Entomophthora muscae resting spore formation in vivo in the host Delia radicum

The formation in vivo of Entomophthora muscae resting spores was investigat ed in the host, Delia radicum (cabbage root fly), by analysis of field data on the seasonal occurrence of E. muscae resting spores over 4 years. E. mu scae resting spores in D. radicum were spherical with an average diameter o f 39.4 mu m, and the average numbers produced were estimated at 5.7 x 10(4) resting spores/female cadaver. Resting spores were found only after midsum mer in D. radicum and almost exclusively in females. The proportion of infe cted females with resting spores was negatively correlated with average wee kly day length after midsummer. We did not detect any significant year effe ct; thus, the results support the hypothesis that the photoperiod is the mo st important abiotic factor controlling E. muscae resting spore formation i n D. radicum. (C) 2000 Academic Press.