Oviposition Strategies of Florida Culex (Melanoconion) Mosquitoes

Abstract

In the genus Culex, oviposition is often generalized as laying floating egg rafts directly on the surface of the water, as reported for arbovirus vectors Culex pipiens L. and Culex tarsalis Coquillett, both members of subgenus Culex. The current work reports on investigations of exceptions to this strategy by species of Melanoconion, a diverse and mostly tropical subgenus of Culex, with many arbovirus vectors. Wild gravid females from Vero Beach, FL, were introduced into outdoor cages with open water, partially covered water, and emergent solid structures for oviposition. Three species, Culex cedecei Stone and Hair, Culex iolambdis Dyar, and Culex pilosus Dyar and Knab laid vast majorities (80-100%) of egg clusters attached to solid surfaces, although at different heights and angles, while Culex atratus Theobald laid floating egg clusters (100%) directly on the water. When offered mud, open water, and woody material, Cx. iolambdis laid 86% of clusters on nearly vertical surfaces of mangrove rootlets. Culex iolambdis eggs laid on solid surfaces hatched within 3-4 d or dried up without hatching. Results suggest that Melanoconion species utilize a variety of oviposition strategies, yet most species studied oviposit out of water. For some species, such as Cx. pilosus, this is a strategy for diapause and desiccation resistance, while for others, such as Cx. iolambdis, ovipositing above water may protect eggs from predators or being flushed from larval habitat. A summary of oviposition strategies in genus Culex shows that above-water oviposition is widespread and that the Culex egg raft paradigm needs reassessment.

Keywords: Culex; Melanoconion; adaptation; oviposition.