By Ed Ricciuti
Despite its name, the pop-eyed insect known as the “kissing bug” is anything but affectionate, at least when it comes to people. Its name is derived from a nasty habit of dropping out of the darkness and biting sleepers, frequently on the face and often around the mouth. In the American tropics, its bite can be a kiss of death, often delivering a dose of potentially lethal Chagas disease via a parasite that can enter the human blood when the wound is contaminated by the bug’s feces. Endemic in many areas from Mexico south, Chagas disease infects about 8 million people there. It is not yet considered a significant threat in the U.S., but it does have a foothold north of the U.S. border with Mexico.
Effective control of Chagas disease depends largely upon monitoring populations of infected bugs. To have real impact, however, monitoring programs now employed need to catch more bugs. The problem, according to researcher Pablo Gustavo Guerenstein of Universidad Nacional de Entre Ríos in Argentina, is that kissing bug monitoring programs lack one of the tried-and-true tools used for sampling other insects: traps baited with synthetic attractants that smell like odors from the vertebrates on which the bugs prey — and, importantly, which are practical to use afield.
A multitude of kissing bug species exist, with 11 in the United States alone. The inch-long insects are also called conenose bugs because of the shape of the mouthparts used to obtain their bloodmeal. Painless in itself, the bite can become inflamed, itchy, and can occasionally trigger serious allergic reactions. The worst-case scenario is a case of Chagas disease, caused by the protozoan Trypanosoma cruzi. Not all kissing bugs carry the disease, and some people who are infected experience no symptoms. Up to 30 percent, however, develop debilitating and sometimes life-threatening medical issues, including fatal scrambling of heart rhythm.
Only about a half dozen cases have occurred in the United States, although about 300,000 immigrants who live here have it. So do several species of wild mammals and, increasingly, dogs in South Texas. Some scientists speculate that warming temperatures could make Chagas disease more of a problem in parts of the nation as kissing bugs spread north from their present range in the southern states. Chagas has also spread to Europe and the Western Pacific, according to the World Health Organization.
The disease has been contained in some areas by control of the vector and the parasite. However, the first line of defense against it is surveillance, which requires efficient monitoring. Utilitarian odor traps would be a major help in this respect.
Guerenstein and colleague Fabio Guidobaldi have come up with a blend that they believe is “getting close to a practical and efficient odor attractant that is worth testing in the field” and which may be deployed in traps for monitoring the presence of the bugs and to reduce their populations.
The Argentine researchers tested attractants delivered by sachets made of low-density polyethylene (LDPE) in a device that evoked a curious natural behavior of the bugs. Attracted by light to dwellings where they hide in crevices, kissing bugs emerge at night to feed, often purposely dropping from ceilings on to people. Attractants that proved effective elicited the same behavior from bugs in the research device, only they dropped down a tube instead of on to a person.
Their quest for a workable attractant is described in a recent paper published in the Journal of Medical Entomology. The scientists scratched CO2 as an attractant because, while it works well, it lacks enough staying power to last for months in the field. CO2 tanks work, but are expensive and can be dangerous.
“Dry ice also an option but also requires preparing each night,” Guerenstein said. “In all cases also it has to be taken into account that regions where kissing bugs are a problem are far from big cities, so it is not easy to find dry ice, or CO2 tanks. Baits using odors like those we use could last several months and are not so expensive.”
The scientists knew that kissing bugs are able to detect three chemical compounds that are produced by the human body. These compounds are contained in a popular CO2-free commercial attractant blend for mosquitoes, so the researchers modeled their mixture after it. The ingredients were lactic acid, ammonia, and a fatty acid called hexanoic, but they replaced the latter with the similar pentatonic because it was more readily available. And it worked. The researchers’ blend attracted the bugs in much larger numbers than with controls.
Like a barista trying to come up with a mix for the perfect designer martini and the glass in which to present it, the Argentine researchers experimented with different ratios of the ingredients that went into the blend and sizes of sachets. They compared the delivery of odors from sachets with those from filter paper dispersers, opting finally for the LDPE. The blend they came up was not as attractive to the bugs as laboratory mice that were used for comparison, but nevertheless drew them in more than sufficient numbers to suggest it will work in the field.
“We will still try to improve our attractant blend using even more challenging behavioral tests, and are getting ready to carry out semi-natural field tests with traps baited with the odor blend that evoked the strongest attraction in our research,” the scientists said.
Eventually, after fine—tuning, the blend that resulted from the experiments in Argentina may help stem the tide of Chagas disease worldwide.
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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.