Ontogeny of a chemical cue in a parasitoid dipteran

CRESPO J; GALLARDO GABRIELA L.; CABRERA, GABRIELA M; CASTELLO MARCELA K

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

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