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News Article

Prevention of deforestation through biological control


Reduction in losses of cassava crop to invasive mealybug slows conversion of forests in SE Asia

In the face of globalised trade, the inter-continental transportation of pests and pathogens has become a constant risk when buying and selling agricultural products internationally. The losses caused by these pests are often substantial as there is no naturally evolved enemy present in the new country. Productivity on crop land therefore declines as a result and, in tropical countries, neighbouring areas of forest are often cleared to create more land for agriculture and fill the yield deficit. A recent study in South East Asia has sought to link the application of biological control for pest suppression to a reduction in conversion of forested areas.

Biological control is a form of pest suppression based on the identification and then introduction of organisms that would naturally control the pest’s population in its native habitat. Whilst this has been applied successfully in the past, examples of the negative effects of poorly selected biological control agents have gained much greater notoriety. A particularly famous example is the introduction of cane toads in Australia which, whilst also not controlling the intended pest, have led to a reduction in native wildlife through their toxic nature. This has led to biological control being dismissed in many situations where is provides an environmentally safer and long-term solution to exotic pest introduction compared to the usage of chemical control.

The mealybug Phenacoccus manihoti (Hemiptera) was first detected in SE Asian cassava crops in 2008 and since then has led to a 27% reduction in Thailand’s aggregate cassava production and a 162% increase in starch price as a consequence. Due to the economic importance of cassava in the region and strong inter-country trade in the crop, this shortfall resonated around the region. The response was an increase in the area of cassava cultivation in neighbouring countries rising from 713,000ha in 2009 to >1 million ha by 2011. Satellite imagery has revealed the cost of this expansion for areas of native forests, showing an increase in deforestation of 388% in Cambodia, 330% in Lao PDR, 185% in Myanmar and 608% in Vietnam.

The parasitoid wasp Anagyrus lopezi, originally from S. America, had already successfully been used to control the mealybug in Africa from 1981. In 2010 the wasp was released into Thailand and over the next three years into Lao PDR, Cambodia and Vietnam, suppressing pest populations. Field surveys taken 6-9 years after P. manihoti detection and 5-9 years after A. lopezi introduction showed that pest abundance was negatively associated with parasitoid presence. This confirmed that the control agent is effective at supressing the pest, with the exact level varying between plantations and countries. The decrease in pest populations and therefore crop losses was linked to a slowing of deforestation rate by 31-95% dependent on country.

The risks of biological control agents are now thought to be minimal due to restrictions and knowledge of best practice. This work provides robust evidence for the ability of this approach to effectively reduce pest populations and therefore aid tropical forest conservation, serving as an example to future pest management planning.

Read the full paper here: Wyckhuys, K.A.G., Hughes, A.C., Buamas, C., Johnson, A.C., Vasseur, L., Reymondin, L., Deguine, J.P. and Sheil, D., 2019. Biological control of an agricultural pest protects tropical forests. Communications biology, 2(1), p.10. https://doi.org/10.1038/s42003-018-0257-6

To find 1,100 similar papers use the search string below in the Forest Science Database: "biological control agents" AND "introduced species"

Article details

  • Author(s)
  • Ellen Baker
  • Date
  • 25 January 2019
  • Source
  • Wyckhuys, K.A.G., Hughes, A.C., Buamas, C., Johnso
  • Subject(s)
  • Environment