Diamondback moths... is there a pattern? by Alec Nicol

Left: Associate Professor Steve McKechnie and graduate student Ms Nancy Endersby in the Monash University laboratory. Right: The migrating moths are a pest of brassica crops around the world.

THE QUESTION everyone in the southern wheatbelt wants answered after last season's devastating diamondback moth attack is: will they be back?

The answer would be simpler if we were sure where they came from. A project recently supported by growers and the Federal Government through the GRDC aims to find out, and eventually to set up an early warning system.

Furthermore, the expectation is that scientists will be able to advise on whether or not the attackers are resistant to particular insecticides and provide alternate management strategies.

Steve McKechnie of Monash University is leading a team to isolate genetic markers that identify particular populations of the moth and provide a rapid analysis of the populations' resistance status. Working with him is entomologist Nancy Endersby, who says that there is a strong association between dry, hot conditions and population increases in the moth, but availability of alternative host plants and movement of moths may also influence whether an outbreak will occur.

"The moths are a pest of brassica crops around the world. They've been known to migrate a thousand kilometres or more from continental Europe to attack crops in the UK. We need much more information on the ecology and movement of the species in Australia and that's part of our work," said Ms Endersby.

Professor McKechnie says that previous work has seen establishment of a high throughput laboratory capable of conducting genotype analysis of moths. "We've already established two or three genetic markers that are robust, and have another eight or nine that we're working with. That will give us the background to identify particular populations of moths.

"The GRDC backing will enable us to collect moths from 10 to 15 areas across WA. We'll use our molecular markers to assess genetic differentiation among populations and then marry that information with ecological work to see if there's any pattern in the development of infestations.

"We'll continue to refine this over the next three years when population structure and movement patterns should become apparent. This gives us the prospect of developing an early warning system for infestations."

Ms Endersby doubts that chemicals alone will ever provide a solution to the problem of diamondback moth. "We'll need to develop an integrated management approach using insecticides, biopesticides, biocontrol agents and perhaps, with crops such as forage brassicas, some sort of trap crop system.

"Different populations of the pest carry different levels of resistance to particular insecticides and another aim of the project will be to identify genetic markers for that resistance."

"There's some commonality of the genes responsible for resistance between insect species," says Professor McKechnie, "and these are the genes we will examine in the diamondback moth. The resistance fluctuates from year to year. Our aim is a system where a rapid analysis of caterpillars will identify the type and level of resistance in a population and provide the farmer with information about control strategies that will slow or stop the spread of resistance.

"There are a number of teams working worldwide at present to identify markers associated with resistant genes and for Australian populations we have already identified a good candidate for pyrethroid resistance and are working on others."

Part of Professor McKechnie's project will be the development of a DNA library for this pest. It should identify the presence of new resistance genes, an essential step in predicting and controlling the spread of resistance before it develops. "We need to keep ahead of the insect instead of trying to deal with problems after they've occurred," he says.

Program 3 Contact: Professor Steve McKechnie 03 9905 3863 email s.mckechnie@sci.monash.edu.au