Mosquito Control (Historical Methods)

 
  Every year the mild weather of Spring and Summer brought renewed productivity to the salt marshes, and unfortunately it also brought a slew of biting insects that hatched from within the marshes. Many of the local citizens that settled around New England regarded the marshes as breeding grounds for unwanted pests and demanded action be taken to control the insect populations, specifically the mosquitoes. They believed that the abandonment of lands and the depreciation of property values all along the coast could be contributed to the presence of these pests. This reasoning was used to push for control methods that resulted in marshes being ditched, sprayed, used as dumps, and filled for development (Hawes 1986).


 

This color infrared photo showing mosquito ditches in Belle Isle Marsh is courtesy of the Massachusetts Department of Environmental Protection: Wetands Conservancy Program (#5-31  4/19/90,  1:12,000 scale). The photo was taken at low tide during the winter season. The marsh is represented by the tan areas. The straight lines cutting through the marsh are mosquito ditches.
 
 
 

  In the early 1900’s mosquito control commissions were formed. Initially mosquito control involved ditching the high marsh to inhibit the success of insect larvae. Grids of ditches were created to drain all standing water from the high marsh. Unfortunately this procedure was not very effective towards controlling mosquitoes; in fact in many cases insect populations actually increased. The method was highly effective, however, in reducing populations of many desirable marsh organisms including birds and fish that were attracted to and relied on the presence of marsh pans or pools, especially at low tide (Teal & Teal 1969). Even so, ditching had been the control method of choice until relatively recent years.

  A less common method of mosquito control involved diking the marsh. The methodology was similar to that used in marsh reclamation, however, instead of preventing water from entering the diked area, water from nearby estuaries was pumped in to maintain a constant water-level. This was believed to inhibit mosquito success since the marsh mosquito lays its eggs just above the water level and relies on the tides to get them wet (Teal & Teal 1969). The constant presence of water from diking, however, was also detrimental to the marsh since the salt marsh hay and cord grasses were unable to survive continuous submersion.

  Although ditching and diking were preferred to the spraying of insecticides, both methods of control significantly alter the natural biology of the marsh and create habitat that is unsuitable for the natural wildlife. Additionally, these methods may create areas with reduced salinity thereby allowing less salt tolerant species to invade the salt marsh (Teal & Teal 1969).

 


New Methods for Mosquito Control
 
Over the last decade or so the Northeast Massachusetts Mosquito Control and Wetland Management District has implemented improved methods for mosquito control in coastal marshes. The new strategy for mosquito control combines short and long term methods. Short term methods used generally involve using biological controls such as spraying marshes with bacteria that targets mosquito larvae by infecting their gut and causing them to die. The down side to this method is that the bacteria used are not completely species specific and may infect nearby flies.
 

For long-term control Northeast Massachusetts Mosquito Control and Wetland Management District uses open marsh water management. Rather than dig ditches, control agencies are slowly filling in old ditches while creating or restoring natural shallow marsh ponds and pans similar to those naturally created in healthy salt marshes. These pans allow water to remain in the higher areas of the marsh even at low tides thus allowing fish to remain within the pools; these fish are potent predators on mosquito larvae. Additionally, many birds are attracted to the pools and they too will eat the mosquito larvae. By restoring the salt pans, the mosquito control district is also helping to restore the bird and wildlife habitats that ditching had destroyed. So far these ecologically based strategies have proven to be about 97% effective in controlling mosquito populations (personal communication with Jim MacDougall) and the Mosquito Control commissions are expecting this success rate to increase. Furthermore, salt pans require less maintenance effort than ditches since the normal disturbance regime of natural salt marshes regularly forms these pans and ponds.
 

This page was created by: Wendy Dalia
Last update: 5/26/98
Please note this page is under construction.

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