Life History and Ecology of Plagithmysus bilineatus,1 an Endemic Hawaiian Borer Associated with Ohia Lehua (Myrtaceae)2

Abstract

Host selection-oviposition by Plagithmysus bilineatus Sharp on its single host, Metrosideros collina (Forst.) Gray polymorpha (Gaud.) Rock, was a response to damaged or stressed hosts. Larval survival was not significantly higher in stressed hosts, but the number of galleries per host increased as the vigor (crown foliage condition) of the host decreased. Of 34 larvae implanted in healthy hosts, only four completed development; however, initial decline symptoms in these hosts did not appear until 10 to 22 months after adult emergence. Artificially girdled trees were monitored for 3 years, by which time four girdled trees had died, three being heavily attacked by P. bilineatus and one by ambrosia beetles. Harley diet with Bacto-Peptone supplement was tested as a culture medium for P. bilineatus larvae, with moderate (66%) success. The ecological functions of P. bilineatus were considered relative to the extensive decline of hosts in rain forests on the island of Hawaii.