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While it is generally well known that female mosquitoes need a meal of blood before laying their eggs, less has been written about their appetite for sweet snacks between meals. It is this diet of 'sweets' - derived from nectar from flowers and nectaries on plant leaves and stems - that provides mosquitoes with their persistent energy.
Hebrew University researcher Professor Yosef Schlein and his co-researcher, Günter Müller, in the Department of Parasitology at the Hebrew University-Hadassah Medical School's Kuvin Center for the Study of Infectious and Tropical Diseases, decided to exploit the mosquitoes' thirst for sweets to bring about their demise - by spraying acacia trees with a sugar solution that had been spiked with the oral insecticide Spinosad.
The experiment was carried out in an oasis in the southern desert region in Israel where some scattered trees flower most of the year, including during a long, dry and otherwise flowerless season. Schlein assumed that in the absence of other sugar sources, nectar-searching mosquitoes would be attracted to these plants.
The oasis was chosen for its isolated mosquito population, so that the experiment could be carried out effectively without influx and exchange of mosquitoes from neighbouring areas.
Sucrose solution spiked with the oral insecticide Spinosad was sprayed on acacia trees in the oasis. The spraying of insecticide had the effect of eliminating almost the entire mosquito population in the oasis. The few mosquitoes that were trapped after spraying were thought to be newly emerging adults, and cumulative population growth was prevented by continuous effect of the insecticide. Thus, the oasis was completely depleted of its mosquito population.
Schlein says that in a desert area, in the dry season, the flowers of sparse perennial trees or bushes are key elements in the habitat of adult mosquitoes, since they are the only source of sugar. In dry areas, the shortage of sugar sources may even limit the life span of mosquitoes and thus decrease their ability to transmit diseases. Even when a large variety of flowers is available, the number of sugar sources is limited by the preferences of the mosquitoes. For example, among 77 flowering plants in Wisconsin, mosquitoes concentrated on four dominant ones.
Schlein believes that blossoms that are nectar-feeding centres may be used for efficient mosquito control, if sprayed with the Spinosad sugar solution bait. Spinosad is an environmental 'reduced-risk' oral insecticide that has little effect on several insect groups, and has low toxicity to birds and mammals.
Places that might be suitable for using floral centres for control of mosquitoes are desert and savannah regions, particularly in sub-Saharan Africa, where the burden of malaria is increasing due to environmental changes, drug resistance and mosquito resistance to conventional insecticides. These areas include large-scale irrigation projects in arid and semi-arid areas, which cover nearly half of the arable land in Africa, and similar projects in the desert in Pakistan. In these regions, irrigated crops, such as rice, are not a source of nectar for adult mosquitoes, while sugar meals are scarce in the surrounding arid areas.
Therefore, the planting of mosquito-attracting trees or bushes in suitable habitats, sprayed with oral insecticide, could provide a relatively easy and cheap way to supplement the limited arsenal against mosquitoes – and the fight against malaria.
Adapted from a news release by the Hebrew University of Jerusalem.
Muller G, Schlein Y. Sugar questing mosquitoes in arid areas gather on scarce blossoms that can be used for control. Int J Parasitol. 2006 Sep;36(10-11):1077-80. Epub 2006 Jul 10. Abstract
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