ULTRASTRUCTURE AND PATHOLOGY OF MICROSPORIDIUM-PHYTOSEIULI N-SP INFECTING THE PREDATORY MITE, PHYTOSEIULUS-PERSIMILIS ATHIAS-HENRIOT (ACARI, PHYTOSEIIDAE)

Ultrastructure and pathology of Microsporidium phytoseiuli n. sp. infe cting the predatory mite Phytoseiulus persimilis Athias-Henriot is des cribed using light and transmission electron microscopy. Infected mite s showed no gross, external symptoms, All observed stages of the paras ite had unpaired nuclei. Schizonts were commonly observed within nucle i of digestive cells of the ventriculus and within the cytoplasm of ce lls lining the cecal wall and in muscle tissue underlying it. Sporobla sts and spores occurred in the nuclei and cytoplasm of digestive cells within the ventriculus, in cortical regions of the sub- and supraesop hageal ganglia, within the cecal wall and muscle tissue, and in parenc hyma cells underlying the cuticle. Mature spores were also observed in developing eggs within gravid females. These were broad- to elongate- ovoid, measured 4.33 +/- 0.35 x 1.27 +/- 0.15 mu m (electron micrograp hs), 5.37 +/- 0.46 x 2.22 +/- 0.17 mu m (fixed and stained), and 5.88 +/- 0.34 x 2.22 +/- 0.19 mu m (fresh) and had an isolfilar polar filam ent coiled 12 to 15 times within the posterior two-thirds. Within cell s, individual spores appeared to be in direct contact with host cytopl asm, while groups of spores were infrequently observed within interfac ial envelopes. Groups of 4, 8, to more than 16 spores were observed by light microscopy, while 8 was the maximum observed by electron micros copy. No spores were observed in Tetranychus urticae, a mite used as f ood during this study. (C) 1996 Academic Press, Inc.