Baker: Finding the best way to repel mosquitos

A surprising number of cultures, as dissimilar and distant from one another as the Khanty of Siberia and the Haudenosaunee (Iroquois) of eastern North America, share a story of a man-eating beast or giant that decimated the people in the days of the ancestors.

But a courageous hero or band of warriors eventually subdued the magical enemy and to ensure its permanent demise, hacked it to bits. To their dismay, however, the blood of the slain foe (in other stories, its charred ashes) swarmed up into the air to the everlasting torment of its executioners.

The mythic origin of mosquitoes. Man-eaters still.

It takes a lot of energy to be a mosquito. One study showed (somehow) that a male Anopheles mosquito beats his wings 450 to 600 times per second while females can manage four hours of continuous flight at speeds of up to 1 mile per hour, covering 7.5 miles in a single night.

To gain the necessary energy, both genders feed on nectar and other sugary plant secretions. But while males leave it at that, females need proteins unavailable in plant juices to produce healthy eggs. And that’s where you come in…

Back in the summer of 2019, I used these paragraphs to introduce an essay on the biology of mosquitos. I still love that fable, so I’ve plagiarized myself to introduce this week’s discussion of what researchers have learned about the most effective repellents to keep females from getting that critical blood meal from your forearm, neck, or ankle.

Let’s begin with the synthetic vs. natural debate: Synthetic chemicals are those that don’t exist in nature; they’re synthesized by chemical methods, commonly from petroleum. Natural chemicals are produced by various living organisms. There are those who swear by synthetic repellents and those who swear at them.

More than 30 synthetic chemicals can repel insects

Of the more than 30 synthetic chemicals used as active ingredients in commercially available insect- and tick-repellents, the most common are DEET, picaridin (or icaridin), and IR3535, each of which has an entertainingly complex official name that helped decide me against a career in organic chemistry.

Natural repellents are typically essential oils, highly volatile compounds extracted from plants. Citronella oil (derived from lemongrass) used in candles and skin applications is the most commonly seen natural repellent, but there are many others found in commercially available and homemade compounds, including oils derived from eucalyptus, lavender, cinnamon, soybean, tea trees, geranium, thyme and a lot of other aromatic spices and herbs.

PMD and permethrins are halfway houses between synthetic and natural compounds. PMD, is a synthesized version of the active ingredient (OLE) in oils derived from the lemon eucalyptus tree, and permethrins are chemically modified forms of compounds (pyrithrins) found in pyrethrum daisies.

All these compounds have been found to repel mosquitos (as well as other arthropod pests such as black flies and ticks). At issue, however, is how effectively, for how long, and with what safety?

To be clear, I am not qualified to offer a professional opinion on how to best and most safely protect yourself and your family members against these pests. Rather, I will state the two factors that have led me to rely more on the synthetic repellents when out in mosquito- and tick-infested areas.

Natural repellents fight off mosquitos for an hour

Both the CDC and the EPA have found, after reviewing extensive research, that DEET, picaridin, IR3535, and PMD offer long-lasting (typically greater than six hours) protection against biting arthropods, when applied to skin surfaces as directed. Permethrin, which is only applied to clothing, remains effective for several weeks, even with washing.

A variety of studies including online summaries of comparisons conducted by Consumer Reports, have shown that most natural repellents lose their effectiveness within an hour.

But it’s concerns over the safety of synthetic compounds that drives many to select natural repellents, even if they are less effective. Considering the many health and  environmental problems associated with once popular, but now banned insecticides, such worries are not unreasonable. And it probably doesn’t help that DEET sounds ominously like DDT.

But repellents are not insecticides, and synthetic doesn’t necessarily mean unsafe nor natural imply healthful. The EPA requires extensive research on the safety of synthetic compounds and those I’ve discussed here have been deemed safe when used appropriately. DEET, the most widely used of the synthetics, has even been certified as safe for use by pregnant women and children as young as 2.

On the other hand, the EPA does not require natural repellents to be tested for either effectiveness or safety. Beyond manufacturer statements implying natural repellents are healthier than synthetics, independent studies of their safety are difficult to find.

A final note: A number of studies have shown that ingestion of garlic and vitamin B-12 have no measurable effect in reducing mosquitos’ tendency to bite. Conversely, eating bananas doesn’t increase your attractiveness to mosquitos…although wearing perfume and drinking beer does.

Ken Baker is a retired professor of biology and environmental studies. If you have a natural history topic you would like Dr. Baker to consider for an upcoming column, please email your idea to fre-newsdesk@gannett.com.

This article originally appeared on Fremont News-Messenger: Baker: Finding the best way to repel mosquitos