Development and pathology of two undescribed species of microsporidia infecting the predatory mite, Phytoseiulus persimilis Athias-Henriot

Two undescribed species of microsporidia were found in mass-reared Phytosei ulus persimilis Athias-Henriot from two commercial sources during a routine examination of these predators for pathogens. Both microsporidian species were described from specimens that had been prepared for transmission elect ron microscopy; live specimens were unavailable for examination. One micros poridium, identified as Species A, was described from two specimens obtaine d from a commercial insectary in North America. All observed stages of this microsporidium were uninucleate. Rounded-to-ovoid schizonts appeared to de velop in direct contact with the cytoplasm of lyrate organ cells (ovarian t issue). Mature spores of Species A were elongate-ovoid and measured 2.88 x 1.21 mum. A polar filament coiled 7 to 10 times in the posterior half of th e spore. Sporoblasts and spores were observed in the cytoplasm of cells of numerous tissues and in developing eggs within gravid females, A second spe cies, identified as Species B, was described from five specimens obtained f rom a commercial source in Israel, All observed stages of this microsporidi um were uninucleate. Schizonts of Species B were observed within the cytopl asm of cecal wall cells and within the nuclei of lyrate organ cells. Mature spores were ovoid and measured 2.65 x 1.21 mum. A polar filament coiled 3 to 4 times in the posterior half of the spore. Densely packed ribosomes oft en concealed the polar filament and other internal spore characteristics. S pores were observed in the cytoplasm of cells of numerous tissues and occas ionally within the nuclei of lyrate organ cells. Numerous spores and prespo ral stages were observed within the ovary and developing eggs. The developm ent and pathology of Species A and B were compared to those of Microsporidi um phytoseiuli Bjornson, Steiner and Keddie, a microsporidium previously de scribed from P. persimilis obtained from a commercial source in Europe, The occurrence of three species of microsporidia within P. persimilis from thr ee sources raises questions regarding the origin of these pathogens. Becaus e microsporidia may have profound impact on the performance of P. persimili s, consideration must be given to the identification and exclusion of micro sporidia from field-collected specimens or from predators that may be share d among commercial sources. (C) 2000 Academic Press.