High abundance of herbivorous Lepidoptera larvae (Acentria ephemerella Denis and Schiffermüller) on submersed macrophytes in Lake Constance(Germany)

Abstract

Seasonal changes in the abundance of the herbivorous moth larvae Acentria ephemere/la on submersed macrophytes in Lake Constance were studied between 1998 and 2000. Acentria were found feeding on many pondweeds (Potamogeton lucens, P. pectinatus, P. perfoliatus), Ceratophyllum demersum and Myriophyllum spicatum, but not on Chara spp., Najas marina ssp. intermedia or Elodea nuttallii. During the vegetated periods of 1998 and 2000 the abundance of larvae on P. perfoliatus and M. spicatum increased exponentially from approx. 10 ind./m2 to a maximum of 10,000 ind./m2 or 20-165 ind./g dm. The much lower abundance in 1999 may be a result of the massive flooding of the lake in spring. Our data suggest that at least part of the Acentria population in Lake Constance may have two generations per year. Larvae use predominantly the upper shoot sections during the active feeding period and move to the lower stern sections for winter diapause. Herbivory caused substantial damage especially to the apical meristems of P. perfoliatus and M. spicatum. This study indicates that aquatic shredder-herbivores may have astronger impact on submersed macrophytes than previously considered.