The disease complex of the gypsy moth: I. Major components

Abstract

A study was undertaken to elucidate the impact of the various components of disease on natural populations of the gypsy moth, Porthetria dispar. Diseased larvae from both sparse and dense populations were examined and categorized on the basis of etiologic and nonetiologic mortality factors. Results indicated a significantly higher incidence of parasitoid involvement—but virtual nonexistence of polyhedral viroses—in the relatively stable sparse populations. Nuclear polyhedrosis probably represented the primary mortality factor in the dense populations. Many insects examined from both population types revealed no infectious agent or overt cause of disease, a fact that may indicate a major regulatory role of noninfectious disease in natural populations. Variation in the disease complex within the populations that have been studied indicates that minor causes of disease in one may well predominate in others. Thus, to fully understand this complex, it must be studied across a number of years within a series of populations from different geographical areas.