Beetle pests are difficult to poison without damaging other insects, and Biological Control can lead to unexpected problems.
The Cane Beetle (Dermolepida albohirtum) is native to Australia and it is one of the serious pests of Sugar Cane there. The adult beetle eats the leaves, and the larvae attack the roots from below ground.
Beetles as Pests
The problem with beetles that are pests is that the adults are incredibly tough. They have solid wing cases and most also have heavily armoured bodies. The larvae often spend time underground and can be difficult to locate. Pesticides that kill beetles are likely to damage a whole range of other – useful – invertebrates, including predatory beetle species. This is why Biological Control of beetles is so attractive.
Biological Control Gone Wrong
In 1935 the Cane Toad was introduced into the sugar cane region of Australia in an attempt to control the cane beetle. The Cane Toad (Bufo marinus) is not native to Australia, but comes from South America where it has evolved as part of the natural fauna. It is a very successful insect predator, but in South America its numbers are controlled by a variety of creatures that can eat it. When they were let loose in Australia the toads had no natural enemies and were incredibly successful, so much so that they are now a pest themselves!
Problems Caused by Cane Toads
The cane toad is not a typical ‘pest species’. It does not eat crop plants, and it does eat a lot of pest insects. The problems lie in the fact that cane toad developed a number of ways to survive in South America. Most toads hunt by sight, but the cane toad can also find food by smell. This has allowed it to become truly omnivorous – it will even eat dog-food! Having such a wide variety of potential foods has allowed rapid population increase. In addition to this the cane toad has glands which produce a toxin, and this means that anything eating it in Australia will not enjoy the experience and might even die.
Other Methods of Controlling Cane Beetles
There is now a lot of research into other types of Biological Control that might be suitable for cane beetles. It looks like there might be a specific variety of the fungus Metarhizium anisopliaethat will only damage these beetles. This could be a safer way to handle the situation, but it would still leave the problem of the toads!
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