Use of Eelgrass, Zostera marina, Wrack by Three Species of Ladybird Beetles (Coleoptera: Coccinellidae) in Prince Edward Island

Résumé

Large numbers of the introduced ladybird beetle, Coccinella septempunctata L., were present at Wood Islands and Green Point, Prince Edward Island, in wrack consisting primarily of Zostera marina L. (Eelgrass). The wrack occurred in a 0.5 to 1.0 m band parallel to the shore, and was from five to 25 cm thick. The other ladybirds, Propylea quatuordecimpunctata (L.), an introduced coccinellid also found in high numbers, and an individual of the native Hippodamia tredecimpunctata (Say) were found only at Wood Islands. At both sites the ladybird beetles occurred in the mid-intertidal zone along at least 100 m of shoreline, and were absent to rare on the terrestrial vegetation above the high tide mark. At four of the other eight sites surveyed, occasional individuals were present in the wrack, but they were no more abundant than could be observed on landward vegetation. Mean densities of C. septempunctata at the two primary sites were 52 m^-2 (Green Point) and 410 m^-2 (Wood Islands).