Effects of photoperiod on induction of diapause in Feltiella acarisuga (Diptera: Cecidomyiidae)

Larvae of the predatory gall midge Feltiella acarisuga (Vallot) diapaused as prepupac in tightly woven, brown, silk cells on leaf surfaces. Photoperiod alone, at daylengths from 16 to 8 It did not induce diapause at either 20 or 25degreesC. A low incidence of diapause was induced by a combined photoperiod and thermoperiod of an 8-h day at 25degreesC and a 16-h night at 15degreesC. The incidence of diapause was higher under these conditions if the larvae were fed diapausing spider mites, Tetranychus urticae (Koch) (Acari: Tetranychidae). Because R acarisuga only diapauses at daylengths equivalent to mid-winter, when its prey, T urticae, is also in diapause, it can be used as a biological control agent for T urticae in British Columbia greenhouses throughout most of the growing season.