It now appears that the malaria mosquito relies on a battery of different types of odour sensors to mediate its most critical behaviours, including how to choose and locate their blood-meal hosts.
In an article in the open access journal PLoS Biology, researchers at Vanderbilt University, US, have characterised two families of molecular odourant sensors in Anopheles gambiae, the mosquito responsible for the majority of human malaria transmission.
However, ORs alone do not appear to be able to account for the breadth of mosquito olfactory sensitivity as several potentially important human-derived odours such as ammonia, butylamine and lactic acid, have consistently failed to activate mosquito ORs.
The experiments described in the paper provide striking new evidence that A. gambiae has a second set of olfactory sensors that are fundamentally different from its primary sensors.
For example, this new study indicates that butylamine sensation requires a member of another family of unrelated molecular sensors known as Ionotropic Receptors (IRs) that have recently been described in the fruitfly Drosophila melanogaster. Thus, two distinct olfactory signaling pathways are active in mosquitoes: one is OR-dependent and accounts for responses to DEET as well as a large number of general odorants, while the other is OR-independent and may be responsible for sensitivities to a specialised subset of odourants, such as amine containing compounds.