Food shortage or toxin overload? How inputs of eucalyptus organic material affect larval mosquito development (Diptera: Culicidae)

Terrestrial inputs of leaf litter provide the base of much of the food web in freshwater ecosystems. Biofilms that develop on leaf litter are the major food source for aquatic invertebrates. Although upland trees often border seasonal wetlands, their leaves have been shown to be poor providers of nutrients necessary to the development and maintenance of biofilms, leading to poor insect development. Previous studies have shown that eucalyptus extracts can be used to control Aedes aegypti, adding a new phytochemical to the integrated mosquito management arsenal, though its broad applicability is untested.

This study examined the ability of three mosquito species (Ae. aegypti, Culex quinquefasciatus, and Cx. tarsalis) to develop in water containing eucalyptus leaves or bark. One hundred second-instars were placed into 750 mL of distilled water that was supplemented with either 7.5 g of dried eucalyptus leaves, 7.5 g of dried eucalyptus bark, or mouse chow added ad libitum. Virtually no adults emerged from treatments containing eucalyptus bark. Cx. tarsalis did not survive in treatments containing leaves. Adult mass of Ae. aegypti reared in water with eucalyptus leaves did not differ significantly from that of individuals reared in water with the mouse chow laboratory diet.

A separate experiment examined the survivorship of mosquitoes in leached leaves with clean water versus leachate and mouse chow. A small number of Cx. taraslis survived to adulthood in both treatments, suggesting that these mosquitoes are likely impacted by the presence of a toxin in the leaves rather than lack of available food.