Monday, 11 January 2021 17:35

When medicine feeds the problem: Are pesticides feeding crop pests?

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SPRINT recently attended a fascinating talk at the Oxford Real Farming Conference. Researchers from the University of Edinburgh shared their findings surrounding why pesticides may, paradoxically, benefit crop pests. The research was born from the work by a French agronomist, Francis Chaboussou. 

Who was Chaboussou?

Chaboussou was an agronomist who observed that agrochemicals were leading to more pressure from pests than without them. He wondered: why is this? He then dedicated his life to finding out both through experiments and reviewing the literature. 

What were Chaboussou’s findings?

The central idea developed by Chaboussou is that most pests depend on the availability of amino acids, which are the building blocks for proteins, which are vital for plant growth and repair.

Plants make proteins out of amino acids through a complex process. Before amino acids have been used up in this process, they provide a good source of food for pests and parasites.

Amino acid concentrations in plant cells are usually kept at low levels because they are quickly used up by the plant when making proteins. Applying pesticides can temporarily prevent the plant from producing proteins and result in proteins converting back to amino acids. These applications can paradoxically result in increased food availability for pests.

This means that pesticides may feed the very problem they attempt to solve. For example, whilst the spray may kill the pest which was originally causing a problem (e.g., greenfly), it then inadvertently be providing food for fungi, resulting in fungal infection. The result is a treadmill of pesticide applications. You can read Chaboussous’ book for free here.

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Re-evaluating Chaboussou’s findings in the present day

Daisy Martinez and colleagues from the University of Edinburgh recently completed a literature review exploring whether Chaboussou’s conclusions are true.

The results of their review confirm many of Chaboussou’s  findings. The review indicates that in addition to providing amino acids which feed pests, crops may become biochemically stressed by pesticide applications. This stress may not be obvious as these changes are subtle and occur within the plant’s cells. The outcome of this shift is an accumulation of amino acids in crop tissues. Again, increasing the availability of food for pests and pathogens.

Similar results have been found in response to Nitrogen fertiliser applications. Further research is needed to explore the effects of fertilisers and pesticides in combination.

Based upon the findings of this research, we conclude that the paradoxical effects of pesticides should be considered when deciding whether and how to apply them. This research also underpins the need to look at the complex nature of ecological interactions when farming. This evidences the importance of the unified global health risk assessment toolbox being developed by SPRINT for helping regulators to decide whether or not to approve pesticides.

Speakers: Ulrich Loening, Daisy Martinez

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