Oilseed rape (OSR) is the world’s second most important oilseed crop and was the UK’s third most valuable crop in 2010, with an estimated economic value of £702 million. Production has declined since this peak, driven in large part by restrictions on neonicotinoid seed treatments in 2013 and their full withdrawal in 2018. Total output value had reduced by approximately 50% to £358 million by 2020, despite rising prices, while the area planted declined by more than 60% to the lowest level since 1989 at 307,000 hectares, though the area planted has rebounded slightly to 342,000 hectares in England by 2023. This general trend of reduction has largely been attributed to pressure from the cabbage stem flea beetle (CSFB). CSFB larval numbers have increased tenfold following the introduction of neonicotinoid seed treatments and CSFB resistance to pyrethroid insecticides has steadily increased over recent years. Combined with damage from secondary pests like weevils, pollen beetles, aphids, extreme weather events, and low profit margins, many farmers have lost confidence in OSR as a viable crop. 

Adult CSFB emerge in late spring-early summer after pupating in the soil and feed on mature leaves, stems and pods of established oilseed rape and other brassicaceous species. The adults then enter a period of aestivation from late June to mid-August before migrating into newly sown oilseed rape crops. Adult CSFB feed on the leaves of OSR seedlings, causing distinctive injury known as ‘shot-holing’. This type of feeding can cause substantial yield losses and in extreme cases can lead to seedling death and even total crop failure. Adults then mate and lay eggs at the base of the crops and these eggs hatch as larvae sometime later. If the crop becomes established early, invasion by the larvae can be a major risk to crop yields. 

Several integrated pest management (IPM) solutions have been proposed by which CSFB could be better managed, such as altering crop rotations, changing cultivation methods, companion planting or controlling via predators. A common theme of these IPM approaches is that the selection and timing of appropriate control methods requires an ability to predict arrival of adult CSFB at the OSR crop. This would allow farmers to drill crops so that CSFB migration and the most susceptible plant growth stages do not coincide with one another. In this work we analysed data from a network of CSFB traps using a Bayesian generalised linear multilevel model to understand the main drivers of cabbage stem flea beetle migration. We found that temperature is the main environmental driver that interacts with the species’ phenology to determine time of arrival at the crop. Wind speed, rainfall and solar radiation had negligible impacts on adult arrival time.

The associated article "Temperature and time of season are the predominant drivers of cabbage stem flea beetle, Psylliodes chrysocephala, arrival at oilseed rape crops" is open access and is now available to read here.

Acknowledgements: This work was led by David Ewing and Helen Kettle at BioSS in conjunction with collaborating researchers from Harper Adams University, ADAS and AHDB. All authors were funded under BBSRC project BB/X012123/1 and David Ewing and Helen Kettle were supported by the Scottish Government's Rural and Environment Science and Analytical Services Division (RESAS). AHDB funded the data collection.