Research using camera traps in UK oilseed rape (OSR) fields has uncovered surprising allies in the battle against two of the crop’s most damaging spring pests.
In a two-year study conducted across two locations, researchers found that the larval stages of predatory ground beetles—particularly Carabid beetles—play a far more significant role in pest control than previously thought.
Ecologists have typically relied on pitfall traps to assess invertebrate predators in farmland, but these traps have been found to underestimate beetle larvae—an important part of the predator community.
The study’s results, published in Biological Control, show that beetle larvae are, in fact, the most frequent predators of pollen beetle (Brassicogethes aeneus) and brassica pod midge (Dasineura brassicae) larvae.
The researchers found that beetle larvae move out of the soil where they live to actively feed on pest larvae at the precise moment they drop to the ground to pupate—when they are most vulnerable.
This synchrony between predator activity and pest susceptibility could offer a new approach to pest management, said Dr Sam Cook of Rothamsted Research, who led the research.
“In-field cameras have uncovered unexpected predators of two major oilseed rape pests, potentially aiding control strategies,” she added.
“Recognising the importance of predatory beetle larvae in natural pest control, farmers could adopt conservation biocontrol strategies that enhance the presence of these beneficial arthropods.
Studying bugs in real-time
Throughout the study, camera traps placed over sentinel prey (lab-reared pest larvae) recorded over 350,000 images, allowing the team to observe real-time predation events.
Unlike previous studies that focused on adult beetles, these images revealed that beetle larvae emerged from the soil and fed actively on pest larvae as they dropped from the crop canopy to pupate in the soil. This stage is critical, as pest larvae remain on the soil surface for only a few minutes before burrowing down, making the timing of predator activity crucial.
The study found that predator and pest activity were well aligned. Most pollen beetle larvae dropped between 18:30 and 23:20, while brassica pod midge larvae dropped later in the night and early morning.
“Predators of the pollen beetle larvae were significantly more active at night compared to morning or afternoon,” explained Dr Cook. “This pattern was consistent across both years, indicating a preference for nocturnal activity among most predators.”
The dominant predators recorded included the larval stages of Carabidae and Staphylinidae beetles, with some input from ants, spiders, and occasional opportunistic predators such as birds and earwigs. Notably, small beetle species like Bembidion and Trechus—largely missed by traditional trapping—were frequently observed by the cameras.
The research team said the findings have practical implications for farmers looking to reduce pesticide use. By encouraging habitats that support beetle larvae—such as maintaining soil cover, minimising tillage, or avoiding unnecessary insecticide applications during peak activity times—growers can enhance biological control in their fields.
“These findings highlight the potential of cameras as powerful tools for ecological research,” Dr Cook added. “As farming continues to seek greener solutions, this innovative approach could contribute to improved pest management rooted in nature’s own defences.”
With OSR yields under growing threat from insect pests and regulatory pressure on chemical controls increasing, understanding and supporting natural predator populations may prove critical for sustainable oilseed rape production across the UK and Europe.
