Effect of temperature on diapause termination and post-diapause development in Eotetranychus smithi (Acari: Tetranychidae)

Previous studies on the spider mite Eotetranychus smithi Pritchard & Baker have shown that diapause in eggs is induced by low temperature alone and that females developed at <= 17.5 degrees C laid diapause eggs, regardless of the photoperiod. In this study, diapause eggs were kept at 5 degrees C and a photoperiod of 16L:8D for 0-120 days and then maintained at 25 degrees C to know the effect of chilling on diapause termination. Diapause eggs mostly hatched when they were maintained at 25 degrees C after chilling for 30-90 days at 5 degrees C, which suggests that diapause termination is favored by low temperatures. To clarify the hatching conditions after diapause termination, diapause eggs kept at 5 degrees C for 45 days were subsequently maintained at various constant temperatures (from 15 to 25 degrees C) under a long-day photoperiod (16L:8D). The hatchability at all temperatures tested was high (> 90%) and did not significantly differ among the high temperatures. Duration of embryonic development was shorter with increasing warming temperature after chilling. The lower thermal threshold (t) and thermal constant (k) for post-diapause egg development were 10.5 degrees C and 76.9 degree-days, respectively. Females, which developed from diapause eggs that were chilled at 5 degrees C for 45 days and then maintained at 15 degrees C, laid only non-diapause eggs, which indicates that they were prevented from re-entering diapause even under diapause-inducing conditions (15 degrees C). Thus, temperature is the main factor to control diapause termination and post-diapause development, which has also been found for other spider mites that enter diapause at the egg stage.