Loss of parasitization efficiency of Trichogramma brassicae (Hym.: Trichogrammatidae) under high-temperature conditions
1996
Chihrane, J. | Lauge, G.
To simulate conditions in the field when Trichoramma brassicae Bezdenko is released against the European corn borer Ostrinia nubilalis Hubner, high-temperature shocks (35 and 44 degrees C) were applied for 6 h to the white pupa (WP) stage of T. 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 of T. brassicae are susceptible to heat shocks (especially 44 degrees C). After WP exposure to 44 degrees C, the loss of parasitization efficiency of the treated generation (G0) was considerable. It reached 85.8% after a double 44 degrees C shock. The female proportion of the progeny (G1) of heat-exposed parasitoids decreased after a 35 or 44 degrees C treatment. For the IRL treated at 44 degrees C, the parasitization efficiency of G0 and the female proportion of G1 were 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 of T. brassicae in the field.
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