Insect-killing biopesticides should not be considered “universally benign,” with more attention needed around doses, timing and ecological contexts, according to an international team of scientists.
Biopesticides such as bacteria, fungi, viruses and nematodes are increasingly in demand from farmers looking to produce food with reduced ecological impacts compared to conventional synthetic pesticides, which in many cases are also facing growing resistance from pest insects.
Looking beyond target pests
But in an opinion paper published in the journal Trends in Ecology and Evolution, the researchers argued that while the benefits of biopesticides over ‘business as usual’ are undeniable, there have been oversights about how these products can affect the broader insect communities found on farmland.
Looking at the available evidence on the lethal, sub-lethal and behavioural effects of these products on beneficial insects such as pollinators and the natural enemies of pests, they argued that it is necessary to move away from the assumptions that they are benign to all but their targets.
Evidence of impacts on beneficial insects
They pointed to the exposures faced by non-target insects on surfaces and flowers, as well as through contact with pest insects that have been infected with biopesticides. Mortality has been recorded in ladybirds and predatory Orius bugs, parasitoid wasp larvae, bees and dung beetles exposed to fungi and nematodes used to control pests, they said. Non-lethal effects include reduced viability of predator eggs, behaviour changes such as avoiding contaminated areas, and reduced colony cohesion in social bees.
Further, impacts can be part of a multi-faceted picture in agricultural environments, they stressed. Infected prey can have less nutritional value, leading to cascading effects, and specialised species can be disproportionately affected compared to generalists, changing community structure and favouring competitors which provide less effective ecosystem services.
“The evidence…neither challenges the value of EP biopesticides nor their clear advantages over synthetic chemical control options,” they said. “Rather, we argue that the ecological risks associated with EP use, especially sublethal, indirect, and multitrophic effects on beneficial insects, have often been under-recognised.”
Reducing harm through smarter application
Suggested solutions include timing applications of products to avoid peak activity periods for pollinators and natural enemies, selecting strains of pest-controlling organisms that have very narrow host range or don’t persist long in the environment. The scientists also called on regulators to employ “greater ecological realism” in risk assessments.
“Current registration protocols for microbial pesticides typically prioritise acute mortality and vertebrate toxicity, while behavioural, sublethal, and indirect effects on beneficial insects are rarely considered,” they said, in spite of evidence suggesting that impacts on foraging and reproductive behaviour, for example, influence the success of broader attempts to control pests through integrated pest management.
Supporting sustainable integrated pest management
Further work should further explore how non-targets insects are exposed to biopesticides, look closer at the specific impact of different strains of pest-controlling organisms and conduct experiments that fully consider the multiple stressors, including biopesticides, that pollinators and natural enemies face in the field.
Such efforts will ensure biopesticides “fulfil their promise as durable, effective, and genuinely sustainable components of future pest management systems,” they added.
Key takeaways
- Biopesticides can affect beneficial insects beyond their intended pest targets.
- Sublethal and behavioural impacts remain underrepresented in risk assessments.
- Ecological effects vary with timing, dose, persistence and environmental context.
- Researchers recommend more realistic regulatory testing of microbial biopesticides.
- Better understanding of non-target impacts could strengthen sustainable pest management.
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