In search of a biocontrol for the Shot Hole Borer

Dr Wilma Nel and Garyn Townsend with collaborators in Vietnam collecting PSHB infested material.

Since it was discovered in KwaZulu-Natal in 2017, the Polyphagous Shot Hole Borer (PSHB) (Euwallacea fornicates) has spread rapidly into every province in South Africa except Limpopo, and has infested thousands of trees in urban areas, native forests and more recently in fruit crops.

This tiny invasive ambrosia beetle, native to Southeast Asia, has set alarm bells ringing as it is able to infest a wide variety of tree species – including seemingly strong, healthy trees - and is capable of spreading far and wide with the aid of human activity. It bores into the sapwood of trees and brings a damaging fungus, Fusarium euwallaceae, along with it.

The economic impact of PSHB in South Africa is still in its infancy, but is expected to run into the billions if allowed to continue unchecked. The environmental impacts are also potentially huge as a number of native trees are susceptible to infestation.

The Polyphagous Shot Hole Borer … pest invader spreading rapidly across South Africa.

One of the management options being explored by scientists at the Forestry and Agricultural Biotechnology Institute (FABI) at the University of Pretoria, is to identify a natural enemy of PSHB in its native range and then introduce it into South Africa where it could play a role in controlling the PSHB population.

This led to a recent trip to northern Vietnam by Prof Brett Hurley and Dr Wilma Nel of FABI and PhD candidate Garyn Townsend to collect material from trees infested by PSHB with the aim of finding, identifying, rearing and testing natural enemies. The visit was highly successful and the team brought PSHB-infested Acacia back to the FABI quarantine facility, after obtaining the required permits from South Africa and Vietnam.

The plan is to monitor the material for the emergence of natural enemies, specifically parasitoids, which could be reared and deployed in South Africa to serve as an effective biocontrol agent for PSHB. This is a lengthy process that involves extensive testing to ensure that the introduced species is sustainable and does not cause any collateral damage to native species in South Africa.

Prof Brett Hurley, Dr Wilma Nel and Garyn Townsend with collaborators at the Vietnamese Academy of Forestry Sciences in Hanoi, Vietnam.

The project has been made possible through the funding of the Department of Forestry, Fisheries & the Environment and through collaboration with the Vietnamese Academy of Forestry Sciences, specifically Prof Pham Quang Thu.

According to a recent article in the South African Journal of Science by a group of FABI scientists, the South African PSHB invasion represents the largest outbreak of this beetle in its invaded range anywhere in the world. It has infested 130 plant species in urban, agricultural, and native ecosystems in South Africa, including 44 previously unreported hosts.

In South Africa, PSHB is currently mostly confined to urban environments, but its presence has also been confirmed in the natural forests around Knysna and George where it is feared it could do extensive environmental damage.

Virgilia oroboides, a native tree species found in the southern Cape natural forests, is a reproductive host for PSHB.

PSHB infected tree showing damage from the fungus.

“It is an important pioneer forest species in the southern Cape that protects forests from severe climatic fluctuations and fire and houses a large number of native organisms. Elimination of this single species could have irreversible consequences for native forest integrity,” the scientists write. 

PSHB control measures using pesticide sprays have been effective in laboratory conditions, but are currently not considered practical in the wild. Deployment of a biocontrol agent looks to be the best management option at this stage, provided a suitable candidate can be found, and the necessary authorisation for its release in South Africa obtained.

The only agricultural crops that appear to be affected by PSHB so far are pecan and macadamia, but they are not reproductive hosts and so the impacts are expected to be limited. Other orchard crops that may be vulnerable to PSHB are cherry, apple, citrus, peach, guava, olive, grape and prune crops.

Initial surveys in invaded urban areas of Johannesburg, Knysna, George and Somerset West indicate that a high percentage of English oak, London plain trees, box elder and other maples will die when infested by PSHB. The cost of disposing of these urban trees and replacing them will be considerable.

Urban trees play a vital role in providing shade, moderating temperatures and creating an attractive environment that enhances the quality of life and boosts the hospitality and tourism sectors. They also provide refuge for numerous birds and insects.

The team in the quarantine facility at FABI, University of Pretoria, where the collected material is being monitored for emergence of natural enemies of PSHB.

How to detect PSHB infestation

The first signs of PSHB infestation are the presence of tiny holes penetrating the bark of trees and leading directly into the sapwood. These random holes, less than 1mm in diameter, look a bit like they could have been caused by shotgun pellets – hence the common name ‘shot hole borer’.

Lesions, wet patches and gum exudation may be visible on the outside of the tree, and a pinkish-brown stain caused by the associated fungusmay be seen spreading from the gallery into the vascular tissues below the bark. PSHB colonisation of reproductive hosts often results in wilting and death of the infested branch - or the entire tree.

The FABI team has had a lot of success with the introduction of biocontrol agents for a number of tree pests in South Africa in the past, and this experience will be invaluable in finding an effective biological enemy for PSHB. The stakes are high as this tiny hitchhiking beetle continues to spread across southern Africa.

Typical Eucalyptus plantation in Vietnam.

Sources:

FABI News;

Article by W. Nel, B. Slippers, M. Wingfield, N. Yilmaz & B. Hurley in South African Journal of Science, April 2023

All photos courtesy of FABI.

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.

FSA secures R18 m funding for forest protection

A Memorandum of Agreement (MoA) concluded between Forestry South Africa and the Department of Forestry, Fisheries and the Environment (DFFE) is set to boost industry’s efforts to counter the impact of pests and diseases on the country’s timber resources with the injection of R18 million funding over two years.

“While long overdue, this partnership with DFFE will add greatly to our efforts to protect our timber resources against pests and diseases, conduct desperately needed research and development, build our human capacity in this crucial area and encourage ongoing investment by our sector,” commented FSA’s Research and Forest Protection Director, Ronald Heath.

The MoA focuses on five main outcomes:-

• Monitoring activities
• Awareness programmes
• Provision of diagnostic services to the forestry industry
• Conducting research on aspects of pests and diseases.

The MoA will be managed on behalf of the Industry by Ronald Heath with oversight provided by the National Pests and Diseases Steering Committee which includes representatives from DFFE, FSA, the National Forest Research Forum and the Tree Protection Cooperative.

After five years of continuous and active engagement with the DFFE, the process was concluded in the short space of one month thanks to the efforts of Mohammed Bhabha of the PPGI, Sabelo Malaza from the Masterplan Programme Management Office in DFFE and Director-General Tshabala, said Ronald.

The importance of securing this funding support from DFFE is underlined by the increasing impacts of pests and diseases on forestry in South Africa and around the world.

It is estimated that over the past 30 years the forestry industry has been losing the equivalent of 11.5% of its harvest to pests and diseases every year. When using current value estimates of 50% of the average value of the timber, the losses amount to R392 million of roundwood annually. This translates into an opportunity cost of R2,05 billion in additional downstream processing that is lost.

The losses outlined above - which exclude losses due to fire - have arisen from just a handful of pests and diseases. Now, with the rate of new pests and diseases landing on our shores increasing rapidly on the back of expanding global trade, the losses incurred from pest and disease damage are expected to increase dramatically in future.

Using drone & satellite to track pest damage

FABI and ICFR researchers are collaborating in an innovative project to develop a system to monitor the impact of the Eucalyptus snout beetle on the health of eucalypts using a combination of drones and satellite remote sensing.

Gonipterus sp. n. 2, is an invasive insect native to Australia and a significant defoliator of Eucalyptus. Management of this pest, commonly known as the Eucalyptus snout beetle, relies mainly on classical biological control by a tiny wasp Anaphes nitens, which was first introduced into South Africa in 1924. The biological control has been effective in keeping Gonipterus infestations under control for decades, but in the past few years Gonipterus infestations have increased and the damage to eucalypt plantations in South Africa is on the rise.

The project is a collaboration between the Forestry and Agricultural Biotechnology Institute (FABI) based at the University of Pretoria, the ICFR’s Dr Ilaria Germishuizen and Dr Benice Sivparsad and international researchers Prof Wouter Maes of the University of Ghent in Belgium and Dr Rene Heim of the Institut für Zuckerrübenforschung.

The use of a drone to measure Gonipterus damage is key as it provides very high resolution images of the tree canopy that cannot be seen from ground level once trees reach more than 2 m height. The satellite imagery is useful in that it can detect canopy damage but is not fine enough to provide the detailed information that the researchers require.

The project has two main objectives:-
• To use satellite and drone imagery to assess and monitor the extent of canopy damage from Gonipterus.
• To understand the relationship between the canopy damage and the productivity of the compartment, which will provide forest managers with the info necessary for them to decide when and where to incur the costs of applying a chemical spray to reduce Gonipterus infestations. The info gathered from the study will also enable the researchers to assess the impact of a chemical spray application on the population of the biological control agent A. nitens.

The model that will be developed through this study will be applicable to monitor the impacts of other pests and diseases that defoliate eucalypts.

Earlier this year PhD candidate Phumlani Nzuza, Dr Michelle Schroder and Ofentse Mathibela from FABI went to the KwaZulu-Natal midlands to map Gonipterus sp. n. 2 defoliation levels using their newly acquired drone. For field ground truthing they are using ICFR’s Gonipterus impact trials at Hodgsons (Greytown) and Sutton (Ixopo)

The ICFR’s work is supported by FSA, Sappi, NCT and TWK.

New wattle rust disease spreading rapidly

New pests and diseases in the spotlight at NCT Midlands field day

Izette Greyling of the TPCP inspecting the rust damaged wattle compartment at Baynesfield.

The latest destructive disease to hit South African forestry is a ‘rust’ that attacks black wattle, Acacia mearnsii. Tree farmers first detected it last year in the KwaZulu-Natal midlands. Since then, the TPCP team has been working around the clock to find out what it is, where it comes from, and how to stop it.

Izette Greyling of the TPCP was in KwaZulu-Natal recently to do some field work and gave a presentation to tree farmers who attended the NCT field day at Baynesfield, where the rust is already causing damage to young wattle compartments.

Izette says that the speed with which the rust is spreading is cause for concern. This last summer, it spread from Harding in KwaZulu-Natal to Mpumalanga. It is a rust fungus and causes defoliation in mild cases, and stem deformation in more severe cases.

The only good news around this disease, according to Izette, is that it has now been positively identified as belonging to the Uromycladium genus, and is thought to be of the fusisporum species, although this has still to be confirmed.

The TPCP is currently working with NCT and the ICFR to come up with management options, including selecting tolerant trees and doing chemical sprays on affected trees. The only short-term option at this stage is chemical control, and NCT is planning a series of trials in conjunction with the ICFR and TPCP.

“The rust is causing stress on the affected trees and there will be follow-up insect and pathogen attacks,” said Izette.

Some of the local farmers at the field day said they had noticed intensified mired infestations in compartments where the rust was present.

Another cause for concern for tree farmers, said Izette, is that the introduction of new pests and diseases attacking Eucalyptus species has accelerated in the past few years. This is consistent with the increasing volumes of cross border trade taking place around the world, allowing pests and pathogens to move around far from their host ranges.

She said that the three major pests in the KwaZulu-Natal midlands were Leptocybe, Thaumastocoris and Gonipterus.

New eucalyptus pests that have arrived in South Africa in the past two years include the red gum lerp psyllid (Glycaspis brimblecombeii) detected in 2012, and the shell lerp psyllid, in the genus Spondyliaspis, detected in 2013.

Both are sap-sucking insects that can cause a lot of damage. The search is on for potential biocontrol agents for these insects.

The biocontrol for Leptocybe (S. neseri) has been released in all major eucalyptus growing areas, and it is spreading on its own, which is good news as this pest has caused extensive damage to susceptible eucalyptus species, especially in Zululand.

Leptocybe is getting worse – but that’s to be expected as it has had three years in which to reproduce. It will be another two years before the biocontrol can catch up,” said Yzette.

Meanwhile, there have been limited releases of the biocontrol agent for Thaumastocoris. According to Izette, the so-called ‘fairy fly’ is very small and difficult to rear in the lab, but evidence suggests it has survived in the field following its release.

Izette also said that there had been more severe outbreaks of old foes like Gonipterus, and the Cossid Moth, which is spreading, and has been reported in the Mooi River area recently.

After the indoor presentations, participants visited various sites on Baynesfield Estate. The 3 000ha Baynesfield estate is planted to wattle (just under 50%) and eucalyptus, mainly Smithii, a little macarthurii and now G x U since the Leptocybe infestations which ruled out the planting of G x C.

At one stop, we saw a young wattle compartment badly affected by the new rust disease. It causes loss of growth and forking and branching, with mortality of over 30% reported in some areas. The younger the trees affected, the higher the mortality rate. Some farmers are using general agricultural sprays to treat the rust, with good results.

Farmers could try and collect seed from resistant trees. Given the accelerating introduction of pests and diseases affecting forestry, it is becoming increasingly important for farmers to spread their risk by planting several different species on their farms.

This Stihl earth augur, equipped with a long lasting, tungsten blade, produces uniform, high quality pits for planting. According to the operator, a pitting/planting team of five people can pit, water and plant 900 to 1 000 trees a day (six-hour shift) using the earth augur. The team needs to be multi-skilled with two or three team members taking turns operating the augur.
Craig Norris of NCT discussing the merits of planting G x U during the field day. Behind him is a compartment of 3.5 year-old G x U clones showing excellent growth at 1 100 metres altitude.

*The TPCP has made a special request to tree farmers to report occurrences of the wattle rust to Jolanda Roux (jolanda.roux@fabi.up.ac.za; 082 909 3202) or the diagnostic clinic (darryl.herron@fabi.up.ac.za). Early detection of the disease in new areas will greatly assist in assessing its status and informing management strategies.

*Published in June 2014