The hotter the better? Climate change and voltinism of Spodoptera eridania estimated with different methods

Abstract

Substantial increases in global temperature are projected for the coming decades due to climate change. Considering that temperature has a strong influence on insect voltinism (i.e., number of generations per year), climate change may affect the population growth of insects, with potential consequences for food production. The southern armyworm, Spodoptera eridania, is a multivoltine species native to the American tropics that causes severe damage to several crops. In this context, this study evaluated the impacts of climate change on the voltinism of S. eridania in southern Brazil. Current and future daily temperature data were combined with non-linear and degree-day models to estimate the voltinism of this pest. Under current climate conditions, the voltinism of S. eridania ranged from 2.9 to 9.2 generations, with fewer cohorts in colder regions and more in warmer ones. A higher number of generations was predicted for the future climate scenarios evaluated, reaching up to 12.1 annual generations in certain regions by 2070. Most of the variation in voltinism was explained by location (87.7%) and by the interaction between location and mathematical model (3.0%). The degree-day model estimated an increase in the number of generations in the entire study area, while the non-linear model predicted a decrease in voltinism in the warmer regions under future climate change scenarios. Given these differences between the predictions provided by degree-day and non-linear models, the selection of the best method to be used in climate change studies should be carried out carefully, considering how species respond to temperature. A considerable increase in the number of generations of S. eridania was projected for most of the study area under the climate change scenarios evaluated, suggesting a possible rise in pest incidence levels in the coming decades.