Prevalence of Entomophthorales mycoses in Populations of Spruce Budworm, Choristoneura fumiferana12

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Abstract
Larval and pupal populations of the spruce budworm, Choristoneura fumiferana (Clemens), were sampled for natural prevalence of fungal pathogens in northern Maine during 1975–77. Three species were isolated and identified: Entomophthora sphaerosperma Fresenius, E. egressa Mac-Leod and Tyrrell, and a species of Conidiobolus Brefeld. Prevalence of these pathogens was shown to vary with sample location, crown position of the host, host density, host instar, and temperature and relative humidity trends. Lower crown samples yielded significantly higher fungal disease prevalence. Significantly higher disease prevalence was also found in more dense spruce bud worm population samples. E. sphaerosperma occurred on hosts with a mean between larval instars 5 and 6 (5.79) compared with a mean between the 6th instar and the prepupal stages (6.69) for E. egressa , and a mean between the prepupal and pupal stages (7.10) for Conidiobolus sp . Cool, wet periods of weather appeared to enhance disease prevalence. These findings were examined in terms of entomopathogen epizootiology. The lower crown level and higher host population density may provide an environment more amenable to the spread of disease.

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