By Daniel Kuhl

Overview

In the previous article, we learnt what constitutes an invasive species and outlined a brief overview of the sort of damage they can do. In this article we will explore a specific method for controlling pests known as “biocontrol”, which has an interesting past, some mighty successes, some fascinating failures. While there are three types of biocontrol¹, we will be focusing on the classical method. In this method, the natural predator of the invasive species is identified and then introduced with the intention that this natural predator will focus on the targeted invasive and work on reducing numbers². This is a highly controversial method, as it involved introducing yet another species into an environment it is not native to. Here we will explore some of the successes and failures of this method.

Success

One of the most famous stories of biocontrol success is with the Prickly pear (Opuntia stricta), or most specifically, reduction of the cactus. This notorious plan was imported into Australia in the early 1800’s for various agricultural and industrial applications³. These quickly became a massive problem, spreading across the Australian landscape and wreaking huge havoc, with historical records showing massive prickly pear forests at once stage. I’m sure most Australians have had some run in with this plant in some form or another. The governments at the time were looking for a solution and decided to employ the use of biocontrol by importing a south American moth that specifically only eats cacti, the Cactus moth (Cactoblastis cactorum)⁴. This was a huge success. The moth was released into Australia and quickly sought out the cacti and reducing them from forest size outbreaks to single plant outbreaks, although sometimes they do pop up in groups.

Failure

The failures of biocontrol in Australia have been devastating. So much so it is difficult to choose a single case, however, an example that many Australians will be familiar with is the Cane Toad (Rhinella marina). With the introduction of sugar agriculture, the native Australian beelt the Grey-backed cane beetle (Dermolepida albohirtum) exploded in numbers and quickly became a pest to the sugar farmers. Researchers and governments in the 1800’s, with the success of the Cacti moth, believed that introducing Cane toads would help with this problem⁵. They did not. In fact, they did not eat the beetle at all, and rather, became the pest Queenslanders know today. The Cane toad presents many ecological problems. Starting with massively outcompeting native frogs and other amphibious species for food and water resources. With their poisons, they present a problem to potential predators, who have all learnt to not eat the toads. Thirdly, the most prolific predator of the Cane toad is the Cane toad, which means trapping and removing efforts just end up being a positive for the remaining Cane toads. And finally, of course, they are a major menace to all pet owners. There are more reasons, however this is just a brief overview. It is sufficient to say, this was a bad move.

Conclusion

This is just a brief overview of one of the numerous methods of controlling invasive animals. Biocontrol has had successes, which is great, however when it fails the failures are absolutely devastating. It is important to recognise all methods of pest control available, how they work, and where and when to implement them. Hopefully you have learnt something in this.

References

1. Biological control. Biological control (Online), 1991.
2. Lockwood, J.L., M.F. Hoopes, and M.P. Marchetti, Invasion ecology. 2nd ed. ed. 2013, Chichester, West Sussex, UK: Wiley-Blackwell.
3. Domico, T., The great cactus war / by Terry Domico. 2018, Anna Bay, NSW: Green Flash Books.
4. Hoffmann, J.H., V.C. Moran, and D.A. Zeller, Evaluation ofCactoblastis cactorum(Lepidoptera: Phycitidae) as a Biological Control Agent ofOpuntia stricta(Cactaceae) in the Kruger National Park, South Africa. Biological Control, 1998. 12(1): p. 20-24.
5. Urban, M.C., et al., The cane toad’s (Chaunus [Bufo] marinus) increasing ability to invade Australia is revealed by a dynamically updated range model. Proceedings of the Royal Society B: Biological Sciences, 2007. 274(1616): p. 1413-1419.