Abstract
BackgroundVolatile 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.MethodsScanning 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.ResultsBoth 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.ConclusionThe 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.
Highlights
Volatile odors are important sensory inputs that shape the behaviour of insects, including agricultural pests and disease vectors
The strong preference for human blood meals by An. gambiae s.s. females is a major contributing factor to human malaria transmission, a disease that afflicts more than 200 million people and causes as many as 3 million deaths annually [3], while An. quadriannulatus, because of its preference for cattle, is not considered a malaria vector [4]
General description Like most dipterans, the heads of An. gambiae s.s. and An. quadriannulatus adults are equipped with three types of appendages – the antennae, maxillary palps, and proboscis – each with associated chemosensory functions (Figure 1)
Summary
Volatile odors are important sensory inputs that shape the behaviour of insects, including agricultural pests and disease vectors. Odors are the principle sensory signals that direct female mosquitoes to their preferred blood meal hosts [1,2]. Two closely related mosquito sibling species, An. gambiae s.s. and An. quadriannulatus, display very different patterns of blood meal host preference. The strong preference for human blood meals by An. gambiae s.s. females is a major contributing factor to human malaria transmission, a disease that afflicts more than 200 million people and causes as many as 3 million deaths annually [3], while An. quadriannulatus, because of its preference for cattle, is not considered a malaria vector [4]
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