Abstract: 【Aim】 Euseius utilis is a generalist and widely distributed in northern areas of China, while Neoseiulus barkeri is widely used in biocontrol of agricultural pests. The study aims to assess the risk of N. barkeri to local species and establish a reasonable combination of different natural enemies in biological control. 【Methods】 In a series of experiments under laboratory conditions, the rates of intra- and interspecific predation on immature mites, survival time, and oviposition for the adult females of N. barkeri bred in the laboratory and E. utilis collected from the campus of Inner Mongolia Agricultural University were compared in order to study the aggressiveness and con- and heterospecific interactions between the two species of phytoseiid mites. 【Results】 The females of the two species had difficulties in piercing phytoseiid eggs, and both phytoseiid mites consumed more con- and heterospecific larvae than protonymphs. E. ulitis was more aggressive than N. barkeri in intraguild predation in absence of shared food (Breslow-Day test: χ²=13.84, df=1, P<0.001). The average daily predation number of E. ulitis on conspecific larvae (9.10±1.65) was higher than that on heterospecific larvae (5.31±1.43) (T test: t=5.487, P<0.001), whereas the average daily predation number of N. barkeri on heterospecific larvae (7.48±0.75) was higher than that on conspecific larvae (4.75±0.58) (T test: t=9.110, P<0.05). 【Conclusion】 E. ulitis is preferentially engaged in cannibalism by consuming the conspecific larvae, whereas N. barkeri is preferentially engaged in intraguild predation by consuming the heterospecific larvae.    

Key words: Euseius utilis, Neoseiulus barkeri, intraguild predation, cannibalism, aggressiveness