Biological control of locusts

The Australian Plague Locust Commission currently uses a biological control agent (Metarhizium anisopliae variety (var) acridium) as one of the control agents to manage populations of Australian plague locust.

Metarhizium is a naturally occurring fungus that is specific to locusts and grasshoppers.  It will only infect and kill insects belonging to these groups. The fungus was originally isolated from a dead spur-throated locust (Austracris guttulosa) found in Queensland.

Becker Underwood Pty Ltd suspend Metarhizium spores (the reproductive stage of the fungus) in oil to form the product known here as Green Guard^TM.

Note: the production of Green Guard does not involve the genetic manipulation of the fungus. The fungus is cultured in bulk (much as other microorganisms such as yeast are cultured) so that sufficient quantities of spores can be harvested to deliver commercial quantities of the product. The spores are suspended in oil to increase the length of time they can endure prolonged dehydration following application and to improve their adherence to locusts.

When Metarhizium spores come in contact with a locust they germinate, penetrate the cuticle of the insect and grow throughout its body. As they grow the threads (hyphae) of the fungus take moisture and nutrients from the living insect, eventually killing it. Green Guard is sprayed onto bands of locust hoppers (nymphs) and flying adults (swarms) using conventional ground-based or aircraft-mounted spray equipment.

Research on Metarhizium began in the early 1990s in both Africa and at CSIRO Entomology in Canberra. Preliminary results were so promising that a joint project involving the Australian Plague Locust Commission, CSIRO Entomology, Queensland Department of Natural Resources, NSW Department of Primary Industries, the Wingless Grasshopper Group and a commercial partner began in 1997. Between 1997 and 2000 field trials covering areas of several hundred hectares showed that Metarhizium could reduce the numbers of locust hoppers in treated bands by up to 80 per cent. The greatest mortality occurred between 7 and 15 days after treatment, depending on ambient temperatures. This success led to the first operational use of Metarhizium anywhere in the world during 2000-2001 when over 20,000 hectares of bands of Australian plague locust were aerially treated.

Locusts infected with the fungus initially turn a characteristic pink colour and later a green colour as the fungus sporulates (produces more spores). These subsequent spores will only develop if living locusts or grasshoppers come into contact with them and the prevailing environmental conditions are suitable for their germination. There is no field evidence that Metarhizium anisopliae var acridium persists at high levels in those areas where it was applied during previous spray operations.

Nymphs killed by Metarhizium - pink stage

Nymphs killed by Metarhizium - green stage

Control of locusts using Metarhizium is considerably more expensive than control using chemical insecticides such as fenitrothion. Therefore it is mainly used on certified organic production properties and in areas where chemical pesticide use is restricted or undesirable. Its use is increasing in inland areas where organinc beef production is becoming more common. Constraints on the use of chemical insecticides are increasing and having a biological control agent will be critical to ensuring the continued effectiveness of the APLC locust management program.

The APLC continues to evaluate and refine the use of Metarhizium through work in Australia and overseas. Post-application evaluation has been undertaken to improve the understanding of the temperature regimes in which it can be most effectively used and to improve estimation of the time between application and impact under different environmental conditions.

The APLC is also working to identify other possible biological control agents, through established national and international networks.