Optimizing cold storage of the ectoparasitic mite Pyemotes zhonghuajia (Acari: Pyemotidae), an efficient biological control agent of stem borers.

Abstract

Pyemotes zhonghuajia Yu, Zhang and He is a newly discovered native ectoparasitic mite that efficiently controls stem borers in China. To provide a steady and sufficient supply, extend adult lifespan and synchronize field augmentative releases of P. zhonghuajia, we determined the optimal cold storage temperature and duration by storing 1-day-old mated females at 8, 10 and 12°C for 10-90days with a 10-day interval in the laboratory. We then recorded mite survival during storage and monitored the post-storage reproductive performance of mites at a control temperature of 25°C. We found that all mites survived at 10 and 12°C for different durations, but mortality occurred when mites were stored at 8°C for ≥ 30days with more than 70% of mites dead when the storage duration prolonged up to 50days. The proportion of reproductive females was higher at 10°C but decreased with the prolonged storage duration at all test temperatures. Storage temperature had no significant effect on the pre-reproductive period and offspring sex ratio, whereas prolonged storage induced longer pre-reproductive period and lower proportion of female offspring. The reproductive period increased with increasing storage temperature and with prolonged storage up to 50 and 60days; however, the longer reproductive period did not directly translate into greater reproductive output. We found that compared with the control, mites stored at 10°C for up to 30days did not significantly reduce their survival, proportion of reproductive success and number and sex ratio of offspring, suggesting that 10°C and ≤ 30days were the optimal cold storage temperature and duration, respectively, for post-mass production storage before the field augmentative release of P. zhonghuajia.