COMPARATIVE CONSUMPTION AND UTILIZATION OF FLORIDA BEGGARWEED AND TWO SOYBEAN GENOTYPES BY PSEUDOPLUSIA INCLUDENS LARVAE (LEPIDOPTERA: NOCTUIDAE)

Larvae of the soybean looper (SBL), Pseudoplusia includens (Walker), were reared on three food types: soybean, Glycine max (L.) Merrill, genotypes ‘Kirby’ (insect susceptible) and GatIR 81-296 (insect resistant), and Florida beggarweed, (Desmodium tortuosum (Swartz) de Candolle. Larval development was longest on GatIR 81-296 (16.7 days) followed by beggarweed (15.5 days) and Kirby (14.1 days). Total consumption and relative consumption rate by ultimate (6th) instar SBL were significantly greatest on Kirby with no difference noted in consumption between GatIR 81-296 and beggarweed. However, approximate digestibility and efficiency of conversion of ingested food by ultimate instars were significantly greatest on beggarweed compared with the two soybean genotypes. Ultimate instar weight gain and growth rate were similar for larvae restricted to Kirby and beggarweed, while larvae restricted to GatIR 81-296 had significantly reduced weight gain and growth rate. Pupal weights of individuals reared on GatIR 81-296 also were significantly reduced compared with those in the Kirby and beggarweed treatments. SBL larvae consumed less beggarweed foliage (mg dry weight) than Kirby soybean, yet compensated to some extent by utilizing beggarweed foliage more efficiently. Beggarweed proved to be a better source of larval nutrition for SBL than the insect-resistant soybean genotype GatIR 81-296.