In this issue:

ECB and CEW Moth Flight Update

Comprehensive Review of Carbaryl (Sevin) Completed

Daily Crop "ET's" at their Peak

Use of Mosquito Trapping Devices on the Homefront

Use of Mosquito Trapping Devices to Control Mosquitoes on the Homefront

Mike Kaufman, Entomology, Michigan State University, E. Lansing, MI, reprinted with permission, Vegetable Crop Advisory Team Alert, MSU, (vol. 18), July 16, 2003

Editor's note: Many residents, in rural and urban areas, are interested in factual information about West Nile virus and mosquito control. Dr. Mike Kaufman is one of the scientists at MSU working in this area. With permission, we are reprinting this information of general interest to our Vegetable IPM readess.

With the onset of mosquito season and the ongoing concern about West Nile virus, Michigan residents have been deluged with a variety of mosquito "control" products. The manufacturers invariably claim that these products offer effective control for large areas and allow the safe, comfortable enjoyment of one's backyard, garden, or deck. Prominent among the advertisements this year are those for propane-driven adult mosquito traps that essentially attempt to mimic the cues given off by large mammals. These devices convert propane from typical gas grill-sized tanks into heat and carbon dioxide - two primary mosquito attractants. Attracted mosquitoes are then sucked into a trap and die. Some of the devices supplement the CO2 with octenol, another general attractant, and others use CO2 released from gas cylinders. The devices are relatively expensive, $200 to more than $1000, and represent a non-trivial investment for the homeowner along with the need to replenish propane, octenol, and CO2 cylinders.

Are these devices useful? Studies have shown that they do trap mosquitoes. Most evaluations have been conducted in large, screened-in rooms where a known number of mosquitoes are released and the percent trapped are evaluated. Some of the devices trapped over 70 percent of the mosquitoes in 24 hours. Field trials have also shown that the devices also capture many mosquitoes of various species. However, there is little evidence that they effectively reduce mosquito populations in the half acre to one acre area coverage claimed. As with most insect traps, it is possible that more mosquitoes would be drawn into one's backyard from surrounding areas, effectively nullifying the effect and purpose of the traps.

The effectiveness of these devices would depend upon placement (upwind) of the desired protection area, use of the device for several days prior to persons' use of the area, etc. It is also noteworthy that the effectiveness of the devices varies for different species of mosquito. The Culex species involved in West Nile virus transmission are not necessarily trapped with high efficiencies in these units.

We cannot yet recommend these devices for mosquito control. Although they show promise, it is unlikely they will achieve the blanket control often claimed. On the plus side, they are certainly better options than devices based upon electric fields, sound generators (one claims to mimic the sound of dragonflies to scare mosquitoes away), or the ubiquitous "bug-zappers." The former (electric or acoustic) are simply ineffective and the latter is almost completely useless in reducing mosquito populations and likely kills proportionately more beneficial insects. Another product that claims to lure mosquitoes into traps by simulating the sound and patterns of a mammal's heartbeat, is not based on our current understanding of how mosquitoes locate hosts. (i.e., There is no evidence that mosquitoes use heartbeat sounds to find an appropriate blood meal.)

Unfortunately, there is no single method that will allow the mosquito-free use of the outdoor areas on one's property. If the homeowner eliminates the standing water breeding sites of mosquitoes, some relief would be obtained. There are also several larvicide options that are extremely safe for humans and pets, and are "environmentally friendly" for instances where removal of breeding sites is illegal or impractical. These include formulations of Bacillus thuringiensis and Bacillus sphaericus, and the insect growth regulating hormone analog, methoprene. However, many mosquitoes can originate from remote breeding sites and where mosquito-borne disease is present, one may also have to deal with small but infected adult populations. Control of adults is best achieved through fog and spray application of insecticides that have some residual effects (e.g., malathion and synthetic pyrethroids). Application can be targeted to adult resting areas in vegetation surrounding lawns, tree foliage, etc. Adulticiding should be considered a "last resort" option because of the chances for over-application and because the insecticides do not specifically target mosquitoes.

Even with the exercise of the above control measures, one cannot eliminate the risk of diseases such as West Nile virus entirely. We also recommend that when engaging in outdoors activities when mosquitoes are active that individuals use proven repellents. The most effective of these are formulations that contain DEET. Other repellents (e.g., botanical oil-based) may be effective for shorter periods of time, so if they are your choice, be prepared to re-apply frequently. The use of citronella candles may offer some very limited and temporary protection in small areas, but is considered inadequate for disease risk reduction. (In one study the use of regular candles had nearly the same weak repellency effect as a citronella candle). The use of marigolds as a mosquito barrier is an even less effective option than citronella-based products.

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Production Editor: Suzanne Wold, Research Fellow, Department of Entomology, University of Minnesota, woldx018@tc.umn.edu

Last Revised July 23, 2003.
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