Effects of heat stresses on fitness of three commercial predatory mites

Predatory mites are important biocontrol agents in controlling small pests in the greenhouse. However, extreme high temperatures often occur during the daytime in greenhouses due to solar radiation in spring and summer. To explore the performances of predatory mites under high temperatures, we selected three popular commercial species Amblyseius orientalis, Neoseiulus californicus, and Neoseiulus barkeri to investigate the survival rate, development duration, and fecundity after their eggs and female adults were treated with high temperatures. The results showed that both eggs and adults of N. barkeri and N. californicus were more tolerant to heat stress than A. orientalis. Compared with 25 °C, the developmental periods and longevity of all three species of predator mites were shortened, and the fecundity was also reduced at 39°C. The total fecundity and longevity of N. californicus reduced by 27% and 29%, respectively. For N. barkeri, the total fecundity reduced by 30% and the longevity decreased by 23%. All A. orientalis died at 40 °C, which also cut half longevity of N. californicus and N. barkeri. Our study confirmed that the N. barkeri and N. californicus had stronger tolerances to high temperatures, while A. orientalis was more heat-sensitive during the egg stage and adult stage. In sum, understanding of the heat resistance of commercial predatory mites can improve the application of biocontrol agents when selecting predator species for pest control in the greenhouse.