Overwintering sites of Chrysophtharta bimaculata (Olivier) (Coleoptera: Chrysomelidae) in commercially managed Eucalyptus obliqua forests

Chrysophtharta bimaculata is a serious pest of eucalypt forests in Tasmania. The beetle overwinters as a diapausing adult, but it is poorly documented whether it forms overwintering aggregations or where it shelters. During winter 1992, we searched 386 possible overwintering sites for C. bimaculata in Eucalyptus obliqua forests. Fourteen types of habitat were identified, of which clumps of Gahnia grandis sheltered the greatest mean number of insects (3.31 ± 0.72 insects/plant, n = 65 plants), while bracken fern litter sheltered the least (0.14 ± 0.14 insects/sample, n = 7, 1 m2 quadrat samples). Of the 14 habitat types, all except two (under the bark of eucalypt stags and in G. grandis clumps) were more often unoccupied. Beetles were more commonly found on mature forest edges or in logged and regenerating forests; few were found within mature forests. Our results show that C. bimaculata rarely forms overwintering aggregations of greater than 20 individuals per site, nor does it appear to have a significant pre-diapause dispersal.