Invasives Blog


Used as an effective method of controlling invasive species, biological control (or biocontrol) is the term given to the use of living organisms for controlling pests and invasive species. It can provide an effective, environmentally-friendly and cost-efficient way of controlling pest populations, helping to restore crop yields and farmer’s profits. However a recent study, focussing on invasive cassava mealybugs, has shown that biocontrol can also have some surprising knock-on effects.

Cassava is the most important root crop grown in the tropics. It’s a major source of food for over 500 million people worldwide and also forms the basis of numerous other products including animal feed, alcohol, starch, sweeteners, prepared foods and bio-degradable products. During 2009-2010, cassava mealybugs, Phenacoccus manihoti, spread through cassava crops in Thailand causing an 18% decline in crop yields. Cassava is an important crop to many local smallholder farmers in Thailand, so this pest outbreak had significant negative impacts on farmers’ incomes and their rural livelihoods. However it also had consequences further afield; cassava prices skyrocketed (increasing by 136-162%), which lead to an increase in cassava cropping in Thailand’s neighbouring countries. By 2011, over 1 million hectares of cassava crops were being grown in these countries. This is thought to be one of the major contributing factors of  the massive increase in deforestation in Cambodia, Lao, Myanmar and Vietnam, which saw an increase of 388%, 330%, 185% and 608%, respectively. At the height of deforestation, this equated to 17,000-51,285 hectares being deforested every week.

Originally native to South America, Anagyrus lopezi is a parasitic wasp which is a natural enemy of the cassava mealybugs. In a combined effort involving CABI, IITA, IAPSC and other agencies, Anagyrus lopezi was brought to the UK and quarantined, then shipped to Africa where it was mass reared. In 1981 after extensive field trials, Anagyrus lopezi was released in Africa, where it was, and continues to be, effective at suppressing the populations of cassava mealybugs. In mid-2010, individuals of Anagyrus lopezi were taken from Benin and released into Thailand with subsequent introductions in Lao, Cambodia and Vietnam. After the parasitic wasp became established, it successfully reduced the populations of cassava mealybug, allowing Thailand’s cassava production to recover. This in turn helped the cassava trade to stabilise, averting the need for insecticides in neighbouring countries, and reducing cassava-driven forest loss in the region; deforestation slowed by 31-95% in Thailand’s neighbouring countries.

Speaking on this publication, Philippe Deguine, co-author of the paper, said “It is often difficult to reconcile socio-economic and ecological issues, and smallholder farmers are regularly tempted to resort to costly and environmentally-damaging chemical pesticides to control pests. This study confirms that appropriate use of biological control can resolve socio-economic, environmental and ecological issues simultaneously, especially in tropical countries”.

For more information on this study, read the article in full: Biological control of an agricultural pest protects tropical forests

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