Batting for rice: The effect of bat exclusion on rice in North-East India

Abstract

Insectivorous bats are gaining increasing attention for their potential as biological agents of pest suppression. Studies around the world have demonstrated their tendency to track and hunt agricultural pests over time and space, and thus to have a positive impact on reducing plant damage and protecting yield of agricultural crops. We documented the effect of insectivorous bats on the health and yield of a rice crop in Assam, India. Using six sets of paired experimental and control plots (of which five were analysed), where bats were selectively excluded from the experimental plots, we collected two measures of plant damage and one measure of total yield to assess the impact of bats on the crop. In parallel, bat activity at the six sites was recorded over the rice growing season using passive acoustic recorders. Our results show that the exclusion of insectivorous bats causes an increase in the degree of defoliation suffered by rice plants. We also report non-significant differences in the degree of yellowing of rice and of the total yield between the experimental and control plots. Bat activity levels showed a mono- or bi-modal peak in activity over the growing season, which broadly tracked the maturity of rice, a pattern also seen in many insect pests. Our results strongly suggest that bats have suppressive impact on pest action in rice fields. The general trend in activity levels, as well as the significant difference in plant damage, would indicate that bats are hunting insect pests and that the non-significant difference in final yield was likely the result of methodological limitations. These findings suggest that bats add significant ecological and economic value to Indian rice ecosystems and hold great potential to be used in integrated pest management (IPM) strategies aimed at suppressing pests.