Slug/Shallow wetlands key for mosquito control

by Dr. Roman Jesien (Jesien is the science coordinator for the Maryland Coastal Bays Program.)

Over the past few months tons of misinformation has been exchanged regarding the types of wetlands which are good for mosquito larvae production and which are not. To clarify these issues it should be made clear that the types of wetlands used for stormwater management, wildlife, and water quality are an integral part of the equation and that aerial adulticide mosquito spraying is self-perpetuating.

First, shallow wetlands, which are used in the newer stormwater management ponds and which are being created for wildlife and water quality by entities like the State Highway Administration, Maryland Department of the Environment and Natural Resources Conservation Service, are much better for controlling mosquitoes than deeper ponds.

Laypeople often think of fish as consummate larvae eaters. This is true but they pale in comparison to their insect and amphibian counterparts which crush mosquito larvae in healthy, shallower wetlands. Deeper stormwater management ponds are not only mosquito breeders, they do not dry up in summer like most shallow wetlands. They have poor habitat for predatory insects and amphibians (fish eat amphibian eggs and mosquito-eating insects), and they provide a direct conduit for nutrients and chemicals into groundwater.

On the other hand, shallow wetlands give sanctuary to frogs, salamanders, dragonflies, damselflies, diving beetles, water striders, and backskimmers - all of which are mosquito-guzzling machines. They are also native species unlike most fish placed in ponds. The majority of West Nile-carrying mosquitoes are breeding in urban areas with old or no stormwater management. These Culex mosquitoes typically breed in small bodies of water that are exposed to direct sunlight. These include puddles in asphalt, old tires, flower pots, dirt roads or anywhere without vegetation or predators.

Furthermore, spraying expensive pesticides has unwittingly killed the amphibians and insects that eat mosquitoes thereby rendering the need for chemical spray self-perpetuating. Aerial mosquito spray kills insects that fly. It does not discriminate. A new crop of mosquitoes can emerge every 7-14 days but it takes a year to replace many of their predators.

Already mosquito-ridden states like Georgia and Florida have abandoned comprehensive state spraying programs in exchange for creating proper wetlands and educating the public. It’s time we caught up to the curve.

Study after study demonstrates that restoring impacted wetlands to their natural state is a boon for mosquito control. Shallow, forested wetlands also serve as the primary means to recharge groundwater and clean runoff before it enters the bays so this effort can have a dual function.

Thus an alternative control method, with several long-term benefits, is to preserve and restore natural wetlands with adequate mosquito bionomics in mind. The advantages are twofold. By providing proper habitat for natural enemies, restored wetlands retain their functions, hold water longer, and allow for native vegetated communities which support amphibians and predatory insects.

Wetlands also control flooding which induces widespread mosquito outbreaks when water gets to places it shouldn’t be and simply sits there. We should also step up enforcement of those illegally filling natural wetlands because when the water can’t run to natural areas, the unnatural places it sits becomes a breeding colony.

The move to cease building deeper wetlands, to restore natural, shallow wetlands and to phase out chemical controls must continue moving forward.

Dr. Bill Grogan, an entomologist at Salisbury State University, also contributed to this article.