Electroantennogram and oviposition bioassay responses of Culex quinquefasciatus and Culex tarsalis (Diptera : Culicidae) to chemicals in odors from Bermuda grass infusions

Odors were collected from the headspace above fermented infusions of Bermud a grass, which commonly are used as attractants in traps for gravid mosquit oes. Coupled gas chromatography-electroantennogram detection (GC-EAD) was u sed to identify 9 compounds (phenol, p-cresol, 4-ethylphenol indole, 3-meth ylindole, nonanal, 2-undecanone, 2-tridecanone, naphthalene) from odor extr acts that elicited significant antennal responses from antennae of gravid f emale Culex quinquefasciatus Say and Culex tarsalis Coquillett mosquitoes. Several of these compounds at appropriate concentrations were weakly attrac tive to gravid female mosquitoes in laboratory bioassays and/or stimulated more oviposition than water controls. In addition, dimethyltrisulfide, a si gnificant component of odor extract which did not elicit strong responses f i om female mosquito antennae in GC-EAD assays, also appeared to stimulate oviposition at I concentration. A reconstituted blend of the 10 compounds r esulted in much stronger and more consistent responses than individual comp ounds. The blend was attractive to gravid Cx, quinquefasciatus and enhanced oviposition over a range of concentrations spanning 3 orders of magnitude. One concentration of the blend also attracted gravid Cr. tarsalis and enha nced oviposition. However, at the highest concentration tested, the blend w as repellent to both species. Overall, these studies demonstrated that grav id mosquitoes are attracted to oviposition sites by blends of compounds rat her than by individual chemicals, and that the concentration of compounds i n the odor is a critical factor in determining whether responses are positi ve (attractive, stimulatory) or negative (repellent, deterrent).