The Horizons Regional Council, a government agency in New Zealand, has recently described a successful example of biological control, which involves the reduction of a pest by using a natural enemy instead of pesticides.
A weed called ragwort (Senecio jacobaeae) competes with plants in pastures and contains alkaloids that are toxic to livestock. In order to combat the weed, three insect bio-control agents — the cinnabar moth, the ragwort flea beetle, and the ragwort plume moth — are currently hard at work to reduce ragwort spreading between properties.
“Ragwort is capable of producing in excess of 50,000 seeds per plant,” said Horizons Regional Council environmental management officer Neil Gallagher. “We have three bio-agents that attack ragwort. All three of these were present at a recent visit to two Manawatu dairy farms and the landowners considered the bio-control to be at a really good level.”
Kiwitea dairy farmer Wayne Bennett said the bio-agents took a few years to establish themselves, but they have been really successful.
“Two years after buying our farm, it was nearly completely covered in ragwort,” he said. “Thanks to the combined efforts of the cinnabar moth, flea beetle and plume moth, ragwort is hardly there now. We’re extremely happy with how well bio-control has worked on our farm, as we don’t like to use a lot of spraying to control weeds.”
Mr. Gallagher said the abundance of cinnabar moth caterpillars is of particular interest this year.
“These caterpillars were originally imported from England in 1926 and then re-released in the 1980’s. The caterpillars damage ragwort by feeding on leaves and flowers, with the severity of the attack depending on the number of caterpillars, as well as working in conjunction with the other two bio-agents,” he said.
“At the two dairy farms visited, there were was an abundance of caterpillars and damage seen at both. It was obvious the combined effects of the bio-agents working together were keeping the ragwort at acceptable levels.”
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