Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 14, 2003
Publication Date: N/A
Interpretive Summary: The gypsy moth is a serious defoliator of forest and shade trees. USDA Forest Service is developing a biological insecticide, Gypchek, as a species specific control agent for the gypsy moth. This is the third in a series of studies on the aerial application of Gypchek mixed in Carrier 038. The first study was an experimental examination of treatment options such as single versus double application that suggested that the one application option, while less effective compared with a split-dose double application,none the less had attractive cost and programmatic considerations. The second study, evaluating a pilot test required by USDA Forest Service before recommending the one application option for operational use, suggested that the one application option could be successfully implemented, but was sensitive to weather conditions. This third study evaluates the use of the one application option as part of a state operational program, the State of Wisconsin Gypsy Moth Suppression Program. Since Wisconsin lies on the leading edge of the expanding gypsy moth population, suppression consists of negatively impacting trace populations. The use of Gypchek against trace populations required new evaluation technology. Our analysis of program efficacy used finding from studies 1 and 2 to explain results of study 3,and integrates the findings from all three studies to suggest future improvements. Specifically, we found that applications made early in the day gave considerably better results than applications made later in the day, with changes in efficacy associated with changes in weather conditions.These studies have implications for all federal, state, local and private users of Gypchek.
A technique (the "bugs-in-bags" approach) was developed and evaluated to measure the operational efficacy of Gypchek application against "trace" populations of gypsy moth in"leading edge" areas (= land just beyond the area of current establishment into which the gypsy moth is spreading) in which the primary measurable gypsy moth life stages are adult male moths caught in pheromone traps. First or second instar gypsy moth larvae were placed, one per bag or 10 per bag, in sleeve cages placed over treated foliage one hour post-treatment. Mortality observed for larvae placed ten per bag was equivalent to that recorded for larvae placed one per bag, and both should fairly reflect mortality occurring to the larvae scattered in nature. While this study was conceived as a test of the evaluation technique and not as an evaluation of Gypchek per se, an insight into Gypchek performance under operational conditions was gained. A single application of Gypchek applied in 9.5 liters of Carrier 038 at 1012 polyhedral inclusion bodies per ha was found to be rather sensitive to weather conditions, performing well in blocks treated in the early morning but evidencing a decline in efficacy as the morning wore on, apparently in response to a lowering of relative humidity and an increase in temperature and wind speed.