By Ed Ricciuti
With Zika, dengue, and chikungunya spreading, and yellow fever re-emerging, health workers are ramping up surveillance of the ubiquitous Aedes aegypti mosquito that carries these arboviral diseases. Several types of traps and killing agents are available for collecting the insects, but there is a catch: the gear now employed is often too costly, cumbersome, or complicated for optimum monitoring of mosquito populations in the field, according to a paper published in the Journal of Medical Entomology, which describes an inexpensive alternative way to trap mosquitoes.
According to lead author Dr. Scott Ritchie of Australia’s James Cook University, in addition to being cheap and easy to operate, the new trapping method kills the sampled insects without insecticides, a bonus when safety and environmental concerns are in play. Even better, the insecticide-free ingredients used in the traps collect and kill mosquitoes in areas — such as parts of Brazil and Southeast Asia — where they have evolved resistance to insecticides.
During field experiments carried out in Cairns, Australia, the researchers compared different insecticides and insecticide-free materials for killing mosquitoes in a bare-bones collecting device called a GAT, which stands for “Gravid Aedes Trap.” These traps capture pregnant females by luring them to lay eggs in a mixture of hay and water. Normally only five percent of the mosquitoes collected in this type of trap are males.
The GAT used by the researchers is a plastic affair, developed by scientists in Puerto Rico, and as far from high-tech as you can get. It allows mosquitoes to enter a black funnel into a translucent bucket, which sits on a black base containing the attractant. The color black is known to attract female mosquitoes, which have been observed entering a GAT that was not even baited.
Unlike the GAT trap, many of the monitoring devices now in use are more complicated. Some even require electric power or batteries. Such traps can present problems if they are too expensive or if electricity is not available.
Likewise, many of the killing agents used in traps have drawbacks. These include insecticides that are sprayed on trap surfaces, and patches of mosquito netting that are treated with insecticides, which are called “long lasting insecticide impregnated nets” (LLINs).
As it turned out, the researchers found that GATs containing two simple agents — canola oil and plain, old-fashioned, non-toxic flypaper boards — worked as well as the insecticide sprays and the insecticide-laden netting.
“The most important finding of the research is the use of canola oil and sticky cards without a loss in capture rates,” Ritchie said. “There were no significant differences in the number of Ae. Aegypti collected per week or the number of traps positive for Ae. Aegypti between the sticky card and canola oil treatments compared to the surface spray and LLIN treatments in semi-field and field trials.”
Canola oil and sticky cards, he adds, “are cheap and widely available and will help maintain the GAT’s usefulness in areas with insecticide-resistant Aedes aegypti populations and in areas where there is substantial resistance to insecticide use.”
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Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.