A Greener View

The growing epidemic caused by the West Nile virus has heightened interest in mosquito control throughout the United States. It has only been known to be in the States since the late 1990's, but it has spread from coast to coast and has caused many deaths across the country. It is an amazing organism that can live in birds, dogs, horses, people and mosquitoes.

There are already plenty of mosquitoes in every neighborhood, so where do they come from? There are several species of mosquitoes in every area of the country. In some species the females lay their eggs directly in water where they grow, become pupas and then adults. Other species lay their eggs on low stems above the water or even in the woods. These eggs can remain dormant for months, even years, until water from a flooding rain reaches them.

Controlling mosquitoes needs to start with making sure they do not hatch in the first place. The larvae of all species need water to grow in, but the water needs only to be as much as can be found in a cup left over from a picnic that holds water for a week or two. Do you or any of your neighbors have any of the following potential mosquito nurseries? Old tires, buckets, swimming pool (even a tiny one), rain gutter, flat roof, leaking faucet, air conditioner unit puddle, bird bath, fountain, pond with no fish, puddles, tree holes, low area flooded by sump pump water or septic tank, animal water bowls, irrigation water that puddles, flower pots with saucers or any other thing left out that could hold water.

The easy way to fix the problem is to at least weekly, drain every one of these locations. Any puddle that lasts more than four days could produce mosquitoes. A small backyard pond with fish may attract mosquitoes, but these ponds do not produce many, because most fish will eat the eggs and larvae as soon as they are spotted. Small goldfish and tropical fish from the pet store are good choices, especially for the half-barrel tub gardens that are easy to grow on a patio. They can get into the small nooks and crannies that larger fish can not and they will eat the larvae of many insects, not just mosquitoes. The tropical fish will not survive the cold water of winter.

The second step, for locations that cannot be drained, is to kill them at the larval stage. A safe, nontoxic way to control mosquitoes is to use a product containing a biological larvicide called B.T.I. (Bacillus thuringiensis subspecies israelensis). There are several brands that use B.T.I. and some of them have a slow release method of dispersal. Mosquito Dunks from Summit have been around the longest and I have found they work very well. They look like small compressed sawdust donuts that float on water and kill mosquito larvae before they become flying, biting, disease-spreading adults.

The bacteria are ingested by the larvae as they feed and the larvae then get sick and die. The bacteria do not affect fish, mammals, birds or bees. Some other varieties of B.T. do affect caterpillars of moths and butterflies.

Float a Mosquito Dunk in ponds, birdbaths, water gardens or any place where water collects and remains for longer than four days at a time. Each Mosquito Dunk will treat up to 100 square feet of surface water for about 30 days. A small piece of a dunk can be used in small containers. For retention ponds that overflow when it rains, they can be tied with a string to a stick, so that they stay in place and do not float away if the rains come. They can also be tied to sticks and left above the normal water level of areas that periodically flood. When the flood waters come, they will dissolve a few B.T.I. bacteria into the stagnant puddles. Alternating wet and dry cycles does not inhibit the effectiveness.

The Summit Company also makes Mosquito Bits that release the bacteria much more quickly. They kill the larvae in less than a day. They will need to be applied weekly to get the continued effect or the dunks and bits can be used together. I used the Bits in a Wine Barrel full of aquatic plants and a zillion mosquito larvae and the larvae died overnight.

A product containing the ingredient Methoprene kills mosquitoes because it mimics the insect's growth regulating hormone and prevents it from becoming an adult. It is not toxic to mammals, birds, fish or bees.

The ingredient Temephos is the organophosphate insecticide that is EPA registered to control mosquito larvae. It is potentially toxic to some birds and to some other insects like bees.

Specific types of oils can be used on the water's surface to kill larvae, pupae and emerging adults. There is little problem with other animals except fish and aquatic organisms if misapplied.

Since most mosquito problems come from a wider source than can be treated by the individual, the third step is to work on a wider territory. To be effective, the insecticidal controls for adult mosquitoes must be applied with the proper wind and temperature conditions and when the mosquitoes are active. A responsible mosquito control program would be an integrated pest management approach that takes into account a monitoring system to see if there is a need to apply a control measure in the first place. It would also include little disruption to natural mosquito controls such as fish and birds, habitat management, and the knowledge that controls are best accomplished when the mosquitoes are concentrated, immobile and accessible, such as in the larval stage. A larval control program may prevent the need for an adult control method.

While larval controls are generally applied to the water, adult controls are generally applied through the air. Ultra low volume sprays dispense fine aerosol droplets that kill mosquitoes on contact. Generally, less than three ounces of active ingredient per acre is applied to minimize the risk to people and the environment. The EPA has concluded that exposure to properly applied mosquito controls is 100 to 10,000 times lower than the level that could cause a health concern. No pesticide should ever be considered 100% safe and normal care should be taken to stay out of any insecticidal spray.

The insecticide Malathion is a commonly used organophosphate that has been used in many formulations for almost fifty years. It quickly decomposes in the environment and has a low toxicity to mammals and birds. It is very toxic to all insects, including bees.

The insecticide Naled is also an organophosphate that has been around since before 1960. It is sometimes used in flea collars and it used on food crops, because it degrades quickly. It has a low toxicity to birds, mammals and fish, but is very toxic to insects, including bees.

Three synthetic Pyrethroids are used in mosquito control. Permethrin is used in household insect foggers, flea and tick sprays and dips for cats and dogs and in termite control. Resmethrin is used to control flying insects in the house and garden and on insects that get on pets and horses. Sumithrin is used to control insects and mites in homes, gardens and on pets.

All three Pyrethroids are lowly toxic to mammals, practically nontoxic to birds, but are toxic to fish and insects, including bees.

If you have a backyard water garden or koi pond, ask your local government that is applying insecticides, which one they use and let them know you have fish so that they will spray less near your house if they use an insecticide that can harm your fish.