Reexamination of Chemically Mediated Oviposition Behavior in Aedes aegypti (L.) (Diptera: Culicidae)1

Abstract

A sequence of behavioral assays was performed in the laboratory to ascertain the contribution of bacteria to the oviposition response of gravid Aedes aegypti to water that previously had held fourth-instar larvae. Experiments using larval holding water with no control over bacterial growth showed an increasing oviposition response with increasing larval densities up to about two larvae per ml, beyond which the response decreased. Glutting larvae with kaolin prior to the preparation of holding water did not significantly reduce bacteria or the oviposition response at one larva per ml. Removing bacteria prior to assay decreased the response, and preventing bacterial growth during the holding and assay periods resulted in significant repellency of larval holding water compared to distilled water. It is concluded that the positive response previously attributed to a larva-produced oviposition pheromone was the result of bacterial contamination of assayed media. Two dominant species of bacteria, Acinitobacter calcoaceticus and Enterobacter cloacae , were identified in holding water. A pure suspension of A. calcoaceticus induced a significantly higher oviposition response than a pure suspension of E. cloacae . Additional assays with A. calcoaceticus showed that both contact-stimulation and olfaction may be involved. The ecological implications of a larva-produced repellent and bacteria-produced stimulants-attractants are discussed.