By Anna Salleh

Increasing pesticide use is changing the profile of insect and other pests
that Australian farmers must contend with, and genetically modified (GM)
crops are set to bring their own changes, experts say.

Ecological geneticist Dr Andrew Weeks from the University of Melbourne and
colleagues report their findings in the Australian Journal of Experimental
Agriculture.

In the first study of its kind, Weeks and colleagues compared recent reports
of winter grain pests with those dating back as far as 1980.

In both Victoria and Western Australia they found pests such as armyworms
and pea weevils have declined, but other pests such as mites and lucerne
fleas have been on the rise.

"One of the big things that we found was that a couple of species of mites,
which weren't even really recorded early on, had become quite prevalent
now," said Dr Weeks, who is based at the Centre for Environmental Stress and
Adaptation Research.

Unfortunately, he says mites are one of the harder pests to control.

While some of these changes are likely to be associated with drier climates,
the researchers say that there has also been an increase in pesticide use.

Dr Weeks says drought-stressed farmers worried about losing their crop to
pests have been carrying out extra "insurance" sprays of pesticides before
they put in their crops.

"While pesticide use has increased, it's knocking out a lot of your other
pests but it's not harming these [the mites] as much," he said.

He also says the greater herbicide use has led to a decline beneficial
species like carabid beetles that are effective predators of slugs and
snails.

Dr Weeks says the drought has also encouraged many farmers to reduce the
tillage of their soil, by using herbicides to kill unwanted plants and
keeping the stubble in the ground to reduce evaporation, but this may help
slugs and snails to thrive.

GM crops

New agricultural technologies, such as GM crops, are also likely to be a
driver in changing the pests that farmers have to face, says Dr Weeks.

For example, he says, canola which has been genetically modified to be
resistant to herbicides will enable farmers to eradicate most weeds.

While this will lead to a decrease in pests that harbour in weeds, it may
lead to a rise in pests that can survive in such environments, he said.

He says the absence of weeds may also reduce the number of beneficial
organisms that act as a natural check on pests.

"If you've got a very barren landscape ... the chances are the pests are
going to be greater," Dr Weeks said.

According to Dr Weeks, there has been no research in Australia on the impact
of how the management of GM crops will affect pests.

"It's one of weak points at this stage of the whole GM debate," he said.

Crops engineered to exude the Bt insecticidal toxin are likely to reduce
pesticide applications, Dr Weeks and colleagues add.

But a major concern is the development of resistance in the insects they are
designed to control, the researchers say.

This resistance can be delayed with the use of "refuges" of non-GM crop,
they add.

"This, however, may not always be the case, and any new insecticidal
transgene incorporated into crop plants must be thoroughly tested on a range
of organisms and ecosystems," the researchers write.

The research was funded by the Grains Research and Development Corporation.
www.checkbiotech.org