A Method for Rearing Large Numbers of Pond Midge Larvae, with Estimates of Productivity and Standing Crop

Abstract

A method for rearing large numbers of larval midges in plastic-lined ponds, with fertilization only, is presented. Estimates of standing crop and productivity of these midges are presented, along with comparative data on standing crop and productivity for other animals from the literature. To test the efficacy of harvesting floating plants for reversing eutrophy in lakes (Yount, 1964), we built a series of small ponds and fertilized them heavily. This fertilization made the ponds highly eutrophic. Within a few days, egg masses of midges were common and larval chironomids occurred in immense numbers on the pond bottoms. We suspended artificial larval substrates in these ponds, which enabled us to estimate not only the standing crop of larval midges but also their productivity. A number of articles report success with rearing pond midges, for example Branch (1923), Sadler (1935) (cf. Needham 1937), Buschkiel (1932; fide Huet, 1960: 85), Beerman (1952), Konstantinov (1961), Biever (1965) and others. These studies are aimed at raising midges for fish food or for special studies on midges, such as that of giant chromosomes, and require a sometimes complex feeding program as well as expensive concrete-lined ponds or laboratory control. In most cases these papers give no quantitative data. The method here described is inexpensive and requires no feeding beyond fertilization of the ponds, thus obviating complexity and reducing the cost and trouble of building the ponds. Data on both standing crop and productivity of the midges obtained by this method will be discussed. METHODS An area of about 10 m2 was dug to a depth of approximately 0.6 m and lined with two layers of 4 mil black polyethylene plastic. Black was chosen so that light would not destroy the plastic quickly as it does transparent polyethylene, and two layers were used to help prevent pinhole leaks from being a problem. The pond basin was