The Analysis of Numerical Change in Gypsy Moth Populations

A study of gypsy moth, Porthetria dispar (L.), population dynamics was carried out over a 7-year period in several areas in northeastern New York. The data were summarized in life tables, stratified by density and sex, and then analyzed by mathematical models. Variation in the survival rates of the instar IV to VI female larvae and the female pupae was the greatest source of variation in density among dense populations. Variation in the survival rates of both instar I to III and IV to VI female larvae was most important among sparse populations. Disease was the primary determinant of variation in the survival rate of dense populations of instar IV to VI larvae, while agents other than disease or parasites were most important at this stage among sparse populations. The survival rate of dense populations of the female pupae varied primarily in response to parasites and disease. Variation in the survival rate of the instar I to III larvae was probably primarily a function of variation in the dispersion rate of the newly hatched larvae. A generation model was developed that describes density at the start of a second generation as a function of the environmental variables associated with the above mortality-causing factors. It was tested against an independent body of data with some success.