Natural Mosquito Control

West Nile Virus and Alternatives to Toxic Chemicals

Lit candles on table at party
Caiaimage/Paul Bradbury/Getty Images

Natural mosquito control calls for a multi-pronged approach to battle malignant mosquitoes, while resisting the temptation to use the chemical bug sprays that some folks feel are just as noxious. If you are asking, "What's all the fuss about?" then read on.

Stating the Problem: When Neither Chemical Sprays nor Mosquito Bites Are Acceptable

Do you spend a significant amount of time landscaping the yard in summer?

Then you know that mosquito control of some sort is a necessity. Such awareness could well save your life in this age of the West Nile virus, when a lack of effective mosquito control can be deadly. But if you are concerned about the long-term health consequences of applying chemical bug sprays to your skin, then the use of natural mosquito control methods may be your best solution to the challenge posed by West Nile virus.

What is so bad about chemical bug sprays? The U.S. National Library of Medicine (NLM) discusses two different and widely-used ingredients in bug sprays:

  1. DEET (N,N-diethyl-m-toluamide)
  2. Pyrethrins

According to NLM, using very high concentrations of DEET (over 50%) over a long period of time may cause not only severe skin reactions, but also insomnia and mood changes. The same source states that the use of pyrethrin-based sprays can lead to breathing problems if large quantities are inhaled (even though the general consensus is that they are not, technically, toxic).

While these facts may not be especially alarming (in and of themselves), remember that not everybody's body responds to substances in precisely the same way. When erring on the side of caution, assume that a chemical spray that might not bother the general public much might cause you substantial difficulties.

If we take "natural mosquito control" in the broadest sense (that is, any mosquito control measures that save you from applying chemical bug sprays), a number of options present themselves.

Examples of Natural Mosquito Control Methods and Substances:

  • Plant oils: for example, those derived from citronella (but see below), castor bean plants (which also discourage moles), or catnip plants
  • Certain bath oils, such as Avon's "Skin-So-Soft"
  • Devices such as the Mosquito Magnet
  • How you dress: avoid dark clothing
  • Attacking the problem at the source: mosquito-larvae control
  • Staying organic in your landscape maintenance so as to avoid killing mosquito predators

You have probably heard of high tech's answer to the problem: the Mosquito Magnet (and similar products). It is a device that gives off a gas simulating natural human breath, whereby it lures mosquitoes into its death chamber. Such gadgets might not seem especially "natural," to be sure; but again, the objective is to avoid the use of chemical bug sprays.

To learn more, read my review of the "Mosquito Magnet".

Even how you dress can influence whether you suffer mosquito bites. Mosquitoes are drawn to dark-colored clothing. So clothes that are light-colored can certainly be viewed as tools in your toolbox for natural mosquito control.

A Tale of Two Citronellas

Before we can discuss citronella properly, we must specify exactly what we mean by that term. The oils, etc. with which you are probably familiar are derived from the tropical grass, Cymbopogon nardus. Don't confuse the latter with a plant named Pelargonium citrosa, which is variously dubbed "mosquito plant," "citronella plant," etc. Its fragrance may remind people of citronella, but it is not related to Cymbopogon spp. More importantly -- and in spite of the hype -- most now agree that it is not effective at repelling mosquitoes (regardless of whether you stand next to the plant while you are out in the yard or crush its leaves and spread the juice on your skin).

As for the effectiveness of Cymbopogon nardus, itself, the jury is still out. Some swear by it, while others are skeptical.

Citronella products made from Cymbopogon nardus are widely used in natural mosquito control. Some people burn citronella in a candle, while others apply it to the skin as a topical oil. In the latter case, citronella is sometimes used in concert with other oils, derived from plants such as castor bean or catnip. Avon's "Skin-So-Soft" is among the most popular products used topically for natural mosquito control.

As we will see on Page 3, attacking the problem at the source (namely, mosquito larvae) is another effective method of natural mosquito control. But before addressing mosquito-larvae issues, let's have a closer look at West Nile virus itself -- the subject of Page 2. West Nile virus has given a new sense of urgency to the mosquito problem, whether you are committed to natural mosquito control or don't mind using chemical bug sprays...

West Nile virus (WNV) is an encephalitis transmitted by mosquitoes. You have perhaps heard of Eastern Equine Encephalitis, which is a related but different illness. WNV is primarily a bird illness and is transmitted from infected birds to other birds by mosquitoes. But the mosquitoes carrying the virus can also transmit it to humans through insect bites. Thus the importance of mosquito control, including the natural mosquito control methods discussed on Page 1, when you plan on spending time outside -- particularly in wooded areas.

While mosquitoes transmit the West Nile virus from blood stream to blood stream, it is the infected birds who serve as the agents that transport it into new areas. Birds infected in one region can fly to another region prior to dying from West Nile virus. Once in the new region, they can be bitten by mosquitoes again, and the latter become new carriers, perpetuating the cycle.

West Nile virus was first detected in 1937 in a province in Uganda by the same name, according to the West Nile Virus Center. Prior to its introduction to North America in 1999, cases of the illness had been reported in Europe, the Middle East, Africa and Asia. In 1999 the first North American cases were reported in New York City. Seven people died in this outbreak.

Since then West Nile virus has spread to most of the states in the U.S. and also to Canada. Although not everyone who is infected dies from it, the threat posed by West Nile virus must be taken seriously.

In the northern U.S. and Canada most cases are reported in late summer and early fall. In warmer regions cases are reported year-round.

From a Landscaping Perspective, What Can be Done About West Nile Virus?

Besides using mosquito repellants to protect your person against insect bites, those working on the landscape can take measures to help stop the spread of West Nile virus.

Since this illness is transmitted to humans via mosquitoes, and since the larvae of mosquitoes are found in standing water, one group of measures should obviously focus on sources of standing water in your landscaping. But just what those sources consist of can be far from obvious. So the nooks and crannies holding up "Welcome" signs to mosquito larvae is the subject of Page 3….

We know that fish eat bugs. So perhaps you have thought, "Too bad there isn't there a 'mosquitofish' I could put in my water garden to eat mosquito larvae." Well, believe it or not, the mosquitofish isn't a mythical beast, a benevolent creature found only in our dreams, like the mermaid. There really is such a thing as a mosquitofish!

I will have more to say about the mosquitofish below. But first, let's consider the role of controlling mosquito larvae in our war against West Nile virus.

Successfully killing mosquitoes is based on a simple yet important observation. When mosquitoes become adults, they rule the skies. Locating and killing winged bugs is difficult. Let's face it: the bugs are small and the sky is big. It is like trying to find a needle in a haystack.

Consequently, mosquito control that focuses instead on killing mosquito larvae or depriving mosquitoes of breeding grounds makes a lot of sense. If you can eliminate sources of standing water on your landscaping (in which mosquito larvae are born), you are hitting mosquitoes where it really hurts. Or else you can kill the mosquito larvae while they are still confined to the water. They are sitting ducks while they remain wingless, swimming in an artificial pond, say, or a swimming pool -- because they are in a medium (water) that is contained in a finite, easily-managed area. This is the time to kill them. And you can even do so without resorting to chemicals, if you prefer; for instance:

  1. By using Bt bacteria (Bacillus thuringiensis), which attack mosquito larvae but pose no threat to other life forms. There are different strains of Bt bacteria; for an example of one used to fight mosquitoes, see below.
  2. Or by acquiring the eaters of mosquito larvae mentioned above, the aptly named "mosquitofish."

    But before considering ways to kill the larvae in areas of your landscaping where you intentionally keep standing water, let's look at some of the sources of standing water that you might not immediately think of:

    1. Water buckets and rain barrels.
    2. Bottles and cans.
    3. Empty plastic pots from the nursery and other concave odds and ends you threw in a pile behind the garage.
    4. Old car tires (notorious rain-catchers).
    5. That wheelbarrow you have been meaning to bring inside, as soon as you fix its flat tire....
    6. Boat tarps or pool covers in which water can puddle.
    7. Uneven areas in lawns or gardens where irrigation water can collect.
    8. Clogged rain gutters and clogged drains.
    9. Birdbaths and water bowls for pets.
    10. Seepage from septic tanks.

    But that still leaves the standing water that you wish to keep, such as that in swimming pools and garden ponds. How can you control or kill the mosquito larvae which may be lurking in these places?

    1. Keep swimming pools clean, aerated and chlorinated.
    2. A bacteria called "Bti" (a strain of the Bacillus thuringiensis mentioned above) is often used for mosquito larvae control in standing water.
    1. Aerate artificial ponds.
    2. Avoid the temptation to mass aquatic plants together excessively in artificial ponds (mosquito larvae can hide from the fish if the vegetation is dense).
    3. Stock artificial ponds with fish that eat mosquito larvae.

    But which fish are the best eaters of mosquito larvae? Minnows and goldfish are common denizens of artificial ponds, and they do a fine job of eating mosquito larvae. But another fish, Gambusia affinis, has acquired such a reputation as an eater of mosquito larvae that it has been nicknamed, "mosquitofish." Contact your local municipality regarding the availability of mosquitofish in your area. Formerly an obscure species, the mosquitofish is now enjoying the limelight due to the West Nile virus' invasion of North America.

    I never thought that a fish might save my life....

    Another bug that poses serious problems for people who spend a lot of time outdoors is the deer tick, which can carry Lyme disease. Again, many folks wonder which is worse, having the bug around or spraying the yard to kill the bug. I explore that question in my article, To Kill Ticks, Should I Spray My Yard?