Nutritional Indices and Excretion of Gossypol by Alabama argillacea (Hübner) and Heliothis virescens (F.) (Lepidoptera: Noctuidae) Fed Glanded and Glandless Cotyledonary Cotton Leaves

Abstract

Ingestion and excretion of cotton pigment gland chemicals (primarily gossypol) were studied to determine the mechanism by which a specialist feeder avoids growth inhibition commonly exhibited by generalist feeders of cotton. Nutritional indices of fourth and fifth-instar cotton leafworm, Alabama argillacea (Hubner), a specialist, and tobacco budworm, Heliothis virescens (F.), a generalist, were compared by feeding glanded and glandless cotyledonary cotton leaves to both species. Relative growth rate (RGR) and efficiency of conversion of ingested food to body weight (ECI) of A. argillacea were not significantly different, but the relative consumption index (RCI) was lower for larvae fed glanded than for larvae fed glandless cotyledons. In contrast, the RGR and the ECI were ca. 50% less for H. virescens fed glanded cotyledons compared with those fed glandless cotyledons. However, RCI was not significantly changed. Excretion of ingested gossypol by larvae fed glanded cotyledons during the last two instars was 71 and 83% for A. argillacea and 45 and 69% for H. virescens. Both species ingested gossypol primarily in the free form and excreted it primarily in the bound form. We conclude that growth inhibition is due to reduced food conversion efficiency, and ECI for the two species seems to be positively related to the ability to excrete, rather than metabolize, gossypol.