Combined Biological Sciences Meeting

Melbourne School of Land and Environment
University of Melbourne

Resistance is Not Futile: Delaying Evolution in Pests and Weeds

Resistance to pesticides has evolved among some 500 species of insects, weeds and plant pathogens and may account for about 5% of crop losses in developed countries such as the US.  It also significantly increases pest management costs, with resistance typically driving the use of higher rates of pesticide use and substitution of more expensive and less favourable pesticides.  In some cases, such as the Ord Irrigation Area of Australia in the 1970s, pesticide resistance has caused the collapse of agricultural industries.  Perhaps the most important impact of resistance has been in mosquitoes that transmit malaria and other diseases, possibly causing human deaths in the millions.  A key area of concern over the last decade has been that insects would evolve resistance to transgenic plants, such as “Bt” cotton, expressing insecticidal proteins.

The challenges of resistance have been so great in many cases that it has often seemed futile to try to do anything about it. Through the 1960s, the primary response was typically to simply synthesize new chemicals, and even into the 1990s, some argued that new genes for tolerance to insects and herbicides would be the answer for GM crops.  Both strategies have faced the problem of an insufficient discovery of new toxicants.

Insecticide resistance was recognised as an evolutionary phenomenon in the 1930s, but it wasn’t until about the 1970s that ecological genetic approaches were applied to try to delay (“manage”) resistance.  This led to a greater realisation that significantly delaying resistance was possible by a combination of good chemistry and tactics to manage evolution, which can be effective with only a modest amount of ecological and genetic information.  Key successes have included some chemical pesticides but perhaps especially Bt cotton, to which resistance management strategies have been intensively applied, and which has outlasted the record of chemical insecticides. There are key lessons from these experiences both for pest management and the context of evolution.

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