical profiles of the three larval instars of M. ruficauda, and to determine if theparasitoid larva orientates to odours from these instars with different levels of intraspecificcompetition. For this work, we performed GC-mass analyses and behavioural experimentsin the laboratory using host body extracts. We found that the chemical profiles of the threehost instars have different kinds and amounts of large saturated hydrocarbons. We alsofound that the parasitoid larva orientates generally to odours from third instar hosts.However, under a high competition situation, larvae also orientate to odours from secondinstar hosts. Finally, when given a choice between second and third instar hosts, parasitoidlarvae orientate to third instar odours when competition was low, but similarly to bothodours under high competition. Our results show that although M. ruficauda orientatespreferentially to third instar host odours due to its chemical properties, and its behaviouraldecisions are also influenced by external factors such as the level of competition.