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Title: DISEASE INTERACTIONS IN GYPSY MOTH POPULATIONS IN SW VIRGINIA

Author
item WEBB, RALPH
item WHITE, GEOFFREY
item THORPE, KEVIN
item TALLEY, S - ROCKBRIDGE CO GM COORD

Submitted to: Virginia Gypsy Moth Advisors Annual Review
Publication Type: Proceedings
Publication Acceptance Date: 6/30/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The gypsy moth fungal pathogen Entomophaga maimaiga has recently become established in North American gypsy moth populations, and has induced massive epizootics throughout its range. However, the ultimate impact of this fungus on gypsy moth population dynamics is unknown. It is especially important to understand the impact of the fungus on leading edge gypsy moth populations such as those found in SW Virginia in 1995. The reported study was a quantitative analysis of the activity of the fungus, and its interactions with the gypsy moth nuclear polyhedrosis virus, in 10 susceptible woodlots near Lexington, VA, that had a wide range of gypsy moth population densities. Based on previous observations and the knowledge that the fungus is aerially spread by conidia while the virus is spread by surface feeding of the caterpillars, we hypothesized that percent fungus attack would tend to be uniform over the general area while levels of virus would be positively density dependent. The gypsy moth is currently advancing southward and westward at about 20 miles per year. The finding that E. maimaiga does indeed heavily attack low level leading edge gypsy moth populations in never before defoliated woodlots could have profound implications for the future rate of spread of this serious forest defoliator. The present paper presents a synopsis of data presented at a meeting of Virginia gypsy moth coordinators and is intended for such an audience.

Technical Abstract: Ten woodlot were chosen to reflect a range of gypsy moth population densities. A one hectare evaluation plot was established in each woodlot. Populations were monitored by weekly burlap band larval counts in all plots. In the five higher density plots, weekly larval samples were also taken. All collected dead larvae were examined under light microscopy for cause of death. These data were used to estimate season long larval mortality, and for mortality specifically caused by the fungus Entomophaga maimaiga and by gypsy moth nuclear polyhedrosis virus. Levels of fungus were high in all plots regardless of gypsy moth density, while virus levels were clearly higher in plots with higher gypsy moth densities than in plots with lower gypsy moth densities.