Comparative analysis of methods for measurements of food intake and utilization using the soybean looper, Pseudoplusia includens and artificial media

An analysis of intake and utilization of an artificial medium by larvae of the soybean looper, Pseudoplusia includens Walker, Lepidoptera: Noctuidae, was performed using 4 methods: standard gravimetric, chromic oxide, Calco Oil Red, and ¹⁴C-glucose. Each method was used in conjunction with standard gravimetry. The relative merits of the indirect methods were analyzed in terms of precision and accuracy for ECI and ECD estimation, cost, and overall versatility. Only the gravimetric method combined ca. 80% precision in ECI and ECD estimation with low cost and maximum versatility. Calco Oil Red at 0.1% w/v was detrimental to the larvae. Cr₂O₃ caused reduced intake but conversion was increased resulting in normal development and growth of larvae. The radioisotopic method had the advantage of providing a direct means of measuring expired CO₂. The need to operate under a totally enclosed system, however, poses some serious difficulties in the use of radioisotopes. There seems to be little advantage in any of the proposed indirect methods, except if there are unusual difficulties in separating the excreta from the medium.Supported in part by the Brazilian Programa de Ensino Agricola Superior (PEAS/Michigan State University Contract); by NSF and EPA through grant (NSF GB-37418) to the University of California; and USDA-SEA grant 616-15-68. The findings and opinions expressed herein are those of the authors and not necessarily those of the sponsoring agencies or institutions.