Identification of 21 polymorphic microsatellites in the African parasitoid wasp, Psyttalia lounsburyi (Silvestri) (Hymenoptera: Braconidae).

We have developed 21 dinucleotide repeat microsatellite loci from African populations of Psyttalia lounsburyi (Silvestri) (Hymenoptera: Braconidae), a parasitoid wasp of the olive fruit fly, as part of a study assessing the role of introgression/hybridization in the success of a biological control introduction. We proposed suitable conditions for polymerase chain reaction multiplexing. All 21 loci were polymorphic with two to 21 alleles per locus within the Kenyan and South African populations tested. Most of them were successfully amplified in two other Psyttalia species.

Mate finding via a trail sex pheromone by a parasitoid wasp.

In field observations and laboratory experiments, we found that virgin females of the solitary parasitoid Aphelinus asychis did not emit a volatile sex pheromone to attract males, contrary to what has been reported in many other parasitoid species. Instead, we found that virgin females deposited a sex pheromone on the substrate to which males responded by intensively searching on and near the marked area. Males did not respond to leaves exposed to mated females or to other males. In patches of 64 wheat leaves, males were dispersed from a central release point, and more males were subsequently observed on leaves exposed to virgin females than on unexposed leaves. The pheromone faded to inactivity in less than 24 h. To examine whether the trail pheromone would be sufficient for mate finding by males in the field, we modeled random movement of males among plant stems where the trail pheromone was the only cue males used to find females. The probability that females encountered at least one male in their lifetime increased with male density and time after female emergence. Given the range of densities of A. asychis in barley and wheat fields near Montpellier, France, the model generated an encounter probability sufficient to explain the survival of established populations. The model also suggested that difficulty in finding mates at low density might be a problem for invading populations.

Male orientation to trail sex pheromones in parasitoid wasps: does the spatial distribution of virgin females matter?

We studied male locomotory response to trails and patches of sex pheromone (left respectively by free-ranging females and females constrained to stay on a small area) in the two parasitoids Aphelinus asychis (Hymenoptera: Aphelinidae) and Trichogramma brassicae (Hymenoptera: Trichogrammatidae). Under the hypothesis that the spatial distribution of virgin females differs between these species (scattered among host plants in A. asychis, gregarious at emergence sites in T. brassicae), we predicted that male locomotory response to their sex pheromones should also differ: A. asychis males should follow pheromone trails on plants in order to encounter the females along these trails, whereas T. brassicae males should stay on pheromone patches, at emergence sites, and mate the females on these patches. Using an improved video-tracking system, we found that males of both species respond to conspecific sex pheromone trails and patches, but that the response does not differ much between species. Males released on marked substrates walked in a more convoluted pattern (i.e. higher path fractal dimension and higher number of crossings within tracks) than males released on unmarked substrates. On pheromone patches, males turned persistently in the same direction when leaving the patch, which explains a higher number of visits on marked patches than on unmarked patches, and possibly, higher track convolution on pheromone trails. Contrary to our hypothesis, male A. asychis did not follow female trails more accurately than male T. brassicae, and male T. brassicae did not stay longer on pheromone patches than male A. asychis. We argue that these discrepancies between our predictions and the observed responses originates from discrepancies between the assumed spatial distribution of virgin females and their actual distribution in the wild.