Cold Hardiness of Neoseiulus californicus and N. womersleyi (Acari: Phytoseiidae)

Abstract

Mites of the genus Neoseiulus are predatory mites that feed on pest species such as the two-spotted spider mite (Tetranychus urticae) and therefore act as biocontrol agents. Since the 1990s, the population of N. californicus in central and southwestern Japan has increased sharply, replacing the native N. womersleyi in many orchards in this area. However, in orchards of northern Japan, N. californicus is much less abundant than N. womersleyi. Here we tested the hypothesis that the lower abundance of N. californicus in the north is due to a lack of cold hardiness. The mean supercooling points of adult females of two strains of N. californicus (an indigenous strain and a commercial strain, neither of which enters diapause) and diapause and non-diapause N. womersleyi were all in the range −21.9 – 23.3°C and were not significantly different. However, more than 50% of diapause females of N. womersleyi survived for more than 7 days exposed to −5°C, while most females of the non-diapause N. womersleyi and the two N. californicus strains died after 3–5 days of exposure to −5°C. Exposure of adult females to −5°C for various periods did not significantly affect subsequent fecundity and egg viability. These results suggest that the lower cold hardiness of N. californicus might be one of the factors halting its northern advance, but it is probably not sufficient to be the only factor.