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How to Determine Mosquito Larval Densities

Mosquitoes breed in multiple habitat types. Storm drains, tires, and other areas containing standing water often contain mosquito larvae. Permanent water bodies such as lakes and ponds will have mosquito larvae in shallow areas near the edges. These types can be assigned into two major larval habitat categories: standing water (transient and permanent) and floodwater (including natural and artificial containers). In order to determine mosquito larval densities, they need to be sampled. The larvae can be collected with dippers, nets, aquatic light traps, and other methods. A commonly used technique is the shallow skim using a dipper.

Things You'll Need

Rubber boots
White 400 ml-capacity dipper
White enamel or plastic pan
Pencil
Waterproof paper

Instructions

Larval sampling techniques
- 1
  Locate the water bodies in your sampling area with larvae present. This will identify the optimal sampling spots.
- 2
  Walk slowly to the edge of the water body (with your boots on) and plunge the dipper under the surface of the water. The shallow skim consists of submerging the leading edge of the dipper, tipped about 45 degrees, about an inch below the surface of the water and quickly moving the dipper along a straight line.
- 3
  Scoop up a full dipper of water but stop before the dipper overflows. Empty the contents of the dipper into the pan.
- 4
  Count the number of larvae in the pan. Write it down. Repeat the process around the site. Sampling routines are often repeated at least 10 times.
- 5
  Calculate larval density by the number of larvae per dip. You could also calculate the larval densities by using this calculation, BI = TLP/ND x BP, where:
  
  BI = the breeding index
  
  TLP = the total number of larvae and pupae taken
  
  ND = the number of dips
  
  BP = the number of breeding places
  
  A "breeding place" is defined as each station within a site from which one to three positive dips are obtained.

Insects & Science