Accuracy of Gypsy Moth (Lepidoptera: Lymantriidae) Population Estimates Based on Counts of Larvae in Artificial Resting Sites

Mark/recapture surveys were carried out to evaluate the relationship between counts of caterpillars under burlap-band resting sites and gypsy moth, Lymantria dispar (L.), populations. Principal component analysis showed that rain on the day of sampling was related to decreases in numbers counted under burlap. Caterpillars did not readily move between burlap resting sites placed high in trees and those lower down, and larvae found under high burlap developed slower and had greater mortality than those under low burlap. Survival rates calculated from the mark/recapture data were higher for larvae under low burlap. Calculations of population levels from the mark/recapture data showed that the part of the population sampled by low burlap was 10-fold as large as that sampled by high burlap. Estimates of daily survival rates of the first four instars were close to the corresponding rates for large larvae. There was a correlation of 0.95 between mark/recapture log population estimates for large caterpillars and log counts over four orders of magnitude, but comparisons with independent data suggest that the relationship between log counts and log populations may be nonlinear.