In-field cameras have uncovered unexpected predators of two major oilseed rape pests, potentially aiding control strategies.

The camera study, conducted over two years in two UK locations, found that larval stages of predatory carabid beetles play a crucial role in tackling the pollen beetle (Brassicogethes aeneus) and the brassica pod midge (Dasineura brassicae), two significant threats to oilseed rape crops.

The research was conducted by Gaetan Semani-Corda as part of his PhD studies at Rothamsted Research under the supervision of Dr. Sam Cook. The main driver for these investigations is the continuing problem of pest control for oilseed rape (OSR).

“Some effective pesticides that UK and European farmers used to use to control pests such as cabbage stem flea beetle, pollen beetle and the brassica pod midge have been banned and farmers are struggling to protect their crops,” said James Clarke with Rothamsted Research. He added that in some areas of England, OSR cultivation is now down by as much as 29 percent as farmers abandon the crop.

Ecologists have long used camera traps to study wildlife, but their application in monitoring invertebrates is relatively new. Traditionally, pitfall traps have been the go-to method for studying predatory arthropods. However, the latest findings reveal that pitfall traps fail to capture large numbers of predatory beetle larvae, underestimating their impact as natural pest controllers.

“A key part of this approach is surveillance – can we tell farmers in real time when pests arrive in their fields so they can act quickly,” said Clarke.

The important finding from the research is that predatory carabid beetle larvae are much more voracious predators than was previously known – so encouraging these beetles in crop fields could help with control of pests.

“Recognizing the importance of predatory beetle larvae in natural pest control, farmers could adopt conservation biocontrol strategies that enhance the presence of these beneficial arthropods,” said Cook, who led the research team. “Adjusting farming practices to support these natural predators may reduce the need for synthetic chemical pesticides, improving sustainability and biodiversity in agricultural landscapes.”

The study also showed differing activity patterns depending on the time of day. Predators of the pollen beetle larvae were significantly more active at night compared to morning or afternoon, with notable activity also recorded at dusk and dawn. This pattern was consistent across data collected in both years, indicating a preference for nocturnal activity among most predators, while some exhibited a diurnal rhythm. The highest numbers of pollen beetle larvae dropped at dusk, while the brassica pod midge larvae dropped significantly more at dawn than at other times of the day.

With European oilseed rape yields under constant threat from pests, this research provides fresh hope for more environmentally friendly farming. Encouraging predatory beetle larvae populations could be a cost-effective and ecologically sound method to keep crops safe while preserving essential predator species.

“These findings highlight the potential of cameras as powerful tools for ecological research,” said Cook. “As farming continues to seek greener solutions, this innovative approach could contribute to improved pest management rooted in nature’s own defences.”