Potential new biocontrol for Gonipterus

Gonipterus snout beetles are leaf feeders. The adults feed on the edges of mature leaves causing defoliation of the tree crowns and stunted growth. Studies have shown that 50% crown defoliation can result in up to 85% loss of wood production over a 10 year period.

The Forestry and Agricultural Biotechnology Institute (FABI) team is testing a tiny fly that could turn out to be an important new biological control agent of the Gonipterus snout beetle, currently the most serious insect pest of Eucalyptus trees in South Africa.

The potential new biocontrol agent is a tachinid fly, Anagonia cf. lasiophthalma, which parasitizes the larval stage of the Gonipterus beetle. The flies were sourced from the Forest and Paper Research Institute in Portugal, which has been studying this insect for its potential use as a biocontrol for Gonipterus species for some time.

The parasitoids were imported into the FABI quarantine facility at the University of Pretoria and are showing great promise as an effective biocontrol for Gonipterus sp. n. 2, which is causing significant damage to Eucalyptus plantations across all major forestry regions in South Africa.

*Anagonia cf. lasiophthalma is a potential new biocontrol agent for the Gonipterus snout beetle, currently damaging Eucalyptus trees in South Africa and neighbouring countries.*

Gonipterus beetles are native to Australia. They were first identified in South Africa in 1916, rapidly spreading across the country and into neighbouring territories. This led to the release in 1926 of Anaphes nitens – a tiny wasp - which was the first biocontrol agent in South African forestry. Anaphes nitens was effective in controlling the spread of the Gonipterus beetles, but in the past few years damage from Gonipterus infestations has been increasing once again and it has become clear that on its own Anaphes nitens is not sufficient to suppress Gonipterus populations.

This has led to renewed interest in Gonipterus in South Africa and the discovery that it is not a single species, but one of several different taxa. Hence the one currently doing the damage in South Africa has not even been formally named yet.

Initially it was not known whether the fly Anagonia cf. lasiophthalma would parasitize Gonipterus sp. n. 2, the species present in South Africa, and whether it would be possible to rear it in quarantine. However, work at the FABI facility led by technical assistant Amy Collop and supported by Samantha Bush, Michelle Schroder and Brett Hurley, has confirmed that Gonipterus sp. n. 2 is a host of this parasitoid and the initial stages of a lab-reared population of the flies has been established.

This is very exciting news, according to the FABI team, as it confirms the possibility of using this parasitic fly as a biological control agent for Gonipterus - although there is still much work to be done before it can be safely released into the field.

According to Brett Hurley of FABI, what makes Anagonia especially exciting is that it parasitizes a different life stage of Gonipterus, namely the larvae, as compared to Anaphes which is an egg parasitoid. Thus it is more likely to add to the overall control of Gonipterus, as compared to releasing another agent that targets the same life stage.

Gonipterus larval stage. The larvae feed on the epidermis and mesophyll of young Eucalyptus leaves.

“The first step before releasing Anagonia in South Africa was to confirm that it would parasitize Gonipterus sp. n. 2 - this has now been done,” says Brett. “The second step is to establish a rearing population for experiments - this is ongoing. The third and very important step is to conduct host specificity tests, i.e. to assess if Anagonia will attack other native insects. This is the step where it is difficult to say how long it will take - it could be one year or it could be 3+ years, it depends on multiple factors such as our success with rearing the different insects needed for these studies. If the tests indicate that Anagonia is specific to Gonipterus and therefore safe to release, then we move to step 4 - applying to the government for permission to release Anagonia into the field. This application would be sent for comment from national / international researchers before a decision is made,” he said.

A number of Eucalyptus species, varieties and clones are negatively affected by Gonipterus including E. dunnii, E. grandis, E. nitens, E. urophylla, E.smithii and GUs.

Gonipterus is not the only pest on the FABI team’s radar, as there are many new potential insect pests and pathogens on the horizon!

“We are currently investigating the most likely future insect pests of eucalypts. One insect pest that is moving around, e.g. recently reported in Portugal and South America, is the eucalypt leaf feeding beetle, Trachymela sloanei. But the reality is that many of the new pests and pathogens are not currently known in their native range or anywhere in the world, so it is very difficult to predict,” concluded Brett.

*Amy Collop busy rearing Anagonia cf. lasiophthalma in a petri dish at the FABI facility in Pretoria.*

EucXylo team set to grow

Left to right: Research leader Prof David Drew with research team members Oluwaseun Gakenou, Dr Leandra Moller, Chris Tonkin, Dr Kim Martin, Rafael Keret, Mpilo Khumalo, Alta Saunders, Dr Letitia Schoeman and Gugu Gama.

A small nursery of 12 newly planted Eucalyptus trees near the Department of Forest and Wood Sciences at Stellenbosch University (SU) represents more than just a research project in the making. The trees are symbols of growth, and of the shaping of bright minds through the endeavours of the Hans Merensky Research Chair in Advanced Modelling of Eucalyptus Wood Formation (or EucXylo).

The flourishing nursery trees also serve as a living memorial to the mining geologist, scientist and prospector, Dr Hans Merensky, a pioneer of forestry and agriculture in South Africa, who was born 150 years ago. The Hans Merensky Foundation is making the work of EucXylo possible.

Aptly therefore, most of the work and laboratory space that this young research group occupies is in the wood-panelled Hans Merensky wing of the Department of Forestry and Wood Science’s Paul Sauer building.

“Through the research done by our postgraduate students and younger researchers we aim to better understand the dynamics behind how the wood of Eucalyptus trees form. They are among others developing appropriate mathematical and computational models and delving into how climate change is and will influence the way in which such species grow,” says EucXylo research leader and senior lecturer Prof David Drew of the SU Department of Forestry and Wood Science.

“Wood formation, technically known as xylogenesis, is fundamental to the fixing of carbon dioxide into the stable, valuable and beautiful material we call wood, and to the production of our planet’s increasingly-important renewable timber resources,” he explains. “We are trying to understand and model the processes of wood formation of Eucalyptus in the context of the physiology of the whole plant, and not only the molecular genetics of wood formation.”

About the Research Chair’s very specific focus on one type of tree, he says: “Eucalyptus or gum trees are arguably the world’s most widely planted hardwood forest species. Their wood is used for a wide variety of purposes, ranging from pulp to solid wood for construction. Most research done on wood formation has so far come from the northern hemisphere and was done on small plant species and poplar and other softwood tree species.”

The group consists of four MSc students, five PhD candidates, two postdoctoral researchers and a technical officer.

PhD student Gugu Gama, who hails Newcastle in KwaZulu-Natal, says she joined the team because of her interest in wood anatomy. “I wanted to further my skill set in this field. This research team encompasses modelling, images analysis and modern computational analysis of wood with a focus on interesting species such as Eucalyptus.”

The Research Chair was established in 2019, with most of the team members joining during the course of the past year. To broaden its scope, the EucXylo team is collaborating closely with scientists in the SU faculties of Agrisciences and Science, and with various leading international researchers.

Prof Drew adds: “To some our research might seem very ‘blue skies’, but I am sure Dr Merensky would have approved of the way in which our endeavours are extending the skills base and research abilities of younger scientists-in-the-making. In this way we are making sure that there are enough bright young minds to fill positions within the forestry and wood sector, in South Africa and abroad.”

Climate change research
Prof Drew notes that his team has received more than just direct funding from the Merensky rank towards its endeavours: “The trees in our nursery were for instance also provided by the Merensky Forestry section and are doing well.”

The trees are being cared for by Mpilo Kumalo, as part of his PhD in Forestry and Natural Resources Sciences. He is drawing on his knowledge of ecosystem ecology and ecophysiology to study seasonal variation in Eucalyptus wood formation, and the relationship between sap flow and wood formation, to understand how it influences the architecture of a tree.

In another part of the nursery complex Raphael Keret is constantly taking plant measurements as part of his PhD in Plant Biotechnology. In light of climate change and changing rainfall patterns, he is investigating the ways in which water stress and droughts influence the movement of sap in trees – and ultimately also influence wood characteristics.

In related work, Alta Saunders, a PhD in Forestry candidate, is using measurements taken in the nursery to build computational models with which to understand how Eucalyptus trees respond to drought situations, how they recover, and the role of stomatal conductance (the rate of water loss through leaves) in all of this.

Diverse fields
Prof Drew is described by his team as an exceptionally enthusiastic, caring leader. He is especially proud of the fact that his group works well together, despite the stressors of Covid-19 and despite being from various academic backgrounds, such as forestry, microbiology, medical research, genetics, and environmental sciences. Postdoctoral fellow Dr Kim Martin, for instance, holds a PhD in Biomedical Science from the University of Edinburgh and has worked in tissue engineering projects previously, while technical officer Dr Leandra Moller is a trained microbiologist who completed postdoctoral research in horticulture. These days she gets to work with anything from dataloggers and different types of sensors, such as dendrometers, sap flow sensors and PAR sensors, all to monitor the growth and physiology of trees.

“I think the ability to do anything as long as it falls within the scope of our funder is a highlight. It has allowed us to procure some specialist equipment and to co-fund the setting up of two laboratories that can be used by the whole department,” says Dr Moller.

“The fact that we are from so many diverse backgrounds means that there’s always someone around with the necessary skills to ask for help,” adds Dr Martin.

“The team is made up of individuals from diverse backgrounds, but the bond and teamwork are exceptional. Each time we bring on a new member, they quickly integrate into the team. reveals Oluwaseun Gakenou, who hails from Nigeria and is now pursuing a data-driven research project to model the productivity of certain Eucalyptus species as part of his MSc degree. “It creates an enchanting atmosphere in which your weakness is balanced by another person’s strength. You are not afraid of making mistakes, which speeds up and simplifies the learning process.”

The Hans Merensky Foundation (HMF) is a successor in title to the Hans Merensky Trust, established by Dr Hans Merensky in 1949. According to trustee Chris Pienaar, it is mandated by a constitution, wherein the discovery and support of science in the natural resource arena, represents a primary objective of the mandate.

“As such the HMF finances and support related research chairs at various South African universities and collaborative overseas institutions,” says Pienaar.

Dr Hans Merensky was born on a mission station called Botshabelo, outside Middelburg Mpumalanga in 1871. Without the assistance of modern prospecting technologies but firm in the belief of his visualisation and calculation of the Bushveld Igneous Complex he discovered the platinum group metals reef in 1924. The Merensky reef still carries his name. In addition, he co-discovered gold deposits in the Free State, copper and phosphate deposits in Phalaborwa and alluvial diamonds along the West Coast of South Africa and Namibia.

Being of German descent and confined to his farm during World War 2, he continued to successfully establish commercial, Eucalyptus forestry plantations and leading research-based farming endeavours on his farm Westfalia. It is situated between Tzaneen and Mojadi in the Limpopo Province.

Being involved in mining and minerals for most of his working life and observing the random application of Eucalyptus in mine shafts, he decided to investigate and experiment with higher order applications of this fast-growing hardwood species. The Merensky organisation became pioneers in cultivating and processing Eucalyptus kiln dried timber, applied in the manufacturing and marketing of furniture, doors, and various other industrial applications.

Apart from the higher order economic value of the Eucalyptus tree, Dr Merensky was firm in the belief of the tree’s hydrological qualities. This work continues.