Killing Mosquitos and other dangerous insects.
By William Isecke
The control of mosquitoes, which has always been a major problem in tropical areas of the world, has now become a serious public health issue in the USA.
With the spread of West Nile Encephalitis to temperate areas of the world, the USA has become vulnerable to this disease. The public health response so far has been to spray large areas with insecticides. The spraying however, can only be a short term solution. Besides the well known problem of the insects developing a tolerance for the insecticides there are other disadvantages of this approach. Insecticides are poisons and they affect other species besides the target species. They kill other beneficial insects and wildlife including the natural predators of the pest species. The health effects on humans are not completely known and may be significant. Since poisons are not safe or effective, another method is needed.
The familiar backyard bug zappers typically use light to attract insects. They kill many insects, many of which are beneficial. Unfortunately, they kill few mosquitoes because these insects are not attracted to them.
A better approach to pest control is to directly target the troublesome species. In the case of mosquitoes, the female must find a blood meal from an animal in order to get the protein necessary for development of her eggs. She locates the animal host by following the plume of heat, carbon dioxide, and other chemicals that the animal emits.
There are commercial devices to trap mosquitoes that take advantage of this behavior. One of them is called the Mosquito Magnet.( http://www.mosquitomagnet.com/). This uses propane and Octenol to provide the heat, carbon dioxide, and chemical plume to attract the mosquitoes which are then sucked into the device, killed, and collected in a bag. This device is advertised as being capable of eliminating the mosquitoes on one acre of land. However, it costs about $1400 and requires a 20 pound tank of propane every three weeks. There is also a model which costs $ 700 but only covers one half acre. It still uses the same amount of propane. This fuel requirement and the high cost limit its applicability. There is another similar device called the Dragonfly (http://www.mosquitosolutions.com/) this costs about $650 and uses an electrified grid to kill the mosquitoes. This device uses about 40 watts of electricity and must be plugged in to operate.
A stand-alone electrified grid that would kill any insect that came in contact with it may be a better solution. The design of this insect killing screen would differ significantly from current designs for electrified bug killers. It would not be desirable to use the same kind of power supply as is used in the common bug zapper because of the danger of shock and because the constant presence of high voltage generates ozone and ionizes the air. This causes a constant power drain which makes it dependant on plug in power. We can use low power and still have sufficient high voltage to kill insects if the high voltage is only generated when an insect is present. This can be done by energizing the grid with a voltage that is not high enough to consume constant power but is high enough so that when an insect contacts the grid a detectable current flows. This current is then used to trigger a high voltage pulse which kills the insect. The power necessary to operate this grid should be low enough to use battery power combined with solar cells
If the high voltage pulse is also high frequency then the grid can be safe for animals because the resulting skin effect prevents the current from penetrating below the skin. An animal will feel a slight burn but no shock. The heating effect of the pulse would be sufficient to kill insects because their small mass would result in a temperature increase that would be lethal. Even if the energy of the pulse is quite small, the insect’s legs or whatever part is in contact with the grid would be destroyed thus permanently crippling the insect and removing it as a threat. Another approach is to use only enough energy to temporarily stun the insect so that it will fall into a trap from which it cannot escape
The simplest way to use the grid is to intercept the mosquitoes that are seeking us. It is necessary to insure that as the insects attempt to get to us, they encounter the electrified screen first. For example, the electrified screen could replace a normal mosquito screen in a house or animal pen. If the screen is covering the opening where air that is attractive to mosquitoes is leaving the enclosure, then mosquitoes that attempt to enter would be killed. It may be that in urban or suburban areas, most of the mosquitoes that bite people outdoors have previously attempted to enter a dwelling and been stopped by a screen. If that screen had been electrified, those mosquitoes would be dead and not able to bite. A complete stand-alone trap that is designed to kill these insects can be built by using one or more chemical attractants inside an electrified grid enclosure


Of course, mosquitoes are not the only insects that are dangerous pests. Tsetse flies, bot flies, black flies, sand flies and many others can also be controlled in this way. The trap may also be used to protect cows and other livestock from the many kinds of flies that prey on them. Agricultural pests may be controlled in this way also. Perhaps the traps could be baited with pheremones for this purpose.
Another application is to use insects as a food source. Many insects are attracted by dead animals and these insects are often quite large. For example, an insect trap baited with a fish head and hung over a fish pond will provide a constant source of flies as fish food. The same thing can be done over a chicken pen.

There are several conditions which must be met for a device such as this to be successful. One is that it must be low cost. Another is that it must be low energy so that it can be used wherever the insects are found. In addition, it must be effective; that is it must have a significant effect on the problems caused by the insects. I believe that this device can be made to meet all of these conditions.

Alternative approaches
In tropical areas, bed nets have been used with some success to control malaria. The bed nets are made of fabric impregnated with insecticide, usually Pyrethrin. These nets must be re impregnated after about 6 months and they only kill the mosquitoes if they remain on the net for a long time (approximately five minutes). The nets do have the advantages of low cost and easy set up. Probably the biggest long term problem with the nets is the fact that the mosquitoes will develop resistance to the insecticide, typically within a few years.

It may be possible to use treated nets to replace window screens. This would kill mosquitoes that are attempting to gain entry to an inhabited dwelling instead of simply keeping them out if they remain on the net long enough to absorb sufficient insecticide. This may have the same result as using the electrified grids described above. Since mosquitoes typically do not travel very far, in areas such as suburbs and summer camps this technique may be sufficient to extinguish the local population of mosquitoes. In other areas, a combination of impregnated nets and electronic traps may be necessary to control mosquitoes
The long term safety and efficacy of the insecticide used to impregnate the nets must be established. We can anticipate that the mosquito population will develop resistance to whatever insecticide is used and its effectiveness will diminish over time.

The electrified grid has the advantage that it kills any insect that comes in contact with it, however briefly, and there is no possibility of insects evolving resistance to it. In addition, the method used by mosquitoes to locate their prey is fixed and it seems that it would be very difficult to evolve a new method that would allow the mosquito to find animal hosts and still avoid the electronic traps. Even if a preference evolved for a different combination of the chemical and other cues that animals emit, it will be a relatively simple job to modify the bait so that mosquitoes will continue to be attracted and killed.
The disadvantages of the electrified grid are cost, complexity, and the delicacy of the wire grid. It will probably be necessary to protect the grid by putting a heavy large mesh netting in front of it to protect against impacts by birds or bats.

It does not seem possible to completely eliminate mosquitoes and other blood seeking insects although the idea is tempting. I don't know what the ecological consequences of that would be, but I think that many people would be willing to find out. If these insects have any beneficial function it may be to make large areas of the world uninhabitable for people and thus protect the other life forms there from people. Of course, mosquitoes prey on any animal that they can reach which means that people are kept away but the animals must still live with the mosquitoes.

It seems that the age-old battle between men and mosquitoes will go on but we may gain at least some relief. As Oscar Wilde said "The goal of science is to build better mousetraps. The goal of nature is to build better mice." Maybe we can shift the balance a little bit toward science.

There are many questions remaining to be answered:

Do large numbers of mosquitoes attempt to enter occupied houses and come into contact with screens?
Can a stand alone trap, baited with Octenol and Lactic Acid kill significant numbers of mosquitoes?
Is it necessary to use heat and carbon dioxide in addition?
Can the power required be low enough to permit the use of solar cells and rechargeable batteries?
How can the other types of insects that prey on animals be attracted?