Mosquito egg hunt: Many Culex species prefer alternatives to standing water

The conventional wisdom about where many mosquitoes lay their eggs—in standing water—is not always wise. Research into a diverse group of mosquitoes shows that many, if not most, regularly lay their eggs on a variety of surfaces, and in a surprising location: above nearby water. The findings run counter to scientific generalizations about the mosquitoes' egg-laying habits and may complicate the work of researchers and mosquito control professionals.

In a study to be published next week in the Entomological Society of America's Journal of Medical Entomology, researchers at the University of Florida (UF) showed that several species of mosquitoes in the genus Culex, subgenus Melanoconion, lay their eggs on surfaces above standing water, contrary to the behavior of other Culex.

"Our findings show us that even the most classic paradigms in medical entomology need to be closely scrutinized," says Nathan D. Burkett-Cadena, Ph.D., assistant professor at the UF Florida Medical Entomology Laboratory and co-author of the study.

The mosquito species Culex pipiens, for instance, has been well studied due to its prominent role in transmission of human pathogens such as West Nile virus. The focus on Culex pipiens and related mosquitoes has resulted in an apparent over-generalization that laying of eggs as a "raft" on the surface of standing water is common across all Culex species. The UF researchers' examination of species in subgenus Melanoconion—along with a review of historical research on other Culex species—suggest that "the generalized floating egg raft strategy does not apply to the vast majority of Culex species," they write.

The mosquitoes egg-laying behaviors were studied with a laboratory setup in which female mosquitoes were placed in screened cages with dishes containing both standing water and partially submerged objects, such as a terra cotta or segments of mangrove roots. The researches then recorded where the mosquitoes laid their eggs. Surprisingly, most egg clusters were laid on surfaces of the terra cotta and roots, not on open water, as textbooks would have predicted.

Mosquito species in subgenus Melanoconion are known vectors of eastern equine encephalitis and Venezuelan equine encephalitis. A clearer understanding of their egg-laying habits will help mosquito control professionals better target them, though Burkett-Cadena says they may "find it challenging to reach their targets due to the odd oviposition of the mosquitoes."

"Oviposition Strategies of Florida Culex (Melanoconion) Mosquitoes," by Erik M. Blosser and Nathan D. Burkett-Cadena, will be published online on April 12 in the Journal of Medical Entomology.