A female attractant for the blue gum chalcid, Leptocybe invasa (Hymenoptera: Eulophidae), from host plant(DH 201-2:Eucalyptus grandisxEucalyptus tereticornis)

The blue gum chalcid, Leptocybe invasa, is a severe insect pest of Eucalyptus trees leading to gall formation, stunting, leaf deformation, and death in cases, China. In the previous studies, we found that the Eucalyptus hybrid, DH 201-2 (Eucalyptus grandisxEucalyptus tereticornis), is highly preferred to L. invasa larvae and adults, but its mechanism has not been fully understood. In the present study, we investigated the volatile organic compounds (VOCs) from DH 201-2 that attract L. invasa. Volatiles were collected from fresh young leaves and identified with gas chromatography-mass spectrometry (GC-MS) and gas chromatography-electroantennogram detection (GC-EAD). The attraction of identified volatiles to L. invasa was then measured under laboratory and field conditions. Two EAD-active compounds, gamma-terpinene and Limonene, were identified. In the dose-response experiments, we found that the EAG response to L. invasa was enhanced with the increased concentration of EAD-active compounds, and gamma-terpinene showed thestronger EAG responsethan Limonene. Both four-arm olfactometer bioassays and field studies showed that the blend of gamma-terpinene and Limonene with a ratio of 8:2 significantlyattracted more L. invasa as compared to other ratios. The potential use of these compounds in the control of L. invasa is ulteriorlydiscussed.