Griffiths 2015). To date it has only been identified from London Plane trees
(Platanus  acerifolia) in the Western Cape. These bugs are sap suckers and form
dense colonies on the underside of leaves with damage becoming apparent in late
summer. These leaves may be excised earlier than normal, and where severe damage
occurs over several consecutive years in the presence of additional stress factors, tree
death may result (Barnard and Dixon 1983).
Other invasive alien pests may initially establish on ornamental species but as
populations build and spread, present a threat to native plants. For example, the
Cycad Aulacaspis Scale (CAS), Aulacaspis yasumatsui, an insect native to Southeast
Asia, is an important pest of cycads. This pest has spread globally through the trade
of cycads and is now a major threat to ornamental and native cycads in many
countries. The International Union for Conservation of Nature, Species Survival
Commission-Cycad Specialist Group refer to CAS as the single most important
threat to natural cycad populations globally and it is listed as a prohibited species in
South Africa’s National Environmental Management: Biodiversity Act (Act No. 10
of 2004) (NEM:BA) Alien & Invasive Species Regulations. In 2015, CAS was
identified from the alien Cycas thouarsii (Madagascar Cycad) in the Durban Botanic
Gardens (Nesamari et al. 2015). Further surveys identified the pest present in three
South African provinces on cultivated Cycas as well as native Encephalartos
species. Infested Cycas were also found in two commercial nurseries, demonstrating
the high risk of spread of this pest through the nursery trade.
A second case is exemplified by the fungal root rot agent Armillaria mellea. First
detected in Cape Town in 1996, there is evidence that it was introduced during the
establishment of Company Gardens by early Dutch settlers in the mid-1600s
(Coetzee et al. 2001). Some years later A. mellea was identified in Kirstenbosch
National Botanical Gardens (Coetzee et al. 2003), and more recently has spread
further and is causing root rot of woody plants and trees in natural ecosystems
around Cape Town. Most significantly it has now invaded the ecologically important
natural environment of Table Mountain National Park, where it is threatening several
rare and endangered woody plant species (Coetzee et al. 2018).
Pests of economically important crop trees and plantation forests are well
documented in comparison to tree pests occurring in urban or natural environments,
an area that has been suggested as under-represented in invasion biology in
South Africa (Wood 2017). The recent discovery of the highly damaging invasive
Polyphagous Shot Hole Borer (Euwallacea fornicatus), however, has brought to
light the extensive economic, ecological and social impacts that urban areas face
with the arrival and establishment of a ‘worst-case scenario’ pest (Box 11.3).
11 Biological Invasions in South Africa’s Urban Ecosystems
295
(Platanus  acerifolia) in the Western Cape. These bugs are sap suckers and form
dense colonies on the underside of leaves with damage becoming apparent in late
summer. These leaves may be excised earlier than normal, and where severe damage
occurs over several consecutive years in the presence of additional stress factors, tree
death may result (Barnard and Dixon 1983).
Other invasive alien pests may initially establish on ornamental species but as
populations build and spread, present a threat to native plants. For example, the
Cycad Aulacaspis Scale (CAS), Aulacaspis yasumatsui, an insect native to Southeast
Asia, is an important pest of cycads. This pest has spread globally through the trade
of cycads and is now a major threat to ornamental and native cycads in many
countries. The International Union for Conservation of Nature, Species Survival
Commission-Cycad Specialist Group refer to CAS as the single most important
threat to natural cycad populations globally and it is listed as a prohibited species in
South Africa’s National Environmental Management: Biodiversity Act (Act No. 10
of 2004) (NEM:BA) Alien & Invasive Species Regulations. In 2015, CAS was
identified from the alien Cycas thouarsii (Madagascar Cycad) in the Durban Botanic
Gardens (Nesamari et al. 2015). Further surveys identified the pest present in three
South African provinces on cultivated Cycas as well as native Encephalartos
species. Infested Cycas were also found in two commercial nurseries, demonstrating
the high risk of spread of this pest through the nursery trade.
A second case is exemplified by the fungal root rot agent Armillaria mellea. First
detected in Cape Town in 1996, there is evidence that it was introduced during the
establishment of Company Gardens by early Dutch settlers in the mid-1600s
(Coetzee et al. 2001). Some years later A. mellea was identified in Kirstenbosch
National Botanical Gardens (Coetzee et al. 2003), and more recently has spread
further and is causing root rot of woody plants and trees in natural ecosystems
around Cape Town. Most significantly it has now invaded the ecologically important
natural environment of Table Mountain National Park, where it is threatening several
rare and endangered woody plant species (Coetzee et al. 2018).
Pests of economically important crop trees and plantation forests are well
documented in comparison to tree pests occurring in urban or natural environments,
an area that has been suggested as under-represented in invasion biology in
South Africa (Wood 2017). The recent discovery of the highly damaging invasive
Polyphagous Shot Hole Borer (Euwallacea fornicatus), however, has brought to
light the extensive economic, ecological and social impacts that urban areas face
with the arrival and establishment of a ‘worst-case scenario’ pest (Box 11.3).
11 Biological Invasions in South Africa’s Urban Ecosystems
295