Using insects such as wasps to control agricultural pests remains a resilient method, despite resistance increasing, a new University of Stirling study has shown.

Research led by Dr Mia McGowan, of the University’s Faculty of Natural Sciences, studied the glasshouse whitefly (Trialeurodes vaporariorum), a common sap-feeding insect, and the Encarsia formosa wasp that is used to control it.

The study found that, although some whiteflies can genetically resist parasitism by Encarsia, survivors have low reproductive success - making the evolution of widespread resistance unlikely.

Using other insects like predators and parasitic wasps to control agricultural pests is considered safer and more environmentally friendly than using chemical pesticides. Encarsia formosa lay their eggs inside whitefly larvae before consuming their host from the inside out, making them a natural pest-controller.

Additionally, these biological control agents have the capacity to evolve alongside the pests they attack, reducing the likelihood that pests will evolve resistance like they rapidly do when confronted with chemical control agents. In recent years, however, there have been reports of pests evolving resistance to biological control agents like parasitoid wasps.

Study lead Dr McGowan explained: “There have been increasing reports of resistance to biocontrol agents presenting a problem in recent years.

“Our study shows that, while this is something that is possible, the complex evolutionary interactions between hosts and parasitoids limit the likelihood, making biocontrol evolutionarily resilient when compared to chemical control.”

Research saw Dr McGowan run two experiments in the Controlled Environment Facility (CEF) at the University.
In the first, she exposed whiteflies of known relatedness to Encarsia and examined whether those that survived parasitism were more likely to be related, to determine whether resistance is likely to be genetically inherited.

Another experiment then took place in the CEF where Dr McGowan collected whitefly that had survived parasitism, looking at how many eggs they laid and whether these hatched successfully. They were then compared to unexposed control whitefly to determine whether resisting parasitism reduced lifetime reproductive success.

Dr Rebecca Boulton, Lecturer in Evolutionary Ecology at the University of Stirling, who supervised the study said: “Our results add to the small but growing number of case studies that demonstrate resistance to parasitoid-based biocontrol can evolve under certain circumstances.

“However these findings reinforce the view that, compared to chemical insecticides, biocontrol is an evolutionarily stable and resilient strategy to resistance evolution.”

Is resistance futile? Life-history costs of escaping parasitoid attack in a major crop pest is published in the Journal of Economic Entomology.

Research was match funded by the University of Stirling through the Natural Environment Research Council (NERC) Iapetus Doctoral Training Partnership. Dr Boulton was funded by a Biotechnology and Biological Sciences Research Council (BBSRC) Discovery fellowship, and the study was supported by Filippo Amatiello, of Bioline Agrosciences.