Abstract
Eucalyptus is frequently attacked by the Brazilian eucalyptus brown looper, Thyrinteina arnobia. This caterpillar is regarded as the main lepidopterous pest of Eucalyptus and yet no practical and environmentally acceptable method of control currently exists. Electroantennographic techniques (EAG) have never before been used to detect semiochemicals that affect the behavior of T. arnobia. Thus, in this work, the ability of T. arnobia males and females to detect volatile essential oils of seven Eucalyptus species was investigated by EAG. We demonstrated that T. arnobia antennal olfactory system clearly showed differential sensitivity to several compounds, by coupled gas chromatography-electroantennographic detection (GC-EAD). Twenty-eight compounds were identified that elicited responses in T. arnobia, indicating that GC-EAD analysis may well be a useful means of screening active plant extracts for compounds that contribute to the observed behavior of this defoliator. The results also suggest that this species uses several volatile cues to find its host.
Highlights
The genus Eucalyptus, native to Australia, is widely cultivated in Brazil, covering an area of more than three million hectares
Mean depolarizations achieved by T. arnobia male and female antennae in response to the essential oils of E. grandis, E. citriodora, E. camaldulensis, E. saligna, E. urophylla, E. cloesiana and E. maculata, are shown in Figures 1 and 2
Electroantennographic responses in both sexes were significantly higher than that for the control. These results indicate that T. arnobia adults recognize some volatile compound in the Eucalyptus essential oils; that is, in the antennae of both sexes there are neuron receptors, present in sensillas, which detected compounds in the essential oils
Summary
The genus Eucalyptus, native to Australia, is widely cultivated in Brazil, covering an area of more than three million hectares. We selected Eucalyptus species that vary from those with sclerophyllous foliage and high oil content (E. camaldulensis and E. citriodora) to those with softer leaves and intermediate oil content (E. grandis, E. saligna, E. urophylla and E. cloesiana), while another has sclerophyllous foliage and low essential oil content (E. maculata).[2,3,10] Besides, choice assays applied to T. arnobia larvae,[4] showed that E. urophylla, E. saligna, E. grandis and E. cloesiana species are preferred hosts of eucalyptus brown looper.
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