Australian Journal of EntomologyVolume 34, Issue 2 p. 97-98 Free Access Effect of the Biotic Insecticide Bacillus thuringiensis on Predators of Chrysophtharta bimaculata: A Comment RICHARD J. MILNER, RICHARD J. MILNER CSIRO, Division of Entomology, G.P.O. Box 1700, Canberra, A.C.T. 2601.Search for more papers by this authorR. J. AKHURST, R. J. AKHURST CSIRO, Division of Entomology, G.P.O. Box 1700, Canberra, A.C.T. 2601.Search for more papers by this author RICHARD J. MILNER, RICHARD J. MILNER CSIRO, Division of Entomology, G.P.O. Box 1700, Canberra, A.C.T. 2601.Search for more papers by this authorR. J. AKHURST, R. J. AKHURST CSIRO, Division of Entomology, G.P.O. Box 1700, Canberra, A.C.T. 2601.Search for more papers by this author First published: May 1995 https://doi.org/10.1111/j.1440-6055.1995.tb01292.xCitations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume34, Issue2May 1995Pages 97-98 ReferencesRelatedInformation

In a laboratory trial Bacillus thuringiensis var. tenebrionis adversely affected survival of Chauliognathus lugubris (F.) (Coleoptera: Cantharidae), a major predator of the target insect Chrysophtharta bimaculata. Survival of two coccinellids and adult C. bimaculata was not affected. The pyrethroid cypermethrin adversely affected all insects tested. Both cypermethrin and B. thuringiensis are used to control C. bimaculata larvae in Tasmanian eucalypt plantations.

Summary Defoliation of Eucalyptus regnans plantations in Tasmania by the leaf beetle Chrysophtharta bimaculata (Olivier) over a two year period significantly reduced growth of one-year-old previously uninfested trees and six-year-old trees with a history of defoliation. One-year-old trees defoliated by C. bimaculata had lost 45.6% and 52.1% of their potential height increment and basal area increment respectively by the end of the two year trial compared to protected trees. Six-year-old trees experienced similar growth losses and the biomass of leaves and stems/branches of unprotected trees at the end of the two year period was reduced by 44% and 39% respectively compared to protected trees. The impact of the defoliation levels recorded in these trials is discussed in relation to the current control strategy for C. bimaculata and the economics of eucalypt plantations in Tasmania.

Summary Defoliation of Eucalyptus regnans plantations in Tasmania by the leaf beetle Chrysophtharta bimaculata (Olivier) over a two year period significantly reduced growth of one-year-old previously uninfested trees and six-year-old trees with a history of defoliation. One-year-old trees defoliated by C. bimaculata had lost 45.6% and 52.1% of their potential height increment and basal area increment respectively by the end of the two year trial compared to protected trees. Six-year-old trees experienced similar growth losses and the biomass of leaves and stems/branches of unprotected trees at the end of the two year period was reduced by 44% and 39% respectively compared to protected trees. The impact of the defoliation levels recorded in these trials is discussed in relation to the current control strategy for C. bimaculata and the economics of eucalypt plantations in Tasmania.

A model of the effect of defoliation by the Tasmanian eucalyptus leaf beetle, Chrysophtharta bimaculata Olivier, on the height growth of Eucalyptus regnans F. Muell. in young plantations is described. Two separate artificial defoliation trials were set up to provide data to calibrate and test the model. The treatments involved combinations of different defoliation levels and timing with and without a repeat of these treatments in the following year as well as a treatment involving regular removal of refoliating shoots (disbudding). The effect of disbudding was found to be greater on growth than was low levels of defoliation. The model gave an adequate fit to the data, but not all combinations of treatments were available to calibrate and test the model. A small simulation study employing the model to investigate the effect of defoliation and disbudding on plantation economics indicated a potentially high benefit to cost ratio for control of C bimaculata, especially where refoliating shoots were grazed.

Chrysophtharta bimaculata is the most economically important pest of eucalypt forests in Tasmania causing severe growth losses in plantations and seeded stands of the major commercial eucalypt species. An integrated pest management (IPM) strategy has been developed which allows peak activity of the natural enemies of C. bimaculata and monitors pest egg and larval populations before significant defoliation takes place. The relationship between beetle population level and degree of defoliation is quantified by regression models which are used to identify potentially damaging populations and the need for additional artificial control measures. The biotic insecticide, Bacillus thuringiensis var. tenebrionis was successfully tested against C. bimaculata larvae, and the use of B. thuringiensis and the synthetic pyrethroid, cypermethrin, in the IPM strategy is discussed.