Sharov, A., B. C. Pijanowski, A. Liebold, and S. H. Gage. 1999. What affects the rate of gypsy moth (Lepidoptera: Lymantriidae) spread in Michigan: Winter temperature or forest susceptibility? Agriculture and Forest Entomology 1:37-45.

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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.

DOI: 10.1046/j.1461-9563.1999.00006.x

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