Traps

An enormous amount of consumer interest has been generated by the marketing of new devices designed to attract, then either trap or kill, mosquitoes. The general idea is to reduce the number of questing mosquitoes that would otherwise be afflicting the homeowner. Many products even claim to significantly reduce or even collapse local mosquito populations by decreasing the number of egg-laying females through their capture.

Power supplies for each type of trap vary. Some are totally self-contained, utilizing propane to provide both power and a source of carbon dioxide as an attractant. These units have the advantage of portability, allowing them to be placed at a considerable distance away from home-sites and electrical outlets. This may be an important consideration on larger properties, i.e. those over an acre in area, by allowing mosquitoes to be intercepted long before they come into the vicinity of human activity. This portability comes at a price, though, for the thermoelectric generator that uses excess heat from the combustion process to generate electricity to run the intake fans is quite expensive. Most units rely upon power cords utilizing AC outlets. This limits them somewhat to smaller areas served by extension cords, but their price is commensurately less than their self-contained counterparts.

All of these traps utilize some form of attractant that lures the host-seeking female mosquitoes to a capture or killing device. In some cases, mosquitoes are captured via an impellor fan that suctions them into a net, where they desiccate (Mosquito Magnet , Lentek ). Other trapping systems use a sticky surface to which the mosquitoes adhere when they land (Sonic Web and Coleman Mosquito Deleto ). Still others utilize an electric grid to electrocute mosquitoes drawn into contact (Dragonfly ). These are not set-and-forget devices each requires some level of maintenance, i.e. capture nets need emptying, adhesive boards require replacement and grids require cleaning to ensure their continued effectiveness, particularly in areas of high catch.

Attractants used are generally variations on a common theme of imitating the mammalian scents and body heat that provide host cues to questing female mosquitoes. The vast majority of these traps use carbon dioxide, produced either through the combustion of propane or via CO2 cylinder as the primary attractant. The CO2 is released at between 350m (for propane) and 500 ml/min (cylinder with regulator). The plume of CO2 produced mimics human exhalation and thus makes these traps quite specific for capturing blood-feeding insects looking for human hosts. Therefore, non-target insects such as moths and beetles will be largely unaffected. The CO2 is often synergized with 1-Octen-3-ol (a derivative of gasses produced in the rumen of cows) to increase attractiveness by several orders of magnitude. The 1-Octen-3-ol is slow-released at a rate of ca. 0.5 mg/h. An intriguing means of attracting mosquitoes to their demise is that used by the Sonic Web . This device attracts the mosquitoes through a combination of 1-Octen-3-ol and a sound pulse that mimics a human heartbeat or pulse.

The process of a mosquito questing for a blood meal involves a complex, interconnected cascade of behaviors, each probably having its own cues, be they visual, thermal, or olfactory. The complexity of these questing behaviors may account for the bewildering variations in trapping efficiency noted for certain species of mosquitoes at different times, seasons and places. With 176 species of mosquitoes currently recognized in the United States, this is no small issue and will require many years before research can provide a clarification. There is some anecdotal evidence that these baited traps, indeed, capture more females of some species than others, depending, to some extent, on the concentration of carbon dioxide emitted and the mosquito species present. There may also be seasonal and circadian variables that affect mosquito responses to certain attractants. For example, a few years ago the Salt Lake City Mosquito Abatement District ran a comparison test of the Mosquito Magnet with an American Biophysics ABC trap. Each trap was operated for one night and then switched to the other's location over a two-week period. The Mosquito Magnet captured enormous numbers of Ochlerotatus sierrensis, the western tree hole mosquito, but few Culex pipiens, Culex. tarsalis, or Ochlerotatus dorsalis. The ABC trap performed just the opposite, capturing great numbers of Culex pipiens. The reasons for this are not entirely clear, but serve to underscore the need for more research and to point out that each trap may have its own operational use.

The advertising claims for acre-wide control by these devices may be somewhat overstated. In most cases they are based upon best-case extrapolations from captures of released mosquitoes made inside screened enclosures. To be sure, it would be very difficult for the manufacturers to conduct controlled studies yielding reliable, statistically significant data with natural occurring mosquito populations due to confounding variables largely beyond the control of the researcher. Meaningful, repeatable data capture requires stability in these factors, generally over a period of years extremely difficult to obtain in nature. In fact, Mosquito Control Districts using several different types of traps in survey operations often experience large variations in mosquito trap counts among traps as well as by location, trap height, and time of season.

Nonetheless, these devices will trap and kill measurable numbers of mosquitoes. Whether this will produce a noticeable reduction in the mosquito population in each case will depend upon a number of factors, e.g. individual tolerance level, absolute mosquito population size, proximity, size and type of breeding habitat producing re-infestation, wind velocity and direction, and species of mosquito present, and others. Depending upon their placement, wind direction, and inherent trapping efficiency, traps may actually draw more mosquitoes into an area than they can possibly catch. Thus, the homeowner must still use repellents and practice source reduction methods as adjuncts to realize any measure of relief. Indeed, the AMCA has received a number of testimonials from buyers who are dissatisfied with these products and the level of support they've received from the manufacturers. Whether these reflect failure to follow placement or baiting directions is unknown. Many districts have used CDC Light Traps baited with dry ice and collected upwards of 65,000 mosquitoes in each trap, each night. A number of studies have shown that traps using CO2 and 1-Octen-3-ol normally catch numbers of mosquitoes several orders of magnitude more than their solely CO2-baited counterparts. Thus, the reasons for the failures reported in the testimonials remain unclear.

AMCA policy prohibits the endorsement of products, but the science behind these mechanisms appears to be solid. The counter-flow technology used in the Mosquito Magnet is particularly promising and has passed muster in peer-reviewed scientific trials conducted by the US Department of Agriculture. The Mosquito Magnet Pro probably offers the greatest flexibility of all devices marketed to date. The propane source for this unit provides power, CO2, and heat portability. It's expensive, though, due to the technology required to convert propane combustion into electricity. Most of the other devices require either an AC power source, e.g. the Coleman traps, the Mosquito Magnet Liberty and Dragonfly traps, or a proprietary CO2 cylinder for the attractant, as in the case of the Dragonfly . In terms of sheer trapping efficiency, the Dragonfly would be hard to beat. Although the CO2 cylinder requirement might reduce its marketability, it allows the plume of carbon dioxide to be metered to optimize attractancy. The electric grid provided in this model is extremely effective.

Several of the trapping systems include a separate device designed to reduce human attractiveness to questing female mosquitoes, thus making the attractants in the capturing device placed elsewhere even more effective. These inhibiting devices usually consist of a plastic casing enclosing a fan powered by 2 AA batteries. The fan helps distribute a plume of a proprietary substance that ostensibly masks human odors to mosquitoes. Thus, female mosquitoes do not recognize humans within the area as food sources. These devices are appropriate for patio use, but the manufacturer's recommended number based upon square footage may need to be doubled in order to receive desirable results. They're inexpensive - $30 for a 2 week supply. At this price, they might be worth a try. As yet, studies on their comparative efficacy have not been reported in peer-reviewed journals. This technology is also offered in the Mosquito Deleto system marketed by Coleman and as an adjunct to the Sonic Web .

A number of studies are currently underway to provide insight into the comparative efficiency of many of these trapping devices. With the continual introduction of improved trapping models onto the consumer market, it's unlikely that this research will provide a definitive winner over the long term. Nonetheless, they should provide a snapshot of which systems capture more mosquitoes in head-to-head competition under identical conditions. The AMCA will post results of these studies on its web page when they become available.

Please be cautioned against putting too much faith in traps as your sole means of control. These traps represent an evolving technology that is a most welcome addition to our mosquito control armamentarium. Their potential is great, but shouldn't be overestimated. It is unclear whether the traps attract mosquitoes into an area where humans may then provide a stronger source of attraction. In other words, will the bug zapper results showing larger numbers of mosquitoes in yards with a zapper be repeated by the CO2 traps? Time will tell. It's highly unlikely that these devices, whatever their improvements, will ever fully supplant organized community-wide mosquito control programs, for there is no single silver bullet that will prove to be the ultimate answer to mosquito problems. Effective mosquito management requires integrating a variety of available control strategies i.e. surveillance, source reduction, biological control methods, traps, environmentally friendly larvicides, and, when necessary, application of public health adulticides, into a comprehensive program that exploits known mosquito vulnerabilities. They are the result of almost one hundred years of experience in making mosquito control in the United States the safest and most technically proficient in the world today.