Maize fields are a potential sink for an outbreaking mirid bug pest in Chinese Bt-cotton agricultural landscapes

Abstract

Agricultural landscapes are fast-changing systems due to crop planting and harvesting. These events strongly influence movements of arthropod pests and their natural enemies, yet they are insufficiently considered to implement informed pest management strategies. In China, the adoption of Bt-cotton crops at very large scales has given rise to the recent pest status of mirid bugs such as Apolygus lucorum in cotton fields. In this study we relied on carbon 13 stable isotope analysis to estimate the dispersal of A. lucorum in the Bt-cotton agricultural landscape, composed of a mosaic of cotton and maize and other minor crops. We showed that a diet on C3-plants including cotton induced a significantly different signature than the C4-plant maize. Based on δ13C ratios, we showed that more than 75% of mirid bugs caught in maize fields did not originate in situ, since they had a C3-diet and therefore most likely dispersed from neighbouring cotton fields. Conversely, less than 10% of mirid bugs in cotton fields had a diet on C4-plants, so the vast majority of them did not disperse from maize fields but instead likely stayed in cotton fields. We also observed a delayed establishment of A. lucorum populations in maize fields compared to cotton fields, likely due to host phenology. Indeed we showed in laboratory that juveniles’ survival rate and adults’ fecundity are high on maize silk and grain only, whose resources are available in the field shortly before harvest. Unidirectional movements of mirids from cotton to maize associated with poor developmental success on maize highlight the high potential of maize fields to act as a sink for A. lucorum mirid bug pests. This could be wisely implemented in IPM programs to enhance the management of mirid bug population outbreaks in cotton fields and reduce yield loss on cotton.