ELECTROPHYSIOLOGICAL RESPONSES OF RECEPTOR NEURONS IN MOSQUITO MAXILLARY PALP SENSILLA TO CARBON-DIOXIDE

Sensilla basiconica on the maxillary palps of female Aedes negypti con tain a receptor neuron which produces a phasic-tonic pattern of action potential response to low concentrations (150-300 ppm) of carbon diox ide (CO2), a stimulus known to be involved with host seeking behavior. These receptor neurons respond reliably to small increments in CO2 co ncentration (e.g., 50 ppm). We were particularly interested in evaluat ing the possibility that the sensitivity to step increases in CO2 conc entration could be modulated by alterations in the background levels o f CO2, over a range which might be encountered during host-seeking beh avior. We report here that the response (impulses/s) to a single pulse of a given concentration of CO2 appears to be independent of the back ground level of CO2, unless that level is equal to or greater than the concentration of the stimulus pulse. Females of other mosquito specie s, including: Anopheles stephensi, Culex quinquefasciatus, Culiseta me lanura, and Aedes taeniorhynchus, also possess sensilla with receptor neurons that respond with comparable sensitivity to CO2 stimulation. H owever, there is much interspecific variation in both the external mor phology of the maxillary palp and the distribution of sensilla along t he palp. Male Ae. aegypti have morphologically similar sensilla which also contain a receptor neuron that responds to CO2.