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Life cycle of a mosquito showing female laying eggs (upper left), raft of eggs (upper left), larvae (lower Left), and pupae (lower right).

Managing Mosquitoes in Stormwater Treatment Devices

Section 2: Mosquitoes and Mosquito Control, Larviciding Versus Preventative Engineering

Published 2004

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Section 2: Mosquitoes and Mosquito Control

Mosquitoes are regarded as undesirable in both rural and urban areas throughout most of the United States. Not only is their biting activity a nuisance, mosquitoes also vector (transmit) pathogens that cause human and animal diseases. The recent threat of West Nile virus compounds concerns and reinforces the need for effective mosquito control.

There are approximately 3,000 species of mosquitoes worldwide (about 200 in the United States) and all require water to complete their life cycle. Mosquito control is most effective when directed at immature stages in standing water rather than at adults and is best conducted using a combination of techniques including biological, physical, chemical, and in states such as California, legal control (California Health & Safety Code [H&S Code], §§2060-2067, 100170, 100175). Biological control uses or enhances natural enemies of mosquitoes such as fish; physical control makes habitats less suitable for mosquito production; chemical control uses insecticides that target immatures or adults; and legal control can force uncooperative parties to eliminate breeding habitats on their property or face financial penalties.

Despite advances in mosquito management, the importance and need for careful preventative design and maintenance plans is paramount. This becomes apparent especially when faced with the limitations imposed by certain treatment BMPs as a result of their design, location, or accessibility. For example, underground treatment devices that hold permanent sources of water and produce mosquitoes are unlikely to support commonly used biological control agents, and physical controls such as exclusion (e.g., valves and covers) can be difficult to implement without affecting the devices’ intended function. In these situations, chemical treatment, and legal abatement in some states, are the only remaining options. Note that in this publication, "chemical treatment" refers to the use of registered pesticides to control the aquatic stages of mosquitoes (larvicides), including bacteria, hormone mimics, and oils.

Larviciding Versus Preventative Engineering

As more and more stormwater programs recognize the importance of integrating mosquito control into their lists of public health priorities, the dilemma of how to effectively manage mosquitoes in designs that favor mosquito breeding becomes obvious. Larvicide treatments are increasingly considered as long-term solutions for mosquito control in lieu of costly retrofits, replacements, or redesigns.

However, sole reliance on larvicides is not a long-term solution for preventing mosquito production. Every possible effort should be made to "design the bugs out" during preconstruction planning or via postconstruction retrofits to avoid creating a possible public health hazard. When all else fails, registered pesticides should be applied only by certified professionals due to the risk of establishing pesticide resistance in target organisms, as well as potential liability issues from misuse.

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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.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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