PERMEABILITY OF THE PERITROPHIC ENVELOPES OF HERBIVOROUS INSECTS TO DEXTRAN SULFATE - A TEST OF THE POLYANION EXCLUSION HYPOTHESIS

We tested the hypothesis that the permeability of the peritrophic enve lope in herbivorous insects is greatly reduced for polyanions as a res ult of an extensive network of anionic sites in the proteoglycans of t he matrix. C-14-Dextran sulfate (polyanionic, 8000 M(w)) and fluoresce in isothiocyanate-labeled (FITC) dextran (monoanionic, 9400 M(w)) were introduced together into the endoperitrophic space of the midguts of Orgyia leucostigma (Lepidoptera) larvae and Melanoplus sanguinipes (Or thoptera) adults. In all cases more of the C-14-dextran sulfate permea ted the peritrophic envelope than the FITC-dextran, the opposite of th e result predicted by the polyanion exclusion hypothesis. We conclude that polyanion exclusion is not a mechanism that contributes significa ntly to the permeability properties of the peritrophic envelopes of th ese two species, or that explains the failure of tannic acid to cross the peritrophic envelopes of lepidopteran larvae. (C) 1997 Elsevier Sc ience Ltd.