GENETICS OF OVIPOSITION SUCCESS OF A THELYTOCOUS FAIRYFLY PARASITOID,ANAGRUS-DELICATUS

The foraging behaviour of the salt-marsh parasitoid, Anagrus delicatus (Hymenoptera: Mymaridae), is distinguished by few eggs laid per patch of hosts and frequent dispersal among patches. We investigated the wi thin-population genetic variability in six quantitative traits associa ted with this unusual behaviour: fecundity (lifetime number of eggs), time on a patch, number of ovipositions per patch, oviposition rate, o vipositor length and tibia length (a measure of body size). Forty-one wasp isolines were initiated from single parthenogenetic females from three isolated salt marshes, and were maintained for up to eight gener ations in the greenhouse. We estimated the genetic variance and broad- sense heritability (h(2)) of these traits and tested trait means for d ifferences among isolines (genetic variation) and sites (geographical variation). We found significant genetic variability among isolines fo r all traits except oviposition rate. The behavioural and morphologica l traits had similar levels of genetic variance, indicating that the e volvability (ability to respond to selection) of the traits is similar ly high. However, the behavioural traits had higher residual variances , resulting in lower heritabilities. Only two traits had significant h eritabilities. Fecundity, which is probably a good proxy for fitness, ceteris paribus, varied from on average 26 to 40 eggs per isoline and had the highest h(2), 0.47+/-0.16 (mean+/-SE). Ovipositor length had a n h(2) of 0.36+/-0.17. These results suggest that the traits comprisin g the foraging strategy of A. delicatus should be amenable to selectio n (e.g. isolines could be selected that lay more eggs per host patch a nd consequently visit fewer patches). Genetic correlations among trait s were numerous and positive. One important prediction from these data is that selection for larger wasps will result in large offspring wit h greater egg loads and higher oviposition rates. Wasps with this comb ination of attributes are likely to be more efficient natural enemies for use in biological control. In addition, there was no significant d ivergence (genetic or otherwise) in wasp morphology or behaviour among the three sites, even though they were separated by 8 km or more.