Night Warming Has Mixed Effects on the Development of the Fall Armyworm, Spodoptera frugiperda (Lepidoptera, Noctuidae), in Southern China

Simple Summary The fall armyworm, Spodoptera frugiperda (Lepidoptera, Noctuidae), invaded China in 2019. The species has been established as a year-round breeding population in most of the southern provinces which are the main winter maize planting areas. The effect of rising nighttime temperatures, driven by the changing climate in this region, on the growth and development of S. frugiperda is unclear. Results of this study show that the survival rate of larvae and pupae significantly declined with daytime temperatures declining and the nighttime temperature range increasing. Development rate accelerated along with the increasing daytime temperatures and nighttime temperatures, except for the intermediate treatments (daytime temperature 24 degrees C and diurnal range from 2-6 degrees C). Predictions of FAW development and warnings to local farmers need to be adjusted to take into account more rapid development when nighttime temperatures increase in the warming climate. Abstract The Fall Armyworm, Spodoptera frugiperda (Lepidoptera, Noctuidae), is a serious migratory pest. After invading China in 2019, the species was established as a year-round breeding population in most of the southern provinces. The area of winter maize in this region has been increasing due to the huge demand of fresh maize consumption, which is potentially at risk from this invasive pest, although the growth and development of S. frugiperda in the region's changing climate is unclear, particularly with rising temperatures at night. Here, we used the highest daytime temperatures of 27 degrees C, 24 degrees C, 20 degrees C and decreased these by 2, 4 and 6 degrees C to reflect the range of nighttime temperatures indicative of winter conditions in a warming climate to evaluate the effect of increasing night temperatures on the growth and development of S. frugiperda. Results show that the survival of larvae and pupae significantly declined with daytime temperatures declining and the nighttime temperature range increasing. Significant developmental effects were observed across all daytime-nighttime temperature treatments, except for adults. Additionally, there were significant interaction effects for all stages, except the egg stage, and generation time. The development rate increased with the increasing daytime temperatures and nighttime temperatures, except for the intermediate treatments (Group II). The uniformity of pupation and emergence times were higher under high daytime temperatures and nighttime temperature treatments. Predictions of FAW development and warnings to local farmers need to be adjusted to take into account the more rapid development when nighttime temperatures increase in the warming climate. These results will support decision makers in developing long-term management strategies for FAW in southern China.