Does mass rearing of field collected Trichogramma brassicae wasps influence acceptance of European corn borer eggs?

The purpose of our study was to identify a trait that changes quickly during Trichogramma mass rearing, and that could therefore be used to monitor stock deterioration. Quality deterioration in mass reared Trichogramma wasps was evaluated by examining host acceptance behaviour of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) on the target host Ostrinia nubilalis Hübner (Lepidoptera: Crambidae). We compared three replicate lines (designated ‘E’) reared in the laboratory on the factitious host Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) for 27 generations, a line ‘O’ reared in the laboratory on O. nubilalis for 24 generations, and a line ‘F’ reared in the laboratory on O. nubilalis for only two generations. All lines were initiated from field collections of O. nubilalis egg masses. We also evaluated natal host effects by rearing each line on E. kuehniella as well as on O. nubilalis for the last generation prior to testing. The percentage of wasps accepting the O. nubilalis egg mass was significantly higher for the E lines (69.6%) than for the F line (46.5%), while wasps of the O line showed intermediate (57.4%) acceptance. Thus, wasps laboratory reared on E. kuehniella performed better than wasps which had recently been collected in the field. Wasps of the O line showed extended probing behaviour compared to the other lines. Lines did not differ in the duration from the first host contact to the beginning of the drilling, probing or trembling behaviour. Natal host (E. kuehniella or O. nubilalis) did not affect acceptance of the target host O. nubilalis. Even though there is some evidence of adaptation to laboratory rearing conditions, we found no indication for quality deterioration in terms of acceptance behaviour of the target host O. nubilalis when T. brassicae was mass reared on the factitious host E. kuehniella.