Distribution, Dispersal, and Apparent Survival of Male Gypsy Moths as Determined by Capture in Pheromone-Baited Traps

An average of 3.9% of laboratory-reared, marked male gypsy moths ( Lymantria dispar L.) released uniformly across a 0.64 km2 area were captured in pheromone-baited traps set out 800 m apart in a 64 km2 grid. In contrast, an average of 0.9% of males released simultaneously from a single point at the center of the grid (566 m from the nearest trap) were captured. The 4.0% recapture can be used to estimate the average density and the 0.9% recapture to estimate the maximal density of a population of feral moths, based on the numbers caught in a trapping grid of the same trap density, if we assume that the feral and laboratory-reared moths behave similarly. Approximately 97% of the recaptured males from the uniform release and 80% from the grid center release were captured within 800 m of the release site and no moths were recaptured beyond 1600 m. An average of 18% of males released from the center of a smaller (0.64 km2) grid of higher trap density (80 m spacing) were recaptured. Once again, recaptures occurred predominantly in traps near the center of the grid. The proportion recaptured was highest on the warmer days. Males were released 1, 2 and 3 days after eclosion to assess the effects of adult age, and mortality plus emigration upon trap catch. A higher proportion of older moths (2- and 3-days-old) were captured than one-day-old moths. The apparent average rate of mortality plus emigration between the first and second day after release was 96%, an estimate that may be influenced by individual differences in responsiveness of males to a pheromone source.