What affects the rate of gypsy moth (Lepidoptera: Lymantriidae) spread: winter temperature or forest susceptibility?
1 The effect of winter temperature and forest susceptibility on the rate of gypsy moth Lymantria dispar (L.) range expansion in the lower peninsula of Michigan was analysed using historical data on moth counts in a grid of pheromone-baited traps collected from 1985 to 1994 by the Michigan Department of Agriculture. The rate of spread was measured by the distance between population boundaries in consecutive years. Boundaries were estimated for population thresholds of 1, 3, 10, 30, and 100 moths per trap using a polar coordinate system.
2 The average rate of spread estimated using all population thresholds was 15.8 km/yr.
3 The rate of spread was higher in the northern part of the lower peninsula than in the southern part, despite lower minimum January temperatures in the north.
4 The rate of spread was positively correlated with forest susceptibility, which was higher in the north than in the south.
Keywords Biological invasions, forest susceptibility, Lymantria dispar, population spread, temperature.
Document Type: Research Article
Affiliations: 1: Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, U.S.A., 2: Department of Entomology, Michigan State University, East Lansing and 3: North-eastern Forest Experiment Station, USDA Forest Service, Morgantown, West Virginia, U.S.A.
Publication date: 1999-02-01