DIAPAUSE INDUCTION AND POST-DIAPAUSE EMERGENCE IN TRICHOGRAMMA MINUTUM RILEY (HYMENOPTERA: TRICHOGRAMMATIDAE): THE ROLE OF HOST SPECIES, TEMPERATURE, AND PHOTOPERIOD
AbstractTrichogramma minutum Riley entered diapause, in the prepupal stage, in eggs of Lambdina fiscellaria fiscellaria Guenée held at 15°C, 12L:12D, but failed to do so in eggs of Ephestia kuehniella (Zeller), Sitotroga cerealella (Olivier), or Choristoneura fumiferana (Clemens) held under these conditions. The parasitoids emerged without diapause from eggs of all host species held at 25°C, 16L:8D, indicating a role of temperature or photoperiod, or both, in the diapause of the parasitoids in eggs of L. fiscellaria held at 15°C, 12L:12D. Percentage emergence of parasitoids from eggs of L. fiscellaria was virtually the same (>80%) after passing the winter outdoors or after approximately 3 months at 2 °C in the laboratory as it was when reared indoors in this host at 25°C, 16L:8D. Emergence of T. minutum was very poor (<20%) after long-term, low-temperature storage in eggs of C. fumiferana, E. kuehniella, or S. cerealella. Apparently, T. minutum must parasitize diapause host eggs in order to enter diapause, and good survival after long-term low-temperature storage is possible only when T. minutum is in diapause. Trichogramma minutum will enter diapause in L. fiscellaria after 14 days at 15°C, 12L:12D, but the parasitoids need a period of storage at 2°C, 0L:24D for a high percentage of emergence to happen. Over 50% emergence was recorded for T. minutum, held for 300 days in eggs of L. fiscellaria.