Impacts of nitrogen fertilizer on major insect pests and their predators in transgenic Bt rice lines T2A-1 and T1C-19

Nitrogen is a critical factor for plant development and nitrogen input is one of the important tactics to enhance the development and yield of crops. Nevertheless, nitrogen input could influence the occurrence of insects positively or negatively. Nitrogen is also one of the main elements composing the insecticidal crystal (Cry) protein. Cry protein production could affect nitrogen partitioning in Bt plants and as such nitrogen input may influence insect pest management in transgenic Bt rice, Oryza sativa L. (Poaceae). To test this possibility, we evaluated the impacts of nitrogen regimes on the main insect pests and their predators on two Bt rice lines, T2A-1 and T1C-19, expressing Cry2A and Cry1C, respectively, and their non-transgenic parental counterpart MH63. The results showed that Cry proteins with different nitrogen regimes have enough insecticidal activity on rice leaffolder, Cnaphalocrocis medinalis Guenee (Lepidoptera: Crambidae), in both laboratory and field experiments. Laboratory studies indicated that relevant parameters of ecological fitness in brown planthopper, Nilaparvata lugens (Stal) (Hemiptera: Delphacidae), a non-target insect pest, were significantly affected by nitrogen input both on Bt and MH63 rice lines. Nymphal survival, female adult longevity, and egg hatchability in N. lugens differed significantly among rice varieties. The experiments conducted in rice fields also demonstrated that nitrogen was positively correlated with the abundance of N. lugens on Bt rice, similar to that on MH63 rice. The abundances of two predators - the wolf spider Pirata subpiraticus (Boesenberg & Strand) (Araneae: Lycosidae) and the bug Cyrthorhinus lividipennis Reuter (Hemiptera: Miridae) - were significantly affected by rice growth stages but not by nitrogen input and rice varieties. In conclusion, the above results indicate that high nitrogen regimes for Bt rice (T2A-1 and T1C-19) and non-Bt rice (MH63) cannot facilitate the management of insect pests.