SEASONAL PREVALENCE OF ENTOMOPHTHORA-MUSCAE AND INTRODUCTION OF ENTOMOPHTHORA-SCHIZOPHORAE (ZYGOMYCOTINA, ENTOMOPHTHORALES) IN MUSCA-DOMESTICA (DIPTERA, MUSCIDAE) POPULATIONS ON CALIFORNIA DAIRIES

Two entomopathogenic fungi in the Entomophthora muscae species complex that infect house flies were used in this study: E. muscae Fresenius (16-17 nuclei/conidium) occurred naturally at four southern California dairies, while Entomophthora schizophorae Keller and Wilding (4-8 nuc lei/conidium) did not. During the first year of the study, onset of me asurable E. muscae infections occurred between September and November but varied among sites. At least 20% of the flies at all four dairies were infected by November, and infection at one site exceeded 70%. Dur ing the fall epizootic period, infection levels were inversely related to temperature. Average weekly temperatures higher than 17-20 degrees C and maximum daily temperatures higher than 26-28 degrees C were sta tistically correlated with low infection levels. In the second year, E . schizophorae was introduced by releasing diseased flies at two dairi es (four times at one dairy and three times at the other). E. schizoph orae was recovered for a brief time in the house fly population after the first two releases at one site but not at the second site. (C) 199 6 Academic Press, Inc.