Population growth and reproduction of Galendromus flumenis (Acari: Phytoseiidae) on Banks grass mite eggs

The predatory mite, Galendromus flumenis (Acari: Phytoseiidae), has shown promising traits for biological control of Banks grass mite (Oligonychus pratensis), a major pest of date palms in California. In the present study, reproduction and population growth parameters of G. flumenis on Banks grass mite eggs were studied at 34ºC, 50±10% RH and a photoperiod of 16: 8 (L: D) hours. 100% of eggs hatched and 63.5% of the emerged larvae survived to adulthood. The total immature developmental time was 5.7 and 5.5 days for females and males, respectively. The sex ratio of G. flumenis was 0.70 (females/ females+ males). Mated females laid an average of 1.6 eggs per day and 19.9 eggs during their mean oviposition period of 12.5 days. The net reproductive rate (R₀), intrinsic rate of increase (r_m), finite rate of increase (λ), mean generation time (T), and doubling time (DT) were 11.5 females/female, 0.200 females/female/day, 1.222 females/female/day, 12.2 days, and 3.5 days, respectively. The lower r_m value of G. flumenis than that of its prey (0.35-0.39 at 33ºC and 0.32-0.48 at 36ºC) explains why Banks grass mite escapes control by G. flumenis in the field. These results suggest that increasing the early season abundance of G. flumenis through augmentative releases will improve the management of Banks grass mite.