Is predation by sunfish (lepomis spp.) an important source of mortality for the eurasian watermilfoil biocontrol agent euhrychiopsis lecontei?

Abstract

The aquatic weevil Euhrychiopsis lecontei is a potential control agent for Eurasian watermilfoil (Myriophyllum spicatum). Predation by fishes may influence populations of this beneficial insect. To determine if fish predation is an important source of mortality for E. lecontei, fish stomachs from two Minnesota lakes, Lake Auburn and Cedar Lake, were sampled monthly during the summer of 1994. None of the black crappie (Pomoxis nigromaculatus) or yellow perch (Perca flavescens) stomachs from either lake contained E. lecontei. The frequency of occurrence of E. lecontei larvae and adults in sunfish (bluegill (Lepomis macrochirus) and pumpkinseed (Lepomis gibbosus)) stomachs from Lake Auburn ranged from 10.3% in September to 28.6% in August. The mean number of E. lecontei adults per sunfish stomach from Lake Auburn ranged from 0.18 ± 0.13 (± 2 S.E.) in May and July to 2.14 ± 2.90 in August. Larvae of E. lecontei were found only in stomachs collected in August (mean = 0.21 ± 0.31) and September (mean = 0.33 ± 0.41). Euhrychiopsis lecontei pupae were not found in fish stomachs from either lake. Euhrychiopsis lecontei was rarely represented in the diet of sunfish from Cedar Lake. Larvae and adults were found in sunfish stomachs from Cedar Lake only during September (3.7% of stomachs; mean = 0.037 ± 0.052 per stomach). Densities of E. lecontei were much higher in Lake Auburn than Cedar Lake, however, within lakes there was no correlation between E. lecontei density and either mean number or percent occurrence in sunfish stomachs. These data suggest that sunfish predation may be important and that with low E. lecontei population densities and high sunfish densities, E. lecontei populations could be limited by sunfish predation. © 1997, Copyright Taylor & Francis Group, LLC.