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.

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.
CONCLUSIONS: 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.

BACKGROUND: Semi-natural habitats are generally considered to be beneficial to natural enemies of crop pests and pollinators. However, they could also be used by pests, such as the Cabbage Stem Flea Beetle (CSFB), Psylliodes chrysocephala, a major pest of winter oilseed rape, Brassica napus. Adults emerge from pupation in late spring and move to aestivation habitats. Published reports identify forest edges as the major shelter used, but flower strips may also constitute an alternative habitat. This study aimed to: (i) determine the role of perennial flower strips in CSFB aestivation in comparison with woodland edges; (ii) determine the influence of landscape composition on the abundance of aestivating CSFB and (iii) identify the characteristics of the local habitat associated with a high abundance of aestivating CSFB.
RESULTS: CSFB emergence from aestivation was monitored with emergence traps from mid-August to mid-October 2021, at 14 sites in France. We found that CSFB preferred woodland edges and did not aestivate in flower strips. We found a negative effect of percentage woodland cover only for the smallest scale studied (250 m radius). We also found positive effects of the percentage of litter and mean tree circumference on the number of aestivating CSFB in woodland edges.
CONCLUSIONS: The aestivation of CSFB is supported by woodland edges, but not by flower strips. This implies that the presence of flower strips near oilseed rape fields does not exacerbate the problems due to this pest. However, the crops in the vicinity of woodlands could be colonized earlier by this pest than more distant fields. © 2023 Society of Chemical Industry.

BACKGROUND: 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.
RESULTS: 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.
CONCLUSIONS: 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.

The cabbage stem flea beetle (Psylliodes chrysocephala) is a key pest of oilseed rape in Europe, and is specialized to feed on Brassicaceae plants armed with the glucosinolate-myrosinase defense system. Upon tissue damage, the β-thioglucosidase enzyme myrosinase hydrolyzes glucosinolates (GLS) to form toxic isothiocyanates (ITCs) which deter non-adapted herbivores. Here, we show that P. chrysocephala selectively sequester GLS from their host plants and store these throughout their life cycle. In addition, P. chrysocephala metabolize GLS to desulfo-GLS, which implies the evolution of GLS sulfatase activity in this specialist. To assess whether P. chrysocephala can largely prevent GLS hydrolysis in ingested plant tissue by sequestration and desulfation, we analyzed the metabolic fate of 4-methylsulfinylbutyl (4MSOB) GLS in adults. Surprisingly, intact and desulfo-GLS together accounted for the metabolic fate of only 26% of the total ingested GLS in P. chrysocephala, indicating that most ingested GLS are nevertheless activated by the plant myrosinase. The presence of 4MSOB-ITC and the corresponding nitrile in feces extracts confirmed the activation of ingested GLS, but the detected amounts of unmetabolized ITCs were low. P. chrysocephala partially detoxifies ITCs by conjugation with glutathione via the conserved mercapturic acid pathway. In addition to known products of the mercapturic acid pathway, we identified two previously unknown cyclic metabolites derived from the cysteine-conjugate of 4MSOB-ITC. In summary, the cabbage stem flea beetle avoids ITC formation by specialized strategies, but also relies on and extends the conserved mercapturic acid pathway to prevent toxicity of formed ITCs.