Dry-matter budgets for Diacrisia casignetum larvae fed on sunflower leaves

Larvae of Diacrisia casignetum Kollar were reared in groups of 100, 50 and 10 on fresh sunflower leaves at 27 ± 1°C temperature, 75 ± 5% r.h. and 12 h light each day. Rates of feeding, excretion and weight gain increased with age of the larva and were greatest in the sixth instar. Differences in these rates attributable to density were statistically heterogeneous (P < 0.001) whereas, of those attributable to instar, the weight gain was significant (P < 0.10). The second-instar larvae had highest levels of protein and carbohydrates in the body tissues; and the sixth-instar larvae had, the least. The pattern of protein assimilation in various instars was similar to that of glycogen except that proportional differences in the latter were pronounced in fifth and sixth instars. Consumption index, growth rate and approximate digestibility were high in the early instars whereas efficiencies of conversion of ingested and digested food were high in advanced instars. Food utilization, as reflected by efficiency of conversion of ingested and digested values in advanced instars, indicated the amount needed for maintenance decreased and more energy was left for growth and reproduction.