Mosquitos. They can be an infuriating nuisance. Occasionally (but increasingly) they can be a vector of disease in my part of the world. This post is going to touch briefly upon some diseases they spread, then focus mostly on which repellents work safely, and conclude with two ways to reduce their numbers in an environmentally friendly way - creating a breeding trap, or feeding them to a voracious, mystery predator.
You would think that living in the city would reduce the number of mosquito bites one endures, but this summer in Philly has been swarming as usual. Recall that we were the historic epicenter of the calamitous Yellow Fever epidemic of 1793. And while I feel pretty safe from ticks in the city, mosquitoes are a three season problem.
The ones that menace my ankles and exposed skin look like this, and I think they are probably Aedes albopictus (Asian Tiger mosquitoes). They feed during the day and show humans little respect. The Philly Department of Public Health confirms tiger mosquitos are here:
Diseases
Besides being a real nuisance, mosquitos can transmit more serious infections like West Nile Virus, Zika, Eastern Equine Encephalitis, dengue fever, Japanese Encephalitis, yellow fever, St. Louis Encephalitis, chikungunya, La Crosse Encephalitis, not to mention dog heartworm disease.
In other parts of the world, malaria is the most feared disease spread by mosquitos of the Anopheles species. Malaria kills up to 2.7 million persons each year, with 90% of these cases + deaths occurring in Africa (with the vast majority of these in children under the age of five). Although malaria cases are showing up in the U.S., no major problems are expected any time soon.
I won’t go through all the above diseases, but I will highlight the emerging problem in the U.S. of dengue fever. From Medpage Today this week:
In just the first five months of 2024, Latin America’s recorded cases are 238 percent higher than they were by this time last year. Other areas are coming up against an uptick, too. Puerto Rico declared a public health emergency in late March, after more than 400 people were hospitalized with the illness.
Dengue fever, also called “break-bone fever” due to the intense body pain it can cause, is a viral infection that spreads from mosquitoes to humans. Many people who contract the virus are asymptomatic, but those with symptoms – one in four – commonly experience a high fever, headache, body aches, nausea and a rash.
Worldwide, dengue causes an estimated 390 million infections and 40,500 deaths each year. Sporadic cases are showing up in the continental U.S., and we can expect more and more as the climate keeps heating up.
Many doctors will not think of testing for mosquito-born illnesses in this country, unless you end up in the ER looking really sick… and even then severe infection symptoms overlap between many causal organisms. For example, one of my patients had most of the above symptoms last week. I worked with the ER to get him evaluated and empirically treated. Several days later his tests revealed the tick-borne illness Ehrlichiosis. Nailing down specific agents can be tricky. Best to try to avoid them.
Mosquito repellents
In order to avoid unpleasant mosquito bites and the itchy welts they leave behind, prudent measures include long sleeve shirts and pants, light colored clothing (mosquitos go after darker colors, reds and oranges - but tend to ignore khaki and light blue), use of fans outdoors as mosquitos are weak flyers, and chemical repellents.
I try not to use chemical repellents unless I’m going to be a sitting duck in a mosquito-prone environment. But here is what I found regarding efficacy and safety (sourced primarily from well-referenced articles in NYT and EWG).
Most research points to an active ingredient called picaridin as the top choice. Endorsed by both the CDC and WHO, a 20% concentration of picaridin can repel mosquitoes and ticks for up to 12 hours. But how does it stack up against other options?
EPA approval: the gold standard
The Environmental Protection Agency approval process is rigorous, involving extensive testing for efficacy, safety, and potential environmental hazards. EPA-approved repellents include:
Picaridin
DEET
IR3535 (also called ethyl butylacetylaminopropionate)
Oil of lemon eucalyptus (OLE) and its synthetic form para-menthane-3,8-diol (PMD)
It's worth noting that many store shelves are stocked with non-EPA approved repellents, often based on essential oils like cedar, lemongrass, peppermint, and citronella. While these may offer some protection, it's typically short-lived. And maybe that supposed protection from essential oils is… essentially not working.
Safety first
Picaridin, developed in the 1980s, has a good safety record. It's considered "practically nontoxic" if inhaled, though this is not recommended, and skin irritation is rare. The EPA has even approved it for use on children as young as 2 months old. For pregnant women, experts recommend a 20% concentration of picaridin or 20-30% DEET. Recall that in utero infections with Zika can be devastating.
Effectiveness: picaridin vs. DEET
A 2018 review in the Journal of Travel Medicine found little difference between picaridin and DEET when applied at the same dosage. However, picaridin may have a slight edge in persistence. EPA-approved labels state that 20% picaridin can provide up to 12 hours of protection, while 25% DEET offers up to 10 hours.
It's important to note that higher concentrations don't necessarily mean better protection. Instead, they often result in just longer-lasting effects. The CDC suggests that DEET's effectiveness plateaus at around 50% concentration.
The downsides
While effective, other EPA-approved repellents have some drawbacks:
DEET: Known for its oily feel and strong smell. It can also damage synthetic fabrics, plastics, and other materials.
Oil of lemon eucalyptus (OLE): While recently approved for use on children under 3 (for certain products), it doesn't last as long as DEET or picaridin, is less effective, and has a strong odor.
IR3535: Like DEET, it can affect plastics. It's often combined with sunscreen, which isn't ideal as sunscreen requires more frequent application.
Permethrin: a special case
Permethrin is a bit different. It's meant for use on clothing and gear, not skin. When properly applied, it can provide protection for about six washes and is particularly effective against ticks. However, it should be used in addition to, not instead of, a skin-applied repellent.
Bottle design matters
A great repellent formula can be let down by poor packaging. Look for spray bottles that provide even coverage. This is particularly important when applying repellent to squirmy kids or hard-to-reach areas. Locking caps are a nice safety feature, especially if you have curious little ones around. I’m trying this one from Sawyer Products as recommended by the NYT article. No affiliation.
Proper application
Regardless of which repellent you choose (though picaridin is favored right now), proper application is crucial. Follow the instructions on the label carefully. Apply evenly to exposed skin, but avoid eyes and mouth. For face application, spray the repellent on your hands first, then apply. Don't forget often-missed spots like the backs of knees and ears.
When using with sunscreen, apply sunscreen first, then the insect repellent. Remember that sunscreen often needs to be reapplied more frequently than repellent.
The bottom line
While no bug spray is perfect, picaridin emerges as a top contender. It offers long-lasting protection against both mosquitoes and ticks, has a good safety profile, and doesn't have most of the downsides associated with DEET or other alternatives.
Reducing mosquito burden around your house
Most mosquitos don’t fly very far from where they hatch. Experts state that most of your mosquito problems can be traced to areas nearby, and it’s most effective to fight mosquito larvae rather than the adults. Its tempting to freak out and spray pesticides all over, but this indiscriminately harms good insects, too. Fogging is not that effective against adult mosquitos anyway. And pesticides have been associated with human health problems like cancer and neurodegenerative diseases.
So here’s an idea that I am currently trying as of tonight.
Construct a little mosquito breeding trap, like filling a small container with water and adding some grass/hay/leaves. After a couple days local mosquitos will start laying their eggs in this fermenting paradise. You can then place a non-toxic “mosquito dunk” to float in the container. Dunks are impregnated with bacteria, spores, and natural larvicides that target any mosquito larvae and kill them before they become flyers. Dunks can also be placed in backyard ponds and fountains if you live larger than I do.
Supposedly we will start to notice a difference in as little as a week. Repeat the cycle in about a month.
Here is what the dunks look like that we ordered (cheaply), as well as some details about the ingredients:
If you want to try this along with me, here are two good resources that can help explain this process in more detail:
*NY.GOV page, and Audubon Society*
Let’s compare notes in a couple weeks?
It’s also a good idea to do the following basics, if applicable. Mosquitoes can breed in small pockets of water - as small as a bottle cap. So, to reduce mosquito breeding:
• Remove, flip or empty standing water in all containers
• Change water frequently in items like birdbaths.
• Fill in tree rot holes or stumps that can hold water.
• Store boats covered or upside down.
• Pull plastic sheeting or tarps covering yard items tightly so water won’t pool.
• Seal & repair cracks in broken or unsealed septic tanks
When all else fails, use an apex predator
I’d like to reintroduce our family betta fish.
Her name is Roygee.
She is available for hire.
When fed a recently swatted mosquito, she shows great ferocity.
This may induce a sense of shock and awe in local mosquito populations, contributing to the mass exodus of pesky insects of all kinds, while preserving cute little grasshoppers, lady bugs, and - yes they are cute - spiders.
Spread the word and forward this at will. I wish you success in reducing a major summertime nuisance, and perhaps we will even avoid a serious infection from mosquito bites together.
Nice summary and glad you picked up on Dengue. Really becoming worrisome and thanks to climate change, the tropics are coming to the subtropics.
I would like to mention about the fogging, I remember the trucks fogging the neighborhoods with DDT. This helped some but really gave rise to resistant little buggers.
We should think about the ecological niche that mossies play in the ecosystem. A lot of species depend on this trophic level.
You might find this interesting. https://en.wikipedia.org/wiki/Mosquitofish
Another eco-clusterfuck
Roygee looks fierce I agree! Thanks for this great run down. I’ve been afraid of some of the repellents, but agree that there is a real risk of infections like WNV. Local control around ones house makes sense, and I’m going for it with the dunks. Online testimony seems to confirm they really help! Keep you posted for sure. Good luck.