Nutrient Regeneration by Fly Larvae in Cattle Dung

Abstract

The effect of fly larvae on bacterial population growth in cow dung was studied. We measured bacterial density and NH'concentration in laboratory cultures of 0, 25, and 100 Orthellia caesarion larvae /50 g dung, and in dung pats in the field within aggregations of sarcophagid and muscid larvae. In the laboratory, larvae increased bacterial turnover and decreased bacterial numbers as larval density increased. In the field, larvae were associated with higher bacterial density, and larvae increased bacterial turnover when feeding at high density but not when feeding at low density. If increased bacterial turnover benefited individual larvae, it might be expected that pupal weights of larvae feeding at high density would be greater than those of larvae feeding at low density. Pupal weights, however, showed no increase in response to density, but simply declined as the density at which they were reared increased. We conclude that increases in bacterial turnover or density are too small relative to high bacterial biomass in dung to benefit individual larvae.