Weather and regional crop composition variation drive spatial synchrony of lepidopteran agricultural pests

1. Spatial synchrony, the tendency for temporal population fluctuations to be correlated across multiple locations at regional scales, is common and contributes to the severity of outbreaks and epidemics, but is little studied in agricultural pests. 2. This study analysed spatial synchrony from 1974 to 2008 in 16 lepidopteran agricultural pests in Maryland, U.S.A., and investigated whether pest synchrony is driven by interannual variability in seasonal weather and the areas planted in different crop types. 3. Lepidopteran pests exhibited high degrees of spatial synchrony, which was driven by environmental variation, a phenomenon known as the Moran effect. Region-wide variation in the areas planted in major crops drove spatially synchronous abundance fluctuations in more than half of studied species. The combination of weather and crop composition explained large fractions of synchrony in black cutworm, corn earworm, European corn borer, and spotted cutworm populations. Other pests, including forage looper and variegated cutworm, displayed a high degree of spatial synchrony, but without dependence on the tested drivers. 4. The study finding that synchronous variation in the area planted in different crop types contributed to synchronous pest abundance fluctuations suggests that strategies to reduce synchrony in changes in crop type across a region could reduce the severity of pest outbreaks and enhance the stability of agricultural systems.