BACKGROUNDOilseed rape (OSR, Brassica napus) faces substantial yield losses in Europe due to the cabbage stem flea beetle (CSFB, Psylliodes chrysocephala). Synthetic insecticide use is constrained by resistance and environmental concerns, necessitating innovative pest control strategies. Understanding CSFB host plant selection, particularly through volatile organic compounds (VOCs), is essential for developing sustainable and efficient methods. This study investigated the olfactory response of CSFB in their pre-aestivation stage to plant VOCs.RESULTSOlfactometer bioassays showed that female CSFB were attracted to VOCs from mechanically damaged OSR plants (BBCH 10 and BBCH 14), while undamaged OSR plants elicited no response. Damaged seedlings of Sinapis alba and Brassica rapa were not attractive. When testing individual isothiocyanates, again only female CSFB showed a positive response in the olfactometer bioassays, while no response was found for two green leaf volatiles.CONCLUSIONThis research provides insights into the olfactory behavior of CSFB and, to our knowledge, is the first to show behavioral responses of adult CSFB towards host plant volatiles in olfactometer tests. Interestingly, only females responded to VOCs, suggesting sexual dimorphism in olfactory sensitivity during this life stage. These findings may help to lay the groundwork for further studies aimed at improving pest management strategies in OSR cultivation. (c) 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Aestivation is a form of seasonal dormancy observed in various insect species, usually coinciding with the summer season. The cabbage stem flea beetle, Psylliodes chrysocephala (Coleoptera: Chrysomelidae), is a key pest of oilseed rape that obligatorily aestivates as adult in late summer. Since the physiological and transcriptional processes linked to aestivation in P. chrysocephala are still little understood, we analyzed relevant physiological parameters and performed RNA-seq analyses on laboratory-reared beetles in their pre-aestivation, aestivation, and post-aestivation stages. We found that the beetles reached aestivation at 15 days post-eclosion, showing strongly reduced metabolic activity, with less than 50% CO2 production, compared to pre-aestivating individuals. Under constant laboratory conditions, the beetles aestivated for about 25 days. Female beetles reached reproductive maturity at a median of 52 days post-eclosion. Furthermore, aestivating beetles had significantly reduced carbohydrate reserves and increased lipid reserves compared with pre-aestivating beetles, indicating that aestivation is associated with drastic changes in energy metabolism. Aestivating beetles contained 30% less water and their survival rates under high-temperature conditions (30 °C) were 40% higher compared to pre-aestivating beetles. RNA-seq studies showed that, in particular, gene ontology terms related to carbohydrate and lipid metabolism, digestion, and mitochondrial activity were enriched, with clear differences in transcript abundance between beetles in aestivation compared to pre- or post-aestivation. Specifically, mitochondrial transcripts, such as respiratory chain I subunits, and digestion-related transcripts, such as trypsin, were less abundant during aestivation, which supports the idea that aestivation is associated with decreased metabolic activity. This study represents the first exploration of the transcriptomic and physiological processes linked to aestivation in P. chrysocephala.

In a semi-field net cage experiment set up in three growing seasons (2015–2018) at Julius-Kühn Institute Braunschweig, Germany, the influence of different release times of adult cabbage stem flea beetles, Psylliodes chrysocephala (early September, mid-September, early October) and different beetle densities (6.7, 13.3 and 20 beetles/m 2 ) on reproduction and damage potential in winter oil seed rape was investigated. In parallel to the cage trials, the number of deposited eggs was assessed in small boxes exposed in the field. Beetles released in early September laid significantly more eggs compared to beetles released early October, with a maximum of 270 eggs per female. The early release of beetles resulted in significantly higher numbers of larvae in autumn, but this differed significantly between the years. Warm autumn or winter conditions led to continued egg laying and development, whereas cold conditions stopped the reproduction. Significant yield losses (25%) and significant plant losses during winter were only found in 2016/17 in treatments with an early release of high numbers of beetles (20 beetles /m 2 ). The German damage threshold of 3–5 larvae per plant was reached when 13 beetles/m 2 were released before 20th September and 20 beetles per m 2 after 20th September. Data of this study can be used for a better damage prediction and a more targeted beetle control.

The introduction of high-yielding and hybrid cultivars and the opening of new markets in the food and feed sector have steadily increased rapeseed production since the 1980s in the main production regions, Canada, Europe, China, India, and Australia. Since the 1990s, however, the average growth rate of yields has declined in Europe and Australia, which has been associated with a less effective control of biotic stresses. A global survey including the knowledge of 22 experts from 10 countries revealed a total of 16 diseases, 37 insect pests, several species of nematodes, and slugs currently affecting rapeseed production globally. A ranking of the top 10 most important biotic stresses in the four global regions where Brassica napus is grown (Canada, China, Europe, Australia) indicated an increase in several important stresses and distinct regional differences in the priority of prevailing diseases and pests. A stronger overlap exists among diseases, with Sclerotinia stem rot, Phoma stem canker, and clubroot occurring in all the four global regions on the top 10 list, while the range of prevailing insect pests was more diverse among the regions, with no top 10 insect playing an equally important role worldwide. Management options are substantially broader in disease than in pest control, making the latter the larger challenge. Since common integrated pest management (IPM) tools such as crop rotation, soil management, resistant cultivars or biocontrol are ineffective or not available, insect control largely relies on insecticides. Increasing restrictions on insecticide use, particularly in Europe, and losses in insecticide efficacy threaten the profitability of oilseed rape production and its role as an important break crop in cereal dominated cropping systems. Since the survival time of insects in the absence of their main host is relatively short (<1 year), a regional synchronization of cropping schemes resulting in one or more years without the crop could lead to a substantial disruption of regional insect populations. If rotation schemes were implemented on the landscape instead the farm level, by coordination among growers in zones covering the range distances of insect pests, an efficient and chemical low management strategy could be established and enable a more sustainable rapeseed production in the future.

The cabbage stem flea beetle (CSFB), Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), is one of the most important pests in European winter oilseed rape production. Adult beetles feed on young leaves whereas larvae mine within the petioles and stems. Larval infestation can cause significant crop damage. In this study, the host quality for CSFB of four oilseed rape ( Brassica napus L.) cultivars and seven other brassicaceous species with different glucosinolate (GSL) profiles was assessed under controlled conditions. Larval instar weights and mortality were measured after 14 and 21 days of feeding in the petioles of test plants. To study the impact of GSL on the performance of larvae, the GSL contents in petioles from non‐infested and infested plants were analysed before, and 21 days after, the start of larval infestation. Larval performance was not significantly different between the four cultivars of oilseed rape, but differed considerably among the other brassicaceous species tested. In comparison to the weight of larvae in the standard B. napus cv. Robust, the larval weight was higher in turnip rape ( Brassica rapa L. var. silvestris ) and significantly reduced in white mustard ( Sinapis alba L.), oil radish ( Raphanus sativa L. var. oleiformis ), and cabbage ( Brassica oleracea L. convar. capitata var. alba ). The duration of larval development increased in white mustard and oilseed radish. The GSL profiles of the petioles showed little difference between non‐infested and infested plants of oilseed rape whereas the content of aliphatic GSL increased in the infested turnip rape plants. In contrast, the aliphatic and benzenic GSL decreased in infested Indian rape ( B. rapa subsp. dichotoma Roxb.). Larval weight was not correlated with the total GSL content of plants, neither before infestation nor 21 days after. Larval weight was positively correlated with progoitrin and 4‐hydroxyglucobrassicin. White mustard, which provides inferior host quality for larval development, has the potential to introduce insect resistance into high‐yielding oilseed rape cultivars in breeding programmes.

To prevent damage by pollen beetles ( Brassicogethes aeneus (Fabricius), syn. Meligethes aeneus (Fabricius)), frequent insecticide applications are often necessary. It would be an advantage if treatments for pollen beetle control would not only avoid yield losses by bud damage by overwintered pollen beetles, but also minimize pest reproduction, and also have side effects on the population development of other pests present in the crop. The effects of the neonicotinoid Biscaya (a.i. thiacloprid) and the pyrethroids Mavrik (tau-fluvalinate) and Karate Zeon (lambda-cyhalothrin) applied at different growth stages of winter oilseed rape on the abundance of overwintered pollen beetles were determined in field trials in Germany (2013–2015). In addition, effects on the two larval instars and new generation of adult pollen beetle were studied. Biscaya and Mavrik significantly reduced the number of overwintered pollen beetles up to seven days after application, whereas Karate Zeon had no effect. Application of Biscaya at the beginning of flowering resulted in a high mortality of L1-larvae in all years. The number of premature L1-larvae dropping down from the plants during the first week after application increased up to 425% compared to the control. The number of L2-larvae dropping down to the ground for pupation was significantly reduced by insecticide applications at different growth stages except for Karate Zeon. In Karate Zeon-treated plots, the number of L2-larvae dropping to the ground increased up to 42% compared to the control. In accordance with the reduced number of L2-larvae in Biscaya- and Mavrik-treated plots, fewer new-generation pollen beetles emerged in the field trials near Braunschweig, efficacy varying between 57 and 76% in Biscaya-treated plots and 32 and 57% in Mavrik-treated plots in 2014 and 2015, respectively. The results indicate that Mavrik, and especially Biscaya, are effective in controlling pollen beetles, reducing infestation pressure and thereby insecticide treatment frequency in following years.

In this study, the effect of the four different insecticides Karate Zeon (a.i. lambda-cyhalothrin), Elado (clothianidin + beta-cyfluthrin), Fortenza Force (cyantraniliprole + tefluthrin) (only 2015), and Lumiposa (cyantraniliprole) (only 2016 and 2017) on the insect autumn pests Delia radicum , Psylliodes chrysocephala , and aphids (mainly Myzus persicae ) and Turnip Yellows Virus in winter oilseed rape was investigated in 3 years of field trials. The results showed that the effects of the Elado seed treatment on P. chrysocephala depend on the time of migration of adults. Due to delayed immigration of beetles into the field in 2015/2016 and 2017/2018, there was no clear effect of the seed treatment on the number of larvae per plant. In contrast in 2016/2017, the beetles colonized the crop in early September, and the number of larvae was significantly reduced by Elado. Cyantraniliprole and clothianidin seed treatments seem to support crop emergence independent of insect pests assessed. Spraying of the pyrethroid Karate Zeon in autumn significantly decreased the number of larvae in all years. Also the number of next-generation beetles was significantly reduced only by Karate Zeon. In all years, the aphid infestation was significantly reduced only by Elado seed treatment. The infection rate by TuYV was very high in all years and only slightly reduced by Elado seed treatment. There was only minimal occurrence of Delia radicum in all years. Cyantraniliprole products did not show any influence on the assessed insect pests in all years. There was no significant effect of any treatment on yield, but in 2015/2016 and 2016/2017, the highest yield was obtained in the Elado seed treatment.

One of the main insect pests in oilseed rape is the pollen beetle (Brassicogethes aeneus (Fabricius), syn. Meligethes aeneus). To maximize efficiency of control of this pest, insecticides are required that ideally, not just prevent yield losses by bud feeding of overwintered pollen beetles, but simultaneously minimize the reproduction of the pest, thereby reducing the size of the following generation infesting next year’s oilseed rape. The neonicotinoid active substance thiacloprid is known to reduce bud infestation with eggs and larvae. However, the mechanisms by which this occurs as well as the effects of other active substances are not known. In this study, the effects of the neonicotinoid insecticide Biscaya (a.i. thiacloprid) and the pyrethroids Mavrik (tau-fluvalinate) and Karate Zeon (lambda-cyhalothrin) applied at the bud stage of winter oilseed rape with recommended field rates on infestation of buds with eggs and larvae of pollen beetles were tested in field trials in Germany in 2013–2015. In additional greenhouse experiments, it was investigated whether effects on bud infestation were caused by lethal effects on pollen beetle or by insecticidal residues on plants causing sublethal effects. In the field trials, application of Biscaya and Mavrik significantly reduced the percentage of buds containing eggs and larvae in contrast to Karate Zeon. In 2014 and 2015, 14 days after application, bud infestation on the main raceme was reduced by 86 and 82%, respectively, in Biscaya-treated plots and by 51 and 71%, respectively, in Mavrik-treated plots compared to the untreated plots. In the greenhouse experiments, the lowest percentage of bud infestation with eggs and larvae was recorded on Biscaya-treated plants whereas on Mavrik-treated plants, there was no significant difference compared with the control. The results of the field trials show that Biscaya and Mavrik reduced oilseed rape bud infestation with eggs and larvae of pollen beetles primarily by lethal effects on overwintered pollen beetles or by repellency. However, Biscaya had additional effects on egg laying, which was supported by the greenhouse experiments.

Larval parasitoids can substantially reduce the population density of the pollen beetle [ Brassicogethes aeneus (Fabricius), syn. Meligethes aeneus (Fabricius)]. The most abundant tersilochine parasitoids of pollen beetle are Tersilochus heterocerus , Phradis interstitialis and P. morionellus . The main activity of these parasitoids was observed in the period shortly before flowering to full flowering of oilseed rape. Insecticide applications during this period may have negative effects on parasitoids. In the present study, the effects of the insecticides Biscaya (a.i. thiacloprid), Mavrik (a.i. tau-fluvalinate) and Karate Zeon (a.i. lambda-cyhalothrin) applied during the bud or flowering stage of winter oilseed rape on parasitization of pollen beetle larvae by T. heterocerus were studied in 12 field trials at different locations in Germany in 2013–2015. The effects on parasitism by Phradis spp. were assessed in 2015. Parasitism of pollen beetle larvae by T. heterocerus was found in all field trials in all experimental years, but in most trials not before full flowering. Maximum percentage of parasitized larvae at different locations ranged between 3.4 and 16.8% in 2013, 8.3 and 22.4% in 2014 and from 11.1 to 29.1% in 2015. Levels of parasitism were not significantly different between the untreated control and insecticide treatments within each location. In contrast to T. heterocerus , Phradis spp. was not detected at all locations and not before flowering declining. In field trials at Lucklum and Puch, the maximum level of parasitism by Phradis spp. was 9.4 and 18.3%, respectively. No significant effect of insecticide application on parasitism by Phradis spp. was observed between the treatments. The results of this study showed that the insecticides used in the field trials did not affect parasitization of pollen beetle larvae by T. heterocerus and Phradis spp., regardless whether applied at the bud stage, at the beginning of flowering or full flowering.

The rape stem weevil, Ceutorhynchus napi Gyll., is a serious pest of winter oilseed rape (Brassica napus L.) crops in Europe causing severe yield loss. In currently used oilseed rape cultivars no resistance to C. napi has been identified. Resynthesized lines of B. napus have potential to broaden the genetic variability and may improve resistance to insect pests. In this study, the susceptibility to C. napi of three cultivars, one breeding line and five resynthesized lines of oilseed rape was compared in a semi-field plot experiment under multi-choice conditions. Plant acceptance for oviposition was estimated by counting the number of C. napi larvae in stems. The larval instar index and the dry body mass were assessed as indicators of larval performance. The extent of larval feeding within stems was determined by the stem injury coefficient. Morphological stem traits and stem contents of glucosinolates were assessed as potential mediators of resistance. The resynthesized line S30 had significantly fewer larvae than the cultivars Express617 and Visby and the resynthesized lines L122 and L16. The low level of larval infestation in S30 was associated with a low larval instar and stem injury index. Low numbers of larvae were not correlated with the length or diameter of stems, and the level of stem glucosinolates. As indicated by the low larval infestation and slow larval development the resistance of S30 to C. napi is based on both antixenotic and antibiotic properties of the genotypes. The resynthesized line S30 should therefore be introduced into B. napus breeding programs to enhance resistance against C. napi.