Mosquitoes

Two thousand five hundred species and 1,000 subspecies of mosquitoes thrive across diverse ecological niches from the arid desert to the subarctic tundra. The life cycle, habitat preference, and temporal behavior of mosquitoes is therefore highly variable and species dependent. Over its life cycle, a mosquito hatches from an egg, develops through aquatic larval stages into a pupae and finally an airborne adult. Larval mosquitoes inhabit almost all temporary natural, human altered or anthropogenic water holding bodies on land. Extraordinary larval habitats include salty water, hot springs, tree holes, inside of plants (e.g., pitcherplants, bromeliads) and even water in between plant cellular tissue. Mosquitoes that transfer diseases to humans preferentially breed in disturbed environments (e.g., burrow pits, hoof prints) or containers (e.g., potable water jars, tires) close to or inside human dwellings.

Only a small fraction of eggs survive environmental hazards, resource scarcity, predation, disease, and competition to develop into adults. Reproductive strategies vary from laying individual eggs or egg clusters across multiple locations to depositing all the eggs in one location as a mosquito raft. Depending on the species, eggs are either deposited into a water body and rapidly develop or are deposited on a surface previously submerged in water. Subsequently re-submerging the eggs combined with other environmental cues initiates hatching of the mosquito into a suitable habitat. The cold-blooded mosquito's rate of development is strongly influenced by the temperature and moisture characteristics of the ambient environment. In general, warm conditions expedite mosquito development while hot or cold conditions stymie mosquito maturation.

Nonpredatory larvae extract and/or browse for food and nutrients from the aqueous environment and store the food for future development. Larvae mature, grow, and shed their exoskeletons three times before metamorphosis accelerates in the pupae stage. Pupae larval muscles and the midgut are completely reconstructed into adult body parts. Pupae are morphologically distinct from larvae, cannot consume food, float at the water's surface, and can survive outside of water. Adult mosquitoes consume nectar, fruit, and honeydew for sustenance and can be important pollinators of plants. Mature males swarm together and attract viable females to copulate and complete the mosquito life cycle. Inseminated females store the sperm and only fertilize their eggs prior to deposition. Of the mosquito species that extract blood, only the females actively seek out blood meals to provide protein for the development of the eggs. Each species has a preferred time of the day to vigorously seek blood and this circadian rhythm informs strategies to minimize mosquito and human contact. Favorable host seeking times of the day are either the nighttime, daytime, [Page 1170]or during the twilight dusk and dawn hours. The degree to which a mosquito hunts for human (anthropophilic) or other vertebrate blood (zoophilic) sources is largely species dependent; however, significant intraspecies variation exists.

Female mosquitoes employ a diverse array of tools to identify appropriate sources of blood and extract plasma without alerting the unwitting victim. She is attracted to the heat our bodies continually emit, carbon dioxide and water vapor we exhale, lactic acid excreted in our sweat, and our body movements. Mosquito repellant masks the body's excretions and makes us less appealing blood sources. Upon landing, the mosquito finds the optimal extraction site by touching and chemically “smelling” the skin with her antennae and mouthparts. She proceeds to find blood, insert her mouthparts, and inject chemical filled saliva similar to a drug cocktail administered to a patient before an operation. Saliva chemicals stop blood clot formation, keep the blood vessels enlarged, and thwart any host inflammatory immune response.

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