Abstract: 【Aim】 Neoseiulus setarius, a newly identified predatory mite species discovered in the Inner Mongolia Region, North China, has great potential to control small pests, such as thrips. When predatory mites were released in regions characterized by considerable temperature variations between day and night, a sudden decrease in temperature may potentially influence their predation capacity. Rapid cold hardening(RCH)can improve the cold tolerance of ectotherms. This study aims to explore whether N. setarius has this phenotypic plasticity and its response to short-term low-temperature stress by examining the RCH response of N. setarius and its fitness before and after cold hardening. 【Methods】 The critical temperature (at which the survival rate is below 10%) for female adults of N. setarius to survive was measured. The survival rates of female adults of N. setarius after exposure to different low temperatures (0, 2.5, 5, 7.5 and 10 ℃) were counted to determine the optimal acclimation temperature and duration. The RCH responses of various developmental stages of N. setarius were also investigated under the optimal acclimation temperature and duration. Moreover, the effects of RCH on the predatory and reproductive potential of female adults of N. setarius were evaluated by using the 1st instar nymphs of Frankliniella intonsa as prey, which were aged 1-2-day-old after hatching from the eggs laid on beans within 1 d. 【Results】 The critical low temperature for survival of female adults of N. setarius was -21 ℃. Exposure to 2.5 ℃ for 2 h was found to be the optimal condition to induce RCH in female adults of N. setarius, effectively increasing their survival rate. There was only 3.33% survival rate when adult females of N. setarius were directly transferred from the room temperature of 25 ℃ to -21 ℃ for 2 h, while the survival rate of adult females was increased to 68.33% after cold hardening at 2.5 ℃ for 2 h and then exposure to -21 ℃ for 2 h. Similarly, the survival rates of other developmental stages of N. setarius significantly increased after cold hardening at 2.5 ℃ for 2 h and then exposure to -21 ℃ for 2 h. The survival rates of non-hardened eggs, larvae, protonymphs, deutonymphs and male adults of N. setarius after exposure to -21 ℃ for 2 h were 6.67%, 21.67%, 1.67%, 5.00% and 5.00%, respectively, while after cold hardening at 2.5 ℃ for 2 h, the survival rates of the corresponding developmental stages of N. setarius after exposure to -21 ℃ for 2 h were increased to 60.00%, 33.33%, 20.00%, 31.67% and 51.67%, respectively. Meanwhile, the predation and oviposition of the female adults of N. setarius on F. intonsa were not reduced after cold hardening. 【Conclusion】 All developmental stages of N. setarius have the ability to respond to RCH. Exposure to 2.5 ℃ for 2 h can improve the cold tolerance of N. setarius without reducing its predation fitness against F. intonsa, which provides a basis for the field releasing of this mite in regions with significant variations in temperature throughout the day.

Key words: Neoseiulus setarius, Frankliniella intonsa, predatory mites, cold tolerance, predation, oviposition