The protective role of the peritrophic membrane in the tannin-tolerant larvae of Orgyia leucostigma (Lepidoptera)

Abstract

Tannic acid had no detrimental effect on the growth rates or digestion efficiencies of Orgyia leucostigma larvae. We examined three potential mechanisms which might allow these larvae to tolerate ingested tannic acid. (1) Little chemical modification of ingested tannic acid was found. Less than 10% of the tannic acid ingested by O. leucostigma was hydrolysed to gallic acid when measured with the rhodanine assay, and virtually all tannic acid was recovered in the frass when measured as total phenolics or with HPLC. (2) Peritrophic membranes were freely permeable to gallic acid but were impermeable to the higher molecular weight polyphenolic components of tannic acid. (3) Peritrophic membranes adsorbed less than 1% of the amount of tannic acid present in the guts of O. leucostigma larvae in vivo. Therefore, adsorption is not the means by which tannins are contained within the endoperitrophic space in O. leucostigma. We conclude that the peritrophic membrane acts as an ultrafilter. Further work is needed to determine whether ultrafiltration is dependent on tannin-binding substances in the gut fluid.