New Control Methods Against the Cabbage Stem Flea Beetle in Oilseed Rape Crops

Cabbage stem flea beetle (CSFB) is one of the most damaging pests of oilseed rape (OSR) grown in the UK. An intensive research effort is underway in the UK and throughout OSR growing regions of continental Europe to develop new control methods for this pest. In the first article of a series of three, we review this research and consider approaches to this pest problem that may be available immediately and in the short-term. Agronomic practices (sowing date, seed rate, crop defoliation, companion crops, etc) are being investigated and several of these approaches are already being used on farm. The use of physically acting biopesticides such as fatty acids, while not yet being used may also provide an effective solution and could be available in the short-term. Each of these approaches has the potential to form part of future Integrated Pest Management (IPM) programmes but importantly none should be seen as simple replacements for conventional synthetic insecticides. Solutions that may be available in the medium and longer-term will be discussed in the next articles. The cabbage stem flea beetle (CSFB), Psylliodes chrysocephala (Coleoptera: Chrysomelidae) is one of the most important pests of winter OSR crops in central and northern European countries. The adult beetle causes 'shot holing' feeding damage on cotyledons and true leaves of young winter OSR plants in late summer-early autumn. The larvae feed inside petioles and stems of the plants, causing additional damage. The focus on making food production more environmentally friendly means reduced chemical inputs, protecting nontarget species and overall biodiversity. This led to the withdrawal of systemic synthetic neonicotinoid pesticide seed treatments in many crops (oilseed rape included) in 2013. Since the withdrawal of neonicotinoid seed treatments, there has been a reliance on pyrethroid insecticides. This has been seen with a shift in the use of insecticides in oilseed rape, with CSFB the target for 28% of insecticide applications in 2012 (before neonicotinoid seed treatments were withdrawn) to 75% in 2020. The result of this shift has been the development of resistance to this group of insecticides in CSFB population. This situation has become so severe that some UK populations of CSFB are now 100% resistant to the pyrethroid insecticide lambda-cyhalothrin. These changes have led to the area of oilseed rape grown in the UK being halved (756,000 hectares in 2012 versus 307,000 hectares in 2021), with growers citing CSFB as one of the main reasons for this decrease. At the same time, the number of insecticide spray rounds has increased from two to three between 2012 and 2020, with these applications dominated by the use of pyrethroids. The most widely used pyrethroid insecticide, lambda-cyhalothrin, has also increased as a proportion of the insecticide-treated area from 32% in 2012 to 76% in 2020. Additional surveys by Fera, completed as part of the CropMonitor information service, between 2009 and 2020 show that the number of CSFB larvae per plant increased from an average of 0.5 larvae per plant in the years before the withdrawal of neonicotinoids, to more than 2 larvae per plant the following year in 2014 in East England, and almost 5 larvae per plant in 2019 in the South West of England. Here we present solutions that are currently available or that could be made available in the short-term. We consider how each of these approaches could be used in Integrated Pest Management (IPM) programmes.