Modeling the Influence of Rainfall and Temperature on the Phenology of Infection of Gypsy Moth, Lymantria dispar, Larvae by the Fungus Entomophaga maimaiga

A computer model driven by daily maximum-minimum temperature and rainfall records was developed to investigate the influence of weather on times when gypsy moth larvae, Lymantria dispar, can become infected by the fungal pathogen Entomophaga maimaiga. In the model, gypsy moth eggs are hatched and neonates are exposed primarily to germinating resting spores in the soil during the spring. Risk of infection is related to forest floor moisture. Larval and fungal development follows a degree-day model. When larvae become 4th instars, they can again become infected by resting spores because they hide in the litter during daylight hours. If rain falls when infected caterpillars die, the fungus sporulates, producing conidia. The number of conidia produced is assumed to directly influence the probability of infection of other larvae. The model was run using weather records from 1990 through 1992. Predicted times of infection were compatible with estimated fungal recruitment rates and changes in field disease prevalence rates. Assumptions about infection mechanisms in the model are discussed as they relate to the real world.