Tran Xuan Hung

Episparis tortuosalis Moore, 1867 is a serious pest of the Chukrasia tabularis A. Juss which is widely planted in plantations in Vietnam. A biocontrol option to manage this pest is a priority for the forest sector. The objective of this study was to evaluate whether there are potential biocontrol candidates within the E. tortuosalis population. Sixteen bacterial strains were isolated from E. tortuosalis larvae that were parasitized in a C. tabularis plantattion in Nghe An province. Four isolates (FPRC06, FPRC07, FPRC14 and FPRC16) had strongest pathogenicity on Galleria mellonella larvae at 1, 24 and 36 hours after the injection and 72, 96 and 120 hours after the spraying experiments. The mortality rate of G. mellonella resulted from these two experimental approaches at the end of experiments was 93.3–100% and 76.7–100%, respectively. In a greenhouse experiment, the four isolates caused 44.3–61.1%, 52.0–68.0%, 54.3–69.1% and 41.4–60.7% mortality of E. tortuosalis larvae after 3, 5 and 7 days of spraying, respectively. These results were similar to applying a commercial Bacillus thuringiensis. The two isolates (FPRC07, FPRC14) were identified as Serratia marcescens based on phylogenetic analysis of 16S rRNA. Thus, this finding reveals the potential opportunities for the development of a natural insecticide of E. tortuosalis in Vietnam.

Xylosandrus crassiusculus is an invasive Asian-origin ambrosia beetle that has spread across many regions of the world, including first records in Queensland, Australia, in 2011 and New Zealand in 2019. To determine the seasonal flight activity of this species in Australia, panel traps using quercivorol + ethanol lures were placed at three study sites in New South Wales. This trapping yielded 1173 beetles, consisting of 21 species from three tribes (Xyleborini, Cryphalini and Hylurgini). Xylosandrus crassiusculus contributed almost half the total number of beetles captured over a period of 12 months, mainly driven by catches at one site. The trapping showed a seasonal peak of X. crassiusculus in late March and early April. The genetic relationships between the Australian and New Zealand specimens of X. crassiusculus were compared with other populations across the world. Phylogenetic analysis of the Australian X. crassiusculus populations showed that the beetle population in Queensland was similar to those found in New Zealand and countries in the Americas (Clade I), while the New South Wales population was closely related to Southeast Asian populations (Clade II). This divergence of genetic populations in Australia infers independent introductions of X. crassiusculus into Australia.

There are over two million hectares of Acacia plantations in Vietnam and loss from infestations of ambrosia beetles is of increasing concern. In this study, we first determined the key taxa and the extent of damage, and then identified effective trap and lure combinations for trapping adult beetles, and finally quantified the seasonality of flight of Euwallacea for informing pest management decisions. Based on analysis of the mitochondrial cytochrome c oxidase subunit I gene, the greatest threats were confirmed as Euwallacea fornicatus and E. similis (Coleoptera: Curculionidae), which are native to Southeast Asia but known as invasive species in South Africa and elsewhere. The damage incidence of Euwallacea ranged from 16.7% to 34.9% in Acacia plantations throughout Vietnam. There were no significant differences in the numbers of beetles captured between the three trap types (plastic bottles, funnels and panels). Ethanol and quercivorol were more effective as lures than cubeb oil, α-pinene or a distilled water control. Trapping from June 2020 to May 2021 revealed a bimodal frequency of E. fornicatus and E. similis in A. mangium and Acacia hybrid plantations, with captures peaking in April (spring) and October (autumn). These findings can be applied to develop early detection and trapping control programmes for Euwallacea in Acacia plantations in Vietnam and elsewhere.

The planted forest area in Vietnam increased from 3.0 to 4.4 million hectares in the period 2010–2020, but the loss of productivity from pests and diseases continues to be a problem. During this period, frequent and systematic plantation forest health surveys were conducted on 12 native and 4 exotic genera of trees as well as bamboo across eight forest geographic regions of Vietnam. Damage caused by insects and pathogens was quantified in the field and laboratory in Hanoi. The threats of greatest concern were from folivores (Antheraea frithi, Arthroschista hilaralis, Atteva fabriciella, Hieroglyphus tonkinensis, Lycaria westermanni,Krananda semihyalina, and Moduza procris), wood borers (Batocera lineolata, Euwallacea fornicatus, Tapinolachnus lacordairei, Xyleborus perforans, and Xystrocera festiva), sap-sucking insects (Aulacaspis tubercularis and Helopeltis theivora) and pathogens (Ceratocystis manginecans, Fusarium solani, and Phytophthora acaciivora). The number of new and emerging pests and pathogens increased over time from 2 in 2011 to 17 in 2020, as the damage became more widespread. To manage these pests and diseases, it is necessary to further invest in the selection and breeding of resistant genotypes, improve nursery hygiene and silvicultural operations, and adopt integrated pest management schemes. Consideration should be given to developing forest health monitoring protocols for forest reserves and other special-purpose forests.