Field dispersal and host location of Trichogramma brassicae is influenced by wing size but not wing shape

This study evaluates if wing size and wing shape could be used to predict the dispersal and host location of mass reared Trichogramma egg parasitoids in the field. Commercially produced Trichogramma brassicae wasps were released in a corn field and recaptured on Ostrinia nubilalis egg cards. The effects of distance from the release point and day since release on wing size and shape of recaptured wasps were evaluated. Wing size of wasps had an impact on recapture probability, but this association was complicated by the fact that wing size effects changed with distance from the release point and time since release. Wing size increased with recapture distance from the release point on both recapture days. However, wasps recaptured on the day of the release had larger wings than those recaptured on the next day, while wasp wings of the release sample were on average of intermediate size. One possible explanation of this pattern is that wasps with larger wings moved out of the experimental area by the end of the release day, leaving behind only wasps with smaller wings to be recaptured on the next day. Unlike in an earlier study, no effect of wing shape on field fitness was detected, although rearing host may affect wing shape. Because wing size is related not only to the host location ability but also to the recapture distance and time of T. brassicae wasps in the field, this effect must be accounted for in the sampling design employed when using this proxy as a measure of field fitness. As wing size influences dispersal and host location in the field, it may be a valuable parameter in quality assessments of mass reared Trichogramma wasps.