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Abstract

Oilseed rape (OSR) has historically been the most profitable break crop in many UK arable rotations. However, growers are now forced to seek alternatives due to increased pest pressure from plant virus (e.g., turnip yellows virus; TuYV) vectoring peach-potato aphids (Myzus persicae Sulzer) (Hemiptera: Aphididae) as well as cabbage stem flea beetle (Psylliodes chrysocephala L.) (Coleoptera: Chrysomelidae). This situation is primarily driven by a lack of effective control options for growers due to EU legislation preventing neonicotinoid insecticide use since 2016, leading to a significant increase in broad-spectrum synthetic pyrethroid insecticide use. Management of soft-bodied insects and chrysomelid beetles in arable crops still heavily relies on foliar application of synthetic pyrethroid insecticides. Increased pyrethroid use has led to populations of insecticide resistant peach-potato aphids and cabbage stem flea beetles being recorded. An inability to effectively control OSR pests has resulted in a 50 % reduction in area sown to OSR between 2012 and 2020. It is, therefore, crucial that alternative control methods for OSR pests are identified and optimised for use in the UK. Bioinsecticides are plant protection products derived from natural sources, such as bacteria or fungi, that offer a potential replacement for synthetic chemical pesticides and currently account for 20 % of all products registered for professional use in the UK. Such products are further encompassed by the newly coined term ‘bioprotectant’. Whilst bioinsecticide products extend to use across a wide range of cropping systems, the majority are only used on high value horticultural crops due to their cost and perceived unreliability in outdoor field conditions. At present there is only one commercial bioinsecticide registered for use in UK winter OSR, IntegralPro manufactured by BASF, used to manage fungal diseases such as Phoma. IntegralPro is an inoculum-based seed treatment containing Bacillus amyloliquefaciens (strain MBI600) that improves plant establishment and vigour. While there is limited evidence that IntegralPro reduces crop damage by cabbage stem flea beetle by stimulating plant defences, efficacy of this product has yet to be independently verified. Most bioinsecticide products registered for use in UK arable cropping systems are used for disease management. There are, however, a greater number of bioinsecticides registered for use in protected cropping systems. A number of commercially available bioinsecticides such as FLiPPER (physically acting fatty acid-based product) and Naturalis-L (entomopathogen-based product) have shown efficacy in the management of soft-bodied insects such as aphids in protected horticulture. Recent research by Hoarau et al., (not published) also highlights the potential of FLiPPER for cabbage stem flea beetle management, despite the contact mode of action of this product previously only being recognised as effective against soft bodied insects. The AHDB projects Sustainable Crop & Environment Protection – Targeted Research for Edibles (SCEPTRE; AHDB, 2022b) and Managing Ornamental Plants Sustainably (MOPS; AHDB, 2022c) further highlight the empirical need for evidence of potential ‘pipeline’ products for registration. Such research should consider commercial products outside of the scope of UK registered insecticides, e.g., ProTac (silicon polymer-based product) and Fizimite (surfactant-based product), yet with evidence to support their efficacy in the management of economically important crop pests. The success of projects such as SCEPTRE and MOPS, alongside the efficacy of commercially available bioinsecticide products to control soft-bodied insects in protected cropping systems highlights an opportunity for their potential use in arable cropping systems. Before widespread adoption of bioinsecticides in arable cropping systems can occur, there are two significant barriers that must be addressed: (1) environmental stability and (2) economic cost. The majority of bioinsecticide products are currently registered for use in protected cropping systems as they are relatively stable environments compared to field cropping systems and product efficacy is more variable under fluctuating field conditions. This limits their use to periods of dry weather or during the evening when humidity is higher and UV radiation is lower in many scenarios (Zaki et al., 2020). Routinely using bioinsecticides in arable cropping systems is, therefore, problematic as the requirement for exact timing may be restricted by other farm-based duties. The current sensitivity of bioinsecticides to environmental variables also creates uncertainty and a lack of confidence in the products by the end user. The average cost of bioinsecticides is also prohibitively expensive, costing £100-£300/ha per application, meaning that it is currently only economically feasible to apply these products on high-value crops where the financial returns would cover the increased production costs. Their cost is further increased as most require repeat applications to be effective due to poor residual effects. This price point combined with the labour costs associated with repeat application using conventional spray equipment makes bioinsecticide use in arable cropping systems economically unfeasible for many growers (Lowenberg-DeBoer et al., 2020). The environmental and economic barriers to bioinsecticide uptake in OSR could be overcome through use of autonomous farm equipment. Autonomous farm equipment provides an opportunity to reduce farm the labour costs associated with repeat applications as well as time-sensitive pressures relating to the multi-purpose use of conventional farm equipment. At present, bioinsecticide applications typically require large volumes of water (e.g., 1500 L/ha) to achieve adequate crop coverage. Such large volumes of water make autonomous applications impossible due to the requirement of large tank sizes and restrictions due to water weight. Whilst the use of autonomous farm equipment has been modelled as an economically feasible solution to current barriers associated with broadacre bioinsecticide use, any registered bioinsecticide products would need to be first optimised for application using light-weight application technologies, such as ultra-low volume spray, to be compatible with autonomous equipment. There has been comparatively little research investigating the potential of bioinsecticides for managing OSR pests. Their cost, high application frequency, large water volume requirements and environmental sensitivity creates significant barriers to effective bioinsecticide application in arable cropping systems. This project aims to address these barriers and help realise the opportunities that bioinsecticides provide for arable cropping environments.

Description

Research question: Are physically acting bioinsecticides practically and economically compatible with UK arable cropping systems?

H1: Commercial bioinsecticides not yet registered for use in OSR show efficacy in the control of a broad range of morphologically and physiologically different OSR pests, including aphids: peach potato aphid and mealy cabbage aphid (Brevicoryne brassicae; differing through the presence of a powdery, waxy cuticle excretion ). 

H2: Commercial bioinsecticides not yet registered for use in OSR remain effective at controlling economically important OSR pests when applied under variable environmental conditions, such as those often seen in the field.

H3: Commercial bioinsecticides not yet registered for use in OSR do not influence plant volatile emissions and their role in host plant selection by pests and natural enemy recruitment at different frequencies of application.

H4: Commercial bioinsecticides not yet registered for use in OSR remain effective at controlling economically important OSR pests when applied with ultra-low volume sprayer technologies.

H5: It is economically feasible, when modelled using linear programming, to apply commercially available bioinsecticides autonomously using ultra-low volume sprayer technologies.