The effects of salinity on growth and development of the euryhaline Ochlerotatus taeniorhynchus and the freshwater Aedes aegypti

Larval mosquitoes are found in a variety of aquatic habitats, including freshwater and saline environments of diverse composition. Larval mosquitoes with three distinct osmoregulatory strategies can be described: freshwater osmoregulators, euryhaline osmoregulators and euryhaline osmoconformers (Bradley, 1987). At least two of these strategies are observed in closely related genera within the tribe Aedini, Ochlerotatus and Aedes (Ochlerotatus was considered a subgenus of Aedes until recently; Reinert, 2000). The evolution of a salt-secreting rectal segment has enabled some species, including O. taeniorhynchus (Wiedemann), to tolerate salinities in excess of seawater (Bradley and Phillips, 1975, 1977). This ability in turn allows them to exploit highly productive habitats that are inhospitable to freshwater forms. For example, O. taeniorhynchus is known as a salt marsh mosquito because it inhabits estuaries and salt marshes where salinities fluctuate from essentially freshwater to greater than seawater following rainfall or evaporation of isolated pools. Obligate freshwater forms including A. aegypti (L.) lack this salt gland, and are thus limited in their distribution to freshwater environments (those more dilute than their normal hemolymph osmotic pressure; Bradley, 1987). Aedes aegypti is found primarily in small, isolated bodies of water such as tin cans and discarded tires. While survival to adulthood has obvious fitness consequences, environmental influences on more subtle aspects of growth and development are also important in determining fitness. Mosquito larvae face a number of threats, including predation and desiccation of habitats, and mosquitoes are typically characterized by rapid completion of the life cycle. Rapid development allows multivoltine insects, including mosquitoes, to complete more generations during the breeding season and accomplish more explosive population growths during favorable periods. Among insects, females are generally larger than males, and female size is related to fecundity. There thus exists a selective trade-off between rapid development and size at maturity. Phenotypic traits such as growth rates and mass are affected by gene–environment interactions, and a number of environmental factors are known to influence mosquito growth and development. These include The Journal of Experimental Biology 207, 2289-2295 Published by The Company of Biologists 2004 doi:10.1242/jeb.01018