University of Stirling researchers in Scotland have uncovered the surprising strength of one of farming's smallest allies: Encarsia formosa, a parasitic wasp that controls crop-damaging insects. The research team's study provided some hope despite "increasing reports of resistance" of pests to parasitic wasps in other growing environments.
Dr. Mia McGowan, a researcher in Stirling's Faculty of Natural Sciences, studies how insects interact and adapt over generations. That focus led her team to Encarsia formosa and its target: the glasshouse whitefly. The glasshouse whitefly is a widespread pest that harms greenhouse crops by feeding on plant sap and spreading rapidly.
Encarsia formosa offers a hands-off, long-standing solution.
The wasp is harmless to people and stays focused on a single purpose: laying eggs inside whitefly larvae. As those eggs develop, the pest is eliminated before it reaches the most damaging stages of its life cycle. For farmers and greenhouse operators, that process can help maintain healthier plants and steadier crop production.
Dr. McGowan and her colleagues ran two controlled experiments. They aimed to understand whether whiteflies could survive parasitism and, if so, whether that survival trait could spread.
One test examined genetic patterns among surviving insects. The second tracked how many eggs those survivors produced and how many hatched successfully.
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Published in the Journal of Economic Entomology, the results revealed that some whiteflies did survive Encarsia attacks, which demonstrates that resistance is possible. However, those survivors reproduced less effectively than whiteflies that were never exposed to the wasps.
Because they produced fewer viable offspring, resistant traits struggled to persist. Pesticides, on the other hand, strengthened those resistant traits over time.
These findings underline the value that Encarsia formosa brings to controlled growing environments, including research facilities and commercial greenhouses. When the wasps perform reliably, growers can limit pest outbreaks without heavy chemical use or repeated intervention.
In a university press release, Dr. McGowan said, "Our study shows that, while [resistance] is possible, the complex evolutionary interactions between hosts and parasitoids limit the likelihood, making biocontrol evolutionarily resilient when compared to chemical control."
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"These findings reinforce the view that, compared to chemical insecticides, biocontrol is an evolutionarily stable and resilient strategy to resistance evolution," affirmed Dr. Rebecca Boulton, lecturer in evolutionary ecology at the University of Stirling and supervisor of the study.
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