POPULATION DYNAMICS OF GYPSY MOTH IN NORTH AMERICA

SUMMARY AND CONCLUSION Recent studies (52) support the earlier conclusions of Bess et al (16) and Campbell & Sloan (30,31) that gypsy moth populations are maintained at low densities primarily by the action of small mammal predators. Spatially densi­ty-dependent parasitism by tachinids such as C. concinnata may also be important in suppressing incipient outbreaks (63). The reasons such factors fail in certain years and allow gypsy moth populations to escape into outbreak phase have not been elucidated. Factors that affect small mammal population density such as overwintering food supply are important possible causes of population release. Other factors that affect predation rates by small mammals such as berry crops which compete with gypsy moth as a food item (147) may also be important. However, changes in factors that affect fecundity or survival of early instars may in certain years result in densities of late instar larvae or pupae that approach the satiation points of predators. The syn­chronous behavior of gypsy moth populations over fairly large regions sug­gests that weather conditions drive the system in some manner, but the mechanisms remain obscure. It is entirely possible that different weather events and the failure of different mortality agents are responsible for the onset of outbreak phase in different years. The factors controlling outbreak populations are better understood. In recent years major advances have occurred in our understanding of

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