Volatile substances from larval habitats mediate species-specific oviposition in Anopheles mosquitoes

Oviposition site selection has been recognized as critical both for the survival and population dynamics of mosquitoes. Volatile substances released from larval habitats have been implicated as potential olfactory cues mediating oviposition. In our continuing studies of cues involved in oviposition site selection, we collected material from the larval habitats of Anopheles albimanus Wiedemann and Anopheles vestitipennis Dyar & Knab, i.e., cyanobacterial mats and Typha domingensis Pers. litter, respectively. The volatile compounds were extracted by freeze-drying the material and trapping the volatilized material on a -55 degrees C titanium condenser. For oviposition trials conducted with wild-caught females, the tested volatile materials were pipetted onto filters floating on the surface of distilled water in Teflon beakers that were placed within oviposition cages. For both species, volatile materials in low concentrations increased oviposition, assessed as egg density, whereas there was a shift to reduced oviposition at higher concentrations. Volatile effect was strongly habitat/species-specific as shown by reciprocal treatment tests.