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The hole in this street utility cover is large enough for mosquitoes to pass through.

Managing Mosquitoes in Stormwater Treatment Devices

Section 4: Mosquito Suppression Through Design and Maintenance

Published 2004

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Section 4: Mosquito Suppression Through Design and Maintenance

The majority of treatment BMPs operate as "passive" systems, meaning that they do not require active operational control or adjustment beyond routine maintenance. As a result, most installations remain unsupervised for extended periods, and if conditions are favorable, mosquito breeding could occur unobserved and uncontrolled.

Conscientious planning that emphasizes mosquito habitat reduction or elimination in both design and maintenance plans can prevent these problems (Metzger et al. 2002; O'Carroll 1978; Schimmenti 1979). Minimizing the mosquito production potential of treatment BMPs requires that standing water not be available for sufficient time to permit emergence of adult mosquitoes. This can be achieved in one of three ways:

  • Rapid discharge of all captured water.
  • Denying mosquitoes access to standing water (e.g., tight-fitting covers).
  • Making the habitat less suitable for breeding (e.g., vegetation management, mosquitofish).

Mosquito development from egg to adult varies by species and is influenced primarily by temperature and food availability. Certain species can complete the aquatic stages of development and emerge as adults in less than 1 week under ideal conditions. Because of this, a 72-hour maximum residence time for captured water in treatment BMPs is recommended in California and elsewhere as a conservative safeguard to prevent emergence of adult mosquitoes (Florida Coordinating Council on Mosquito Control 1998; Metzger et al. 2003; Santana et al. 1994).

In reality, many treatment BMPs hold water for over 72 hours, sometimes due to their outdated designs, and more recently in order to meet stringent effluent water quality requirements. To ensure that public health and safety is maintained, the following suggestions should be considered for any structure that holds water for over 72 hours.

  • Select or design an alternative (or modified) device that provides adequate constituent removal and complete drainage in 72 hours. This is the most reliable and cost-effective choice.
  • Contact state or local public health or vector control agencies to determine whether local mosquito species and local factors (e.g., high elevation) may preclude rapid mosquito emergence, thus safely allowing water residence times to exceed 72 hours. In some areas this may require a detailed study that should be funded by the soliciting party.
  • Provide adequate funds necessary to support routine mosquito monitoring and control.

Possibly the most overlooked aspect of treatment BMP implementation is the long-term commitment of funds necessary for proper maintenance of structures. Routine and timely maintenance is critical for suppressing mosquito breeding as well as for meeting local water quality goals. If maintenance is neglected or inappropriate for a given site, even structures designed to be the least "mosquito friendly" may become significant breeding sites.

Table 2 lists conditions that may increase the probability of breeding mosquitoes over time in various treatment BMPs. Maintenance guidelines for individual BMPs are often site-specific and are beyond the scope of this publication.

Table 2. Postconstruction conditions that may increase the probability of mosquito production in treatment BMPs.
  • Clogging (e.g., effluent pipes, media filters, infiltration basins)
  • Establishment of invasive or exotic vegetation
  • Groundwater fluctuations
  • Nonstormwater runoff (i.e., increases in runoff frequency, residence time, and/or volume)
  • Scouring and erosion
  • Structural damage (e.g., shifting or settling, roots)
  • Trash and sediment accumulation (e.g., formation of pools, clogging, redirected water flows)
  • Vandalism
  • Vegetation overgrowth

Note: This list may be incomplete. Other conditions favorable to mosquito production may become apparent as structures age.
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[UC Peer Reviewed]

Managing Mosquitoes in Stormwater Treatment Devices, UC ANR Publication 8125
Marco E. Metzger, Vector-Borne Disease Section, California Department of Health Services, Sacramento

Copyright © 2004 The Regents of the University of California, Division of Agriculture and Natural Resources. All rights reserved.


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