Cochineal biocontrol in Onkaparinga Gorge

News release
13 March 2019

Friends of Onkaparinga Park volunteer Graham Thomas, with National Park Ranger Steve Johnson and Natural Resources AMLR Volunteer Coordinator Rachel Godoy.

Friends of Onkaparinga Park volunteer Graham Thomas, with National Park Ranger Steve Johnson and Natural Resources AMLR Volunteer Coordinator Rachel Godoy.

Thousands of Cochineal insects will soon be released in Onkaparinga River National Park to help combat declared pest plant, Drooping Pear (Opuntia monocantha) cactus.

Natural Resources Adelaide and Mount Lofty Ranges (AMLR) staff, Friends of Onkaparinga Park and other volunteers will disperse the bugs on infected cactus pieces, throughout infestations in the Onkaparinga Gorge.

Drooping Pear has been spreading up the gorge and because it is large, spikey and in inaccessible terrain, it is a major problem to control.

Cochineal is already known to be an effective biological control agent for another species of the same family, the invasive common Prickly Pear (Opuntia stricta).

The females of this insect suck the juice out of the cactus until it becomes exhausted and dies. 

Opuntia cacti, which includes Drooping Pear and the invasive common Prickly Pear, have a notorious reputation: their sharp spines can injure people, stock and wildlife, it is a host for fruit fly, and provides refuge for other pests such as foxes and rabbits.

It is also a significant environmental weed which competes with native vegetation. 

An opuntia plant, infested with cochineal, being used to spread the biocontrol onto healthy specimens in Onkaparinga Gorge.

An opuntia plant, infested with cochineal, being used to spread the biocontrol onto healthy specimens in Onkaparinga Gorge.

Cochineal, which was first released in this area in 2015, has been used across five to 10 sites, where the bugs have spread several hundred metres.

Between 20 and 50 mature plants have already been killed by these insects, with thousands more infected.

It is expected that the insects will continue to breed and expand their range over the next couple of years.

Then, as plants die so will the insects. Over time the plants recover and re-establish themselves, creating a fresh food source for the insects to feed on, to reinitiate the breeding cycle.

This cycle should repeat on and on into the future, with widespread Opuntia mortality extremely probable.

More information

Natural Resources Adelaide and Mount Lofty Ranges