Nitrogen fertilization of rice plants improves ecological fitness of an entomophagous predator but dampens its impact on prey, the rice brown planthopper, Nilaparvata lugens

Nitrogen fertilizers are widely used to maximize crop productivity but are also known to benefit pest insects. Here we show that nitrogen not only increased the egg size of the key pest, brown planthopper (BPH), Nilaparvata lugens Stal, but also benefitted the predatory mirid bug, Cyrtorhinus lividipennis Reuter (Hemiptera: Miridae). Predator nymph survival and development rate, female adult weight, longevity and fecundity were all enhanced. Importantly, however, high nitrogen levels also extended the predator handling time (Th), reducing the number of prey eggs attacked per predator and signalling a weakening of top-down control. We conclude that nitrogen fertilizer can exacerbate pest impact by natural enemy-mediated effects in addition to previously reported direct effects on herbivores. Our results highlighted the need to moderate the use of nitrogen fertilizers to maintain effective biological control of these rice pests to reduce dependence on insecticides, another potentially hazardous input.