[Mosquito Control] Storm Water Management & Mosquitoes

Have you ever wondered where all the water goes when it rains “cats and dogs”? Have you ever watched the water pile up along the street of your neighborhood during and after a severe rainstorm? Storm water runoff is something that most of us don’t think about very often, but it is this very phenomenon that is a lead contributing factor to one of the most challenging and potentially dangerous pest problems in the urban environment: mosquitoes.
Unlike many of the other “nuisance” pests pest control professionals are dealing with, mosquitoes are more of a concern today than ever due to the potentially harmful diseases they can carry and transmit to humans. We are all familiar with the most recent of these “bugs”: West Nile virus (WNV), and with the sickness and death that this pathogen has caused in many parts of the United States over the last five years.
Government pressure to achieve increasingly higher levels of pollution abatement has led to a large industry that has developed literally hundreds of different designs of storm water treatment devices (Metzger et. al. 2002, Chanda and Shisler 1980). While these treatment devices are designed to maximize the capture and removal of pollutants from storm water, they unintentionally provide habitats suitable for mosquito breeding.
Public health is always a major component of storm water management, but the focus is often on waterborne pathogens while mosquito control can sometimes be overlooked (Metzger, 2004). Controlling mosquito populations in these situations is often beyond the reach of the individual PCO from the standpoint of being a first responder. Local and state government agencies are responsible for effecting control measures in community wide spaces. Control measures typically consist of area-wide spraying or treating water with larvicides, and they are usually scheduled based on complaints and notices filed by home- and landowners. These notices are best filed through the local mosquito abatement authorities.

DO OPPORTUNITIES AWAIT? PCOs may be able to involve themselves in this line of work by being contracted by local mosquito abatement agencies to make the actual insecticide applications. PCOs can, however, do their part “up-stream” by educating consumers of the importance of physical, cultural and chemical control practices in their own backyards. While homeowners may not be able to affect what takes place in a storm water retention pond just a block away from their house, they certainly can take steps to ensure that mosquito breeding sites in their own areas of influence are removed. Additionally, PCOs can provide up-to-date handouts on how to file a formal mosquito complaint in their community. While this doesn’t necessarily get you a direct application job, it certainly adds to your professional appearance, expertise and customer satisfaction.
Of course, mosquitoes require water to complete their life cycle. What kinds of waters breed mosquitoes? Natural wetlands such as salt marshes, freshwater marshes, forested swamps, woodland pools and coastal plain ponds almost always make for outstanding mosquito breeding habitats. Degraded wetlands (such as those with altered hydrology, excessive sedimentation, wetland filling or pollution runoff) in both urban and rural settings can also be great breeding habitats. And human-constructed wetlands such as storm water management basins (SWMBs), constructed mitigation wetlands (e.g., highway compensation projects), and even discarded containers can create “micro-wetlands” in the urban environment. In short, almost any kind of water source can support mosquito breeding, however some are worse than others.

CONTROL OPTIONS. In reference to mosquito control, it is vitally important to eliminate sources of standing water in our yards and environment in such areas as bird baths, clogged gutters, old tires, children’s toys, and discarded trash, as these can all provide breeding opportunities for certain female mosquitoes. Basically, any object that is capable of holding even a small amount of water (say, the cap of a 16-ounce soda bottle) can serve as an oviposition site for a female mosquito. This is why storm water management poses such a huge effort with local mosquito control programs. There is an almost endless supply of breeding sites for mosquitoes in certain urban areas. Not all SWMBs pose a problem as far as mosquito breeding is concerned, however the reality is that most of them do. Utilizing best practices to identify which areas are problematic and then targeting efforts at these “hot spots” are the keys to efficient mosquito management.
There are a variety of ways that storm water mosquito issues can be addressed. Natural larval predators, such as dragonfly nymphs (aquatic hunters), water boatmen, backswimmers, water striders and predacious diving beetles, as well as salamander larvae and small fish (Gambusia spp.) all feed on mosquito larvae. Additionally, dragonflies, purple martins, swallow and other birds as well as bats are key contributors to feeding on adult mosquitoes.
Unfortunately, whether you are dealing with natural “healthy” wetlands, degraded wetlands or man-made wetlands, mosquito populations are almost sure to out-perform these natural predators. In almost every case, natural predators simply do not stack up to the demand for mosquito control in the urban environment. As is the case with many pest problems, the principles of IPM come into play to effectively mitigate storm water mosquito populations.
Surveillance and monitoring are two key principles to this effort. Remember that not all bodies of water pose a threat.
Source reduction is generally preferred.  Water sanitation for resident and business structures is a must. Storm water management basins should include at least the following:  sound engineering design, water and vegetation management practices, good maintenance practices, biological control such as Gambusia spp. stocking (if applicable), and implementation of chemical controls — both larvicides and adulticides.
In attacking these often large structures, the most effective control method is to target the larval or immature stage of the mosquito; however, in some cases adulticides may also be implemented, oftentimes as a last resort. Larvicides are preferred to treat the actual breeding habitat, as they result in more localized applications and less exposure to non-targets. Commonly used compounds  include B.t.i., methoprene and sumithrin. Adulticide applications can be made using methods such as thermal fogs, mist sprayers, cold aerosol in ULV ground equipment and aerial spraying. Common AIs for these jobs include naled, resmethrin, sumithrin, pyrethrum, pyrethrins, cyfluthrin and deltamethrin. Active choice depends on the application method.

CONCLUSION. The best solution to managing mosquito populations in storm water structures lies in fostering multi-disciplinary cooperation among storm water professionals, municipal planners, public health officials and vector control agencies. A proactive, rather than reactive, approach can save money, time and effort, and can ultimately ensure the public’s health (Metzger, 2004). Pest management professionals can do their part by educating their clients about mosquito behavior and biology and the benefits of keeping their backyards and private property free of unnecessary mosquito breeding habitats.

The author is a senior research scientist at SC Johnson & Son Inc., Racine, Wis., in the Pest Control Division of the company’s Worldwide Consumer Products Business.

References
Chanda, D. A. and J. K. Shisler. 1980. Mosquito control problems associated with storm water control facilities. Proceedings of the New Jersey Mosquito Control Association 67: 193-200.
Merideth, W., T. Moran, D. Callaway, and K. Conaway. 2005. Mosquito production issues in stormwater management basins (SWMBs)  http://www.epa.gov/maia/pdf/SWMMeredith.pdf
Metzger, M. E., D. F. Messer, C. L. Beitia, C. M. Myers, and V. L. Dramer. 2002. The dark side of storm water runoff management. Disease vectors associated with structural BMP’s. Stormwater. 3(2): 24-39.
Metzger, M. E.  2004.  Managing mosquitoes in storm water treatment devices. Publication 8125.  University of California, Division of Agriculture and Natural Resources. http://anrcatalog.ucdavis.edu