![]() ![]() Chrysolina quadrigemina |
A chrysomelid beetle, Chrysolina quadrigemina, and a pyralid moth, Cactobastis cactorum, are probably the two most dramatic examples of beneficial insects that have been successfully introduced for the control of weeds.
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![]() ![]() Cactoblastis cactorum |
Prickly-pear cacti (Opuntia inermis and O. stricta) were brought into Australia around 1839 as horticultural curiosities. The plants soon escaped cultivation and became established as major weed pests of farms and rangeland. They formed dense, impenetrable thickets that grew 2-3 meters (6-10 feet) tall and choked out all beneficial plants. By 1920, the cacti had overrun nearly 25 million acres of pastureland in Queensland and New South Wales and were expanding their range at the rate of nearly 250,000 acres a year.
After the successful control of O. inermis and O. stricta in Australia, a similar program was started in South Africa using C. cactorum to control tiger pears (Opuntia aurantiaca). The moths, however, were far less effective against this species. Instead, several insects that had shown only moderate promise in Australia before the introduction of C. cactorum proved to be more effective in South Africa. These included a scale insect, Dactylopius sp., and a plant bug, Chelinidea tabulata.
In the 1950's, C. cactorum was again recommended as a biocontrol agent for Opuntia megacantha in Hawaii. This time, violent opposition to the control program arose from cattle ranchers who felt the cactus was a useful source of food and water for their livestock. This conflict of interest developed because the biological control program could not be selectively applied to geographical areas where the plant was considered a pest. If the insect became established, it could potentially infest the cactus wherever it grew. The conflict was eventually resolved when the rangelands became so overgrown with cactus that the ranchers recognized it as a nuisance. C. cactorum was released and soon brought the pest population under contol.
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Last Updated: 4 November 2003 Return to ENT 425 Homepage |
John R. Meyer
Department of Entomology NC State University |