The increased use of irrigation in sub-Saharan Africa has benefited the Anopheles Arabiensis mosquito — an important malaria vector — particularly in rice paddies. A research team led from the Swedish University of Agricultural Sciences now shows that rice odours attract females, and elicit egg laying. The team has also produced a synthetic odour blend that triggers the same behavior. Their findings may be an important step in the development of novel and cost-effective control measures.
In sub-Saharan Africa, systematic efforts are undertaken to increase the areas under irrigated cultivation. Irrigated crops provide mosquito larvae with shelter from various threats, as well as nutrients in the form of pollen, detritus and microorganisms. The conditions in rice paddies are particularly well suited, and can offer permanent mosquito larval habitats. As a consequence, in many areas where irrigated rice is now common, emergence of well-known malaria vector Anopheles Arabiensis habitats are found and an increased risk of malaria is evident. A key-factor for the build-up of viable mosquito populations, and for the spread of malaria, is that the female mosquitoes are able to find suitable aquatic habitats where they can lay their eggs.
Rickard Ignell, leader of the study and professor of chemical ecology at Swedish University of Agricultural Sciences (SLU) explained, “We know that smells are extremely important for the behaviour of mosquitoes in most phases of their life cycle, but it is only now that we begin to understand what attracts the egg-laying females to rice fields and other egg-laying sites and this synthetic lure may well become a tool in future control strategies against malaria, and it is the first one that targets egg-laying females.” says Rickard Ignell, “It can be used as an important complement to other control methods that target females searching for blood meals.”
Together with colleagues from SLU and scientists in Ethiopia, Kenya and England he has now shown that gravid females of Anopheles Arabiensis are attracted and lay eggs in response to the odour present in the air surrounding rice. The research team has also identified a synthetic rice odour, consisting of a mixture of eight compounds in specific proportions, which triggers the same behaviour, both under laboratory and semi-field conditions.