Mosquito dehydration tolerance is dependent on the expression of heat shock proteins

In this study, we examined the role of two heat shock proteins (Hsp70 ad Hsp90) in response to dehydration stress for three mosquito species, Aedes aegypti, Anopheles gambiae and Culex pipiens. To do so, water balance characteristics were analyzed, hsp transcript expression was monitored throughout dehydration, and RNA interference (RNAi) was performed on A. aegypti to determine the precise role of Hsps during dehydration. Female mosquitoes of all species displayed percent water content between 66-68% when fully-hydrated. The lowest water loss rate was for A. aegypti (2.6%/h), followed by C. pipiens (3.3%/h), and A. gambiae (5.1%/h). During dehydration, A. aegypti and C. pipiens tolerated a loss of 34-36% of their body water, but A. gambiae was able to tolerate a water loss of only 29%. Throughout dehydration, hsp70 expression was increased in all three species, but only C. pipiens continued to express this gene during rehydration. Hsp90 was expressed in fully-hydrated and dehydrated individuals for all three species, but was only expressed in A. aegypti and A. gambiae during rehydration. Water content and water loss of A. aegypti were not altered following RNAi directed toward hsp70 and hsp90, however dehydration tolerance was lower. Females were able to tolerate only a 29% water loss after dsRNA directed against hsp70 and only a 27% water loss after dsRNA directed against hsp90, whereas the controls tolerated a loss of 36% of their body water. Thus, we conclude that Hsps play a critical function in mosquito dehydration tolerance.