Promoting natural predators and parasites may be the way for graingrowers to save millions of dollars in their fight againsT the major insect pest Heliothis.
Scientists at Agriculture Western Australia, with support from growers through the GRDC, are examining Heliothis predators and parasites in lupins to see which are more effective at eating the pests before they grow large enough to damage crops.
Each year Heliothis moths cost the grains industry millions of dollars in yield loss and control measures. Naturally occurring predators are emerging as a practical and cost-saving alternative, as the pest becomes resistant to insecticides.
Agriculture WA entomologist, Jatinderpal Bhathal, said migrant Heliothis insects damage lupin, faba bean and chickpea crops throughout the wheatbelt every year.
Predator species include spiders, ants, ladybird beetles, lacewings, shield bugs and mirid bugs. "Insecticides used to control Heliothis also kill beneficial insects like ladybird beetles and lace wings which feed on Heliothis eggs, dramatically reducing Heliothis numbers early in the season," Dr Bhathal said.
Parasite species include Ichneumonid wasps (horsefly) and Tachinid flies. They reduce the number of lupin-eating Heliothis insects by laying eggs on or in the immature larvae. The parasite species then use the Heliothis larvae as a food source and eat the immature Heliothis before it develops into an adult moth.
The current research is focusing only on Heliothis and lupins. In one trial, the researchers found natural predators and parasites devoured 500,000 Heliothis eggs and small larvae per hectare before they were able to mature into large, lupin-destroying grubs.
Although beneficial species may not reduce Heliothis numbers in years when major outbreaks infest crops, an increased number of predators and parasites will reduce Heliothis damage in other years and lower the industry's reliance on insecticide sprays.
After the researchers have identified which predators and parasites are most effective at destroying Heliothis insects, they will look at ways to promote the presence of the beneficial species in lupin crops.
"Graingrowers are now totally reliant on insecticides to control Heliothis infestations, but with such large areas treated with insecticides, alternative options must be explored." said Dr Bhathal.
"Queensland grain and cotton grower are already facing major crop losses because repeated chemical sprays have allowed Heliothis insects to develop resistance to commonly used sprays.
"Naturally occurring predators of Heliothis are the only alternative control measure in the foreseeable future to give growers practical, low-cost control options for their crops," he said.
"Many farmers have questioned the value of applying broadacre insecticide sprays when predators and parasites are present.
By looking closely at Heliothis numbers and studying their predators we aim to help growers make more informed decisions about whether or not to spray crops to control Heliothis infestations," he said.
Subprogram 2.7.01 Contact: Dr Jatinderpal Bhathal 099 210 555