The brown planthopper (Nilaparvata lugens) is the main migratory pest in many rice growing areas in Asia.  E78 is a member of the nuclear hormone receptor superfamily which plays an important role in egg development and maternal regulation of early embryogenesis.  In this study, brown planthopper E78 (NlE78) was cloned, and the predicted amino acid sequence showed that it contains two conserved domains: NR-LBD and DBD.  qRT-PCR showed that the expression of NlE78 is high in the fifth instar nymphs and the ovaries of females.  After downregulation of NlE78, the rate of moulting failure (33.2%) increased significantly, and ovarian development was delayed.  However, when NlE78 was downregulated together with NlE93, the emergence rate increased significantly (78.79%), and ovarian development was similar to that when NlE78 was downregulated but not delayed.  A co-immunoprecipitation experiment showed that NlE78 interacts with NlE93, a crucial downstream transcription factor of the ecdysone signalling pathway.  Cellular localization by immunofluorescence revealed that NlE78 and NlE93 are expressed in the nucleus.  This study indicates that NlE78 regulates ovarian development and moulting, possibly through its interaction with NlE93.  This study is of great significance for the development of new pesticides and control methods based on newly discovered targets.

The brown planthopper, Nilaparvata lugens (Stål), is the most serious insect pest of rice. It has developed high resistance to traditional insecticides because of their intensive use. Juvenile hormone (JH) analogs have been used successfully to control this species and other pest insects. However, the molecular mechanism of JH signaling is not well understood. Krüppel-homolog 1 (Kr-h1) is a transcription factor involved in the JH pathway. In this study, the Kr-h1 cDNA was cloned and characterized from N. lugens by rapid amplification of cDNA ends (RACE) and reverse transcription PCR (RT-PCR). Its spatial and temporal expression profiles were examined by real-time quantitative PCR, and its function was also studied by RNA interference (RNAi). The open reading frame of NlKr-h1 is 1 833 bp encoding for 611 amino acids. The protein contains eight conserved zinc-finger motifs. NlKr-h1 was expressed at all life stages, with the highest mRNA level in the 4-day embryo. NlKr-h1 mRNA levels rose during each nymphal molt after the 2nd instar. In the adults, the mRNA level in males was significantly higher than that in females of either the macropterous or brachypterous type. The highest expression was observed in the female midgut. NlKr-h1 was activated by juvenile hormone III (JH III) in the 3rd-5th instar nymphs. Disruption of Nlkr-h1 expression by RNAi caused stunted wing development and malformations of both male and female external genitalia. Our findings suggest that Kr-h1 may be a useful target for pest insect management.