New beetle poses major threat to country's trees

Date: 28 October 2018 By: Jo Robinson

In an August media release, the Department of Agriculture, Forestry and Fisheries (DAFF) informed farmers and the public of the detection of a new pest of concern - the polyphagous shot hole beetle. So far, it has been identified across the country, including slightly north of Polokwane, and more recently in the Kruger National Park.

The Zoutpansberger contacted one of the arborists in South Africa who are currently working on the identification of infestations and the control of this pest for more information. Jaco Pitzer of Arbor Care Tree Specialists in Pretoria has come to know this bug very well as it has already become a catastrophic problem for trees in the Johannesburg area. He explained that this two-millimetre-long ambrosia beetle is one of a trio of cryptic species in the Euwallacea fornicatus complex and is native to Asia.

The polyphagous shot hole borer (PHBS) carries in its mycangia a fungal symbiont named Fusarium euwallacea that it depends on for its survival. Mycangia are the structures in the beetle’s body that have adapted to transport its symbiotic fungi in spore form. The beetles then drill into host trees where the live wood is used by them to farm the fungus, which they and their larvae eat. The beetles create tunnels and galleries that they line with the fungus and the action of the fungus, called fusarium dieback, is the cause of the trees’ death.

One female can produce up to 500 eggs and these beetles can infest a large variety of trees for feeding purposes, even though they do not use all of them for breeding. Even so, many reproductive-host-tree possibilities favoured by the PSHB are available to them in South Africa, including black wattle, jacaranda, avocado, pin oak, and the white and Cape willow trees. Non-reproductive hosts that are also destroyed by PSHB include the pecan nut, macadamia nut, lemon and orange trees, loquat, syringa, mulberry, frangipani, peach, guava and grapevines.

Pitzer said that people could not sit back and wait for the DAFF or municipalities to act. Even though some have issued media releases, many have not acted. He said that beetle finds had been confirmed in KwaZulu Natal and Hartswater as well as in George and Knysna. “At this point, it is difficult to say how widely infestation is taking place in South Africa. What is needed is for inspections to be carried out in as many parts as possible of all provinces.”

Transfer of these beetles generally happens with the transport of “live” wood (the tree might be cut down and/or sawn up, but the wood is not completely dry yet). Pitzer said that once any host tree was truly dead (with the wood dried out), the beetles left in search of new hosts, but some leeway obviously existed. People buying fresh firewood in one part of the country and taking it to another could easily transport these beetles to new territory. Another mode of transfer could be buying a newly infected sapling at a nursery in Gauteng, for instance, and taking it home to Louis Trichardt. According to Pitzer, many ways exist that these beetles could now be, and probably are, travelling around the country.

PSHB is already a national problem, according to Pitzer. Of the hundreds of thousands of trees planted for the Greening-of-Soweto project from 2010, thousands are now infected and dying.

Dr Trudy Paap of the Forestry and Agricultural Biotechnology Institute (FABI) initially discovered the PSHB in South Africa. On a routine study for diseases in the KwaZulu-Natal Botanical Gardens in Pietermaritzburg, Paap found a series of infested trees. This led to the identification of the beetle in 2017. Only then was it discovered that an adult specimen of this beetle had been found previously by biologists Z Shoba and M Ziganira in March 2012 in KwaZulu-Natal, not far from the Durban harbour. Studies have shown that invasive pests are usually brought in via the importation of live flora, although many reports about PSHB state that it probably came in with wooden packaging.

Whichever way PSHB arrived, it is now known to have been present in South Africa as far back as 2012. The two biologists who found it failed to identify it at the time and so loaded an image of it, together with its genetic code, onto the BOLDSystems database, which is a sequence database specifically devoted to DNA barcoding. This information stayed there, unrecognised, until the finding of the infested tree in the Pietermaritzburg Botanical Gardens by Dr Paap.

This is not simply a problem for farmers. Trees dying in their tens of thousands over a short period of time in urban areas will affect both heat and carbon dioxide levels, and so the well-being of the inhabitants as well before replanted trees will be big enough to make any impact.

People who have questions or need information about this pest, are welcome to phone Jaco Pitzer on 083 430 2000 or email him at [email protected]. People interested in tracking the PSHB in South Africa or reporting a finding are encouraged to log on to  http://www.pshb.co.za/Tree-Survey/. The law requires that any findings of this beetle be reported to the DAFF.

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Jo Robinson

Jo joined the Zoutpansberger and Limpopo Mirror in 2018 pursuing a career in journalism after many years of writing fiction and non-fiction for other sectors.

More photos... 

Fungus-lined tunnels of the polyphagous shot hole borer beetle. Image supplied.

So-called noodles made up of compacted frass (sawdust) being pushed through bored holes in a tree trunk. Photo supplied.