Heat curing Metaseiulus occidentalis (Nesbitt) (Acari,Phytoseiidae) of a fitness-reducing microsporidium

Laboratory colonies of the predatory mite Metaseiulus occidentalis in Gainesville, FL were found to be infected with an undescribed microsporidium. Experiments were performed to quantify the effect of infection on the fitness of M. occidentalis and to determine if heat treatment can cure mites of the microsporidium. The colonies tested were derived from an isofemale line so that differences in performance could be attributed to the presence of microsporidia. A subcolony of an uninfected isofemale line was infected with the microsporidium by feeding females infected eggs from another colony of M. occidentalis. Infected mites had a shorter mean (+/-SD) female life span (7.4 +/- 2.9 vs. 10.0 +/- 2.8 days), lower mean oviposition (1.6 +/- 0.7 vs. 2.2 +/- 0.4 eggs/day), and a male-biased sex ratio (43 +/- 16% vs. 57 +/- 15% female progeny). The infection was reduced temporarily in colonies initiated from mites that were reared in a growth chamber at 33 degrees C from egg to adult, but healthy colonies only were established from the progeny of the heat-treated adults. These colonies remained free of infection for 10 weeks.