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 phytoseiuli on short-term oviposition, survival, and prey consumption rates of Phytoseiulus persimilis, a predator of phytophagous mites, from a European source. Sex ratios, lifetime oviposition rates, and lifetime longevity of microsporidian-infected females were compared to those of uninfected females from a second source. All tests were conducted under controlled conditions (16L:8D; 25 degrees C: 20 degrees C; 70 +/- 10% RH). Mean fecundity and prey consumption of microsporidian-infected females were significantly lower than those of uninfected females from the same source. Uninfected and microsporidian-infected females produced 2.6 +/- 0.2 and 1.7 +/- 0.2 eggs/female/day, respectively, over a B-day period, Fecundity values were similar for 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/female/day for uninfected and infected mites, respectively. Short-term survivability 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 significantly longer than infected females. Results of short-term performance tests were compared to minimum performance standards outlined in current quality control guidelines. Mean fecundity for uninfected female predators exceeded recommended standards whereas the fecundity of microsporidian-infected females remained below minimal performance standards, In this study, performance was evaluated for predators in which all individuals in a sample were either infected or uninfected with the microsporidium, Random sampling of populations with moderate infection rates is more likely to occur in commercial settings and performance may remain relatively high in samples in which not all individuals are infected, Therefore, performance values alone may provide insufficient information to fully assess predator quality. Without routine examination of individuals for microsporidia, it is likely that these pathogens will. remain undetected, only to be discovered when poor performance or mortality is noted due to high disease prevalence. (C) 1994 Academic Press.