Effects of Microsporidium phytoseiuli (Microsporidia) on the performance of the predatory mite, Phytoseiulus persimilis (Acari : Phytoseiidae)

Five-day test periods were used to evaluate the effects of Microsporidium p hytoseiuli on short-term oviposition, survival, and prey consumption rates of Phytoseiulus persimilis, a predator of phytophagous mites, from a Europe an source. Sex ratios, lifetime oviposition rates, and lifetime longevity o f microsporidian-infected females were compared to those of uninfected fema les from a second source. All tests were conducted under controlled conditi ons (16L:8D; 25 degrees C: 20 degrees C; 70 +/- 10% RH). Mean fecundity and prey consumption of microsporidian-infected females were significantly low er than those of uninfected females from the same source. Uninfected and mi crosporidian-infected females produced 2.6 +/- 0.2 and 1.7 +/- 0.2 eggs/fem ale/day, respectively, over a B-day period, Fecundity values were similar f or predators during prey consumption studies. Mean prey consumption over 5 days was 18.7 a 1.0 and 13.4 +/- 1.2 deuteronymph Tetranychus urticae/femal e/day for uninfected and infected mites, respectively. Short-term survivabi lity was variable and proved to be an unreliable means to evaluate predator quality, Microsporidian-infected females produced significantly fewer eggs and female progeny during their lifetimes and uninfected females lived sig nificantly longer than infected females. Results of short-term performance tests were compared to minimum performance standards outlined in current qu ality control guidelines. Mean fecundity for uninfected female predators ex ceeded recommended standards whereas the fecundity of microsporidian-infect ed females remained below minimal performance standards, In this study, per formance was evaluated for predators in which all individuals in a sample w ere either infected or uninfected with the microsporidium, Random sampling of populations with moderate infection rates is more likely to occur in com mercial settings and performance may remain relatively high in samples in w hich not all individuals are infected, Therefore, performance values alone may provide insufficient information to fully assess predator quality. With out routine examination of individuals for microsporidia, it is likely that these pathogens will. remain undetected, only to be discovered when poor p erformance or mortality is noted due to high disease prevalence. (C) 1994 A cademic Press.