The Collapsible Passive Trap: Mosquito Monitoring in a Lightweight Package
By Edward Ricciuti
Like the proverbial quest for a better mouse trap, scientists concerned with mosquito surveillance continually tinker with the technology of traps to make them more effective and practical. A research team at James Cook University, in Cairns, Australia, recently has engineered an eminently portable mosquito trap that could make life much easier for workers who conduct mosquito-borne disease surveillance in the field.
The “collapsible passive trap” (CPT), say the researchers who developed it, works quite well and yet, unlike most collecting devices that are lugged afield, is lightweight, easy to carry, and does not require electrical power.
The CPT weighs 0.36 kilograms. Other traps studied weighed up to almost 4 kilograms.
When it comes to collecting mosquitoes, the blue-and-white CPT “outperformed the other trap types tested,” say the scientists, who matched the CPT against devices in regular use.
“Most traps used to collect mosquitoes either need a source of electricity or are bulky and inflexible, making transportation awkward,” the Australian researchers write in a paper published January 29 in the Journal of Medical Entomology that describes their foldable device and how it was evaluated. They tested it in a mixed melaleuca and mangrove swamp near Cairns, in Australia’s lush tropical Queensland.
Batteries typically power traps that rely on light to attract mosquitoes and a fan or suction device to apprehend them. Weight adds up quickly when several must be carried into the field. Other traps, using attractants such as carbon dioxide or honey, do not need power but are usually boxy and cumbersome and thus tough to cart around. The carbon dioxide-baited CPT, say its developers, is ideal for surveys in places that are off the beaten path.
The CPT is cylindrical and encased by lightweight fabric, three types of which were evaluated. Flexible clear vinyl fabric failed the test because it collected moisture that damaged mosquitoes such it was difficult to distinguish species. That problem was solved by using a combination of water-repellent, breathable, polytetrafluoroethylene resin fabric, and fine no-see-um mesh. A version in which the resinous fabric was blue and the mesh white collected many more mosquitoes than an all-white model, perhaps because mosquitoes seem attracted to dark colors.
“Some species are attracted to dark colors, especially when highlighted with a contrasting color such as white,” says James Cook University’s Dagmar B. Meyer, Ph.D., lead author of the report. Olfactory attractants draw mosquitoes from long distance then visual cues kick in from short range, Meyer explains. “Reflectivity and wavelength of colors can also be important,” she says. Of two entry holes evaluated, an inverted cone collected more mosquitoes than a simple hole in a flat surface and was chosen for the experimental CPT.
The blue-and-white CPT had a leg up on the light-baited Encephalitis Vector Surveillance (EVS) trap and the Sentinel Mosquito Arbovirus Capture Kit (SMACK), baited with carbon dioxie or sweet substances such as sugar and honey.
When the CPT went up against the trap that has been described as the “gold standard,” a light trap developed by the U.S. Centers for Disease Control and Prevention (CDC), it proved equally as effective at catching mosquitoes. Importantly, for the most part, other insects ignored it while they swarmed to the CDC trap. In one test, 31 percent of the CDC trap’s catch, or 525 individuals, were other insects. Only two non-mosquitoes showed up in the CPT’s haul, a big plus because researchers do not have to sort out mosquitoes from a mishmash of other insects. “Captured mosquitoes are in pristine condition,” says Meyer.
When they examined the catch in the traps, the researchers discovered that the CPT captured more of the genus Aedes, which spreads diseases such as yellow fever, dengue and Zika, than the CDC trap. On the other hand, the CDC trap captured more of the genus Culex, vector of diseases such as West Nile, various forms of encephalitis and avian malaria. “We suspect that the differences or non-differences of Aedes and Culex species captures could be due to varying species responses to environmentalvariables such as rainfall, wind, humidity, or moonlight,” the researchers say.
Enhancements, such as producing carbon dioxide from fermenting yeast and sugar where other sources are not available, have been added to the trap, making the CPT a solid choice for use “in remote locations where logistics and the absence of electricity sources prevent the use of traditional surveillance tools,” says Meyer. The trap already is on the market but, says Meyer, “One also needs keep in mind that no trap will capture every single species of mosquitoes—that’s why a variety of traps are used, depending on the situation. Each trap type has advantages and disadvantages.”
Journal of Medical Entomology
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.