Video monitoring of brown planthopper in rice shows importance of frogs for biological pest control

Abstract: The contribution of different predator guilds to biological pest control is usually inferred from the abundance of these guilds or from selective exclusion, but direct observation is rarely used. However, the best evidence for predation is obtained by catching the predator in the act. We used direct observation by video recording to identify the most important predators of brown plant hopper (BPH), Nilaparvata lugens, a pest of major importance in rice. In the first experiment, we used dead BPH and demonstrate that long-horned grasshoppers (Tettigoniidae: Conocephalus longipennis), which are primarily herbivorous, but scavenging if given opportunity, were responsible for most removals of dead prey. Wolf spiders (Lycosidae) were the second most important. In a second experiment we compared the consumer guilds removing (i) dead BPH, (ii) live, immobilized BPH, and (iii) live, mobile BPH. Long-horned grasshoppers (C. longipennis) were again the main removal agents of dead BPH, ground beetles (Carabidae) of live, immobilized BPH, and frogs (Ranidae: Rana limnocharis) of live, mobile BPH. This study highlights for the first time the important contribution of frogs to predation on BPH in rice. Furthermore, we show that removal of immobilized sentinel prey is not representative for predation of live mobile prey, underlining the need for a critical assessment of commonly used sentinel methods.