Parasitic wasps remain an effective and resilient alternative to chemical pesticides for controlling crop pests, despite growing concerns over resistance, according to new research.
The University of Stirling's findings will reassure farmers and growers increasingly under pressure to reduce chemical inputs, with the study showing that biological pest control continues to perform well even when pests begin to adapt.
Researchers focused on the glasshouse whitefly, a widespread sap-feeding pest in protected cropping, and Encarsia formosa, a parasitic wasp commonly used to control it.
Led by Dr Mia McGowan, the study found that although some whiteflies can develop genetic resistance to parasitism, those that survive pay a significant biological cost. Survivors were found to have low reproductive success, making the spread of resistance across pest populations unlikely.
Using predators and parasitic insects to control pests is widely viewed as safer and more environmentally sustainable than chemical pesticides, which pests are known to adapt to rapidly. In the case of Encarsia formosa, the wasps lay their eggs inside whitefly larvae, preventing them from reaching adulthood and reducing pest populations naturally.
Crucially, the researchers found that biological control agents can evolve alongside the pests they target. This co-evolution reduces the risk of rapid resistance development that often undermines chemical insecticides.
While there have been increasing reports in recent years of pests showing resistance to biological control agents, the study suggests such resistance is far less likely to become widespread.
Dr McGowan said concerns about resistance should be kept in perspective. “There have been increasing reports of resistance to biocontrol agents presenting a problem in recent years,” she said.
“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.”
The research involved two controlled experiments carried out at the University’s Controlled Environment Facility. In one, whiteflies of known relatedness were exposed to parasitism to assess whether survival was genetically inherited. In a second experiment, whiteflies that survived parasitism were monitored to assess their lifetime reproductive success.
The results showed that whiteflies able to resist parasitism laid fewer eggs and produced fewer viable offspring than unexposed insects, confirming that resistance comes at a significant fitness cost.
Dr Rebecca Boulton, lecturer in evolutionary ecology at the University of Stirling, said the findings strengthen confidence in biological pest control as a long-term strategy.
“Our results add to the small but growing number of case studies that demonstrate resistance to parasitoid-based biocontrol can evolve under certain circumstances,” she said.
“However these findings reinforce the view that, compared to chemical insecticides, biocontrol is an evolutionarily stable and resilient strategy to resistance evolution.”
The researchers said the study supports continued use of biological control as part of integrated pest management, particularly as farming systems adapt to tighter pesticide regulations and environmental targets.
They added that biocontrol offers a durable, science-backed solution for managing pests while reducing reliance on chemical sprays.
