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Existing biological control agents
Potential biological control agents that have been tested
and rejected
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Feeding damage
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Mozena obtusa |
History of mesquite biological control
A biological control program was first initiated against mesquite
by the South Africans in 1985. Seed-feeders were chosen with
the intention of reducing the invasiveness of mesquite whilst
preserving its beneficial properties. Three seed-feeders were
subsequently released and have become established in South
Africa. Of those, two were later tested and released in Australia
by QNRME in 1996/7. QNRME also tested a psyllid (Heteropsylla
texana Crawford) in 1992 but it was not considered specific
enough to release.
A biocontrol program against mesquite in Australia was initiated
by CSIRO in 1994 and focussed on insect species which targeted
vegetative foliage and reproductives (bud, flowers and pods)
prior to their consumption by vertebrate herbivores. Four
potential agents were studied: a coreid bug (Mozena
obtusa) which feeds on immature reproductives and
vegetative foliage; a stem-girdling cerambycid (Oncideres
rhodosticta); a sap-sucking psyllid (Prosopidopsylla
flava) which causes dieback; and a leaf-tying gelechiid
(Evippe sp. #1) which
is a defoliator. Only the latter two insects, both from Argentina,
were specific to mesquite and subsequently released throughout
Australia since 1998. The psyllid is only tenuously established
in some regions. However, the moth is widely established,
and is causing prolonged damage and impact in the Pilbara
region of Western Australia.
The South Africans have recently restarted their biological
control program against mesquite. It has not yet resulted
in the release of any new agents.
The potential for new biological control agents
New biological control agents will undoubtedly be required
in Australia, and elsewhere, if mesquite is to be successfully
contained and managed. Additional agents in the Pilbara region,
where the leaf-tier has dramatically reduced seed production,
will almost certainly be required to reduce the longevity
of mesquite plants. Elsewhere in Australia new agents will
be required that are better climatically adapted to local
conditions.
The native fauna of mesquite has been relatively well surveyed
in the United States (Ward et al. 1977), Argentina
and Paraguay (Cordo and DeLoach 1987). Considerable information
has also been obtained from other countries, including Peru.
As a result, over 945 phytophagous insects species, which
attack all parts of the plant, and many pathogens, have now
been recorded from Prosopis in its native range. This
is likely to increase further with additional systematic surveying
in areas that have received relatively little systematic attention
(such as northern and north-western parts of South America)
and on insect and pathogen groups that have remained largely
overlooked (such as stem-borers and root-feeders).
There is therefore a large pool of potential biological control
agents available, many of which are likely to be specific
to mesquite and therefore safe to release. The challenge is,
however, to identify which potential agents are most likely
to impact on mesquite in the target regions. Climatic suitability
will be important. Mesquite grows in diverse climates and
therefore it may not be possible to find agents that will
do equally well in all regions. Also, ecological
research on mesquite is ongoing to help determine what
type of damage will result in greatest impact, but it is already
clear that agents will be required which decrease adult longevity
of mesquite.
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