Effects Of Different Frog Species And Densities On Main Insect Pests, Natural Enemies And Rice Yield

Frogs are naturally occurring natural enemies of pests in rice fields, and protecting and rationally using it is of great significance to control rice insect pests. In this study, three frogs such as Rana nigromaculata, Rana catesbeiana and Rana limnocharis, was chosen as the experiment material and each frogs set two different density levels, taking general prevention area (CK1) and blank area (CK2) as control area, through continuous testing of early season rice (Xiangzaoxian NO.45) and double cropping late rice (Yuzhenxiang), do system research of the effect of different frog species and densities on major agronomic traits of rice, yield formation, main insect pests and their natural enemies. The main findings are as follows:1. There was significant difference in the number of planthopper among three frogs. The Rana nigromaculata was the best for controlling planthopper, the Rana catesbeiana followed. As three frogs’ densities increased, the number of planthopper had decreased. Laboratoty experiments showed that the Rana nigromaculata could feed13.17planthoppers everyday and the maximum numbers were19.00. However, the Rana catesbeiana and the Rana limnocharis just fed8.17and5.33planthoppers, respectively. Besides, young Rana nigromaculata and Rana catesbeiana after metamorphosis had a strong predation on borer moth of rice, it helped to reduce the rice borer infestation and rice rolled rate. At the same time, with the Rana nigromaculata’s and the Rana catesbeiana’s densities increasing, rice rolled rate had decreased. But the Rana limnocharis had a bad effect on controlling borer moth of rice.2. Effects of three frogs on spiders divided with one another, and the Rana nigromaculata and the Rana limnocharis had no significant effects on spiders, but the Rana catesbeiana had significant effects on them. As the Rana catesbeiana’s densities increase, the numbers of spider had decreased. Laboratoty experiments showed that the Rana catesbeiana liked feeding Lycosidae. The study also showed that three frogs had no significant effects on Cyrtorrhinus lividipennis Reuter, but there was small difference in preying it between different frogs.3. Three frogs had no significant effects on tillering, leaf area index (LAI) and height of rice. But with Rana nigromaculata and Rana catesbeiana densities increasing, they had an inclination to decrease leaf loose rate (LLR). In comparison with blank area (CK2), frogs also had an inclination to increase the rate of dry matter. In addition, dry weight accumulation of rice increased as three frogs’ densities increased, and that the Rana catesbeiana and the Rana nigromaculata promote the role of dry matter accumulation was greater than the Rana limnocharis. Comparing with blank area (CK2), three frogs improved rice yield to a certain extent. As three frogs’ densities increased, rice yield heightened. Early season rice and double cropping late rices’ average yield of each treatment were as follows:CK1>3000Rana nigromaculata/hm2>1800Rana catesbeiana/hm2>1500Rana nigromaculata/hm2>900Rana catesbeiana/hm2>9000Rana limnocharis/hm2>4500Rana limnocharis/hm2> CK2. The difference in the grain number and the seed setting rate were significant among three frogs. With their densities increasing, the grain number and the seed setting rate heightened, and it is greater than the Rana catesbeiana and the Rana limnocharis that the Rana nigromaculata improve the effect of the grain number and the seed setting rate.