Dehydration prompts increased activity and blood feeding by mosquitoes

Abstract

Current insights into the mosquito dehydration response rely on studies that examine specific responses but ultimately fail to provide an encompassing view of mosquito biology. Here, we examined underlying changes in the biology of mosquitoes associated with dehydration. Specifically, we show that dehydration increases blood feeding in the northern house mosquito, Culex pipiens, which was the result of both higher activity and a greater tendency to land on a host. Similar observations were noted for Aedes aegypti and Anopheles quadrimaculatus. RNA-seq and metabolome analyses in C. pipiens following dehydration revealed that factors associated with carbohydrate metabolism are altered, specifically the breakdown of trehalose. Suppression of trehalose breakdown in C. pipiens by RNA interference reduced phenotypes associated with lower hydration levels. Lastly, mesocosm studies for C. pipiens confirmed that dehydrated mosquitoes were more likely to host feed under ecologically relevant conditions. Disease modeling indicates dehydration bouts will likely enhance viral transmission. This dehydration-induced increase in blood feeding is therefore likely to occur regularly and intensify during periods when availability of water is low.

Figure 1

Dehydration increased mosquito activity and blood feeding for C. pipiens females. (A) Activity measured by a Locomotor Activity Monitor 25 (LAM25) system through the course of dehydration, inset represents averaged results from 38–44 hours. Each point is the mean ± SE of 36–48 mosquitoes. ¹Mosquitoes have access to water for drinking to remain hydrated. ²Free water is present, but mosquitoes are prevented from drinking by a mesh barrier. (B) Number of landing events per mosquito over the course of one hour. Mean ± SE represents 12 independent replicates of 30–40 mosquitoes. (C) Proportion of mosquitoes following varying levels of dehydration that blood fed within two hours of host availability. Mean ± SE represents 10 replicates of 50 mosquitoes. (D) Time until the 20% dehydration point under varying temperatures and relative humidity (RH). Three replicates of 40 mosquitoes were conducted at each RH (33, 75, and 100%) at each temperature. Statistical analyses for (A–D) were conducted by a t-test or one- and two-way ANOVA followed by Tukey’s HSD post-hoc analysis where appropriate.

Figure 2

Dehydration enriched carbohydrate metabolism and prompted a trehalose to glucose shift for C. pipiens females. Blue denotes decreased levels during dehydration, gray indicates no difference, and yellow is increased during dehydration compared to hydrated individuals. (A) RNA-seq analyses following dehydration yielded differential expression of 1231 genes. (B) Expression levels for multiple carbohydrate-associated genes, many of which were upregulated. (C) Metabolomics following dehydration stress. Each value represents the average of eight replicates of combined samples with 20–30 mosquitoes.

Figure 3

Glucose and trehalose changes are related to the rate of dehydration for C. pipiens females. Rapid and slow dehydration differentially altered levels of glucose and trehalose. Mean ± SE for 10 replicates of samples from four-five mosquitoes at each time point. Statistical values refer to the control versus dehydrated mosquitoes at each time point.

Figure 4

Glucose and trehalose shifts directly impacted mosquito blood feeding-dehydration dynamics for C. pipiens females. (A–C) Knockdown of trehalase prevented the trehalose to glucose conversion during dehydration by suppressing trehalase activity. Trehalase activity is in mol glucose/µg protein/minute. Mean ± SE for 12 mosquitoes at each time point. (D,E). Landing on the host (mean ± SE for 8 replicates at each time point) and blood feeding (mean ± SE for 8 replicates at each time point) changed following trehalase suppression and dehydration. Statistical analyses were conducted by a one- or two-way ANOVA followed by Tukey’s HSD post-hoc analysis where appropriate. 5d and 25d are periods following injection of dsRNA. Control, mosquitoes held at 100% RH for 18 h. Dehydrated, mosquitoes held at 75% RH for 18 h. Baseline denotes levels before 18 h of dehydration.

Figure 5

Dry field and laboratory conditions increased host landing and impacted disease transmission based on West Nile virus transmission modeling for C. pipiens females. (A) Body water content (% of total mass) assessment of females attempting to blood feed following 24 hours with and without precipitation from field mesocosm studies. Mean ± SE for 8 replicates at each time point. (B) Water content of females attempting to blood feed under laboratory conditions. Mean ± SE of 8 replicates at each time point. (C) Predicted transmission of WNV will increase as the result of increased blood feeding due to dehydration exposure. Modeling and wet vs. dry conditions described in Supplemental Materials 1.