Squamura, Heylaerts, 1890

Symptoms of Squamura View in CoL damage on Bauhinia variegata and Dipterocarpus alatus trees

Squamura maculata was found in both B. variegata and D. alatus , while S. disciplaga was present only in D. alatus ( Fig. 4 View Figure 4 ). Damage from both species is characterized by large lesions on the trunks or branches. Silk-lined galleries on the bark were filled with faecal pellets and silk of larvae. Numerous galleries were found from the base of the trunk to the canopy.

Damage symptoms of the two cossids showed distinctive differences ( Table 1). The most obvious difference is that S. disciplaga only damages the bark ( Fig. 4a–d View Figure 4 ), while S. maculata consumes bark and wood beneath ( Fig. 4e–k View Figure 4 ). Larvae feed singly, each within its individual silk-lined gallery and can move quickly when disturbed. Larvae remain within the gallery cover during the entire feeding period ( Fig. 4a, b, f, h, k View Figure 4 ). Galleries expand over time until they reach a maximum diameter of 0.8–1.0 cm. Pupation occured 25 March to 10 April, followed by eclosion 15 April to 2 May. Adult emergence occurred in the late afternoon, with a 1:1 sex ratio. The life cycle information indicates that the pests cause damage once annually. Although tree mortality has not been recorded, the feeding wounds significantly impact the growth and quality of the plants resulting in yellow, underdeveloped foliage and many feeding wounds ( Fig. 4d View Figure 4 ) that reduce the aesthetic value of urban trees.

Damage index and damage severity

Damage caused by the two species was more severe in Hanoi than in Dak Lak. Damage incidence (P%) of S. disciplaga in D. alatus trees in Hanoi was 68.1% and 56.3% in Dak Lak; and the damage severity (R%) was 39.5% and 25.7%, respectively ( Table 2). Damage from S. maculata was higher in B. variegata than in D. alatus with P% of 25.8–39.3% and R% of 16.8–28.6%. The damage incidence and damage severity of this pest in D. alatus trees was 11.9–13.5% and 6.5–6.8%, respectively ( Table 2).

Note: n = 100 for Bauhinia variegata and n = 200 for Dipterocarpus alatus ; NA is no data, values are means with SE

Discussion

This is the first report of Squamura disciplaga damaging Dipterocarpus alatus , and S. maculata damaging Bauhinia variegata and D. alatus trees. Both species concurrently attack D. alatus , but their infestations can be distinguished by the different larval feeding locations. Squamura disciplaga is a recognized pest of Annona muricata in Vietnam ( Nga et al. 2005); Hura crepitans and Polyalthia longifolia ( Chung et al. 2010; Ong and Sajap 2022), Khaya senegalensis ( Chung 2011; Ong and Sajap 2022), Adinobotrys atropurpureus , Casuarina equisetifolia and Pithecellobium dulce ( Lee 2013) in Malaysia; and fruit trees such as Durio zibethinus and Nephelium lappaceum ( Mani 2022) . In addition, S. maculata has been recorded as a pest on Persea americana ( Geddes 1992) , Albizzia spp. , Citrus spp. , Delonix spp. , Mangifera spp. , Nephelium spp. and Theobroma spp. ( Yakovlev and Zolotuhin 2020) in Indonesia. Although the two metarbelid borers have been recorded on many host plants, there is little detailed description of their larval and pupal morphologies, and damage symptoms and severity on individual host plants are not well documented. The observation in this study that S. disciplaga only damages the bark while S. maculata damages both the bark and sapwood of trunks and branches will facilitate recognition and identification of these pests in plantations, urban and rural settings in SE Asia.

Vietnamese forestry managers and scientists have focused on species that are recognized as a severe threat to forest health and productivity, including ambrosia beetles in Acacia plantations ( Hung et al. 2022), Batocera lineolata ( Quang et al. 2022a) , Endoclita spp. ( Buchsbaum et al. 2022; Pham et al. 2024) in Eucalyptus plantations, Hypsipyla robusta ( Chi et al. 2023) and Zeuzera coffeae ( Phuong et al. 2025) in Chukrasia tabularis plantations. Although there are records of metarbelid borers of forest trees, no attention has been given to their management even though S. disciplaga is known to be a serious pest on A. muricata in southern Vietnam ( Nga et al. 2005). Our study shows that the impacts of Squamura pecies may be extensive in urban environments.

Management of the two metarbelid borers will be imperative as local knowledge by foresters and urban planners suggest their populations have increased rapidly over recent years. In this study it was observed that approximately 15% of S. disciplaga larvae were parasitized by a wasp species in the family Elasmidae . Nga et al. (2006) recorded two natural enemies of S. disciplaga including Macrocentrus sp. ( Braconidae ) and Solenopsis geminate ( Formicidae ).

The Vietnamese government's strategy for forestry development set a target to reforest an area of about 5,000 hectares annually, using native tree species ( Vietnam 2021), of which D. alatus is one of the main candidates ( MARD 2014). The two metarbelid borers are polyphagous, having a wide range of host plants that could result in high population densities and persistence.

Manual elimination methods, used in species such as Kamalia priapus in Homalium ceylanicum trees ( Danh et al. 2024) or Aetherastis grandisalba in Cinnamomum cassia trees ( Quang et al. 2022b) where the larvae or pupae are located on the outside of the bark, is not feasible for Squamura species as larvae retreat into their tunnels inside the trunk, branch or bark as soon as they sense danger. Previous studies suggest the injection of pesticides such as dichlorvos, chlorpyrifos and quinalphos into tunnels ( Mani 2022) may be worth exploring, but risks of environmental contamination need to be considered. Alternatively, the use of biological agents such as Bacillus spp. Beauveria bassiana and Metarhizium anisopliae should be evaluated as promising results have been obtained with the shoot-tip borer Hypsipyla robusta ( Tra et al. 2022; Chi et al. 2023), the longhorn beetle Batocera lineolata ( Quang et al. 2022a) and the stem borer Neurozerra conferta ( Chi et al. 2022) in Vietnam.

Conclusion

In Hanoi and the Central Highlands of Vietnam, Bauhinia variegata in urban areas have suffered considerable damage by Squamura maculata , and Dipterocarpus alatus trees have widely damaged by S. disciplaga and S. maculata . Damage from these two metarbelid borers is compromising the growth and quality of urban trees.

Acknowledgments

The authors would like to thank the Tay Nguyen University for sponsoring this work, and local governments for their support in collecting samples. The authors would like to thank Professor Emeritus Bernard Dell for his suggestions, revisions, and English language editing.

Conflict of interest The authors declare no conflicts of interest.

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