Environmental Engineering Reference
In-Depth Information
resulted in long-term control in open sites but only partial control in more shaded
areas (Briese 1997).
Invasive insect species have also been targeted with classical biological control
and this has been a particularly active area of research and activity. h e cypress
aphid (
Cinara cupressi
), which originates from the Middle East, caused a major
threat to native cedars in eastern and southern Africa in the late 1980s/early 1990s
but a biological control programme was started because the aphid was considered
a major threat to the plantation forestry industry (Day
et al
. 2003). Nonetheless,
over the last decade or so, there have been several biological control initiatives
or projects set up against invasive insect pests because of the threats these spe-
cies pose to biodiversity. Examples include the horse-chestnut leaf miner, a North
American species that has rapidly spread in Europe causing extensive damage to its
host tree (Kenis
et al
. 2005) and an invasive weevil from the central Americas that
feeds on native bromeliads in the state of Florida, USA (Frank and Cave 2005).
In both these projects, potential biological control agents have been identifi ed and
are being considered for further assessment. One of the best examples of how bio-
logical control has been used eff ectively comes from the island of St Helena in the
south Atlantic (Box 6.1).
Box 6.1
Saving natural populations of endemic gumwood trees on the
island of St Helena in the south Atlantic through biological control
At sometime in the 1970s or 1980s, a scale insect called the Jacaranda bug
(
Orthezia insignis
) was found to be attacking a precious endemic tree belonging
to the daisy family, the gumwood (
Commidendrum robustrum
), of which there
were only about 2000 individual trees left on the island. The Jacaranda bug is
native to South America but has long been recorded as a common pest in tropical
countries. By the early 1990s the Jacaranda bug had infested many of the gum-
wood trees and by 1993 it had killed trees; the insect sucks the sap of a tree but it
also produces honeydew on which sooty moulds grow and these then smother the
tree. Given the polyphagous nature of the bug, there was concern that it would
attack other plants on the island.
A biological control agent, a specialist ladybird,
Hyperaspis pantherina
, was
already known and had been used for the control of the Jacaranda bug in Hawaii,
four African countries, and Peru, where in most cases it had substantial impact on
the target. After further study of the taxonomy, life history, and environmental
safety of the beetle, the Government of St Helena gave permission for the release
of the agent in 1993. Mass rearing was started on the island in May 1993 using
the large natural supply of the Jacaranda bug available on the island. In early
1994, 5000 beetles had been reared and released and this soon had the Jacaranda
bug under control. Since 1995 there have been no further problems with the bug
and restoration projects were started to replant gumwood trees (Fowler 2004).
