FIELD-EVALUATION OF SYNTHETIC COMPOUNDS MEDIATING OVIPOSITION IN CULEX MOSQUITOS (DIPTERA, CULICIDAE)

3-Methylindole (skatole), a compound shown to be an oviposition attractant/stimulant for Culex quinquefasciatus in laboratory tests, was evaluated against natural populations of mosquitoes in the field. In experiments using paired black plastic tubs that contained water treated with an attractant solution containing a mixture of 3-methylindole, 4-methylphenol, 4-ethylphenol, phenol, and indole or that contained only tap water, the attractant-baited traps received significantly more Cx. quinquefasciatus egg rafts than did the untreated tap water. Gravid female traps that were baited with attractant solution collected significantly more Cx. quinquefasciatus females than did traps containing only tap water. There was no significant difference in number of Cx. quinquefasciatus collected in the traps baited with the attractant solution compared to the traps that contained water with 3-methylindole alone, indicating that 3-methylindole was solely responsible for the attraction. In replicated experiments conducted in experimental ponds, ponds that were treated with 3-methylindole received significantly more Cx. quinquefasciatus, Cx. tarsalis, and Cx. stigmatosoma egg rafts than did untreated ponds. Experimental ponds treated with 3-methylindole at two levels (0.12 and 0.6 mg/liter) were equally attractive to ovipositing Cx. quinquefasciatus. This is the first record of 3-methylindole showing attractancy/stimulation to ovipositing Cx. stigmatosoma and Cx. tarsalis under field or laboratory conditions.