The important role of semiochemicals in the interactions between plants and insects has been extensively investigated. The volatiles produced by oak trees are thought to attract the ambrosia beetle Platypus quercivorus (Murayama), which causes wilt disease in Quercus trees, resulting in widespread damage. In the present study, we hypothesized that (a) P. quercivorus is attracted to the leaf volatiles emitted by host trees and (b) the response of P. quercivorus to leaf volatiles is affected by flight. An experiment was performed to survey the preferences of both sexes of P. quercivorus for the leaf volatiles of Quercus crispula Blume at various stages of leaf deterioration, represented by different number of days after cutting. Additionally, the effect of flight on both sexes was evaluated by testing the beetle flight on a flight mill. The results showed that P. quercivorus was attracted to the volatiles emitted from fresh leaves and was not attracted to those emitted from dry leaves. This suggests that leaf volatiles from healthy hosts are primary attractants for P. quercivorus. Further, males exhibited increased olfactory responses to leaf volatiles as their flight duration increased, whereas the opposite pattern was observed in females. These results suggest that the different ecological roles of the sexes contribute to differences in olfactory responses. K E Y W O R D S flight mill, host selection, olfactory response, Quercus crispula, volatile, Y-tube olfactometer

Although chemical volatiles emitted from host and non-host trees have been suggested as important cues for bark and ambrosia beetles, their responses to leaf volatiles is poorly understood. The oak ambrosia beetle, Platypus quercivorus (Murayama) (Coleoptera: Curculionidae), is a vector for the fungus that causes Japanese oak wilt. Using a Y-tube olfactometer, we tested the behavioral response of P. quercivorus to leaf volatiles emitted from four host trees-Quercus crispula Blume, Quercus serrata Murray, Quercus salicina Blume, and Castanea crenata Sieb. & Zucc. (all Fagaceae)and two non-host trees, Fagus crenata Blume (Fagaceae) and Cryptomeria japonica D. Don (Cupressaceae). A flight mill was used to evaluate the effect of flight on the behavioral response to leaf volatiles. The bioassays were repeated 109 before and 109 after flight in the flight mill for each of the 54 individual beetles. Leaf volatile components were analyzed using gas chromatography-mass spectrometry. The bioassay results supported our hypothesis: P. quercivorus was attracted by the leaf volatiles of hosts and was deterred by the leaf volatiles of non-hosts. The behavioral response of P. quercivorus to the leaf volatiles was stronger after flight. Males had a stronger behavioral response than females to leaf volatiles. The leaf volatile chemical profile of the non-host C. japonica differed from the profile of the host plants. However, the chemical profile of the non-host F. crenata was similar to the profile of the hosts. Our findings provide insight into the functions of leaf chemical volatiles in the interaction of P. quercivorus with its hosts and non-hosts and may help improve the control of P. quercivorus and Japanese oak wilt.

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Melaleuca leucadendra and M. cajuputi are grown widely in Vietnam, with plantation areas in 2020 of 32,000 ha and 36,000 ha respectively. A stem borer, Neurozerra conferta (Walker) (Lepidoptera: Cossidae), has significantly damaged plantations of both species. Field surveys in 2021 found N. conferta damage to M. leucadendra in the four provinces of Ninh Binh, Long An, Dong Thap and Kien Giang with a damage incidence (P%, percentage of plants attacked) of 22.4–33.2% and an average damage index (DI) of 0.77–1.01. In Long An province, surveys in 2022 found frequent damage to M. leucadendra plantations at the age of 2–3 years with P% ranging from 22.7 to 27.3% and DI from 0.46 to 0.54. Beauveria bassiana and Metarhizium anisopliae were identified as potential biological agents with control effectiveness of 59.6–63.3%. Screening to identify resistant varieties of M. leucadendra and development of an integrated pest management strategy for N. conferta are recommended.

Zeuzera multistrigata Moore, 1881 (Lepidoptera: Cossidae) is a dangerous stem borer that damages the Eucalyptus plantations in Vietnam. Field surveys in Lao Cai and Phu Tho provinces in 2022 showed that Z. multistrigata frequently damaged Eucalyptus hybrid plantations (clone DH32-29) at the age of 16‒28 months with damage incidence ranging from 16.93 to 28.74% and the damage index from 0.49 to 1.08. This study showed that three E. urophylla clones (PN3d, PN46, PN54) were not damaged by Z. multistrigata, and five clones (PN10, PN21, PN24, PN47, PN108) were less damaged. Further studies are recommended to screen tolorance Eucalyptus varieties and develop an integrated pest management plan for this pest.