Cactus going cactus with insect
Tiny wind-borne insect is a mighty bio-control
NEAR Longreach, a tiny bug is doing some seriously disruptive regeneration work.
Leander Station has had its challenges in recent years, not only facing the sad pressure of drought de-stocking and the slow process of restocking now as pastures improve.
The sheep station has also been the site of a serious infestation of coral cactus, an introduced ornamental, species, central American
Cylindropuntia tends to crowd out pasture.
The station has also been the site for trialling an army of tiny weed warriors, a plantspecies specific variety of sap-sucking mealy bug, or cochineal, Dactylopius tomentosus.
Station owners Elizabeth and Peter Clark first discovered their lurking menace when they took up a permission-to-occupy agreement on a neighbouring 3000ha lot in the mid-1980s, where they discovered an outcrop of the cactus in a creekline thicket.
Elizabeth said when the area had been fenced off from Leander, it had not presented them with any issue. They worked with council to spray the weed, but to no effect, with traffic of sheep and kangaroos then spreading the cladodes (body sections) of the weed into other areas of Leander, eventually infesting 1500ha of country.
“It took five years to identify something that could kill it,” Elizabeth said.
“Eventually we got tied up with a man called Earl Sparkes, who was with Department of Primary Industries, he put us on to Access, we’d tried some pretty deadly poisons, but we found that Access and diesel was the best. You had to spray the plant to run-off, there was no point just hitting it, and any part of the plant that didn’t get hit just lived. As a plant, it’s pretty tenacious.
“We had a piece hanging on a meathook, and it lived for years without a drop of water.”
The obvious concern for Elizabeth and Peter was that in fighting the cactus, they were exposing themselves, the many friends that came to help out on spray days, and the country to chemical treatment, with potential flow on effects of chemical leach and plant-escape into channel country and on into the Lake Eyre Basin. Water-diluted Garlon was also used. “There was also a lot of man-hours in that, because some of the plants are as big as your fingernail and very hard to see.”
The couple worked with Queensland Department of Agriculture and Fisheries, Landcare and Desert Channels Queensland to have coral cactus declared a weed of national significance as a broader means of tackling the pasture-gobbling weed, and continued the battle.
Two years ago, a game-changing trial began, with tiny D.tomentosus launched onto the cactus population.
Wind-borne, it is only effective with plants that are reasonably close, and is best released at the upwind end of the paddock. The insect dies if isn’t blown onto the right fodder plant.
“It’s been a godsend,” Elizabeth said.
Biosecurity Queensland principal entomologist Michael Day said the project had commenced with an exploration phase, where specimens of the plants natural enemies were collected in the plant’s
❝ It’s been a godsend. — Elizabeth Clark
country of origin.
These were imported and host tested, ensuring that the
D.tomentosus biotype did not attack other plant species, including natives.
“We’ve got a number of cylindropuntia species, and because we’re using the same insect but collected off different species, we want to make sure we are matching the right biotype to the right target cactus,” he said.
Following approvals processes and mass rearing, a release and monitoring trial was launched at Leander.
“The site at Leander had a pretty high density, a couple of thousand at least, and after 18 months, we counted about four or five plants,” he said.
The project is co-operative, with work occurring in NSW, Western Australia and Queensland. As the project developed, it attracted Federal funding from the Department of Agriculture and Water.
“Bio-control tends to lend itself to collaboration. This project began with NSW [DPI] working on another cylindropuntia species, and it morphed into looking at all eight cylindropuntia species in Australia,” he said.
“The species of insect that we are looking at was already brought into Australia in 1925
to control Cylindropuntia
imbricata, but that particular population of insect didn’t attack other cylindropuntias so NSW had a particular severe species they wanted to control, Hudson pear, and they asked us if we were interested [in collaborating].
“So the insect we were looking at didn’t like Hudson pear, but it did like coral cactus.”
Mr Day wanted to reinforce that D.tomentosus wasnota silver bullet.
“Biocontrol is not going to do everything, but it can be viewed as another strategy,” he said.
“Obviously, as the cactus population goes down, people spend less on weed control, pasture regenerates, there are reduced weed-related issues for stock, and productivity increases, and for the natural environment, less weeds means that native biodiversity increases.”
Meanwhile, Elizabeth Clark is so thrilled with the insect, she likes to give them a helping hand.
“I get a bit impatient, I expect it all to be done tomorrow! I go out and hand spread it as much as I can, by breaking a piece off that’s got the bug on it, and putting it on another coral cactus.”