Climate-Change Driven Decline of an Insect Pathogen Increases the Risk of Defoliation by a Forest Pest Insect

Abstract

The effects of climate change on forest-defoliating insects are poorly understood, a problem that is especially urgent in the case of the spongy moth (formerly "the gypsy moth", Lymantria dispar). For decades following its introduction in 1869, the spongy moth severely defoliated North American forests, but the introduction of the pathogen Entomophaga maimaiga in 1989 drastically lowered defoliation levels. E. maimaiga, however, needs cool, moist conditions, whereas climate change is bringing hot, dry conditions to the range of the spongy moth. Here we use an empirically validated mathematical model to project that climate change will sharply reduce E. maimaiga infection rates, greatly increasing spongy moth defoliation. Recent data show that defoliation has strongly rebounded, supporting our projections. Our work shows that the effects of climate change on insect pathogens can have dire consequences for forests, and demonstrates the importance of understanding how climate change can alter species interactions.