Rates of feeding and assimilation in the grasshopper Poecilocerus pictus

Abstract

Food consumption of Poecilocerus pictus from hatching to death averaged 101 and 61 g wet leaves of Calotropis gigantea for females and males respectively; 37 and 50 per cent respectively of the total food intake was eaten during the hopper period (160 days). Feeding rate was highest (females: 662 and males: 904 mg/g per day) during the second instar in either sex. Regressions obtained for feeding rate-body weight relations indicate that per mg increase in body weight, feeding rate decreased three times faster in males than in females. The assimilation rate also decreased from about 300 mg/g per day during the first instar to about 9 mg/g per day during the last fortnight of adult life in both sexes. Per mg increase in body weight, assimilation rate decreased 2·5 times faster in males than in females. The relatively faster decreases in the rates of feeding and assimilation in males are correlated with the maximum weight attained (2·6 g); females attain 5·0 g in a similar life span (about 265 days at 26°C). For the sake of comparison, regressions were calculated for feeding and assimilation rates-body weight relations in insects for which data are available. The significance of feeding level (a) and weight exponent (b) obtained for Oxya velox, Schistocerca gregaria, and Bombyx mori are discussed. The incomparably high feeding and assimilation rates exhibited by the fifth instar individuals of B. mori are correlated with the accumulation of food energy to meet the energy demands of metabolic processes of the subsequent non-feeding pupal and adult stages, and to synthesize the cocoon.