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

BACKGROUND: 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. RESULTS: 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. CONCLUSION: 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.

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

BACKGROUND: 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. RESULTS: 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%. CONCLUSION: 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.

Deposition of dust with active substances in pesticides from treated seeds in adjacent fields during drilling: disentangling the effects of various factors using an 8-year field experiment.

The side effects from the use of plant protection products and their potential effects on non-target arthropods (NTAs) such as honey bees, other insects within the vegetation layer and epigeic arthropods nowadays receive more attention. However, uncertainties about the factors driving the deposition of active substances (a.s.) into off-crop areas persist, in particular during sowing of treated seeds. Analysing a highly standardised 8-year field experiment, we assessed the importance of various factors potentially affecting dust drift and deposition of a.s., emitted during the sowing process of treated seeds and deposited on fields adjacent to the drilling field, i.e. on the ground, on flowers, and on nonflowering plant parts. Regarding a.s. deposition, the Heubach a.s. value has a predictive capability, which is independent from all other factors taken into account in this study, and can thus be considered as a scenario-independent measure of potential dust deposition. Petri dish samplers, an established standard method for measuring a.s. deposition, were representative of the results from the plant samplers for a given combination of drilling technique and adjacent crop type. Adjacent crop type is likely to impact on a.s. deposition. The present work will enable a more field-realistic exposure assessment for bees and other NTAs.

Two-year field data on neonicotinoid concentrations in guttation drops of seed treated maize (Zea mays).

We present neonicotinoid concentrations in guttation drops of commonly used maize (Zea mays) cultivars, germinated from seeds coated with active substances (a.s.): i) imidacloprid (IMD), ii) clothianidin (CTN) and iii) thiamethoxam (THM) over two growing seasons. In one variant clothianidin was applied as seed granule. The trial took place at the experimental fields of the Julius Kühn-Institut in Berlin in 2010 and 2011. Data from 2010 are related to a presentation of "Pesticides in guttation droplets following seed treatment - field studies" (Schenke et al., 2011) [1] presented at the SETAC North America conference and only some figures were used in the "Scientific opinion on the science behind the development of a risk assessement of plant protection products on bees (Apis mellifera, Bombus spp. and solitary bees)" (EFSA, 2012) [2]. Only parts of the data from 2011 was presented in relation to the "Exposure of Coccinellidae to guttation droplets on maize seedlings with seed or granule treatment of neonicotinoids" (Schenke and Heimbach, 2014) [3]. The article describes the study sites, the variants of treated maize seeds, sample collection and the analytical methods used to quantify the neonicotinoids and relevant metabolites of IMD (5-OH-IMD and IMD-olefine) and of THM (CTN) in guttation drop samples. The complete field data set is publicly available at the OpenAgrar repository under https://doi.org/10.5073/20180907-142020 (Schenke et al., 2018) [4].

Quantitative 3D shape description of dust particles from treated seeds by means of X-ray micro-CT.

Crop seeds are often treated with pesticides before planting. Pesticide-laden dust particles can be abraded from the seed coating during planting and expelled into the environment, damaging nontarget organisms. Drift of these dust particles depends on their size, shape and density. In this work, we used X-ray micro-CT to examine the size, shape (sphericity) and porosity of dust particles from treated seeds of various crops. The dust properties quantified in this work were very variable in different crops. This variability may be a result of seed morphology, seed batch, treatment composition, treatment technology, seed cleaning or an interaction of these factors. The intraparticle porosity of seed treatment dust particles varied from 0.02 to 0.51 according to the crop and generally increased with particle size. Calculated settling velocities demonstrated that accounting for particle shape and porosity is important in drift studies. For example, the settling velocity of dust particles with an equivalent diameter of 200 µm may vary between 0.1 and 1.2 m s(-1), depending on their shape and density. Our analysis shows that in a wind velocity of 5 m s(-1), such particles ejected at 1 m height may travel between 4 and 50 m from the source before settling. Although micro-CT is a valuable tool to characterize dust particles, the current image processing methodology limits the number of particles that can be analyzed.

Target-site resistance to pyrethroid insecticides in German populations of the cabbage stem flea beetle, Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae).

Cabbage stem flea beetle, Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae) is a major pest of winter oilseed rape in several European countries particularly attacking young emerging plants in autumn. Over the last several decades, pyrethroid insecticides have been foliarly applied to control flea beetle outbreaks. Recent control failures in northern Germany suggested pyrethroid resistance development in cabbage stem flea beetles, which were confirmed by resistance monitoring bioassays using lambda-cyhalothrin in an adult vial test. The purpose of this study was to investigate the presence of polymorphisms in the para-type voltage-gated sodium channel gene of P. chrysocephala known to be involved in knock-down resistance (kdr). By using a degenerate primer approach we PCR amplified part of the para-type sodium channel gene and identified in resistant flea beetles a single nucleotide polymorphism resulting in an L1014F (kdr) mutation within domain IIS6 of the channel protein, known as one of the chief pyrethroid target-site resistance mechanisms in several other pest insects. Twenty populations including four archived museum samples collected between 1945 and 1958 were analyzed using a newly developed pyrosequencing diagnostic assay. The assay revealed a kdr allele frequency of 90-100% in those flea beetle populations expressing high-level cross-resistance in discriminating dose bioassays against different pyrethroids such as lambda-cyhalothrin, tau-fluvalinate, etofenprox and bifenthrin. The presence of target-site resistance to pyrethroids in cabbage stem flea beetle is extremely worrying considering the lack of effective alternative modes of action to control this pest in Germany and other European countries, and is likely to result in major control problems once it expands to other geographies. The striking fact that cabbage stem flea beetle is next to pollen beetle, Meligethes aeneus the second coleopteran pest in European winter oilseed rape resisting pyrethroid treatments by expressing a target-site mutation, underpins the importance of diversity in available chemistry for resistance management tactics based on mode of action rotation in order to guarantee sustainable winter oilseed rape cultivation in Europe.

Incidence of pyrethroid-resistant oilseed rape pests in Germany.

BACKGROUND: Failures in pollen beetle control using pyrethroids since 2005 indicated pyrethroid resistance in Germany. Therefore, resistance monitoring using bioassays was established in Germany for oilseed rape pest insects. RESULTS: The spread and intensity of pyrethroid resistance of Meligethes aeneus increased from 2005 onwards, with no sensitive samples left in any region of Germany in 2011. Sensitivity also declined for the newly introduced actives bifenthrin, etofenprox (both class-I pyrethroids) and tau-fluvalinate; all three claimed to be less affected by resistance, although there was no clear cross-resistance to lambda-cyhalothrin (class-II pyrethroid). In the German region with the longest tradition and high intensity of oilseed rape production, pyrethroid resistance of Psylliodes chrysocephala and Ceutorhynchus obstrictus, with resistance factors of up to 81 and 140 respectively, was detected. CONCLUSION: The intensive use of only one mode of action for many years is risky, because even pest insects with a low intrinsic resistance risk may develop resistance. Therefore, resistance strategies need to include several control options for pest insects needing regular treatments.

Pyrethroid resistance monitoring in European populations of pollen beetle (Meligethes spp.): a coordinated approach through the Insecticide Resistance Action Committee (IRAC).

BACKGROUND: Pollen beetle (Meligethes spp.) is a major pest of European oilseed rape crops. Its resistance to pyrethroid insecticides has been recorded in samples of beetles collected in Europe since at least 1999, and problems with the control of the beetle in the field have been widely reported. In 2007, a Pollen Beetle Working Group was formed through the Insecticide Resistance Action Committee (IRAC) in order to coordinate efforts for surveying pyrethroid resistance development. RESULTS: The results of the first 3 years of the pollen beetle pyrethroid susceptibility survey using a laboratory test are presented in this paper. Resistant beetle samples were collected from 20 of the 21 countries surveyed, with a general trend of increasing frequency and spread of resistant samples in European oilseed-rape-growing regions. CONCLUSION: Pyrethroid-resistant beetles dominate in Western and Central Europe and are becoming established in the North and East, the main oilseed-rape-growing areas of Europe. The development and spread of pyrethroid-resistant pollen beetles highlights the need for effective management strategies for oilseed rape insect pests.

Characterization of the multiple resistance traits of somatic hybrids between Solanum cardiophyllum Lindl. and two commercial potato cultivars.

Interspecific somatic hybrids between commercial cultivars of potato Solanum tuberosum L. Agave and Delikat and the wild diploid species Solanum cardiophyllum Lindl. (cph) were produced by protoplast electrofusion. The hybrid nature of the regenerated plants was confirmed by flow cytometry, simple sequence repeat (SSR), amplified fragment length polymorphism (AFLP), microsatellite-anchored fragment length polymorphism (MFLP) markers and morphological analysis. Somatic hybrids were assessed for their resistance to Colorado potato beetle (CPB) using a laboratory bioassay, to Potato virus Y (PVY) by mechanical inoculation and field trials, and foliage blight in a greenhouse and by field trials. Twenty-four and 26 somatic hybrids of cph + cv. Agave or cph + cv. Delikat, respectively, showed no symptoms of infection with PVY, of which 3 and 12, respectively, were also resistant to foliage blight. One hybrid of cph + Agave performed best in CPB and PVY resistance tests. Of the somatic hybrids that were evaluated for their morphology and tuber yield in the field for 3 years, four did not differ significantly in tuber yield from the parental and standard cultivars. Progeny of hybrids was obtained by pollinating them with pollen from a cultivar, selfing or cross-pollination. The results confirm that protoplast electrofusion can be used to transfer the CPB, PVY and late blight resistance of cph into somatic hybrids. These resistant somatic hybrids can be used in pre-breeding studies, molecular characterization and for increasing the genetic diversity available for potato breeding by marker-assisted combinatorial introgression into the potato gene pool.

Novel somatic hybrids (Solanum tuberosum L.+Solanum tarnii) and their fertile BC1 progenies express extreme resistance to potato virus Y and late blight.

Solanum tarnii, a wild diploid, tuber-bearing Mexican species belonging to the series Pinnatisecta is highly resistant to Potato virus Y (PVY) and Colorado potato beetle and shows a strong hypersensitive reaction to Phytophthora infestans. Therefore, it could be a potential source of resistance to pathogens for potato breeders. S. tarnii (2n=2x=24) is reproductively isolated from tetraploid Solanum tuberosum and hence difficult to include in potato breeding programmes. In this study, interspecific somatic hybrids were produced for the first time by protoplast electrofusion of the cells of potato cv. Delikat (Solanum tuberosum L.) and Solanum tarnii. The hybrid nature of the regenerants was confirmed by simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers and by morphological analysis and flow cytometry. Selected somatic hybrids were successfully backcrossed with cv. Delikat. Parental lines, primary somatic hybrids and BC1 progeny were assessed for resistance to PVY by mechanical inoculation, grafting and exposure to viruliferous aphid vectors in the field, and resistance to late blight (P. infestans) by detached leaflet and whole tuber tests. The somatic hybrids showed no symptoms of viral infection and most of them displayed high levels of resistance to foliage blight. The BC1 progenies were highly resistant to PVY and a few were resistant to foliage blight. Selected hybrids and BC1 clones were evaluated in the field for tuber quality and tuber yield. Some BC1 clones produced yields of good quality tubers. The results confirm that both the resistance to PVY and to late blight of S. tarnii is expressed in somatic hybrids, and PVY resistance is transferred to BC1 progeny, whereas blight resistance is harder to transfer. Somatic hybridization again proved to be a valuable tool for producing pre-breeding material with increased genetic diversity.

EU regulatory aspects of resistance risk assessment.

The EPPO Standard PP 1/213(1) on resistance risk analysis is the basis for risk assessment within the authorisation process in Germany. Data for resistance risk analysis have to be provided by the applicant and risk-mitigation strategies prepared if necessary. The extent of data requirements and the intensity of the evaluation process depend mainly on the type of target organism, crop, mode of action of the active substance and the resistance history of the organism in combination with products of similar mode of action as the one being applied for. Because resistance risk is a very complicated issue during the authorisation of plant-protection products, intensive co-operation between applicants and regulators is essential prior to submission of the dossier, with due consideration of the amount of data necessary and, where required, the proposed resistance-management strategy.