Prolonged coldness on eggs reduces immature survival and reproductive fitness in Tetranychus urticae (Acari: Tetranychidae)

Tetranychus urticae Koch (Arachnida: Acari: Tetranychidae) is an economically important agricultural and horticultural pest around the world. The present study investigated the prolonged exposure of eggs (i.e., 0, 24, 48, 72, and 96 hours) to low temperature (i.e., 5 degrees C) affecting the egg hatching, and subsequent immature development and survival as well as the reproductive fitness of resultant females. Our results show that chilling had no significant effect on egg hatching rate, but significantly shortened egg development. It was found that prolonged chilling significantly decreased the survival of immature stages. Prolonged chilling also significantly delayed the development of males and thus adult emergence, but had not significantly effect on female development and survival. Results further indicate that the negative effect of lengthy chilling extended to the resultant females resulting in the significantly shorter longevity and lower fecundity. It is interesting that the resultant females might benefit from parental egg chilling, i.e., they started oviposition significantly early and produced significantly higher female-biased sex ratio. The implications from the results of this study in forecasting spring populations and outbreak of this pest in the growing season were discussed.