Population Cycles of Western Tent Caterpillars: Experimental Introductions and Synchrony of Fluctuations

Abstract

To test several of the hypotheses to explain population cycles of forest Lepidoptera, it must be known if the decline phase is related to the local history of the insect population, and if population declines are synchronous among populations in a geographic region. To determine if out—of—phase population cycles could be initiated experimentally, egg masses of western tent caterpillars, Malacosoma californicum pluviale, were introduced to seven sites of low caterpillar density during the increase and peak phases of population fluctuation. The beginning of the decline phase occurred in 1986 in most introduced and source populations, but was delayed until 1987 in three populations initiated from egg—mass introductions in 1984 or 1985. Regardless of the history of the population, or the size and species of food—plant trees, all populations were very low by 1988. In 1986, the year of peak density at most sites, early larva