ANALYSIS OF GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) POPULATION-DYNAMICS IN MICHIGAN USING GEOGRAPHIC INFORMATION-SYSTEMS

We studied the 9-yr (1986-1994) statewide gypsy moth, Lymantria dispar (L.), population distribution dynamics in Michigan using geographic i nformation systems (GIS) based on an analysis of pheromone trap data o f male moth catch from more than 3,000 permanent sites. A time series of male moth contour maps with 7 density categories (0, 1-25, 26-100, 101-200, 201-300, 301-400 and >400 moths . trap(-1) . year(-1)) was cr eated using the GIS. The statewide gypsy moth population expanded at a n alarming rate of 6,053 km(2)/yr with the largest area infested being 128,164 km(2) (85% of the state) in 1993. The population-weighted mea n center staved in the Lower Peninsula, but a low density population w as developing in the Upper Peninsula during the 9-yr period. Map analy sis showed that the statewide population gradually increased from 1986 to 1990 and then became relatively stable thereafter. Both the highes t weighted average density (191 moths.trap 1 . year(-1)) and the great est coefficient of relative dispersion ( 307%) occurred in 1990. Linea r regression slopes between successive) ears were >1.0 before 1990 and <1.0 thereafter, indicating an increasing and then decreasing populat ion density change. Regression results between successive years indica te that the previous years' population map is a good linear approximat ion for the following (r(2) >70%). In the 9-yr study, 55% of the popul ation cells staved in the same density class in the following year. A general pattern of population density shifts was that increase prevail ed over decrease. Research methodology, population distribution, tempo ral dynamics, and density shifts are discussed.