JACK PINE BUDWORM POPULATION BEHAVIOR IN NORTHWESTERN WISCONSIN

Long-term (17-31 year) density estimates of jack pine budworm, Choristoneura pinus pinus Free. (Lepidoptera: Tortricidae), populations from 31 townships in northwestern Wisconsin were analyzed to investigate variation in population behaviour. Populations had varying combinations of cyclic components with periods of 5, 6, and 10 years. Populations that fluctuated with higher frequencies (shorter periods between outbreaks) tended to be found in locations where the habitat type was indicative of nutrient-poor and extremely dry soils. Many populations in these habitat types had high mean densities, and the coefficient of variation in density was smaller than that in other populations. Just under half (14) of the populations were regulated by statistically significant second-order density-dependent processes. Nevertheless, second-order processes were present to some extent in all populations examined. These results demonstrated that detection of density dependence and population regulation of jack pine budworm depends on the local site where studies are undertaken. Population fluctuations encountered in these populations are of the phase-forgetting quasi-cyclic kind. Studies of mechanisms that account for these cycles and cause populations to fluctuate at three different characteristic frequencies promise to be rewarding.