Electron microscope scan of grain weevil.

Insects breathe through numerous spiracles that puncture the hard cuticle.

Unlocking the ways insects survive without air

CSIRO scientists are discovering the mechanisms used by grain insects to survive low oxygen environments and how this knowledge can be used to control these pests.

15 May 2008 | Updated 14 October 2011

Background
Current research
Working in partnership with industry

Background

Fumigants are widely used for disinfestation and for protection against insect infestation of stored durable products. Phosphine is the preferred fumigant and up to 80 per cent of all grain in the Australian system is fumigated with phosphine during storage.

The over-reliance on phosphine and its continued and repeated use in poorly sealed stores has selected low level resistance in a number of insect species, and high level resistance in isolated cases.

Alternative treatments to phosphine include modified atmospheres which use either low oxygen or high carbon dioxide to kill insect pests. These treatments are non-chemical and leave no residues and, in the case of low oxygen, result in no harmful emissions to the environment.

However, they are not cost competitive because they take up to 28 days to control insects and require a high level of atmosphere control in well-sealed stores.

The use of modified atmospheres to maintain durable commodities insect free is an ancient technology and practiced in some form for centuries past. The effectiveness of modified atmospheres is therefore well known, but still questions remain to be answered.

One aspect of the technology that is being investigated is why are some insects able to survive incredibly low levels of oxygen?

Current research

By breaking down this protective response, insects will become vulnerable to low oxygen and rapidly succumb to its effects.

Dr Victoria Haritos, CSIRO

CSIRO studies have shown that some insects can survive in a depleted oxygen atmosphere down to two per cent by breathing significantly more regularly and they can maintain this for many days. The ability of some insect to adapt their physiology to a low oxygen situation is of interest to researchers.

This protective response is triggered by the insects sensing low levels of oxygen. If this immediate protective response can be made ineffective, then this will leave insects very vulnerable to low oxygen atmospheres and a consequent rapid death.

CSIRO is searching for the specific trigger or mechanism, and once this is known with certainty, researchers will be able to explore chemical, physical or genetic means to override it. The ultimate goal of this research is to enable low oxygen atmospheres to be faster acting against insect pests and a more cost competitive treatment to toxic fumigants.

Research is also focusing on the effect phosphine has on the respiration of insects that show some level of resistance to the fumigant. Resistant insects are known to exhale carbon dioxide in the same pattern and maintain the same metabolic rate in a phosphine atmosphere that would normally be very toxic to them.

By contrast, respiration patterns in insects that are susceptible to phosphine become irregular followed by a sharp decrease in carbon dioxide release indicating a toxic response.

Researchers will continue to determine how respiration is affected in susceptible, weakly and strongly resistant insects in the presence of phosphine. The potential use of respirometry as a method of detection of phosphine resistance status will also be evaluated.