Selective feeding on green bean Phaseolus vulgaris by Heliothis zea

Abstract

First and early second instar Heliothis zea larvae, feeding on the green bean Phaseolus vulgaris, fed preferentially on the leaf. The leaf feeding tendency decreased after about 12 h in the second instar. Third, fourth and fifth instar larvae fed preferentially on bean pod. Leaf-fed last instar larvae had lowered growth rate and weight gain, due largely to a lower rate of feeding rather than an inability to utilize leaves efficiently for growth.

Overall utilization efficiencies did not differ between last instar larvae fed seeds or a mix of seeds and pulp. Larvae fed either seeds or a mix ate significantly less and completed the instar in a significantly shorter time than larvae fed only on pulp. Seed-fed larvae, however, ate significantly less and had a higher ECD than larvae that either fed on the mix or pulp alone. Pulp contained about 93-95% water as compared to the 84-86% water content of seeds. Pulp-feeding larvae increased their fresh weight RCR to about 2.9 times that of seed-fed larvae and about 1.8 times that of mix-fed larvae by increasing the time spent feeding and decreasing the interfeed gaps. (Abstract shortened with permission of author.)