Research carried out in Mali, West Africa, has demonstrated that a new, safe and uncomplicated insect control method, developed at the Hebrew University of Jerusalem, can bring about a serious decline in malaria-bearing mosquitoes in afflicted regions in the world.
The research in Africa was based on work carried out earlier in Israel by researchers at the Kuvin Center for the Study of Tropical and Infectious Diseases at the Hebrew University of Jerusalem that showed how attractants of plant origin (fruit or flowers) with a toxic sugar bait can reduce the populations of the malaria-transmitting mosquitoes.
Their work is detailed in a recent issue of the Malaria Journal. The scientists involved in the project are Prof. Yosef Schlein and Dr. Gunter C . Muller of the Kuvin Center and the Institute for Medical Research Israel-Canada (IMRIC), Prof. John C. Beier of the University of Miami, Florida, and Prof. Sekou F. Traore, Prof. Seydou Doumbia, Dr. Mahamadou B. Toure, Dr. Mohamed B. Traore and Dr. Sekou Bah, all of the University of Bamako, Mali.
Their work in the use of the Hebrew University-developed Attractive Toxic Sugar Bait Method (ATSB) was applied to control malaria-bearing mosquitoes in the semi-arid Bandiagara District of Mali, West Africa.
Control and treatment sites were selected along a road that connects villages and that had man-made ponds that were the primary larval habitats of Anopheles gambiae and Anopheles arabiensis mosquitoes. Guava and honey melons, two local fruits that have been found to be attractive to both species of mosquitoes, were used to prepare solutions of Attractive Sugar Bait (ASB) and ATSB, the latter containing an additive of boric acid as an oral insecticide. Both included a color dye marker to facilitate determination of mosquitoes feeding on the solutions.
ASB solution in the control site and ATSB solution in the treatment site were sprayed on patches of the vegetation. Consequently, it was seen that the relative abundance of female and male mosquitoes in the ATSB-treated site declined dramatically by about 90% and remained low during one month of monitoring. The females in the diminished population were mostly too young to transmit malaria. In parallel, dye marking in the solutions sprayed in the control site provided evidence that most of the mosquitoes were feeding on the sprayed solutions.
The researchers concluded that the study in Mali shows that even a single application of ATSB can substantially decrease malaria-bearing mosquito population densities and longevity. It is thus likely that ATSB methods can be used as a new, powerful tool for the control of malaria insect carriers, since this approach is highly effective for mosquito control, technologically simple, inexpensive and environmentally safe.
The work in Mali is very much connected to Bill and Melinda Gates Foundation funding of early studies, and this initial report can set the stage for bigger efforts in African countries. It is one of the first new dimensions to control African malaria vectors, yielding good indications that use of ATSB in outdoor environments will complement the current measures to control mosquitoes inside houses.
Editor's Note: This article is not intended to provide medical advice, diagnosis or treatment.
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by The Hebrew University of Jerusalem, via EurekAlert!, a service of AAAS.
- Günter C Müller, John C Beier, Sekou F Traore, Mahamoudou B Toure, Mohamed M Traore, Sekou Bah, Seydou Doumbia, Yosef Schlein. Field experiments of Anopheles gambiae attraction to local fruits/seedpods and flowering plants in Mali to optimize strategies for malaria vector control in Africa using attractive toxic sugar bait methods. Malaria Journal, 2010; 9 (1): 262 DOI: 10.1186/1475-2875-9-262
Based on recent studies in Israel demonstrating that attractive toxic sugar bait (ATSB) methods can be used to decimate local anopheline and culicine mosquito populations, an important consideration is whether the same methods can be adapted and improved to attract and kill malaria vectors in Africa. The ATSB approach uses fruit or flower scent as an attractant, sugar solution as a feeding stimulant, and an oral toxin. The ATSB solutions are either sprayed on vegetation or suspended in simple bait stations, and the mosquitoes ingesting the toxic solutions are killed. As such, this approach targets sugar-feeding female and male mosquitoes. This study examines the attractiveness of African malaria vectors to local fruits/seedpods and flowering plants, key biological elements of the ATSB approach for mosquito control.
Three field experiments were conducted at sites in Mali. The attraction of Anopheles gambiae s.l. to 26 different local fruits and seedpods was determined at a site in the semi-arid Bandiagara District of Mali. Wire mesh glue traps with fruits/seedpods suspended on skewers inside were set along a seasonal lagoon. Seven replicates of each fruit/seedpod species were tested, with a water-soaked sponge and a sugar-soaked sponge as controls. The attraction of An. gambiae s.l. to 26 different types of flowering plants was determined at a site near Mopti in Mali. The flowering plants held in a water-filled buried container were tested using the same glue traps, with controls including water only and sugar solution. Six replicates of each selected plant type were tested on transects between rice paddies. Additional studies using CDC light traps were done to determine the relative densities and periodicity of An. gambiae s.l. attraction to branches of the most highly attractive flowering plant, branches without flowers, human odor, and candescent light.
Of the 26 fruits and seedpods tested, 6 were attractive to An. gambiae s.l. females and males, respectively. Guava (Psidium guajava) and honey melon (Cucumis melo) were the two most attractive fruits for both females and males. Of the 26 flowering plants tested, 9 were significantly attractive for females, and 8 were attractive for males. Acacia macrostachya was the most attractive flowering plant. Periodicity studies using this plant showed peaks of An. gambiae s.l. attraction between 1930 and 2200 h and 0400-0500 h, which differed considerably from the response to human odors, which expectedly peaked at around midnight.
These field experiments in Mali highlight that female and male An. gambiae s.l. have pronounced differences in attraction for diverse types of indigenous fruits/seedpods and flowering plants. The identification of attractive fruits and seedpods shows that a variety of indigenous and locally abundant natural products could potentially be used as juices to make ATSB solution for mosquito control. As well, the simple methods used to identify the most attractive flowering plants provide valuable insights into the natural history of sugar feeding for An. gambiae s.l. These observations can be used to guide future strategies for employing ATSB methods for malaria vector control in Africa. They also provide a basis for subsequent chemical analysis and development of attractive baits for mosquito control.