January 29, 2003

Hungry pests, with a thirst for an insecticide chaser served up at $50 per hectare, last year cut a swathe through canola crops already wavering on the back of a dry season.

This nightmare first became reality in 2001 when diamondback moth (DBM), which had previously kept to vegetable brassicas, began attacking Western Australia’s 400,000 hectare canola crop, cutting yields in the northern agricultural region (NAR) by 5-10 per cent.

Up to five insecticide applications only dropped populations by 70-80 per cent at best, but often only by half.

If ryegrass had wings it would be DBM, according to Helen Spafford-Jacob of the University of Western Australia, who leads a new Grains Research and Development Corporation (GRDC) supported research project to tackle the pest.

"DBM has great genetic variability, quickly overcoming and resisting insecticides."

Larvae collected from horticultural crops in Perth during 1999 were 4.8 to 6.9 times more resistant to synthetic pyrethroid permethrin than susceptible laboratory populations, but by 2001 samples from the NAR were 15 to 17 times more resistant.

The GRDC’s Western Regional Panel immediately allocated emergency funding to review DBM, after being briefed on the coming tide during its 2001 spring tour.

Subsequent information underpinned three new GRDC projects in 2002, including Dr Spafford-Jacob’s, which will involve collaboration with Dr John Scott of CSIRO, Francoise Berlandier of the Department of Agriculture and a new PhD student.

Ms Berlandier has so far identified eight species of parasitic wasp attacking DBM in Western Australia vegetable brassica crops, which could help as a biological control. Encouragingly, some trials have managed 100 per cent parasitism of DBM on cabbage.

"Many parasites use known host plants as a cue to help identify prey and so may not recognise DBM in a novel environment, such as on canola," Dr Spafford-Jacob noted.

Much of this GRDC project’s biocontrol focus therefore centres around finding existing enemies of DBM which can be transferred to canola crops.

Canola crops and other weed DBM hosts, such as wild radish, will be swept for larvae and any parasites attacking those larvae.

In addition to the eight known now, newly found parasitoid wasp species will have their locality matched to other potentially suitable environments across Western Australia using CLIMEX software, to indicate where in Western Australia they could be used as biocontrol agents.

"If this exercise shows that existing parasitoids will have limited impact on DBM in Western Australia’s grainbelt, then we will examine the feasibility of importing more suitable species from elsewhere, such as South Africa, where 23 species of DBM parasitoids have been found," Dr Spafford-Jacob said.