Temperature and strain effects on reproduction and survival of Trichogramma oleae and Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae)

To assess differences in temperature sensitivity during development, life tables for two lines derived from the species Trichogramma oleae Voegele and Pointel and a strain of Trichogramma cacoeciae Marchal (Hymenoptera: Trichogrammatidae) were elaborated at 15, 20, 25, 30, 35, 36, and 37 degrees C in the laboratory. Eggs of Ephestia kuehniella Zeller together with a fresh drop of honey were supplied every 2 days until the death of the test females, and the removed host egg batches were placed in the equivalent rearing cabinet. The line '2F' of T. oleae was found to be the most efficient at any range of temperatures except at 20 and 37 degrees C, in comparison to the other tested strains. For all species, no progeny emerged from eggs incubated at 36 degrees C and none of the parasitized eggs turned black at 37 degrees C. The better performance at a broader range of temperatures by T. oleae (line 2 F) might be caused by a shorter history in artificial rearing in comparison to the other strains. Fewer generations at laboratory conditions and frequent multiplication on eggs of its natural host (the olive moth Prays oleae) may have prevented a deterioration in the rearing population of this strain, maintaining its genetic diversity at a higher scale. Applying varying temperature regimes on the rearing stock at regular intervals during the mass production process may help to maintain the essential quality of the biological control agents for field performance at higher temperatures.