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Newsgroups: bionet.biology.tropical,sci.agriculture,,,soc.culture.australian
Subject: Prickly pear control [Was: invasive plant species]
From: (Ian Staples)
Date: Fri, 18 Apr 1997 02:55:05 GMT (Reno Lindberg) writes:

>I have heard a couple of examples of species introduced to Australia that
>invaded large areas until its species specific herbivore also was
>introduced (biological pest control).

If you're including herbivorous insects in your field of interest, then
the classic example is the control of prickly pear (_Opuntia stricta_) in
Australia by the moth _Cactoblastis cactorum_; with the help of a prickly
pear cochineal insect, _Dactylopius opuntiae, in some parts of the country.
The latter insect has probably been more important in other parts of the
world, but the effect of cactoblastis in the worst infested parts of
Australia was spectacular.

Prickly pear was introduced into Australia before 1839, and was taken to
many parts of NSW and Qld as a pot plant or hedgerow.  It quickly spread
from these domestic plantings and covered a large area in Qld by 1900
(perhaps 4 million hectare by then).  Spread was encouraged during the
1902 drought when it was cut and fed out as fodder.

By 1926, 24 million hectares were infested, especially in central and
southern Qld (particularly the brigalow scrub country), and in northern
NSW.  About half of this area was so thickly infested that it could
no longer be used for grazing or agriculture, and properties were
abandoned by landholders.

Early in the Century there was no effective control -- 3,000 tonnes of
arsenic pentoxide were used, to little effect; some 335,000 birds
(mostly the large emu, an Australian flightless bird) were killed under
a Govt scheme based on the mistaken belief that birds were responsible
for spreading the weed; and the offer of a reward by the Govt in 1901
(increased to $20,000 in 1907) brought forth more than 600 ineffectual
schemes for dealing with the problem.

At its peak, the weed was estimated to be spreading at 100 ha/hour
(for the trivia minded :).

The Commonwealth Prickly Pear Board was established in 1920 (following
the earlier Prickly Pear Travelling Commission established by the
Qld Govt in 1912) and entomologists studied about 150 insects found
feeding on the pears in their natural habitats in N C and S America.
Of these, 52 were introduced to Australia, but only the two mentioned
above gave effective control.

Cactoblastis was introduced in 1925 and most of the prickly pear in
the worst infested areas had been killed by 1932 (more than 90% of
the infestation in Qld had been killed by 1933) and settlers were
moving back onto the land they had walked off only a few years earlier.

Ref:  PARSONS, W.T & CUTHBERTSON, E.G. (1992) "Noxious Weeds of Australia."
	(Melbourne: Inkata Press). Pp.xii + 692.  ISBN 0 909605 81 5.

Also: DODD, A.P. (1940) "The Biological Campaign Against Prickly-pear."
	Commonwealth Prickly Pear Board Bulletin. Govt Printer, Brisbane.

>Do any of you know of introduced plant species that are invading rain
>forest areas?

The blue trumpet vine (_Thunbergia grandiflora_) has been declared a
noxious weed in the "rainforest shires" of NE Queensland between
Cooktown and Ingham, and it has shown an ability to penetrate the
rainforest in some places.  There have been public-spirited campaigns
to eradicate it in the remnant riverine rainforest along the Mulgrave
River near Gordonvale, for example.  [See above Ref. for its biology.]

Cheers,  Ian S.


Ian Staples                        MS-Mail:
c/- P.O. Box 1054 MAREEBA          Phone  : +61 (0)70 928 555 Home 924 847
Queensland Australia 4880            Fax  : +61 (0)70 923 593   "   "   "

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