Neurozerra conferta, Walker, 1856

Chi, Nguyen Minh, Huong, Vu Dinh, Pham, Duy Long, Binh, Le Van, Luu, Nguyen Van, Ha, Kieu Manh, Loi, Vu Van & Yakovlev, Roman V., 2022, Neurozerra conferta (Lepidoptera: Cossidae) damaging Melaleuca plantations in Vietnam and its biological control, Ecologica Montenegrina 60, pp. 13-24 : 18-21

Neurozerra conferta damage in Melaleuca leucadendra and M. cajuputi at different age stages

The results of two-wat analysis of variance ( Table 3) showed that there was a significant difference in damage incidence and damage index between the two host species, tree ages and their interaction (P <0.001).

Damage index (DI) and damage incidence (P%) due to N. conferta in M. cajuputi plantations at all 4 age stages were very low, 0.02–0.04 and 2.0–3.3%, respectively. DI and P% in M. leucadendra plantations were significant higher than in M. cajuputi plantations. By year 1, M. leucadendra trees were slightly damaged with (DI = 0.14 and P% = 4.6%). By year 2, damage was severe with DI and P% 0.46–0.54 and 22.7–27.3%, respectively.

Efficacy of biological agents

The average number of active holes before the experiment ranged from 2.26 to 2.31 holes per damaged tree, and there was no significant difference between treatments (P = 0.984), indicating homogeneity of the experiment before treatment with biological agents.

The number of active holes in the untreated control did not significantly change over time, while all biological control treatments resulted in a decline in N. conferta damage to M. leucadendra ( Table 4) There was a significant (P <0.001) difference between the biological treatments in reducing damage ( Table 4). Thirty days after treatment, trees spayed with Beauveria bassiana (Fig. 4a) and Metarhizium anisopliae (Fig. 4b) had the lowest number of active holes with new droppings (0.85 and 0.92 holes/damaged tree, respectively), and the greatest damage inhibition effect (63.3 and 59.6%, respectively). Bacillus thuringiensis and B. thuringiensis + Granulosis virus were less effective with damage inhibition effect sof 47.8 and 49.5%, respectively.

The number of dead larvae 30 days after spraying also differeed significantly (P <0.001) between treatments. Treatment with B. bassiana resulted in the highest number of dead larvae (mean of 1.42 dead larvae per damaged tree), while the control had only 0.03 dead larvae per damaged tree.

over eight-year-old trees ( Kalita et al. 2015). It was recorded as damaging Rhizophora apiculata in Malaysia ( Ong et al. 2010), and Sonneratia apetala Bangladesh ( Saenger and Siddiqi 1993). N. conferta caused damage in A. sinensis plantations in China ( Yan et al. 2010), A. malaccensis and A. sinensis plantations in Malaysia ( Syazwan et al. 2019), and Eucalyptus plantations in south-eastern Asia ( Yakovlev 2011).

Some insect pests have been recorded as damaging Melaleuca spp , for example Oxyops vitios ( Balciunas et al. 1994) , Fergusonina turneri ( Scheffer et al. 2004) in M. quinquenervia , and Trioza melaleucae in M. alternifolia ( Martoni and Blacket 2021) in Australia. Helopeltis theivora has been reported to cause widespread damage on young shoots of M. leucadendra and M. cajuputi in Vietnam ( Thu et al. 2021). However, N. conferta is a very common pest of M. leucadendra plantations in Vietnam with damage incidence over 22%. It burrows in the boles of M. leucadendra , releases a lot of droppings around the base of the tree, and can result in stem breakage from winds or storms. The damage symptoms resulted from this stem borer in M. leucadendra since 2000 is similar to those observed in the present study ( Hong et al. 2010). N. conferta ( Z. conferta ) also damages the branches of R. apiculata with broken branches, dead brown foliage, and sawdust or droppings around the base of the damaged trees ( Solomon 1995).

This study found low levels of damage to M. cajuputi with from N. conferta . This species also had a low damage in a previous study in Vietnam ( Hong et al. 2010). In Bangladesh, there was a significant relationship between the number of Bruguiera conjugata trees and the damage incidence caused by N. conferta ( Z. conferta ) in the coastal subdivisions. In monoculture stands, 51% of trees were attacked by N. conferta , while 32% were attacked in mixed stands. Therefore, to reduce the attack of N. conferta , planting of B. conjugata mixed with other species has been recommended for the coastal areas of Bangladesh ( Wazihullah et al. 1996). The current study showed that the indigenous M. cajuputi was less susceptible to this pest than the introduced M. leucadendra , and it is suggested further studies should consider intercropping of the two Melaleuca species to limit the damage to M. leucadendra .

This study identified two potential biological agents ( Beauveria bassiana and Metarhizium anisopliae ) to control larval N. conferta , with control efficiencies of 63.3 and 59.6% respectively. Melaleuca plantations in Vietnam are wetland areas ( Hong et al. 2010; Huong et al. 2017). In order to reduce negative impacts of pesticide useage, Vietnamese government has required to use biological agents for the management of insect peasts and diseases ( MARD 2020). There have been very few studies on the management of N. conferta , but some studies on the management of other species of the genera Zeuzera have shown some biological agents were highly effective for killing larvae ( El-Ashry et al. 2018; Jinshui et al. 1988; Yang et al. 1990). To control Z. multistrigata damaging Casuarina equisetifilia in China, the injection of B. bassiana ( Jinshui et al. 1988) and Steinernema feltiae ( Yang et al. 1990) solution into the tunnels have killed 86% and 93% of larvae, respectively. The entomopathogenic nematode Heterorhabditis bacteriophora mixed with B. thuringiensis was used to control Z. pyrina damage in apple trees in Egypt with percentage mortality reached 77.5% ( El-Ashry et al. 2018). B. bassiana was recorded as a natural epizootic in Z. pyrina ( Ibrahim et al. 2019) . These biological agents are potentially of value for the control of stem borers. Successful integrated management of Z. coffeae in Juglans regia ( Ahmad 2017) involving cultural, chemical and biological espects might be an useful model for studies on the management of N. conferta . Although the sparying of B. bassiana and M. anisopliae in this study is not sufficiently high to control larval N. conferta . However, this measure is applicable to deploy in wide areas of Melaleuca plantations, especially in integrated pest management programs.

Due to the influence of climate change and changes in water flow of the Mekong River, the agricultural farming environment in the Mekong delta region of Vietnam has been changing in a negative direction ( Ho et al. 2022; Huy et al. 2021). As a result, many areas of agricultural cultivation and fruit trees have been contaminated with salt or alum ( Ho et al. 2022), and the Government of Vietnam has developed a strategy to replace with forest tree species in some severely affected areas ( Vietnam 2021). M. leucadendra has been identified as a major planting species for the Mekong delta ( MARD 2014) with superior growth compared to M. cajuputi ( Hong et al. 2010; Huong et al. 2017), and the area planted with this species is expanding in recent years ( Thu et al. 2021). However, a major obstacle to this plan is the damage of a stem borer ( N. conferta ). For effective management of N. conferta , further studies are needed to develop an integrated pest management plan for this pest. At the same time, it would be appropriate to carry out genetic screening to search for varieties of M. leucadendra that are resistant to this pest.