Suitable doses screening for mutagenesis in Phytoseiulus persimilis induced by 60Co-γ

Abstract

Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) is a specialist predator of Tetranychus sp.; however, the lack of resistance to high temperatures and drought may result in the lower biological control efficiency of P. persimilis in the adverse climatic conditions. In breeding programs, ⁶⁰Co-γ irradiation is commonly used to quickly screen suitable mutants, optimize biological characteristics, and improve resistance. It is expected that ⁶⁰Co-γ irradiation could be useful in resistance screening in P. persimilis. The purpose of this study is to determine the suitable doses of ⁶⁰Co-γ with high levels of mutagenesis in P. persimilis. P. persimilis individuals were irradiated using ⁶⁰Co-γ at 0, 20, 40, 60, 70, 75, 80, 85, 90, 95, 100, 200, 300, and 400 Gy, with a dose rate of 0.5 Gy/min. The mortality of irradiated individuals was used to estimate the LD₅₀. The fecundity of survived individuals and egg hatch rate were applied to estimate the mutagenesis frequency. The mortality of P. persimilis increased with increasing irradiation dose with a rapid increase between 70 to 95 Gy. When irradiation dose exceeded 100 Gy, almost all P. persimilis died. The LD₅₀ of irradiation dose was ca. 80 Gy. When irradiation doses increased from 70 to 95 Gy, sterility rate increased from 5% to 20%, fecundity decreased from 97% to 80%, and egg hatch rate decreased from 98% to 60%. We suggest that the appropriate irradiation doses of ⁶⁰Co-γ inducing higher P. persimilis mutagenesis were between 70 Gy and 95 Gy. Results of this study allow future large-scale screening for resistant strains of P. persimilis.