Spatio-temporal variation in voltinism of insect pests: sensitivity to location and temperature anomalies

The development, survival, and reproduction of ectothermic organisms such as insects are strongly influenced by temperature. Because insects respond to temperature by accelerating or reducing their development rate, population growth is directly associated with temperature variations. Here, daily minimum and maximum temperatures and degree-day model approaches were used to estimate the number generation per year (voltinism) of Mythimna sequax Franclemont, Neoleucinodes elegantalis (Guenée), Spodoptera cosmioides (Walker), and Spodoptera eridania (Cramer) over a 34-year period in southern Brazil. Additionally, we assessed the effects of El Niño Southern Oscillation (ENSO) events on voltinism. While an increased number of generations were estimated in warmer regions, comprising mainly northwestern Paraná, fewer generations were estimated in the colder regions of Santa Catarina and Rio Grande do Sul. For all species, the location was the factor that explained most of the variation observed in voltinism (average of 76.9%). Inter-annual changes in voltinism also varied depending on location, and differences of up to five generations among years were obtained in colder regions. On the other hand, ENSO events had a minor influence on the species voltinism. Our findings provide an important contribution to the understanding of spatio-temporal variations in voltinism of insects, and how temperature changes may increase their population growth.