Passive copper release from ornamental rain chains is harmful to mosquito larvae and deters egg-laying

Urban mosquitoes use accumulated rainwater in private gardens and public green spaces for reproduction. We found that ornamental copper chains, which direct rainwater from gutters into open containers, can significantly reduce the number of mosquito larvae in the collected water, sometimes eliminating them entirely. Although the impact of copper salts or copper objects in water on mosquito larvae is well documented, a detailed analysis of the effects of dissolved copper in terms of concentration and biological impact has yet to be conducted. In this study, we present the results of two experimental analyses: one conducted in gardens and the other in the laboratory. These experiments were designed to corroborate consistent, albeit circumstantial, observations, and to describe the sensitivity of mosquito larvae to rainwater containing low quantities of copper. Field experiments were conducted during a period of high tiger mosquito (Aedes albopictus) abundance, while laboratory experiments used the yellow fever mosquito (Aedes aegypti) as a biological model. Our field experiments revealed that rain chains release sufficient copper into the water to drastically reduce the number of juvenile mosquitoes. In the laboratory, rainwater containing copper released by the chains affected hatching and larval development; however, the most significant effect was that females laid almost no eggs in the presence of copper-containing water.