Defdef

If used in the wrong combination, environmentally and health-friendly pest control strategies might actually increase crop pest populations. A new European research project will put this counter-intuitive idea to the test.  

Pests on agricultural crops can be a serious nuisance so farmers do their best to keep the unwanted bugs in check. In order to limit impacts on the environment and human health, crop protection in the EU relies increasingly on the use of biological control, pest-resistant plants, and ”green” pesticides containing natural compounds instead of synthetic compounds. This seems like a sound combination of strategies, right? Not necessarily. It seems the strategies may be counterproductive to each other. 

- Predator-prey models predict that resistance breeding and pesticides – with synthetic or natural – may hamper biological control to an extent that the level of overall crop protection will often decrease rather than increase, says Dr. Merijn Kant of the University of Amsterdam in the Netherlands. 

Dr. Kant is the coordinator of a new European project involving scientists from three different research institutions in the Netherlands, Belgium and Spain that will assess to which extent prey densities in a predator-prey system, i.e. a biocontrol agent and its target pest, are influenced by chemical plant resistance traits and natural pesticides. The three-year project, entitled Defdef (short for ”Defenseless defenses”), has a total budget of €591,909 and has been granted €524,909 through the C-IPM second call. 

 Using the the wrong combination of strategies may actually lead to an increase in crop pest populations. The predator-prey models show that prey quality and predator mortality are the two key determinants of pest equilibrium densities. These two parameters are affected by plant resistance traits and pesticides with the result that pests can become more populous instead of less.  

- This counter-intuitive concept should be tested because the results can profoundly alter the rationale behind the design of IPM strategies, says Dr. Merijn Kant. 

Through aeons plants have evolved defenses to protect themselves against plant-eating insects and mites. Giving plants a helping hand by tweaking their genes through targeted breeding to create resistant plants might hinder the actions of biological control agents just as they hinder unwanted pests. 

One instance in which this can happen is when the plant is resistant because it is less palatable for insects. This will affect not only the harmful insects but also the beneficial ones since their prey will be of poorer quality. Mathematical models predict that under these conditions harmful insects may actually escape predation better than if they feed on plants void of resistance. They can thus reach higher densities and inflict more damage to the crop. In this case, plants without defenses may be defended better with biological control. 

To test if the theory holds true, the project partners will use tomatoes, spider mites and predatory mites in the greenhouse and field to establish model parameters and validate model predictions. The researchers will use their findings to bring together seed companies and biological control companies with the aim of aligning their strategic agendas for developing new products.