Biocontrol: set a bug to catch a bug

 

Challenge: reduce food loss to pestsTractor spraying crop. © Valio84sl/ Dreamstime

Natural inspiration: biocontrol

 
 
The 20th century saw major breakthroughs in agricultural science.  Better crop varieties and increased use of fertilisers and pesticides allowed farmers to achieve a huge leap in food production.1 Chemical pesticides provided a much less labour-intensive way of controlling pests than previous methods.  In 2001, farmers across the world used an estimated five billion tonnes of pesticides, with the global pesticide market valued at $31.8 billion. 2 Nevertheless, around 25% of the world’s crops are still lost to pests or diseases. 3Farmer with pesticide © Leaf/ Dreamstime
 

 

 

 

Chemical pesticide use is not without problems.  If a field is sprayed with a pesticide, any of the pests that can resist this particular chemical will survive and have offspring that are also less vulnerable to it.  After several generations an increasing proportion of the pest population will be resistant, and the pesticide is rendered useless.  Other problems with pesticides include health risk to people 4 and the economic and environmental cost of manufacturing the chemicals.  Pesticides can kill other insects that are not pests.  Furthermore, if they accumulate in the bodies of creatures that eat insects, or if they run off into rivers or seep down to the groundwater, they can build up in the environment and become a danger to many more animals. 5 For these reasons, regulation on pesticide use is being tightened up. Farmers must find alternatives to some of the chemicals they once used. 7

 

 

 

In nature, predator and prey continually evolve: the prey species develops a new defence, the predator develops a way of overcoming it, so the prey evolves a  better defence, and so on.  The two species tend to keep each other in balance, neither allowing the other to become too numerous.  Rather than trying to come up with ever more toxic chemical pesticides, scientists are learning to make use of the natural mechanisms that keep pests under control.  This approach is called biocontrol.

 

Ladybirds eating aphids © FalconStock/ Dreamstime

 

 

 

Since the natural enemies of pest species are already present in the environment, one obvious step is to encourage their population to increase.  This can be achieved by planting hedges and wildflower meadows around crops, providing a home for many helpful birds and insects. In other situations, useful species can be directly introduced onto the land.  Wireworms, the larvae of click beetles, are a major pest of several crops including potatoes.   A recent study has showed that certain types of fungus and roundworm, natural parasites of wireworms, are very effective at keeping the wireworm population under control.  8caterpillar © jm2c, www.sxc.hu

 

 

 

 

 

In nature, plants must defend themselves from pests, and many plants do this by producing their own pesticides.  Plant essential oils are easy to extract and soon break down into harmless compounds when released into the environment.  Unlike man-made pesticides which are usually based on a single chemical, essential oils are a complex mixture of substances.  This makes it less likely that pests will develop resistance to them.  One recently-studied example is eucalyptus oil. It is a natural insect repellent and is toxic to some bacteria and fungi, but non-toxic to humans.  It can protect crops from certain insect pests, moulds and mildew, and may also help in controlling some weed species. 9Wildflower meadow © mn-que, www.sxc.hu

 

 

 

 

 

There are believed to be around 400,000 species of plant in the world 10, each with its own unique blend of natural defences.  This is a huge resource for agricultural scientists to draw upon.  However, the resource is dwindling: about one in four plant species worldwide is now threatened with extinction. 10Farming family © Vanbeets/ Dreamstime

 

 

 

 

 

Combining biocontrol with careful use of pesticides is known as Integrated Pest Management (IPM) and is very effective. 7  Used well, IPM can reduce pesticide use, provide economic savings for the farmer and protect both the environment and human health. 11 Farmers in the near future may be able to rely on the biodiversity of the countryside, along with natural pesticides extracted from plants, to keep pests under control without resorting to toxic chemicals.

 

 

 

 

 

References
1. International Food Policy Research Institute (2002) Green Revolution: curse or blessing?  Accessed February 2010.
2. Kiely, T., D. Donaldson, and A. Grube (2004). Pesticides Industry Sales and Usage: 2000 and 2001 Market Estimates. EPA's Biological and Economic Analysis Division, Office of Pesticide Programs, and Office of Prevention, Pesticides, and Toxic Substances.  Accessed February 2010.
3. Biotechnology and Biological Sciences Research Council: The Bioscience behind secure harvests.  Accessed February 2010. 
4. Andreotti, G., Beane Freeman, L.E., Hou, L. et al. (2009). Agricultural pesticide use and pancreatic cancer risk in the Agricultural Health Study Cohort. International Journal of Cancer: 124(10):2495-2500.
5. JNCC: pesticides and toxic substances.  Accessed February 2010. 
6. Defra (2010). Consultation on implementing European pesticides legislation.  Accessed February 2010. 
7. Relu (2009) Overcoming Market and Technical Obstacles to Alternative Pest Management in Arable Systems.  Accessed February 2010/
8. Ansari, M.A., Evans, M. and Butt, T.M. (2009). Identification of pathogenic strains of entomopathogenic nematodes and fungi for wireworm control. Crop Protection 28: 269-272
9. Batish, D.R., Singh, H.P, Kohli, R.K. et al. (2008). Eucalyptus essential oil as a natural pesticide. Forest Ecology and Management. 256: 2166-2174.
10. Botanic Gardens Conservation International.  Accessed February 2010.
11. Ehler, L.E. (2006) Integrated pest management (IPM): definition, historical development and implementation, and the other IPMPest Management Science 62:787–789.  Accessed February 2010. 


Further reading
Wild Solutions, Andrew Beattie and Paul R. Erlich.  Pub. Yale University Press (2001). Chapter 7 “Natural enemies are best friends”, pp 107- 124.