Temperature-dependent differences in biological traits between two strains of Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae)

Parasitoids' efficiency in controlling pests depends not only on their ability to parasitize their hosts but also on how much they are adapted to climatic conditions (notably temperature) of the area where they are planned to be released. In addition, the optimal conditions for production of parasitoids used for inundative releases like Trichogramma spp. may also vary largely as a function of strains. Using the parasitoid Trichogramma cacoeciae Marchal as biological model, we studied how temperature affects important parasitoid efficiency-related biological traits under laboratory conditions. Emergence, mortality rates and fecundity of two strains of T. cacoeciae, one originating from France (Alsace) and the other one from Tunisia (Degache), were compared at constant temperatures of 15, 20, 25 and 30 degrees C. The parasitoids of the French strain showed highest fecundity at 25 degrees C with wasps that had been reared at 20 or 25 degrees C. The Tunisian strain showed the highest fecundity at 25 degrees C, but only when wasps were previously reared at 25 or 30 degrees C. For both strains, the highest mortality occurred among wasps that had laid eggs at 30 degrees C. Emergence rates were relatively high at all temperatures, although the French strain did better at 15-25 degrees C and the Tunisian one at 20-30 degrees C. Because of the differences in biological traits of these two T. cacoeciae strains in relation to the temperature, a judicious choice must be made among the various strains when using this species in biological control programs.