Abstract:
It is well-known that herbivorous insects respond to host plant volatiles. Yet
details of how these insects perceive the complex profile of volatiles from different
potential host plants has not been studied for most insects. Gonipterus spp. are important
pests of Eucalyptus worldwide, but differ in their preference for different species of this
host. In this study we consider whether host volatiles affect the host choice for a
Gonipterus sp., and we characterize the response of the female insect to the volatile
profiles from these hosts in an electro-antennographic (EAG) experiment. We sampled
volatiles from freshly damaged leaves of three Eucalyptus species, and analyzed the
profiles by gas chromatography coupled to electroantennography (GC-EAD) and gas
chromatography coupled to mass spectrometry (GC-MS). Female weevils gave a mixed
range of electro-physiological responses to volatile puffs from leaves of different tree
species. This suggests that differences in volatile profiles of different trees play a role in
how these beetles discriminate between potential hosts. GC-EAD analysis showed that
responses were as complex as the volatile chemical compositions of the leaves. A number
of these chemicals were identified and responses were mostly due to general green leaf
volatiles. This was also evident from the fact that the insects showed a markedly greater
response to the total volatile profile from freshly damaged leaves for all species. The
females of the Gonipterus sp. can therefore detect damaged leaves, which may indicate
host quality. Host specificity information is further expected to lie in the relative
differences in emission ratios and synergism between different host chemical compounds,
rather than specific individual compounds.
