Information about mosquito traps and how they work

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A PRIMER ON MOSQUITO TRAPS

As mosquito season gathers momentum, an enormous amount of consumer interest continues to be generated by the marketing of new devices designed to attract, trap, and kill
mosquitoes. The general idea behind these devices is to reduce the number of questing
mosquitoes. Many products, by extension, claim to significantly reduce or even
collapse the local mosquito populations by decreasing the number of egg-laying females.

The power supplies for each type of trap varies. Some traps are totally self-contained,
utilizing propane to provide both power and a source of carbon dioxide as an attractant.
The advantage of these units is portability. This allows the unit to be placed
at a considerable distance away from home-sites, allowing mosquitoes to be intercepted
long before they come into the vicinity of human activity. On large properties,
those over an acre in area, this may be an important consideration. This portability
comes at a price. Thermoelectric generators that use excess heat from combustion
to generate electricity that run the intake fans are quite expensive. Some 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 are.

All of these traps utilize some form of attractant to lure the host-seeking female
mosquitoes into a capture or killing device. In some cases, mosquitoes are captured
by an impellor fan that draws them into a net, where they desiccate. Other trapping
systems use a sticky surface to which the mosquitoes adhere when they land. While
others utilize an electric grid to electrocute mosquitoes drawn into contact. These
are not set-and-forget devices - each requires some level of maintenance. The 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 the common theme of mimicking mammalian
exhalations, scents, and body heat to provide host cues for questing female mosquitoes.
The vast majority of these traps use carbon dioxide, produced either through the
combustion of propane or via CO2 cylinder and released at between 350m and 500 ml/min.
The plume of CO2 produced mimics human exhalation and makes these traps specific
for capturing blood-feeding insects. 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.
The 1-Octen-3-ol is slow-released at a rate of ca. 0.5 mg/h. A fascinating means
of attracting mosquitoes to their death is that used by the Sonic Web tm. This
device lures the mosquitoes through a combination of 1-Octen-3-ol and a sound pulse
mimicking a human heartbeat.

A mosquitoes process of questing for a blood meal involves a complex, interconnected
cascade of behaviors. Each step of this process probably having its own cues, rather
they are visual, thermal, or olfactory. There are 176 species of mosquitoes currently
recognized in the United States. The complexities of the questing behaviors noted
by certain species of mosquitoes during different times, may account for the bewildering
variations in trapping effectiveness. There is some subjective evidence that baited
traps, indeed, capture more females of some species than others, depending on the
concentration of carbon dioxide emitted and the season when they are used. There
may also be seasonal and circadian variables that affect 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 others 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 emphasize 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 maybe somewhat overstated, in most
cases based upon best case extrapolations from captures of released mosquitoes made
inside screened enclosures. Due to confounding variables largely beyond the control
of the researcher, it would be very difficult for manufacturers to conduct controlled
studies yielding reliable, statistically significant data with natural occurring
mosquito populations. In fact, Mosquito Control Districts using different types
of traps in survey operations often experience large variations between mosquito
trap counts, due to location, trap height, and time of season.

These devices will trap and kill measurable numbers of mosquitoes. Whether this
produces, a noticeable reduction in the mosquito population in your area depends
upon a number of factors. The absolute mosquito population size and species present,
plus the proximity, size and type of breeding habitat-producing re-infestation,
wind velocity, and direction, among other things all factor into how well a device
will work. Depending upon their placement, wind direction, and trapping efficiency,
traps may actually draw more mosquitoes into your area than they can possibly catch.
Consequently, the homeowner will still have to use repellents and practice source
reduction methods in order to achieve any measure of relief.

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 more effective. These masking 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 apparently masks human
odors to mosquitoes. Thus, female mosquitoes do not recognize humans within the
area as food sources. These devices are appropriate for patio and small area use.
However, the manufacturers recommended number based upon square footage may need
to be doubled in order to receive desirable results.

Studies are currently underway to provide insight into the relative effectiveness
of many of these trapping devices currently on the market. The continual introduction
of improved trapping models onto the consumer market makes it unlikely that this
research will provide a definitive winner. Nonetheless, these studies 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. Traps represent an evolving technology that is a most welcome addition
to our mosquito control arsenal. Its highly unlikely that these devices, will
ever fully replace organized community-wide mosquito control programs. There is
no single solution to the mosquito problem. Effective mosquito management requires
integrating a variety of available control strategies. These must include, but
are not limited to surveillance, source reduction, biological control methods, traps,
environmentally friendly larvicides, and, when necessary, application of public
health pesticides.