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Title: CONCENTRATION-RESPONSE AND TEMPERATURE-RELATED SUSCEPTIBILITY OF THE FOREST TENT CATERPILLAR TO THE ENTOMOPATHOGENIC FUNGUS FURIA GASTROPACHAE

Author
item FILOTAS, M - CORNELL UNIVERSITY
item HAJEK, A - CORNELL UNIVERSITY
item Vandenberg, John

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2006
Publication Date: 6/1/2006
Citation: Filotas, M.J., Hajek, A.E., Vandenberg, J.D. 2006. Concentration-response and temperature-related susceptibility of the forest tent caterpillar to the entomopathogenic fungus furia gastropachae. Biological Control. 39:218-224.

Interpretive Summary: The fungus Furia gastropachae is an important but little known pathogen of the forest tent caterpillar. This caterpillar is a cyclic and potentially devastating pest of hardwood forests in eastern North America. The fungus can cause significant mortality in some caterpillar populations. We wished to obtain basic information to characterize the impact of this fungus. We developed a means of assessing its potential as a biological control agent by using a laboratory bioassay. We estimated the virulence of two strains of this fungus and examined the effect of selected temperatures on them. We found the two strains (one originally from New York and one from Maryland) varied by nearly 10 times in their relative virulence. Survival time varied with dose for larvae inoculated with the less virulent strain. Infection was highest at lower temperatures and was greatly reduced at the highest temperature tested (86 deg F). Both of the two fungal spore types were produced in cadavers infected with either of the strains. Based on these data the fungus appears well-adapted to early spring conditions. The results help develop an understanding of natural control agents in populations of caterpillars.

Technical Abstract: Furia gastropachae (Raciborski) is an important but little known fungal pathogen of the forest tent caterpillar, a hardwood forest pest. As a means of assessing its potential as a biological control agent, a bioassay was developed to estimate virulence of two isolates of F. gastropachae (ARSEF 5544 and 5545 from NY and MD, USA, respectively) against the forest tent caterpillar and to investigate the effect of temperature on fungal virulence and activity. Dose-response assays of showered spores resulted in differing LC50 values for the two isolates (0.5 more or less 0.4 conidia/mm2 and 36.5 more or less 16.9 conidia/mm2 for 5544 and 5545, respectively). Survival time was greatest at intermediate doses for ARSEF 5545 and was independent of dose for ARSEF 5544. Resting spores and conidia were produced by both isolates, and there was no effect of dose on the type of spore produced. For both isolates, infection was maximized at cooler to intermediate temperatures. Infection was greatly reduced at 30ºC, however at 25ºC infection by the more southern isolate (ARSEF 5545) was higher. For both isolates, survival time and production of conidia was lowest and production of resting spores was highest at 25ºC. We conclude that at least some isolates of this fungus can be very virulent to host larvae and that F. gastropachae appears to be well adapted to the early spring temperatures in which it is most likely to be active.