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Biological control of locusts using the fungus Metarhizium
The Australian Plague Locust Commission also uses a biological control agent (Metarhizium anisopliae variety (var) acridium) to manage populations of Australian plague locust.
Metarhizium is a naturally occurring fungus that is specific to locusts and grasshoppers. That is, 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 suspend Metarhizium spores (the reproductive stage of the fungus) in oil to form the product known here as Green GuardTM(formerly produced by the Australian biotechnology business Bio-Care Technology Pty Ltd).
Note: the production of Green Guard does not involve the genetic manipulation of the fungus. The fungus is simply cultured en masse (much as other microorganisms are cultured en masse, eg. yeast) so that sufficient quantities of spores can be harvested to deliver commercial quantities of the product. The spores are suspended in oil partially to increase the length of time they can endure prolonged dehydration following application and partially 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 mositure and nutrients from the living insect, thereby eventually killing it. Green Gaurd is sprayed onto bands of locust hoppers (nymphs) and flying adults (swarms) using conventional ground-based (for bands) or aircraft-mounted (for swarms) 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 begun 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 >90 per cent. The nature of the fungus eventually kills the insect with the greatest mortality occurring sometime between 7 to 15 days after treatment (depending upon ambient temperature). This success led to the first operational use of Metarhizium anywhere in the world during 2000-2001 in which over 20,000 hectares of bands and swarms of Australian plague locust were aerial treated.
Locusts infected with the fungus will initially turn a characteristic pink colour and later a green colour as the fungus sporulates, ie. produces more spores. These non-artificially cultured spores will only develop if living locusts or grasshoppers come into contact with them and the prevailing environmental conditions are suitable for their germination. Otherwise they will soon die. Consequently, Metarhizium anisopliae var acridium should not remain in high abundance in those areas where it was applied during previous spray operations.
Nymphs infected with MetarhiziumPink stage
Green stage
Metarhizium is more expensive than chemical insecticides such as fenitrothion. Consequently, it is mainly used by organic producers and in environmentally sensitive habitats. Because many locust outbreaks originate in the outback where organic beef production is common, it is also used there. 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's program of preventive locust management.Other Metarhizium links:
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