Insect and host-tree species influence the effectiveness of a Bacillus thuringiensis ssp tenebrionis-based insecticide for controlling chrysomelid leaf beetles

Laboratory trials were conducted to examine the role of insect and host-tree species on the effectiveness of the bioinsecticide Novodor(R) [Bacillus thuringiensis ssp. tenebrionis (Btt)]. Novodor(R) was sprayed onto Eucalyptus nitens foliage to compare its effect on larvae of two eucalypt leaf beetles, Chrysophtharta bimaculata (Olivier) and Chrysophtharta agricola (Chapuis) (Coleoptera: Chrysomelidae). Novodor(R) caused higher mortalities of first and second instars of C. agricola than of C. bimaculata larvae at similar application rates. Novodor(R) sprayed onto foliage of two host-tree species, E. nitens and Eucalyptus regnans, resulted in mortality of C. bimaculata first and second instars 18% and 104% higher, respectively, on E. regnans than on E. nitens foliage. They ate an average of 39% less and were half an instar less developed after 7 days feeding on unsprayed E. regnans than E. nitens foliage. Spraying with Novodor(R) further reduced foliage consumption by an average of 50% and developmental stage by half an instar for both tree species and larval instars. The present study demonstrated that biological factors may influence the performance of insects and the effectiveness of a bioinsecticide application, so that extrapolation of results from any host or insect species to other host or insect species needs to be applied with caution.