What’s the best bug spray to take when you travel? How about keeping mosquitos away in your backyard?
Because I’ve conducted fieldwork in the tropical rainforest of Central and South America for more than two decades, people assumed that I’m an expert of staying alive in the mosquito-infested wilderness. I know the dangers of mosquito, tick, and other insect bites because of my interest in infectious diseases.
My clinical focus is on viral immunity – how to prevent and effectively treat viral infections – and insects are a primary vector of spreading viruses to plants and humans.
The truth is that in virgin rainforests bugs are kept in balance by other creatures and plants. Bats, birds, and lizards devour mosquitos. Carnivorous plants digest bugs. It’s when humans disrupt the balance of natural habitats that poisonous plants proliferate and stinging, biting insects thrive. Don’t think that mosquitos thrive only in the impenetrable forests. Deadly mosquitos thrive just as easily in the city and your backyard.
Mosquitos Like Wet and Hot Weather
Mosquitos are active when temperatures get above 50 degrees Fahrenheit. They swarm in hot, humid weather from July through September. In the southern states, mosquitos don’t go dormant. The longer hot season increases the need for bug protection that starts in February and lasts through the fall. In the tropics, like Cuba and South American countries, mosquitos are active year-round.
In subtropical South Florida and hot, humid East Texas along the Gulf of Mexico, Aedes aegypti, the yellow fever mosquito moved in. This bug spreads dengue fever, chikungunya, Mayaro virus, Yellow fever, and Zika.
Mosquito-borne infections are an enormous public health problem. Scientists and public health professionals are concerned because these diseases spread fast and explode into epidemics.
The tiny Aedes mosquito causes over one million deaths every year from deadly viruses. Over a million people everyday contract Zika, dengue, chikungunya, and yellow fever. It’s not uncommon to get infected at the same time from two or more mosquito-borne viruses. More viruses are out there.
Mayaro virus occurs in the Caribbean and northern South America. So far, it’s a little-known virus but so was Zika a few years ago. Mayaro is in the same viral family as Dengue, chikungunya, and Zika. It causes similar symptoms including fever, rash, and severe joint pain.
Female mosquitoes are the ones that bite and transmit disease. They use the protein and iron in blood to feed their eggs. The average lifecycle of female mosquitos is about one month, but they can live as long as sixty days. One female Aedes can lay five hundred eggs during her lifetime. They are most active during the daytime. But their favorite times are a few hours before sunset and sunrise. Aedes love to be around people. They breed in damp, dark places like flower pots, discarded plastic cups, or standing water.
Cleaning up your immediate outdoor environment, using screens, and in the tropics sleeping under mosquito netting prevents most bites. Burning mosquito coils keep bugs away but may contain toxic chemicals. Mosquito traps and electric zappers help too, but can’t eliminate every bug. Spraying insecticides helps reduce mosquito populations, but like all pests, Aedes have become resistant to pesticides.
Wearing protective clothing when outdoors is essential. The final line of defense is mosquito repellent. Let’s take a look at which ones work best.
Are There Safe and Effective Mosquito Repellents?
The CDC recommends several compounds as mosquito repellents. Four have proven efficient and are widely available. The EPA publishes extensive information on how to safely use insect repellents. For my personal use, especially when in the tropical rainforest, I want to use the most effective but least toxic repellent.
Researchers at the University of New Mexico found that DEET and PMD are the best bug repellents. These are the same repellents I use and recommend. These researchers also found that wearable devices are ineffective in repelling mosquitoes.
The Two Most Effect Repellents:
- DEET – N, N-Diethyl-meta-toluamide was developed in 1944 by the U.S. Army to protect soldiers from mosquito-borne diseases in jungle warfare during World War II. The original form had to be frequently applied. When first using DEET, I often forgot to repeat application. I got lots of mosquito bites when the effectiveness wore off.
In 1991, an extended-release form was approved by the EPA. The window of effectiveness varies according to concentration. 100% DEET gives up to 12 hours of protection while 20-30% provides 3–6 hours of protection.
Although DEET is very effective, it is neurotoxic at high concentrations and might cause seizures. And, DEET contaminates the environment. Showering after applying DEET finds its way into ground water. Nearly three-quarters of streams in the United States contain traces of the chemical. To reduce toxicity, do not use more than 10 percent DEET on children under twelve. Adults should use 30 percent or less. Higher concentrations do not increase effectiveness; it just lasts longer. When using lower concentrations, apply DEET every 3-4 hours.
- PMD – The scientific name for PMD is p-Menthane-3,8-diol or para-menthane-3,8-diol. PMD is from a species of eucalyptus tree native to Australia, Corymbia citriodora. It’s called oil of lemon eucalyptus in the U.S., and sold under the tradename Citriodiol. PMD repels ticks almost as good as DEET. PMD is considered safe, but is not recommended for children under three years old.
Useful Tips When Using Bug Spray
- Use the least amount needed to repel mosquitoes.
- Avoid aerosol sprays because you can inhale the fine mist from aerosols.
- DEET is an irritant, so don’t use under clothing, on wounds, or damaged skin.
- Pump-action sprays or lotions keep the repellent where you want it, not in the air. A thin layer is all it takes.
- Spread it on evenly with the palm of your hand. Wash your hands when done applying.
- Do not spray DEET or PMD on your face. Avoid contact with your eyes.
- When you’re shopping for a repellent, read the ingredient list on the back of the product to see what it contains and the percentage of DEET or PMD.
When I pack for fieldwork in the Amazon rainforest, I take DEET. For home use where I live in South Florida, I apply PMD when working outdoors in my garden.