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​Ongoing Research

Leishmaniases caused by parasitic protozoa of the genus Leishmania, that are transmitted by bite of infected sand flies, present a large variety of disease manifestations. These diseases are a serious public health problem in many countries and they are difficult to control by conventional methods. In addition to blood, sand flies feed on plants and this diet and its effect on disease transmission is a subject of our investigations for several years. In recent field and laboratory studies we demonstrated that some common garden plants cause mortality of sand flies that feed on them. We have also demonstrated in the wild that one of these plants (Bougainvillea glabra) drastically reduces the sand fly population in its neighborhood. This plant and apparently also other species can be used for biological control against leishmaniasis. In an initial experiment in Kfar Adumim, coordinated by Dr. Laor Orshan from the Ministry of Health, a planted hedge of Bougainvillea is expected to serve as a barrier for sandflies that come uphill to the village.
The basic observation in another line of studies was that the competence of Phlebotomus papatasi as a host for Leishmania major is related to adult survival on sugar-poor foods. Desert sand flies, provided with excess sugar, became progressively resistant to infection. Selection for survival under sugar-poor conditions increased susceptibility. About 85% of flies colonized from a desert habitat retain experimental Leishmania infection compared to 25% from irrigated sites. It appears that hunger tolerance of sand flies modulates the susceptibility to leishmanial infection.
Sugar questing mosquitoes in arid areas gather on scarce blossoms that can be used for control
Günter Müller and Yosef Schlein:
Biting female mosquitoes utilize the ingested blood primarily for egg development while floral nectar sugars are the main source of energy for other functions. Flowering plants are scarce in arid mosquito habitats including large malaria endemic regions in Asia and Africa. We showed that such flowers are highly attractive. Experiments in small isolated oases demonstrated that the few flowering acacia trees were visited by most of the local mosquitoes and spraying the trees with oral insecticide eliminated the mosquitoes. The study showed that scarce sugar sources in desert areas are key elements for mosquitoes and can be used for their control.
Most of the sugars for the mosquito diet are obtained from flowers and our study pertains to an extreme but widespread situation of floral sugar scarcity in a dry climate and arid areas. We show that in this situation the flowers of some perennial plants are highly attractive and even in the spring they are much more attractive than seasonal flowers. We also show for the first time the dependence of mosquitoes on defined and limited sugar sources.
An intriguing question raised by this study is the apparent influence that sugar scarcity might have on the transmission of malaria, whether it limits mosquito life span and thus fecundity and malaria transmission. A second question is whether the definition of sugar sources as key elements in mosquito habitats can be used for targeted control methods that would be less damaging to the environment than the use of insecticides in wide areas. The mosquito control approach may be useful in the pattern described by us and it may also or lead to other ways of using attractive floral fragrance. Suitable areas for application are primarily in arid regions such as the malaria endemic areas in the sub- Saharan Sahel and other similar malaria foci in Africa and Asia.