Abstract:
Gonipterus sp. n. 2 (Coleoptera, Curculionidae) is an invasive, commercially
important weevil that causes large‐scale defoliation of Eucalyptus trees. The
weevil specifically feeds on young leaves and new shoots, thus reducing tree
growth. The weevil displays a very strong preference for certain Eucalyptus
genotypes, however, this behaviour and the chemistry underlying it is poorly
understood, thereby complicating the selection of resistant trees. To elucidate
the feeding preference of Gonipterus sp. n. 2, we assessed the relative levels of
susceptibility of 62 Eucalyptus genotypes from 23 species using a laboratory
choice assay. This revealed large intraspecific variation in susceptibility to
weevil feeding, which for certain species, exceeded the interspecific variation. A
semiquantitative metabolite profile analysis on 13 genotypes revealed strong
correlations of 10 metabolites to feeding damage. The behavioural effects of
the identified compounds were assessed through an in vitro feeding preference
assay using artificial diets as well as under field conditions. This revealed three
phagostimulants (1,8‐cineole, oxalic acid and sucrose) and two feeding
deterrent compounds (shikimic acid and palmitic acid) for Gonipterus sp. n. 2.
These chemical markers can be applied to tree breeding programmes for the
selection of resistant genotypes to reduce damage caused by Gonipterus
weevils.
