Smelly Hangups for Mosquitoes... and Bedbugs?

It works against mosquitoes... can it work against bedbugs?

A study in Nature this month reveals a promising new line of defense¹ against disease-carrying, bloodthirsty critters, namely the mosquito. This insect is majorly responsible for ongoing malaria epidemics overseas, by spreading the tiny parasites that cause the disease from host to host as the insect feeds on human blood. The new line of defense is based on smelly chemicals, or inhibitory odorants, that disrupt the mosquito's ability to detect and travel towards human breath. Mosquitoes, as well as other blood-feeding insects, are attracted towards the carbon dioxide that we exhale with every breathe cycle (oxygen in, carbon dioxide out). The new insect-repellent technology as presented in Nature takes advantage of this attraction, used by the mosquito to find a delicious host even at long range, in preventing these and other such insects from ever reaching their bloody meal.

Smelly inhibitions. Essentially, the mosquito's carbon dioxide detection machinery, or it's ‘nose', can be overwhelmed by certain chemical odorants. These inhibitory odorants over-activate the neurons (nervous system excitable cells) behind the mosquito's ‘nose', preventing the insect from then sensing the carbon dioxide coming out of a nearby human's mouth. The solution is rather ingenious - we completely confuse the mosquito from recognizing our breath as a "come and eat!" signal.

Of a pesky nature. Although the malaria-carrier mosquito is a prime candidate for this new insect repellent technology, we might foresee its use against a critter of a peskier if not necessarily disease-carrying nature. Here in the United States, as well as abroad, the bedbug is making a steady comeback. The common bedbug, scientifically known as Cimex lectularius, like the mosquito feeds exclusively on animal blood, including that of humans. Indeed, the common bedbug is adept at finding and infesting human residences. Bedbugs, once kept at bay in developed countries with chemical repellents and other insect populations such as cockroaches and ants², are resurging at near epidemic proportions in large cities of the United States, Australia, and across Europe. The reappearance of bedbugs is attributed to factors including pesticide resistance and increased ease of international travel. While bedbugs have not to date been associated with the transfer of disease, risks of anemia in heavy infestation conditions, as well as the lack of sleep and the stress that the infestations cause are certainly risks to human health.

Sleep tight, don't let the bed bugs bite! I never thought much about this bedtime lyric, but now the saying makes my skin crawl. Before I go on, let me state a disclaimer: bedbug infestations are ‘no longer limited to crowded, unclean, or urban locations'² ; one could walk into a hotel room at the Four Seasons and walk out with one of the pesky hitchhikers. So now that no judgment will pass, I will let the world know that I once lived in an apartment that became infested with bedbugs. Fortunately, or perhaps unfortunately, for me, I am allergic to the little bloodsuckers. While my significant other showed no telltale signs of a problem, my skin broke out in large itchy welts. I dare say that the only way we got rid of the pests was by moving apartments, throwing away almost all of our furniture (perhaps rash, but I would not have it any other way), and washing every piece of fabric we owned. Of course, my significant other and I being the science nerds that we are, we have more books in our possession than any other material item put together. During the move, I took a hair dryer to the pages of each and every single book, in order to make sure that no flat-bodied bedbug caught a ride to our new apartment. We originally called Terminex to our rescue. However, they offered to do little more than steam clean our carpets for an exorbitant price. Bug ‘bombs', pesticide sprays, and even the typically effective insect repellent DEET is useless against bedbugs. They hide in the tiniest of cracks, and can lie dormant for months while awaiting their next safe meal.

So, can the new inhibitory odorant technology, which disrupts breath-seeking behavior in bloodthirsty critters like mosquitoes, be an effective defense against bedbugs? While scientific studies of the common bedbug are limited³, several studies have revealed that this insect is attracted to chemical components of human breath, as is the mosquito. A 2011 study⁴ showed random, stop-start host-seeking movement for bedbugs in environments lacking human breath, whereas those bedbugs exposed to a human breath stimulus demonstrated long-range host-seeking behavior directed toward the stimulus (see image below). This study and others reveal the importance of human breath, and specifically carbon dioxide in that breath, as a long range cue to bedbugs that a blood meal is on the horizon. Bedbugs have been reported to travel distances of more than 6 meters to reach a host, purportedly under the influence of carbon-dioxide-containing breath stimuli⁵.

Scientific studies would be required to tease out how the carbon dioxide detection machinery, or the ‘nose', of the bedbug works, and which inhibitory odorants may potentially overwhelm the ‘nose' of the insect and thus prevent it from reaching its meal. However, the basic concept of disrupting breath-seeking behavior in bloodthirsty insects would remain the same. While bedbug populations continue to grow and affect human health and general wellbeing, effective repellents or bug traps based upon odorants that inhibit breath detection would be a welcome solution to growing pesky epidemics. However, bedbugs are also attracted to heat and chemical odors in human skin. Although carbon dioxide has been shown to be the best bait for attracting bedbugs in field studies⁶, the effects of heat and other chemical odors would need to be overcome for an inhibitory odorant technology to work against hardy bedbugs.

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This blog post was chosen as a ResearchBlogging.org Editor's Selection.

References:

1. S. Turner et al. Ultra-prolonged activation of CO2-sensing neurons disorients mosquitoes. Nature 474: 87-91 (2011)

2. Anderson, Leffler. Bedbug Infestations in the News: A Picture of an Emerging Public Health Problem in the United States. Journal of Environmental Health 70,9: 24-27 (2008)

3. J. Goddard, R. deShazo. Bed Bugs (Cimex lectularius) and Clinical Consequences of Their Bites. JAMA 301, 13: 1358-1366 (2009)

4. J. Suchy, V. Lewis. Host-Seeking Behavior in the Bed Bug, Cimex lectularius. Insects 2: 22-35 (2011) doi:10.3390/insects2010022 (Open Access)

5. R. Usinger. Monograph of Cimicidae (Hemiptera-Heteroptera). The Thomas Say Foundation, Entomological Society of America. Baltimore, MD, USA, 1966; p. 585

6. J. Anderson et al. A carbon dioxide, heat and chemical lure trap for the bedbug, Cimex lectularius. Medical and Veterinary Entomology 23, 99-105 (2009) Doi: 10.1111/j.1365-2915.2008.00790.x

ResearchBlogging.org Reference:

Turner SL, Li N, Guda T, Githure J, Cardé RT, & Ray A (2011). Ultra-prolonged activation of CO2-sensing neurons disorients mosquitoes. Nature, 474 (7349), 87-91 PMID: 21637258