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| CSIRO | SOLVE | Issue 9 | NOV 06 | |
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ARTICLE
AGRIBUSINESS:
Insect Sharpshooter By Gio Braidotti
A technique to create chemicals that selectively kill only some types of insects is the platform for the development of high-performance agriculture.The ability to kill any creepy-crawly fast is a key selling point for a household pesticide, given the panicky response aroused by cockroaches, centipedes and spiders. But when it comes to genuine pestilence and the need to control insect-borne diseases (such as malaria) or agricultural pests, many chemicals hit insects indiscriminately, potentially creating long-term environmental imbalances that outweigh the immediate triumph. Such unwanted impacts make up a list of health and environmental issues:
To Dr Ron Hill and his team at CSIRO Molecular and Health Technologies, the unintended side effects all point to the same, basic design fault. Insecticides generally fail to distinguish different insect subtypes. It is a problem, but like many problems, it also becomes a potential opportunity.
"We have known for years that more than 99 per cent of insect species are innocuous or even useful to humans," Dr Hill says. "It is just 0.1 per cent that require control measures." For this reason, scientists are working on the next generation of high-performance insecticide that can chemically 'see' what kind of animal it has come into contact with and spare mammals, birds, fish, reptiles, bees, ladybugs and other insects that are not the intended target. "Target-specificity is a fascinating challenge," Dr Hill says. "It requires integrating molecular biology and protein-structure analysis into the synthetic chemical process of designing insecticides. At the same time, you don't want to have to solve the specificity problem from scratch for every situation. "In other words, the insecticide needs to be insect-specific, but the method we use to develop that specificity needs to be universally applicable – otherwise the R&D effort would be enormous." As paradoxical as that requirement sounds, it has been met. Dr Lloyd Graham and Dr Noni Johnson from the CSIRO team, with support from a $1 million Start grant, have developed a screening method for a new type of insecticide. "This new system is based on the hormone receptor that triggers moulting of an insect's hard outer skeleton," Dr Hill says. "The use of chemicals that mimic the hormone ecdysone allows us to activate moulting inappropriately, causing the insect to die. Best of all, ecdysone mimics are innocuous to most other animal groups." To achieve the desired target-specificity, Dr Mike Lawrence is examining the three-dimensional structure of the hormone receptor, looking at the way it binds the hormone, to identify differences among insect types. "These variations are the key to discovering hormone-like chemicals that are active in a selected subtype of insect only," Dr Hill says. "But to realise that potential, we had to invent a way to mass-screen the hormone mimics." The result is a patented, automated, high-throughput assay performed in standard laboratory equipment. To set the assay against a particular insect, the ecdysone-receptor gene from the target insect is cloned and expressed in a cell line to make the receptor protein used in the automated assay. Industry is already expressing interest in the new assay, with Australian Wool Innovation (AWI) investing in the technology to target the blowfly, which costs the sheep industry $280 million a year in fly-strike. Fly-strike is the reason for the controversial mulesing procedure, which cuts away the loose skin where flies lay maggots. AWI is also supporting Dr Matt Pollard to clone the ecdysone receptor from the sheep body louse as another target for insecticide development. In freezers in the CSIRO laboratories, genes for ecdysone receptors from other pest species – cloned under the direction of Dr Garry Hannan – are also available, with the team eager for investment to pursue other economic pests such as aphids and whiteflies. CSIRO business development manager Dr Tim O'Meara estimates that it has been a decade since the last development of a new class of insecticides, and the sheep industry is not the only sector in need of new, high-performance compounds. With chemical treatment still one of the most effective ways of maximising crop yields – and crops finding new uses as sources of fuel and 'biofactories' – the worldwide sale of agrichemicals is exceeding $20 billion a year. However, as population growth continues to put pressure on arable land, the need for sustainable agricultural practices is lifting the demand for selective, environmentally friendly insecticides. For further information contact: |
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