Sunday, January 16, 2011
Luring mosquitoes with seductive sugar
Technologically simple, inexpensive and environmentally safe, an Israeli-devised toxic sugar bait promises to control the disease-spreading mosquito.
If mosquitoes have a sweet tooth, then it seems only logical to use sugar to lure and kill these disease-spreading insects.
That was the simple thinking behind a new method for controlling malaria developed at the Hebrew University of Jerusalem's Kuvin Center for the Study of Tropical and Infectious Diseases with a grant from the Bill and Melinda Gates Foundation. Recent experiments in Mali, West Africa, have demonstrated that this safe, uncomplicated insect control method really works.
"An obvious question is how people didn't see it before," Prof. Yosef Schlein comments to ISRAEL21c. The emeritus medical entomology professor says it was well-known that the sweet smell of nectar is irresistible to the buzzing, blood-sucking insects. A previous American study had even pinpointed which flowers they prefer.
The perfect bait
Schlein took the next step of baiting traps with flowers in the Jordan Valley to determine which kind attracts the most mosquitoes. Then, his team sprayed a food-dyed sugar and toxin mixture on acacia trees, the sole flowering plant in the dry Arava region. As a control, a non-toxic solution dyed a different color was sprayed in a different area. Because mosquitoes' bellies are transparent, it was easy to see the results. The toxic brew virtually wiped out the local mosquito population that feasted on it.
"But this was not a good practical method, because it depended on the season for flowering," Schlein points out. "We had to find a bait to put in a solution and then put it in places near breeding sites and other areas where many mosquitoes gather."
The answer was lightly-fermented fruit juice mixed with brown sugar. As detailed in a recent issue of the Malaria Journal, an international research team tested the Israeli-devised attractive toxic sugar bait method (ATSB) to determine how it might control malaria-bearing mosquitoes in the semi-arid Bandiagara District of Mali, West Africa. In Israel, using juice from the local guava and honey melons that mosquitoes adore, the Arava experiment was duplicated at primary larval habitats, using boric acid in the toxic batch.
Both the poison and harmless solutions proved popular with mosquitoes, as evidenced by the colors of their bellies. But in the ATSB-treated site, the population of both female and male mosquitoes declined by about 90 percent and remained low during one month of monitoring. The females that survived were mostly too young to transmit malaria.
The researchers conclude that a single application of ATSB can substantially decrease malaria-bearing mosquito population density and longevity. Since it is also technologically simple, inexpensive and environmentally safe, the ATSB method holds great promise for bigger efforts to control mosquitoes in outdoor environments in African countries.
Schlein notes that ATSB could just as successfully be applied to many other situations where mosquitoes are a problem, such as Florida sewage canals. However, malaria is a top priority in global health and for the Gates Foundation, which funded his research through a three-year, $875,242 grant that expires at the end of 2010.
Schlein and Dr. Gunter C. Muller of the Institute for Medical Research Israel-Canada have been working on formulating a shelf-stable powdered ATSB that could be mixed with water for ease of use. Hoping to win continued Gates funding, they are seeking industrial partners to further develop their experimental carob-seed-based powder and to act as commercial distributors for a saleable product.
In addition to Muller, the scientists involved in the Mali project were Prof. John C. Beier of the University of Miami, Florida; and Professors Sekou F. Traore, Seydou Doumbia, Mahamadou B. Toure, Mohamed B. Traore and Sekou Bah of the University of Bamako, Mali.