Effects of temperature and relative humidity on development, reproduction, and predation in Feltiella acarisuga (Vallot) (Diptera: Cecidomyiidae)

The predatory gall midge Feltiella acarisuga (Vallot) (Diptera: Cecidomyiidae) is a biological control agent for twospotted spider mites on greenhouse vegetable crops. Effects of temperature and relative humidity (RH) on development of immatures, reproduction, and prey capture were determined in order to confirm the suitability of F. acarisuga for use in greenhouses. Developmental time ranged from 10 days at 27 degrees C to 34 days at 15 degrees C. At 20 degrees C, developmental time was significantly shorter at 96% RH than at 84% RH. There was very poor survival of immatures at 64% RH and none at 36%. Lifespan of adult females decreased with increasing temperature, but temperature had no significant effect on number of eggs laid. At 20 degrees C, lifespan was longer at 84 and 96% RH than at 64 or 36% RH. The number of spider mites attacked by 3-day-old larvae over 8 h increased with increasing temperature from 15 to 27 degrees C. The number of mites attacked also increased with increasing RR at 27 degrees C. We conclude that F. acarisuga will complete its life cycle and reproduce under conditions typically found in vegetable greenhouses in northern temperate climates. However, extended periods of low RH (<60% RH) could reduce reproduction and survivorship sufficiently to impair the predator's action against spider mite populations. (C) 2000 Academic Press.