Proprioseiopsis asetus (Chant) (Acari: Phytoseiidae) is a relatively unknown predacious mite with potential as a biological control agent of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) and Tetranychus urticae Koch (Acari: Tetranychidae). In this study, the developmental rate and other biological parameters of P. asetus were investigated. Development of P. asetus was temperature dependent from 10 to 40 degrees C. Nonlinear models were fitted to development rate (1/time) data from egg to adult and by sex to estimate development times. The model of Sharpe and De Michele (1977) best fits the developmental data. The shortest development time on cattail (Typha latifolia (L.)) pollen occurred at 35 degrees C for all stages except for the egg stage, for which it was longer. The optimum development time at 35 degrees C is above the temperature optimum of most phytoseiid mites. Fecundity increased when P. asetus mated more than once. Males were needed at all times for maximum oviposition, although their consumption was negligible. Oviposition, prey killed (Franklinella occidentalis or T. urticae) and longevity of P. asetus females were recorded in the presence of males. Egg production increased with number of prey killed and P. asetus has the characteristics of successful predators of thrips.

The intrinsic rate of increase (rm) was estimated for Proprioseiopsis asetus Muma (Acari: Phytoseiidae) on pollen and two prey species at 35°C. Cattail, Typha latifolia L., pollen and Frankliniella occidentalis (Pergande) were equally favorable as food and superior to Tetranychus urticae Koch. More females were produced in a shorter time when P. asetus was fed F. occidentalis or pollen; however, survivorship was longer when the predator was fed T. urticae. On an F. occidentalis diet, calculated rm values ranged from 0.2789 to 0.2925. The net reproductive rate was lower on a diet of T. urticae (6.48) than on pollen (9.76) or on F. occidentalis (21.39). The finite rate of increase was lower on T. urticae (1.1868) than on pollen (1.3274) or F. occidentalis (1.3398). The mean generation time was similar on the three diets. That the data reported here were collected at 35°C makes it remarkable. P. asetus may have great potential as a biological control agent of arthropods, especially thrips under climatic conditions of high temperatures such as in protected culture.