Fine structure of pegs on the palps of female culicine mosquitoes

The fine structure of the thin-walled pegs known to respond to carbon dioxide was studied in Aedes aegypti (L.), Culex pipiens L., and Culex territans Walker. Each peg is composed of an external cuticular structure with numerous pores which occur in groups, three bipolar neurons, and sheath cells. In A. aegypti two morphologically different types of neurons were found innervating the same sensillum: two electron-dense neurons and one electron-lucid neuron per peg. In addition to distinctive cell bodies and nuclei, the two types of neurons have different organization patterns of their dendritic processes within the lumen. Culex pipiens is shown to have several times more area available for perception of carbon dioxide than A. aegypti.