Repeated bouts of dehydration deplete nutrient reserves and reduce egg production in the mosquito Culex pipiens

Abstract

In this study of the mosquito, Culex pipiens, we examined the impact of multiple bouts of dehydration and rehydration on survival, depletion of metabolic reserves and egg production in both non-diapausing and diapausing females. Mosquitoes provided with access to sugar during rehydration survived longer than those allowed to rehydrate without sugar, and their survival was similar to that of mosquitoes of the same age that were not dehydrated. Among mosquitoes not provided with sugar, each dehydration bout reduced the mosquito's dry mass - an effect likely to be due to the utilization of carbohydrates and lipid reserves. The toll on glycogen and lipid reserves is likely to be especially costly for diapausing mosquitoes that are dependent on these stored reserves for winter survival. Egg production in both non-diapausing and post-diapausing C. pipiens was also reduced in response to multiple bouts of dehydration. Although egg quality was not compromised, the number of eggs produced was reduced. Both non-diapausing and diapausing females can compensate for the nutrient loss due to dehydration by sugar feeding but the opportunity to feed on sugar is likely to be rarely available in the overwintering habitat of diapausing females, thus the impact of dehydration may be especially pronounced in overwintering populations of C. pipiens.

Fig. 1.

Schematic representation of the experimental protocol, showing three bouts of dehydration and rehydration. The duration of each bout of dehydration/rehydration was 20–30 h. ND, non-diapause; D, diapause; RH, relative humidity.

Fig. 2.

Water balance characteristics of non-diapausing adult females of Culex pipiens after multiple bouts of dehydration. ▴, water only during recovery; ▪, 10% sucrose and water during recovery; ♦, fully hydrated controls. Each point is the mean ± s.e.m. of 24 individuals. a, denotes significance (P<0.05) between the three treatments based on ANOVA. RH, relative humidity.

Fig. 3.

Nutrient reserves in non-diapausing adult females after multiple bouts of dehydration. ▴, water only during recovery; ▪, 10% sucrose and water during recovery; ♦, fully hydrated controls. Each point is the mean ± s.e.m. of 24 individuals. a, denotes significance (P<0.05) between the three treatments groups based on ANOVA.

Fig. 4.

Changes in (A) nutrient reserves and (B) survival of diapausing adult females after multiple bouts of dehydration. ▴, sugar; ▪, lipids; ♦, glycogen. Each point is the mean ± s.e.m. of 15 individuals. Superscripts denote significance (P<0.05).

Fig. 5.

Egg production in (A) non-diapausing and (B) post-diapause adult females following blood ingestion after multiple bouts (N=0–20) of dehydration. Each point is the mean ± s.e.m. of 15 individuals. Superscripts denote significance (P<0.05).

Fig. 6.

Relative humidity levels in three hibernacula utilized by diapausing Culex pipiens near Columbus, OH, USA, during a one-week period in December 2006.

Fig. 7.

Water content of diapausing female adults of Culex pipiens collected from their overwintering hibernacula near Columbus, OH, USA, during eight weeks in December 2006 and January 2007. Each point is the mean ± s.e.m. of 10 mosquitoes.