Temperature-dependent development of Galendromus flumenis (Acari: Phytoseiidae), a predator of Banks grass mite

The Banks grass mite, Oligonychus pratensis (Banks) (Acari: Tetranychidae) has been a persistent pest of California dates since the early 1900s. The mites feed on green date fruits causing rasping and bronzing of the surface, leaving scarred and cracked fruits that are unmarketable. In order to develop biological control strategies against the Banks grass mite, the survival and development of the predator, Galendromus flumenis (Chant) (Acari: Phytoseiidae), at eleven constant temperatures between 12°C and 44°C were determined. Galendromus flumenis developed successfully from egg to adult at temperatures ranging from 18°C to 42°C, but survival rates were highest (67.4- 89.5%) between 26°C and 38°C. The lower temperature threshold was 13.3°C and, the thermal constant (K) for total immature development was calculated to be 145.3 degree-days. The upper temperature threshold and the optimal temperature for total development were best estimated by Logan 6 model as 44.2°C and 37.6°C, respectively. These results indicate that G. flumenis is better adapted to high temperatures than most predators in the Phytoseiidae. Also, the thermal requirements for total development of G. flumenis was found to be very close to those of O. pratensis indicating that there should be synchrony between the occurrence of the prey and the predator. However, dates are heavily damaged by O. pratensis early in the season. This lack of predation could be related to the developmental time between O. pratensis and G. flumenis, or the inability of the predator to establish at the same time, and in the same location, as the prey.