Abstract: Irradiation is an important tool for chromosome aberration, and is often used in investigating reproduction mechanisms of insects and mites. In this study, we investigated the impact of gamma irradiation on female adults, male adults and eggs of different ages of Phytoseiulus persimilis Athias-Henriot. When irradiated males (at 160-640 Gy) were mated with unmated females, all F1 offspring were males and only 1/3 were fertile. When irradiated females (at 45-90 Gy) were mated with unmated males, the proportion of females in F1 offspring decreased with increasing irradiation dose, and no offspring were able to complete embryonic development when the irradiation dose was 90 Gy. No significant impact on proportion of female (0.78-0.85) in offspring was observed when fertilized females were irradiated during preoviposition stage. When 0-12 h old eggs were irradiated, no larva emerged. When 12-24 h old eggs were irradiated, all individuals that completed development to adult stage were females. When 24-48 h old eggs were irradiated, proportion of female increased with increasing irradiation dose. Our study shows that paternal chromosome is involved in sex determination in offspring. Possible timing of paternal chromosome heterogenization is between egg shell formation and 12 h after oviposition. This study provides new explanations for the mechanism of offspring sex determination and the role played by paternal chromosome in P. persimilis, which is important for further study of reproductive mechanisms of predatory mites.

Key words: Phytoseiulus persimilis, gamma rays, reproduction, sex determination