WILL THE GYPSY-MOTH BECOME A PEST IN FLORIDA

We consider the questions of invasion, establishment and subsequent pest status of the gypsy moth, Lymantria dispar (L.), in Florida. Invasion is occurring by ''hitch-hiking'' egg masses and other life stages arriving in Florida from northern states where the gypsy moth is established. Another likely mode of invasion is the gradual diffusive spread of the established area which is moving south at about 10-20 km/yr. We predict the arrival of this spreading front in north Florida in about 2025. Warm winters in Florida present one obstacle to successful diapause in the egg stage. Gray's diapause model predicts emergence of northern eggs of about 25% in Tallahassee, 10% in Gainesville and zero further south. Comparison of laboratory data with north Florida weather is in good agreement with Gray's model as are predictions with climate-matching software (CLIMEX). Genetic selection may modify the diapause requirements if invasion occurs by gradual diffusion making establishment this way more likely. We define pest status in Florida as the occurrence of large oscillations typical of northern populations. Localized outbreak densities are likely to occur if local patches are larger than ''critical patch size'' where reproductive growth outstrips diffusive loss. If this occurs in north Florida forests, and there are strong nonlinear interactions with the forest and the natural enemies then large oscillations are likely to occur.