Field margins should be sited to encourage beetle species that predate on crop pests, says Dr Kelly Jowett of Rothamsted Research. Wendy Short reports.

Early research indicates that the strategic siting of field margins may have the potential to encourage beetle species that predate on crop pests, according to Dr Kelly Jowett of Rothamsted Research.

Initial findings by Dr Jowett have detected greater numbers of beetles within the crop, compared with populations found in field margins.

“The highest numbers of beetles are consistently found within the crop itself,” said Dr Jowett. “Overall, field margins have a positive effect on wildlife, but they may act as a barrier to prevent beneficial beetles from spreading out around the farm. Roads and urban areas adjacent to arable fields can also present a barrier to beetle movement.

The Northern Farmer: Dr Kelly Jowett of Rothamsted Research

“I am not proposing that field margins should be omitted from field design, but in relation to beetles which prey on crop pests, their siting can be planned with this factor in mind. Instead of positioning a field margin, which divides two arable fields, for example, it may be more advantageous to plant a strip that is roughly equal in length but is sited alongside a road or urban area. This will encourage the movement of beetles around the crop, with the potential to boost populations and increase pest control.”

Beetles from the carabid family are found across the country, with roughly 30 carabid species commonly found on UK farms. Dr Jowett highlighted two of the main predatory species, the violet ground beetle and the common blackclock. These species eat crop pests from slugs to aphids. Predatory beetles can also have an impact on the cabbage stem flea beetle (CSFB), which has wreaked havoc on oilseed rape crops since the ban on neonicotinoid pesticide treatments.

Dr Jowett explained that the beetles are most active during the spring and autumn.

“The main effect of carabids is to suppress pest populations, and the beetles will also react to a population explosion of aphids, for example, and will move towards the source of their food. This underlines the benefits of growing crops without field divisions, where possible.”

Trials have extensively demonstrated the predatory capacity of carabids in controlling pests. In one study, they were linked to an 81 per cent decrease in the emerging adults of orange wheat blossom midge. Meanwhile, another trial found that carabids could reduce egg and larvae numbers in the cabbage root fly population by 90 per cent. Research evidence on the level of slug control achieved by beetles is limited, she said, but one study showed a slug predation level by beetles of 16-39 per cent.

“We have found that the sienna flat beetle can control CSFB, and this is among the top ten carabid species that are found on UK arable farms. Carabids mostly tackle the pest at the larval stage. The CSFB is also preyed upon by parasitic wasps and research into how to promote their numbers is ongoing, to try and prevent losses in oilseed rape.”

The Northern Farmer: Blackclock beetle is one of the main predatory species of crop pests – Picture: Rothamsted Research

Other pest control options include direct drilling and min-till, as well as techniques like cover cropping and undersowing, although Dr Jowett acknowledged that these may not suit every farm circumstance.

“Active tillage, including ploughing, will harm beetle populations. However, the success of direct drilling and min-till will depend on soil type and conditions. In addition, anecdotal evidence strongly suggests that slug numbers may rise following reduced tillage during the first couple of years, after which they will compare favourably with the former active tillage establishment method. Initial research at Rothamsted backs up this theory.

“Undersowing crops with grass and clover mixes appears to be particularly beneficial for providing a habitat for food sources of predatory beetle species. At harvest time, the main invertebrates on which the beetle feeds will move out of the area, so an underlying grass/clover mix will encourage them to remain.”

Dr Jowett is working on the first year of a five-year project, AgZero+, with one element dedicated to investigating the effects of various field margin systems for encouraging insect pest predators. Growers who are participating in the pilot project have been given access to the ‘E-Surveyor’ phone app, to monitor beetle populations and use location tagging to generate data on beetle movements. Launched this March, the phone app makes use of artificial intelligence for the photographic identification of plant species.

“One grower in the pilot project discovered the positive effect of beetles on aphid numbers. He had been advised to spray the crop, but he was concerned that the chemical would also harm the beetle population. Therefore, he decided to withhold the spray treatment and is exploring ways of creating a better habitat for crop pest predators. In general, an integrated approach to pest management has good potential for making a positive difference to crop yields on arable units,” said Dr Jowett.

More information about signing up for the E-Surveyor phone app can be found on the website at www. agzeroplus.org.uk.