Aedes aegypti is the primary disease vector for both Dengue and Yellow Fever. Climate change is affecting the natural environment of these mosquitoes, yet the extent to which individuals and populations can physiologically respond to environmental stressors is unknown. Understanding the mechanics of A. aegypti stress responses has important implications for predicting both mosquito and disease distribution patterns in the context of a rapidly changing global environment. In this research, the genetic response of adult female A. aegypti mosquitoes to dehydration stress is investigated using quantitative PCR. Homologs of four physiologically relevant genes (Frost, Desat2, HSP70 and Pepck) are examined in A. aegypti. Mosquitoes were subjected to acute desiccation stress and then analyzed via qPCR to determine the extent to which these genes' expression patterns were altered. Altered gene expression in response to desiccation stress was observed for HSP 70, while evidence suggesting the evolutionary divergence of Frost was also uncovered. These results provide clues as to which physiological mechanisms are utilized by A. aegypti to mediate survival in desiccating environments. Genetic indicators of these mechanisms can be used in comparative studies against geographically distinct populations to generate an understanding of stress resistance mechanisms in A. aegypti as a function of geography and environment.
Aedes aegypti occupies several regions of the world and transmits well-known diseases such as yellow fever. The unique life cycle of this species displays its resilience with the initial laying of eggs, in short-lived puddles, that do not hatch until a subsequent period of flooding. Larvae accumulate resources while growing in the puddle but face the risk of habitat loss until they eventually pupate into an adult. While much is known about the ecology and molecular biology of this vector, there is an absence of information on the possible life history trade-offs that occur as a result of choosing this particular larval habitat. Growing faster and pupating sooner increase their probability of larval survival; however, this rapid growth rate results in smaller adult body size, which may impact survival as adults. Our study involved investigating the effect of age at pupation on fitness traits in the adult. Mosquitoes were tested for desiccation resistance as well as dry mass, water content, carbohydrate and lipid on the day of emergence, and their values were compared to each individual’s age at pupation. Results showed mosquitoes that pupated later displayed increased desiccation resistance as well as increased lipid content. This study demonstrates that time spent as a larva has positive effects on desiccation resistance, and this is not mediated by increased body size or body water stores. Larval development time also boosts lipid stores, which likely promote starvation resistance and may also be involved in enhanced desiccation resistance. Knowledge about life-history trade-offs affecting adult viability can be gained from this study. Thus, this information concerning pupation and emergence promotes a greater awareness of when to prepare for these mosquitoes such as after rainy seasons, as well as how to limit the available larval habitats.
Worldwide Aedes aegypti is the principal urban vector of several major human pathogens, including dengue, Zika, chikungunya and yellow fever viruses. In Mexico, control of this mosquito strongly relies on the use of pyrethroids against adults and larvae. In consequence, many Ae. aegypti field populations have become resistant to insecticides. Pyrethroids kill mosquitoes by binding to the voltage gated sodium channel (VGSC) and preventing its proper functioning. Resistance to pyrethroids arises through nonsynonymous mutations in the VGSC gene that reduce pyrethroid binding, known as knockdown resistance (kdr). The insecticide resistance mutations have been shown to have a large fitness benefit in the presence of insecticide treatment. However, in the absence of insecticide, there is frequently reported reduced frequency of the mutant allele which suggests the mutation has a fitness cost. We evaluated the fitness cost of some kdr mutations on several life-history parameters as well as common abiotic stresses faced in the field. Specifically, we compared 2 populations differing in the frequency of the kdr mutations but otherwise of identical genetic background and we found a significant difference between the resistant and susceptible strains in adult dry mass upon emergence, adult water reserves, adult lipid reserves, and larval thermal tolerance. In contrast, both strains responded similarly to larval salinity stress and adult desiccation stress. Our results suggest that these Ae. aegypti kdr mutations indeed have some fitness cost, whether directly or indirectly associated with them. This is critical to determining the extent to which insecticide resistance interacts with life history traits and should provide key information for vector control in the future.