Suppression of allatotropin simulates reproductive diapause in the mosquito Culex pipiens

- Higher levels of allatotropin (AT) mRNA are present in nondiapausing females than in diapausing females of Culex pipiens.
- Allatostatin (AS-C) mRNA levels are not altered by diapause.
- RNAi knockdown of AT in nondiapausing females mimics the diapause status of the ovaries.
- The knockdown effect can be reversed with an application of juvenile hormone III.

The cessation of juvenile hormone (JH) production is a key endocrine event that halts ovarian development and hence initiates diapause in females of the mosquito, Culex pipiens. The shutdown in endocrine activity of the corpora allata (CA), the source of JH, was manifested in the smaller size of CA in females reared under short daylengths (diapause) compared to those reared under long daylengths (nondiapause), as well as in low expression of the mRNA encoding allatotropin, the neuropeptide that promotes JH biosynthesis in the CA. Genes encoding both allatotropin and allatostatin were identified in C. pipiens, but only expression levels of allatotropin differed in the two types of females. Knockdown of allatotropin mRNA using RNA interference in females programmed for nondiapause resulted in a cessation of ovarian development akin to diapause. This arrest in development could be reversed with an application of JH. Our results thus suggest that suppression of allatotropin is a critical link in regulating the shutdown of the CA during diapause.