The spread of shot hole
borer beetles in South Africa
is proving tough to control
A
Wilhelm de Beer, Associate Professor,
University of Pretoria
Trudy Paap, Postdoctoral Fellow
Forestry and Agricultural Biotechnology Institute, University of Pretoria
tiny tree-killing beetle with the
awkwardly long name of Polyphagous
Shot hole Borer was detected in South
Africa for the first time last year. It’s
now attacking and inserting its deadly fungal
ally, Fusarium euwallaceae, in a wider array of
tree species across a much wider geographical
area.
The beetle was initially discovered in a
Botanical Garden on the country’s east
coast. It has since been detected along the
southern Cape coast line as well as in several
inland urban areas. The number of tree
species attacked in South Africa has also risen
alarmingly. It currently stands at more than
80, 35 of which are native.
The shot hole borer, which is native to
Southeast Asia, has the potential to affect
fruit, nut and wood production, but also to
permanently change urban landscapes and
natural forest ecosystems. This has happened
on farms, in suburbs and in forests along river
valleys in California.
The South African government has started
to take steps to manage the problem. The
Department of Agriculture, Fisheries and
Forestry has set up a steering committee
to guide national efforts. It’s made up of
representatives from various government
departments, the forestry and agriculture
sectors, as well as academics, arborists, and
nurserymen.
The major challenge with the beetle
infestation is that the insect is crossing the
boundaries between agriculture, commercial
AgriKultuur |AgriCulture
forestry, natural forests, and urban trees.
Never in the country’s history has any insect
attacked and killed trees in all these sectors.
The protection of trees the different sectors
is typically dealt with by different government
departments, namely Department of
Agriculture, Fisheries and Forestry, the
Department of Environmental Affairs, and
municipalities. But given the beetle’s unusual
behaviour, routine action plans aren’t enough
to curb the problem.
The threat to South Africa’s trees
Of the 80 species of trees under attack in
South Africa, about 20 are reproductive hosts
in which the beetle inoculates its fungus and
then multiplies. These trees pose a serious
risk to the environment around them as they
become a source of infestation.
In the remaining 60 host species the beetle
also inserts the fungus, but it doesn’t
reproduce in them. Although some of these
trees may eventually die, they don’t pose a
threat to the other trees around them.
The species of ornamental and street trees
most affected in South Africa’s cities are the
London plane, Boxelder, Japanese maple,
Chinese maple, English oak and Liquidambar.
Several streets of maples and liquidambar
have died in some cities, and large, old English
oaks and plane trees have been severely
affected in some areas.
During countrywide surveys conducted by
our team at FABI, we found several fruit trees
(peach, olive, grapevine, guava, fig) infested in
urban areas. However, the only commercial
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