Can pesticides affect invasion by exotic species?: Examples from a container community

The Asian mosquitoes, Aedes albopictus and Ae. japonicus are highly invasive and have infested much of the U.S. since their initial discovery. Culex pipiens form molestus is an introduced mosquito in the U.S. and are shown to be more resistant to pesticides than other Cu. pipiens strains. Although data on the co occurrence of Cu. pipiens molestus with other mosquitoes is lacking, Ae. japonicus are sympatric with Ae. albopictus. Malathion is one of the common pesticides applied to control adult mosquitoes and agricultural pests but they inadvertently get into mosquito larval habitats. We tested the impact of low levels of malathion on larval competition between: 1) Ae. albopictus and Ae. japonicus; 2) Ae. albopictus and Cu. pipiens molestus. Unlike Ae. albopictus, Ae. japonicus and Cu. pipiens molestus larvae did not survive to become adults in the presence of malathion. Survival of Ae. albopictus decreased with increase in Ae. japonicus density, but this interspecific competition was absent in the presence of malathion. There was intraspecific competition among Ae. albopictus in the control but there was no competition in the presence of malathion. This is the first report to show that low levels of mosquito adulticides can affect mosquito larvae and in turn could alter the competitive interactions in container communities.