Loss of Parasitization Efficiency ofTrichogramma brassicae(Hym.: Trichogrammatidae) under High-Temperature Conditions

To simulate conditions in the field whenTrichogramma brassicaeBezdenko is released against the European corn borerOstrinia nubilalisHübner, high-temperature shocks (35 and 44°C) were applied for 6 h to the white pupa (WP) stage ofT. brassicae(single or double shocks) and to the imago ready to leave a parasitized egg (IRL) (single shock). The aim was to determine the parasitization efficiency as the temperature increased. The results showed that the WP and IRL stages ofT. brassicaeare susceptible to heat shocks (especially 44°C). After WP exposure to 44°C, the loss of parasitization efficiency of the treated generation (G0) was considerable. It reached 85.8% after a double 44°C shock. The female proportion of the progeny (G1) of heat-exposed parasitoids decreased after a 35 or 44°C treatment. For the IRL treated at 44°C, the parasitization efficiency of G0and the female proportion of G1were substantially reduced. This study also shows that IRLs are more susceptible to a high temperature than WPs. Consequently, it would be more suitable to choose the WP rather than the IRL stage for inundative releases ofT. brassicaein the field.