Mosquito Egg Hunt

(Photo credit: Nathan D. Burkett-Cadena, Ph.D.)

Editor’s Note: This article originally appeared in Entomology Today, a project of the Entomological Society of America with the goal of reporting interesting discoveries in the world of insect science and news from various entomological societies. To learn more, visit www.entomologytoday.org.

The conventional wisdom about where many Culex mosquitoes lay their eggs — in standing water — is not always wise. Research into the diverse subgenus Melanoconion shows that many, if not most, mosquito species in this subgenus 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 Culex mosquitoes’ egg-laying habits and may complicate the work of researchers and mosquito control professionals.

“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 Florida Medical Entomology Laboratory at the University of Florida (UF) and co-author of a new study published in the Journal of Medical Entomology. Burkett-Cadena and colleagues have showed that several species of mosquitoes in the genus Culex, subgenus Melanoconion, lay their eggs on the surface above standing water, contrary to the behavior of other Culex.

(Image credit: Jim Newman)

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 C. pipiens and related mosquitoes has resulted in an overgeneralization that laying eggs as a “raft” on the surface of standing water is common across all Culex species. The UF researchers’ examination of species in the subgenus Melanoconion — along with a review of historical research on other Culex species — suggests that “the generalized floating egg-raft strategy does not apply to the vast majority of Culex species.”

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 researchers 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 the 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.”