Concentration-response and temperature-related susceptibility of the forest tent caterpillar (Lepidoptera: Lasiocampidae) to the entomopathogenic fungus Furia gastropachae (Zygomycetes: Entomophthorales)

Abstract

Furia gastropachae (Raciborski) Filotas, Hajek & Humber is an important but little studied fungal pathogen of the forest tent caterpillar, Malacosoma disstria Hübner, a hardwood forest pest. As a means of assessing its potential as a biological control agent, a bioassay methodology was developed to estimate virulence of two isolates of F. gastropachae (ARSEF 5544 and 5545 from NY and MD, USA, respectively) and to investigate the effect of temperature on fungal virulence and activity. To assess virulence, fourth instar M. disstria larvae were exposed to conidial showers, with duration of exposure varied to produce different concentrations. Resulting LC 50 estimates were low for both isolates (0.5 ± 0.4 and 36.5 ± 16.9 conidia/mm 2 for the NY and MD isolate, respectively), though the NY isolate was more virulent. Both isolates had a relatively rapid rate of kill (ca. 5 days). To study the effect of temperature on fungal activity, M. disstria larvae were exposed to a single concentration of the NY or MD isolates, and then incubated at 10, 15, 20, 25, or 30 °C. Both isolates caused mycoses at all temperatures, however, percent infection by the NY isolate was maximized at cooler temperatures (⩽20 °C). Percent infection by the more southerly MD isolate also tended to decline with increasing temperature, however a significant difference was observed only between 15 and 30 °C. Results suggest that F. gastropachae is well adapted to the early spring temperatures in which its host is most likely to be active. The virulence of this fungus suggests that it may be a good candidate for biological control of the forest tent caterpillar.