Pest Of Oilseed Rape Research Articles

Identifying insect predators using camera traps reveal unexpected predator communities in oilseed rape fields

Cameras are common tools for ecologists studying species abundance, richness, and interactions. They are mainly used to study large animals but are increasingly used to study invertebrates. Camera traps could be a powerful tool to identify and quantify the natural enemies, such as predators, of specific agricultural pests. This knowledge can then be applied to adapt farming practices to favour the predators identified and improve conservation biocontrol.Here, cameras were used to identify predators of two insect pests of oilseed rape (Brassica napus): the pollen beetle (Brassicogethes aeneus) and the brassica pod midge (Dasineura brassicae). These insects are spring pests of oilseed rape and are both susceptible to predation by ground-dwelling arthropods during their development cycle. The objectives of this study were to 1) identify the predators of the pest species, and 2) investigate the hypothesis that the diel activity periods of the predators match the timing of pest larval presence on the ground. Field observations were conducted in two locations over two consecutive years in the UK.In contrast to previous reports, our data collected using cameras showed that larval stages of predatory beetles are responsible for most of the predation events and that adult stages were not frequently observed feeding on the prey. Our data also showed that the traditional method, using pitfall traps, failed to detect the presence of large numbers of beetle larvae. Interestingly, the pests dropped to the ground and were therefore most susceptible to predation at the time when predators were most active.These results give new insight on the predators of the two most important spring pests of oilseed rape in Europe. This knowledge can be used by practitioners to develop framing practices targeted on enhancing the abundance of the larval stages of these beneficial arthropods to better control the pests in a more sustainable way.

Modelling the impact of cabbage stem flea beetle larval feeding on oilseed rape lodging risk.

Cabbage stem flea beetle (CSFB, Psylliodes chrysocephala L.) is a major pest of oilseed rape (OSR, Brassica napus L.) in the UK and low availability of effective chemical control has increased the need for integrated pest management approaches. The risk of OSR to lodging is strongly related to stem strength, however, the impact of CSFB larval tunnelling on stem strength and subsequent risk to stem lodging is unknown. The study investigated this by applying the Generalised Crop Lodging Model to conventionally grown OSR crops scored for varying levels of CSFB larval tunnelling. Lodging risk mitigation strategies including plant growth regulators (PGR) and varying nitrogen regimes were tested under high CSFB larval pressure. Stems of OSR plants were categorised by the proportion of visual damage (< 5%; 5-25%; 26-50%; 51-75%; 75-100%). Stems of 26-50% damage had significantly lower breaking strengths and diameters compared to plants that scored < 5%, with the associated reduction in stem failure windspeed equivalent to an order of magnitude increase in the risk of a lodging event occurring in the UK. PGR use reduced plant height and subsequently lodging risk variably across the sites. Estimating the proportion of stem tunnelling alongside larval pressure may be a useful tool in considering the contribution of CSFB pressure to lodging risk. The research demonstrates that the use of canopy management principles to optimise canopy size through nitrogen management and PGR use may help offset increased lodging risk caused by CSFB tunnelling. © 2024 Society of Chemical Industry.

Effective target genes for RNA interference-based management of the cabbage stem flea beetle.

The cabbage stem flea beetle (CSFB, Psylliodes chrysocephala) is a key pest of oilseed rape. The ban on neonicotinoids in the European Union due to environmental concerns and the emergence of pyrethroid-resistant populations have made the control of CSFB extremely challenging. In search of a solution, we have recently shown that RNA interference (RNAi) has potential in the management of CSFB. However, the previously tested target genes for RNAi-mediated pest control (subsequently called target genes) exhibited moderate and slow-acting lethal effects. In this study, 27 double-stranded RNAs (dsRNAs) were orally delivered to identify highly effective target genes in CSFB adults by leveraging the findings of a genome-wide RNAi screen in Tribolium castaneum. Our screen using 500 ng of dsRNA identified 10 moderately effective (> 50% mortality) and 4 highly effective target genes (100% mortality in 8-13 days). The latter mainly included proteasome subunits. Gene expression measurements confirmed target gene silencing and dose-response studies revealed LD50 values as low as ~20 ng in 14 days following a single exposure to dsRNA. Four highly effective dsRNAs also inhibited leaf damage (up to ~75%) and one affected locomotion. The sequences of promising target genes were subjected to in silico target prediction in non-target organisms, for example, beneficials such as honeybees, to design environmentally friendly dsRNAs. Overall, the study provides valuable insights for the development of dsRNA-based insecticides against CSFB.

Biology, Ecology, and Management of Flea Beetles in Brassica Crops.

Brassica vegetable and oilseed crops are attacked by several different flea beetle species (Chrysomelidae: Alticini). Over the past decades, most research has focused on two Phyllotreta species, Phyllotreta striolata and Phyllotreta cruciferae, which are major pests of oilseed rape in North America. More recently, and especially after the ban of neonicotinoids in the European Union, the cabbage stem flea beetle, Psylliodes chrysocephala, has become greatly important and is now considered to be the major pest of winter oilseed rape in Europe. The major challenges to flea beetle control are the prediction of population dynamics in the field, differential susceptibility to insecticides, and the lack of resistant plant cultivars and other economically viable alternative management strategies. At the same time, many fundamental aspects of flea beetle biology and ecology, which may be relevant for the development of sustainable control strategies, are not well understood. This review focuses on the interactions between flea beetles and plants and summarizes the literature on current management strategies with an emphasis on the potential for biological control in flea beetle management.

Diversity of parasitoid wasps (Insecta, Hymenoptera) in oilseed rape fields in Serbia

Oilseed rape is an important crop grown worldwide and used for various purposes, including oil extraction and animal feed. In Europe, there are six major pest species and several other minor pests that can significantly affect oilseed rape production, requiring growers to effectively control them in order to ensure crop yield. The host-parasitoid complexes of these pests have been studied in detail and recorded mainly in western, central and northern Europe. As an abundant source of pollen and nectar, oilseed rape may also be attractive to other parasitoids that do not have direct trophic interactions with oilseed rape pest species. The aim of this study is to fill the knowledge gap regarding the wider parasitoid community in oilseed rape fields, particularly in southern Europe. During the two-year study, a total of 3135 specimens of primary and secondary parasitoids were sampled, of which 2855 were found in oilseed rape fields and 280 in semi-natural habitats. We found 153 taxa, of which 119 were found in oilseed rape fields and 87 in semi-natural habitats. We identified 31 genera (33 species) as parasitoids of oilseed rape pests, 54 genera (97 species) parasitising non-pest species and 10 genera (23 species) as possible parasitoids of oilseed rape pests. This study shows that the parasitoid community in oilseed rape fields is very diverse and that includes parasitoids of both oilseed rape pest and non-pest species.

Effects of regional crop rotations on autumn insect pests in winter oilseed rape.

Chemical control of insect pests in oilseed rape (OSR) is becoming increasingly difficult due to the development of resistance and restrictive insecticide approvals in Europe. At the same time, there is a lack of preventive and alternative control measures. Crop rotation mostly fails to control insects due to their mobility; however, changing regional cropping densities can dilute or concentrate pest pressure. In this study, we investigated whether the local occurrence of Psylliodes chrysocephala and Delia radicum, serious insect pests in winter OSR, is influenced by distance from the previous year's OSR fields and how changes in OSR rape cropping density at a regional scale (up to 10 km radius) affect pest pressure. Abundance of P. chrysocephala in yellow water traps decreased with increasing distance to previous year's OSR. Estimated catches in the first 3 weeks of migration were about 68-76% lower at 10 km distance compared to 1 km in autumn 2019 and 2020. However, in both seasons P. chrysocephala was able to disperse over distances of 10 km. Probability of root damage by D. radicum was affected by changes of OSR cropping area at a spatial scale of 2.5 km radius; it increased if acreage of OSR decreased. Furthermore, aphid infestation was lower when OSR was distant in the previous year. This study could enable field-specific risk assessment and prediction of pest pressure. To decide about the effectiveness of cropping breaks at a regional level as a preventive crop protection measure, more knowledge on other pest species and antagonists is needed. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Use of insect pest thresholds in oilseed rape and cereals: is it worth it?

Integrated pest management (IPM) uses thresholds to minimize pesticide use, and field monitoring of damaging organisms is an important component to evaluate whether or not thresholds have been breached. However, monitoring requires time and knowledge which impacts costs and benefits. In this study, we evaluated the effects of using insect pest thresholds on time effort, frequency of insecticide treatment and economics in comparison with common farm practices (business as usual) in winter wheat (WW), winter barley (WB) and winter oilseed rape (OSR). This study was done over 2 years (2018 to 2020) on 24 conventionally managed farms in North Rhine-Westphalia (Germany). Farmers spent significantly more time (42 min ha-1/season) monitoring insect pests in OSR than in WW (16 min ha-1/season) and WB (19 min ha-1/season). The use of insecticides in OSR was significantly reduced by 42% in comparison to business as usual. In cereal crops, the use of insecticide treatment was reduced by 50% but this was not significantly different to business as usual. Yields were not significantly reduced when crops were managed in accordance with IPM, and negative differences were small and not significant. However, economically, the costs of monitoring can only be recovered when labor costs and commodity prices are low and insecticide cost is high. Insect pest thresholds can help link the policy and environmental goals of insecticide reduction and the agronomic goal of production security. In the future, the time and cost required for monitoring should be reduced through intelligent solutions and tools, increasing the economic viability of monitoring and IPM. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Potential of Entomopathogenic Nematodes to Control the Cabbage Stem Flea Beetle Psylliodes chrysocephala.

Cabbage stem flea beetle (CSFB) is an important pest of oilseed rape that was controlled by neonicotinoid seed treatments until they were banned for this use in 2013. Since then, CSFB has been a difficult pest to control, partly due to widespread resistance to pyrethroid insecticides. Alternate solutions are necessary. Here, four entomopathogenic nematode (EPN) species were tested against CSFB adults under laboratory conditions. In addition, a bioassay was completed to test for EPN compatibility with a range of adjuvants (glycerin, xanthan gum and flame retardant) to protect EPNs from UV radiation and desiccation. Results show that EPNs have the potential to control CSFB adults under laboratory conditions. Heterorhabditis bacteriophora caused 75% CSFB mortality at a concentration of 4000 nematodes/mL after six days, Steinernema feltiae caused 80% CSFB mortality when applied at a concentration of 40,000 nematodes/mL after two days, Steinernema carpocapsae caused 85% mortality at a concentration of 10,000 nematodes/mL after six days, and Steinernema kraussei caused no more than 70% CSFB mortality overall compared to the water control, which led to 23% mortality. Steinernema feltiae and H. bacteriophora survival was 100% when exposed to adjuvants, except S. feltiae with glycerin and H. bacteriophora with flame retardant. Further research to evaluate the efficacy of EPN and adjuvants under field conditions is necessary.

Pollen Beetles in Oilseed Rape Fields: Spectrum and Distribution in Czech Republic during 2011–2013

Oilseed rape is frequently damaged by insect pests. Much attention is paid to the protection of oilseed rape against Brassicogethes aeneus (Coleoptera: Nitidulidae), which is one of the most significant pests of spring and winter oilseed rape. The presence of different pollen beetle species was monitored in the Czech Republic in the years 2011–2013. A minimum of 500 individuals were captured at each site. Morphometric characteristics and the morphology of male and/or female genitalia were used to determine species. B. aeneus, B. subaeneus, B. viridescens and B. coracinus were most abundant. Other species presented in oilseed rape were B. coeruleovirens, B. czwalinai, B. matronalis, B. anthracinus, Boragogethes symphyti, Cychramus luteus, Fabogethes nigrescens, Genistogethes carinulatus, Meligethes atratus, Sagitogethes maurus, and Lamiogethes atramentarius. Our main conclusion is that the reason for the presence of the pollen beetle species associated with their development into non-cruciferous plants in oilseeds is the sufficiency of pollen as food for beetles. In addition, they may occur here incidentally, as they can be transported relatively long distances by air. Accompanying species of pollen beetles probably also have a positive effect on abundance reduction in species considered to be harmful as they are hosts to parasitoids of the oilseed rape pest.

Frequency and spatial distribution of knock-down resistance (kdr) to pyrethroids in multiple oilseed rape pest species of the genus Ceutorhynchus.

The protection of European oilseed rape (OSR) from damaging insects relies on pyrethroid insecticides, but the development of resistance in key coleopteran pests such as the pollen beetle (Brassicogethes aeneus) and the cabbage stem flea beetle (Psylliodes chrysocephala) has resulted in reduced effectiveness of these insecticides. The sodium channel gene mutation L1014F knock-down resistance (kdr) is a contributing factor in resistance to pyrethroids in B. aeneus and P. chrysocephala, but little is known about the status of resistance in weevils of the genus Ceutorhynchus (Coleoptera: Curculonidae). Therefore, the present study investigated pyrethroid susceptibility and the presence of the kdr mutation in four Ceutorhynchus species. The kdr mutation in either its heterozygous or homozygous form was found in all investigated Ceutorhynchus species (C. picitarsis, C. pallidactylus, C. napi and C. obstrictus). Samples where pyrethroids in bioassays still provided control at 100% field rate or below contained kdr at frequencies of ≤12.5%, whilst bioassays using 100% field rate that did not control Ceutorhynchus populations contained homozygous resistant individuals at frequencies of greater than 55%. Field sampling demonstrated that kdr frequencies in populations of C. picitarsis and C. obstrictus collected from across France and Germany ranged from 0 to 100%. The present study demonstrated the potential of all four Ceutorhynchus species tested to develop pyrethroid resistance via the L1014F (kdr) mutation. Although kdr frequency varies among species and geographic locations, the risk of loss of pyrethroid insecticide effectiveness is high. Integration of other control tools for resistance management is therefore needed. © 2023 Society of Chemical Industry.

Lethal and sublethal effects of orally delivered double-stranded RNA on the cabbage stem flea beetle, Psylliodes chrysocephala.

The cabbage stem flea beetle (Psylliodes chrysocephala) is one of the most important insect pests of oilseed rape (Brassica napus) in northern Europe. The emergence of insecticide-resistant populations and the ban on neonicotinoid seed treatments have made the management of this pest challenging and research is needed to develop alternative strategies such as RNA interference (RNAi). We investigated lethal and sublethal effects of orally delivered double-stranded (ds)RNAs targeting P. chrysocephala orthologs of Sec23 and vacuolar adenosine triphosphatase subunit G (VatpG), which are involved in endoplasmic reticulum-Golgi transport and organelle acidification, respectively. Feeding bioassays on P. chrysocephala adults showed that the highest concentration (200 ng/leaf disk) of dsSec23 caused mortalities of 76% and 56% in pre-aestivating and post-aestivating beetles, respectively, while the same concentration of dsVatpG led to mortality rates of ~34% in both stages. Moreover, sublethal effects, such as decreased feeding rates and attenuated locomotion were observed. Small RNA sequencing and gene expression measurements following the delivery of dsRNAs demonstrated the generation of ~21 nucleotide-long small interfering RNAs and a systemic RNAi response in P. chrysocephala. We demonstrate that P. chrysocephala is a promising candidate for developing RNAi-based pest management strategies. Further research is necessary to identify more effective target genes and to assess potential non-target effects. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Banker Plant Bonuses? The Benefits and Risks of Including Brassicas in Field Margins to Promote Conservation Biocontrol of Specialist Pests in Oilseed Rape.

European agri-environment schemes include the use of flower-rich field margins to promote on-farm biodiversity, but species mixtures rarely include Brassicaceae. As pests of oilseed rape (OSR; Brassica napus) and their parasitoids are mostly brassica specialists, including brassica 'banker plants' in the mixtures would help support these important biocontrol agents and improve pest control throughout the crop rotation. We assessed the potential of six brassicaceous plants (replicated plots grown in the field) to enhance populations of parasitoids of OSR pests whilst minimising proliferation of their pest hosts. Fodder radish (Raphanus sativus) facilitated high production of parasitoids of the pollen beetle pest (Brassicogethes aeneus) but may proliferate Ceutorhynchus weevil pests due to low parasitism. Turnip rape (B. rapa) and the B. rapa hybrid 'Tyfon' showed potential to perform a trap cropping function for pests, but their early flowering phenology resulted in B. aeneus larvae escaping parasitisation, potentially assisting proliferation of this pest. Forage rape B. napus exhibited similarly high B. aeneus parasitoid production characteristics to R. sativus but did not potentiate problems with other pests, indicating that it would be a favourable banker plant option. Careful selection of plants in field margin mixtures is therefore needed to maximise their benefits and ideally the whole crop pest-beneficial complex needs to be studied, as focus on a single major pest risks unintended consequences with other pest problems.

Toxicity of essential oils on cabbage seedpod weevil (Ceutorhynchus obstrictus) and a model parasitoid (Nasonia vitripennis)

Plant essential oils are being increasingly studied as a potential environmentally friendly alternative to synthetic insecticides. The insecticidal efficacy of essential oils on the cabbage seedpod weevil (Ceutorhynchus obstrictus), an important oilseed rape pest, has not been previously tested. We examined the impact of six essential oils on C. obstrictus via contact with dry residues on leaf and flower surfaces. We also examined the effect of these essential oils on a model non-target parasitoid wasp, Nasonia vitripennis. Exposure to dry residues of cumin (Cuminum cyminum) and cinnamon (Cinnamomum verum) essential oils (applied to oilseed rape leaves) resulted in significant loss of mortality and immobility in C. obstrictus adults. Treatment with C. cyminum essential oil at 1.5% resulted in 50.71% mortality and 87.3% combined mortality and immobility in C. obstrictus. Cinnamomum verum oil, at 1.5% concentration, resulted in 88.8% mortality and immobility among C. obstrictus 24 h post-treatment. All treatments studied with essential oil dry residues at 0.3% concentration caused high mortality and immobility in N. vitripennis. The greatest mortality and immobility were observed at 0.3% concentration in F. vulgare and C. verum treatments (54 and 53% loss respectively). At 0.1% concentration, F. vulgare and T. vulgaris significantly reduced parasitoids mobility and at 1.5% concentration all essential oils resulted in 100% mortality of N. vitripennis after 3 h. Our study revealed that C. cyminum and C. verum essential oils may have potential in the management of C. obstrictus. However, their impact on non-target organisms, including parasitoids, needs to be studied more thoroughly to determine the potential of essential oil main compounds in integrated pest management.

Earlier flowering of winter oilseed rape compensates for higher pest pressure in warmer climates

Abstract Global warming can increase insect pest pressure by enhancing reproductive rates. Whether this translates into yield losses depends on phenological synchronisation of pests with their host plants and natural enemies. Simultaneously, landscape composition may mitigate climate effects by shaping the resource availability for pests and their antagonists. Here, we study the combined effects of temperature and landscape composition on pest abundances, larval parasitism, crop damage and yield, while also considering crop phenology, to identify strategies for sustainable management of oilseed rape (OSR) pests under warming climates. In all, 29 winter OSR crop fields were investigated in different climates (defined by multi‐annual mean temperature, MAT) and landscape contexts in Bavaria, Germany. We measured abundances of adult pollen beetles and stem weevil larvae, pollen beetle larval parasitism, bud loss, stem damage and seed yield, and calculated the flowering date from growth stage observations. Landscape parameters (proportion of non‐crop and OSR area, change in OSR area relative to the previous year) were calculated at six spatial scales (0.6–5 km). Pollen beetle abundance increased with MAT but to different degrees depending on the landscape context, that is, increased less strongly when OSR proportions were high (1‐km scale), interannually constant (5‐km scale) or both. In contrast, stem weevil abundance and stem damage did not respond to landscape composition nor MAT. Pollen beetle larval parasitism was overall low, but occasionally exceeded 30% under both low and high MAT and with reduced OSR area (0.6‐km scale). Despite high pollen beetle abundance in warm climates, yields were high when OSR flowered early. Thereby, higher temperatures favoured early flowering. Only among late‐flowering OSR crop fields yield was higher in cooler than warmer climates. Bud loss responded analogously. Landscape composition did not substantially affect bud loss and yield. Synthesis and applications: Earlier flowering of winter OSR compensates for higher pollen beetle abundance in warmer climates, while interannual continuity of OSR area prevents high pollen beetle abundance in the first place. Thus, regional coordination of crop rotation and crop management promoting early flowering may contribute to sustainable pest management in OSR under current and future climatic conditions.

Within-field floral resources have the potential to increase parasitism rates in winter oilseed rape pests more than resources at field margins

Pollen beetles (Brassicogethes spp.) and stem flea beetles (Psylliodes chrysocephala) are among the main pests of oilseed rape crops in Europe, causing high yield losses. Increasing insecticide resistance and environmental concerns have highlighted the need for alternatives to chemical control, such as conservation biological control. Conservation biological control can be enhanced by providing resources to beneficial organisms in and around crop fields. Flower strips are a promising tool to provide nectar resources for parasitoids. In addition, the planting of such resources in field margins should be reinforced by the absence of insecticide application. However, the presence and amount of weeds within the field could mitigate the effect of flower strips and needs to be explored. We surveyed 25 oilseed rape fields in 2019 and 2020. Ten of these fields were adjacent to a sown wildflower strip. We compared an eco-friendly strategy (wildflower strip without insecticide in spring) to a conventional approach (no wildflower strip and chemical control of pests). We assessed the parasitism of stem flea beetle and pollen beetle larvae in the spring, at distances of 5 m and 30 m from the wildflower strip or the natural field margin. We performed botanical surveys in wildflower strips and natural field margins and within the field, to assess the availability of accessible nectar resources to parasitoids. Stem flea beetle parasitism rates were not affected by the strategy used, but the eco-friendly strategy had a weak positive effect on pollen beetle parasitism. Unexpectedly, the amount of accessible nectar did not differ significantly between wildflower strips in the eco-friendly strategy and natural herbaceous field margins in the conventional strategy. The amount of accessible nectar provided by weeds in the field was positively related only to pollen beetle parasitism rates. By contrast, the amount of accessible nectar for both spontaneous field margin and flower strips had no effect on the rates of parasitism of either species. Parasitism rate decreased significantly with decreasing distance to the field edge, for both species. Our results suggest that further studies are required: (i) to improve the composition of wildflower strips, so as to provide more accessible nectar resources at the start of spring and (ii) to explore more management strategy options, notably on in-field resources management such as unsown patches or intercropping.

A protocol for increased throughput phenotyping of plant resistance to the pollen beetle.

Improving crop resistance to insect herbivores is a major research objective in breeding programs. Although genomic technologies have increased the speed at which large populations can be genotyped, breeding programs still suffer from phenotyping constraints. The pollen beetle (Brassicogethes aeneus) is a major pest of oilseed rape for which no resistant cultivar is available to date, but previous studies have highlighted the potential of white mustard as a source of resistance and introgression of this resistance appears to be a promising strategy. Here we present a phenotyping protocol allowing mid-throughput (i.e., increased throughput compared to current methods) acquisition of resistance data, which could then be used for genetic mapping of QTLs. Contrasted white mustard genotypes were selected from an initial field screening and then evaluated for their resistance under controlled conditions using a standard phenotyping method on entire plants. We then upgraded this protocol for mid-throughput phenotyping, by testing two alternative methods. We found that phenotyping on detached buds did not provide the same resistance contrasts as observed with the standard protocol, in contrast to the phenotyping protocol with miniaturized plants. This protocol was then tested on a large panel composed of hundreds of plants. A significant variation in resistance among genotypes was observed, which validates the large-scale application of this new phenotyping protocol. The combination of this mid-throughput phenotyping protocol and white mustard as a source of resistance against the pollen beetle offers a promising avenue for breeding programs aiming to improve oilseed rape resistance. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Weather and landscape drivers of the regional level of pest occurrence in arable agriculture: A multi-pest analysis at the French national scale

Limiting crop pests while favouring environmentally friendly practices is challenging. It is required to identify the main drivers of infestation for multiple pests at different scales. In particular, large scale approaches are missing, while they could contribute to increase the predictability of pest infestation. In this study, the French national Epiphyt dataset (part of the national epidemiological monitoring service) was used to assess the relative importance of weather and landscape drivers on the between-region variability in the level of occurrence of some agricultural pests. Using a regional resolution, we analysed the proportion of occurrence of slugs, cereal aphids and oilseed rape pests over 181 small agricultural areas (‘regions’) across France in 2018. The mean proportion of occurrence per region was 0.17 for slugs, 0.25 for cereal aphids and 0.61 for oilseed rape pests. Weather variables were more explanatory than landscape ones for the proportion of occurrence of slugs and oilseed rape pests while the two types of variables had a similar level of explanation for the regional proportion of aphid occurrence. Slugs were favoured by high winter temperatures, high soil wetness index and important proportions of hedgerows in the region but negatively influenced by high winter rainfalls. Cereal aphids and oilseed rape pests were negatively influenced by the regional proportion of grassland. Additionally, the winter air humidity and the proportion of perennial crops in the region decreased the proportion of occurrence of oilseed rape pests. We detected no effect of the proportion of host crop or the proportion of organic farming in the region. This study emphasises that, in line with findings derived from more local studies, weather characteristics are an important driver of the regional level of pest occurrence in arable fields; it also highlights that the proportion of grassland at the regional scale could be a key tool to design insect-pest suppressive landscapes.

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.

Pteromalid fauna (Hymenoptera, Pteromalidae) in oilseed rape (Brassica napus L.) fields in Bulgaria – species composition and perspectives for biological control

Parasitoid wasps belonging to the family Pteromalidae are widespread and abundant members of the insect communities in the temperate regions of the world. As many other chalcids do, pteromalids serve as natural enemies of the pests in various crops and play an important role in the biological control of these harmful insects. Here we present the results of a field study in Bulgaria which was focused on the diversity of family Pteromalidae in ten oilseed rape fields. All samples were collected by sweep netting on the border line or inside the crop field. A total of 93 pteromalid specimens belonging to 26 taxa were gathered. The most abundant genus was Mesopolobus – 67% of the sampled pteromalids. The most numerous species in the samples was Mesopolobus morys – a well-known key parasitoid of the cabbage seed weevil, Ceutorhynchus obstrictus, in Europe. One species – Halticoptera patellana, is recorded for the first time in Bulgarian fauna. Clearfield oilseed rape fields had relatively higher parasitoid abundance and richness than the fields treated by conventional technology. In the present work we discuss the overall species composition of Pteromalidae obtained from the studied areas and present our point of view on the perspectives for biological control of oilseed rape pests.

First record of &lt;em&gt;Microctonus brassicae&lt;/em&gt; in Czechia, a potential biological control agent against a primary oilseed rape pest

After the ban on treating oilseed rape seeds with neonicotinoids in European Union, cabbage stem flea beetles (Psylliodes chrysocephala Linnaeus, 1758) again became one of its main pests. In Czechia, the impact of this pest increases every year, given with the narrowing spectrum of suitable insecticides and growing damage to oilseed rape plants in autumn. Based on this scenario, it is appropriate to look for alternative options to control oilseed rape pests. One option could be supporting beneficial organisms. One of these organisms is the hymenopteran braconid parasitoid Microctonus brassicae (Haeselbarth, 2008), which parasitizes adult cabbage stem flea beetles. Its occurrence has now been confirmed outside Great Britain in Czechia and continental Europe respectively. Five male specimens of M. brassicae emerged from 50 collected adults of cabbage stem flea beetle by sweep netting from two localities in central Bohemia. This parasitoid of adult cabbage stem flea beetles and its larval parasitoids probably play an important role in the life cycle and population dynamics of this pest. Current knowledge about the biology, taxonomic classification and identification of this parasitoid is summarized in this paper.