Impact of polyphenols on growth of the aquatic herbivore Acentria ephemerella

Larvae of Acentria ephemerella live fully submerged, feeding on submersed aquatic angiosperms such as pondweeds (Potamogeton spp.) and Myriophyllum spicatum. Only the latter contains high concentrations of hydrolyzable tannins known to interfere with the growth of insect herbivores. We tested whether larvae grow faster on Potamogeton perfoliatus or M. spicatum and whether this is due to polyphenols in their food source. Larvae originating from the same egg clutch grew faster and larger on P. perfoliatus than on M. spicatum. The same growth response was observed with larvae that spent winter diapause on either P. perfoliatus or M. spicatum. These larvae were fed either with their host plant or the other macrophyte. No prior feeding effect was found, but growth of larvae reared on M. spicatum was less than when grown on P. perfoliatus. Larvae from another egg-clutch reared on M. spicatum, either from lake or cultivated in aquaria, exhibited reduced growth on the lake plants. P. perfoliatus contained less than 1% and M. spicatum (aquarium or field material) between 5 and 9% phenolic compounds. No differences in nitrogen content of leaves were found, but apical shoot sections of M. spicatum exhibited a significantly higher nitrogen content than P. perfoliatus. Our results indicate that hydrolyzable tannins are responsible for the reduced growth of Acentria when fed with M. spicatum.