Antennal sensilla of two female anopheline sibling species with differing host ranges.
BACKGROUND
Volatile odors are important sensory inputs that shape the behaviour of insects, including agricultural pests and disease vectors. Anopheles gambiae s.s. is a highly anthropophilic mosquito and is the major vector for human malaria in sub-Sahara Africa, while Anopheles quadriannulatus, largely due to its zoophilic behaviour, is considered a non-vector species in the same region. Careful studies of olfaction in these sibling species may lead to insights about the mechanisms that drive host preference behaviour. In the present study, the external anatomy of the antenna, the principle olfactory organ in the female mosquito of both species, was examined as an initial step toward more detailed comparisons.


METHODS
Scanning electron and light microscopy were used to examine the antennae ultrastructures of adult female An. gambiae s.s. and An. quadriannulatus. Sensory structures, called sensilla, were categorized and counted; their distributions are reported here as well as densities calculated for each species.


RESULTS
Both An. gambiae s.s. and An. quadriannulatus bear five classes of sensilla on their antennae: chaetica (bristles), trichodea (hairs), basiconica (pegs), coeloconica (pitted pegs), and ampullacea (pegs in tubes). Female An. quadriannulatus antennae have approximately one-third more sensilla, and a proportionally larger surface area, than female An. gambiae s.s. antennae.


CONCLUSIONS
The same types of sensilla are found on the antennae of both species. While An. quadriannulatus has greater numbers of each sensilla type, sensilla densities are very similar for each species, suggesting that other factors may be more important to such olfactory-driven behaviours as host preference.
Department of Biological Sciences, Program in Developmental Biology, Institute for Chemical Biology and Center for Molecular Neuroscience, Vanderbilt University, Station B 351634, Nashville, TN 37235-3582, USA. j.pitts@vanderbilt.edu
R Jason
RJ
Pitts
Laurence J
LJ
Zwiebel
D000818:Animals; D000852:Anopheles / Q000033:anatomy & histology* / Q000502:physiology; D005260:Female; D008853:Microscopy; D008855:Microscopy, Electron, Scanning; D012679:Sense Organs / Q000648:ultrastructure*; D012903:Smell / Q000502:physiology*