Exploitation of host plant preferences in pest management strategies for oilseed rape (Brassica napus)

New control strategies for insect pests of arable agriculture are needed to reduce current dependence on synthetic insecticides, the use of which is unsustainable. We investigated the potential of a simple control strategy to protect spring‐sown oilseed rape, Brassica napus L. (Brassicaceae), from two major inflorescence pests: the pollen beetle, Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), and the seed weevil, Ceutorhynchus assimilis (Paykull) (Coleoptera: Curculionidae), through exploitation of their host plant preferences. The strategy comprised, for the main crop, Starlight [an oilseed rape cultivar with relatively low proportions of alkenyl glucosinolates in the leaves (thereby releasing lower levels of attractive isothiocyanates than conventional cultivars)] and turnip rape, Brassica rapa (L.) (Brassicaceae), as a trap crop. We tested the system in laboratory, polytunnel semifield arena, and field experiments. The odours of Starlight were less attractive in olfactometer tests to both pests than those from a conventional cultivar, Canyon, and the plants were less heavily colonized in both polytunnel and field experiments. Turnip rape showed good potential as a trap crop for oilseed rape pests, particularly the pollen beetle as its odour was more attractive to both pests than that of oilseed rape. Polytunnel and field experiments showed the importance of relative growth stage in the system. As turnip rape flowers earlier than oilseed rape, beetles would be maintained on turnip rape past the damage‐susceptible growth stage of oilseed rape. The development of a pest control regime based on this strategy is discussed.     

Red oilseed rape? The potential for manipulation of petal colour in control strategies for the pollen beetle (Meligethes aeneus)

The pollen beetle (Meligethes aeneus) is a major pest of oilseed rape (Brassica napus) at the inflorescence stage and is well known to prefer colours called yellow by human observers over many other colours. While commercial cultivars of oilseed rape have yellow flowers, little is known about the potential to manipulate host plant location and reduce subsequent infestation by this pest through variation in flower colour. We investigated the responses of pollen beetles to flowers of a white-petalled oilseed rape variety that had been dyed different colours in semi-field arena and field experiments. Flowers dyed blue or red were less heavily infested than those dyed yellow or the white flowers, indicating that blue and red flowers were less attractive than yellow and white ones. This response was most likely due to differences in petal colour because olfactometer studies showed that beetle responses to the odours of the coloured treatments did not differ. The comparatively high infestation of untreated white flowers is interpreted as a consequence of their high UV reflectance; the presence of a UV receptor in M. aeneus is suggested, and its role in visually guided insect–plant interactions in this species described. The potential for manipulation of petal colour in control strategies for the pollen beetle is discussed.     

Divergent responses of two cereal aphids to previous infestation of their host plant

The role of pollen odour in resource location by the pollen beetle, Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), a pollen-feeding insect regarded as a pest of oilseed rape, Brassica napus L., (Brassicaceae) crops, was investigated in a linear track olfactometer. Both male and female beetles were attracted to the odour of whole oilseed rape flowers, indicating that these insects can locate their host plants using floral odours as cues. The attractive odour of flowers was found to emanate from all floral parts tested: the petals/sepals, the anthers, and from pollen itself. Therefore, at least part of the attractive odour of oilseed rape flowers emanates from pollen. Beetles were more attracted to floral samples containing anthers than those without anthers when these odours were directly compared in a choice-test, and this indicates that there were detectable differences between them. Anthers and pollen may therefore release distinctive odours that are quantitatively and/or qualitatively different from the odour of the rest of the flower. These experiments support the hypothesis that pollen-seeking insects use pollen odour cues to locate this food source.     

Behavioural responses in three ichneumonid pollen beetle parasitoids to volatiles emitted from different phenological stages of oilseed rape

Pollen beetles (Meligethes spp.; Coleoptera: Nitiduliae) are a major pest of oilseed rape, Brassica napus L. (Brassicaceae) in northern Europe. Phradis interstitialis Thomson, P. morionellus Holmgr., and Tersilochus heterocerus Thomson (Hymenoptera: Ichneumonidae) are among the most frequent pollen beetle parasitoids. These three species differ in temporal occurrence, as well as in preferred host stage. The behavioural responses of female parasitoids to odours from oilseed rape at bud and flowering stage were evaluated in two‐choice experiments. The role of visual stimuli was examined by combining green and yellow colours with odour stimuli. All three species were attracted to odours from the bud stage of oilseed rape. Tersilochus heterocerus was attracted to odours of flowering rape, but the two Phradis species avoided the flower odours. However, when the odours of flowering rape were combined with yellow, and odours of the bud stage were combined with green, P. interstitialis was equally attracted to both stimuli, and T. heterocerus showed an increased preference for flower odours, while no effect of colours could be found in P. morionellus. The observed differences in responses between the parasitoids may reflect differences in their biology and may be involved in the niche segregation of these often coexisting species. The volatile blends released from the two phenological stages were identified and compared. Clearly, odours can be reliable cues for differentiating between oilseed rape in the bud and flowering stage. Of 20 identified compounds, 18 were released at a significantly higher rate from flowering plants. The terpenes sabinene, myrcene, limonene, and (E,E)‐α‐farnesene were the dominant volatiles in the bud and flower headspace. A group of aromatic compounds including benzaldehyde, methyl benzoate, and phenyl acetaldehyde were mainly released from flowering rape.     

Effect of pea lectin expressed transgenically in oilseed rape on pollen beetle life-history parameters

When investigating resistance to herbivorous insects in transgenic plants, it is primarily the damaging stage of the insect that is targeted. In our study, we showed that small effects of the transgenic plant on the pest performance might lead to a clear effect on the pest population level. Pollen beetle, Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), larvae were reared on three transgenic lines of Brassica napus L. (Brassicaceae) expressing pea (Pisum sativum L.) lectin at 0.2, 0.6, and 0.7% of total soluble protein in anthers, and then monitored until the adult stage. Two lines without the gene construct and consequently containing no pea lectin were used as controls. The egg viability, larval weight, development time, and survival rate were recorded. In a separate experiment, the development time from egg to adult, adult weight, and winter survival of pollen beetles developed on intact plants were recorded. Survival of larvae to adult stage was significantly lower on the transgenic plant lines, independent of lectin level. Survival during hibernation was only 2.4% and was not affected by plant line. Combining previously published results from adult feeding and oviposition assays with the new data on larval development we summarize the effect of the transgenic oilseed rape on the pollen beetle, from oviposition in spring to overwintered adults of the new generation. Net reproductive rate was then shown to be reduced by half on the transgenic oilseed rape compared to the control plants.     

Electrophysiological and behavioural responses of the pollen beetle, Meligethes aeneus, to volatiles from a non-host plant, lavender, Lavandula angustifolia (Lamiaceae)

A semiochemical based push-pull strategy for control of oilseed rape pests is being developed at Rothamsted Research. This strategy uses insect and plant derived semiochemicals to manipulate pests and their natural enemies. An important element within this strategy is an understanding of the importance of non-host plant cues for pest insects and how such signals could be used to manipulate their behaviour. Previous studies using a range of non-host plants have shown that, for the pollen beetle Meligethes aeneus (Coleoptera: Nitidulidae), the essential oil of lavender, Lavandula angustifolia (Lamiaceae), was the most repellent. The aim of this study was to identify the active components in L. angustifolia oil, and to investigate the behaviour of M. aeneus to these chemicals, to establish the most effective use of repellent stimuli to disrupt colonisation of oilseed rape crops. Coupled gas chromatography-electroantennography (GC-EAG) and gas chromatography-mass spectrometry (GC-MS) resulted in the identification of seven active compounds which were tested for behavioural activity using a 4-way olfactometer. Repellent responses were observed with (±)-linalool and (±)-linalyl acetate. The use of these chemicals within a push-pull pest control strategy is discussed. Handling Editor: Yvan Rahbe.     

Relative attractiveness of Brassica napus, Brassica nigra, Eruca sativa and Raphanus sativus for pollen beetle (Meligethes aeneus) and their potential for use in trap cropping

Oilseed rape (Brassica napus) is a valuable crop, attacked by several insect pests, of which the pollen beetle (Meligethes aeneus) is one of the most widespread and important in Europe. The relative attractiveness for the pollen beetle of Brassica nigra, Eruca sativa and Raphanus sativus was compared with that of spring oilseed rape, to assess the potential of these plant species as trap crops for the pest. At early growth stages, B. nigra and R. sativus were more attractive to over-wintered adult pollen beetles than B. napus. At the bud and flowering stages, B. nigra was the most attractive while E. sativa was the least attractive. At flowering, B. nigra was more attractive for oviposition than the other species. Thus, of the species tested, B. nigra has the most potential as a prospective trap crop to protect spring oilseed rape before flowering when it is at its most vulnerable developmental phase, due to its faster development and its acceptability both for feeding and oviposition to overwintered pollen beetle adults. Raphanus sativus was accepted both for feeding and oviposition, but pollen beetle larvae failed to develop in its flowers; it therefore has the potential for use as a dead-end crop. At the end of the growing season, both E. sativa and R. sativus, as late-flowering species, attracted the new generation of pollen beetles and thereby have potential to extend the effectiveness of a trap-cropping system at this time.     

Plant genotype affects the quality of oilseed rape (Brassica napus) for adults and larvae of the pollen beetle (Meligethes aeneus)

Plant quality is one of the main factors influencing the fitness of phytophagous insects. Plant quality can vary not only among genotypes of the same host plant species, but also relative to the insect sex or its life stage. In the present study, the performance of larvae and adults of the pollen beetle (Meligethes aeneus F., Coleoptera: Nitidulidae), a major insect pest of oilseed rape crops, is compared on six genotypes of oilseed rape (Brassica napus). All of the traits that are measured vary among genotypes, and comprise larval developmental duration, life span of unfed emerging adults and survival time of field‐sampled adults fed with pollen from the different genotypes. No correlation is found between insect performance and quantity of food available, showing that the quality of the food (i.e. pollen) is the fitness determinant for this insect species. Additionally, the performance of larvae and adults is also not correlated despite use of the same plant genotypes, suggesting that the determinants of pollen quality differ at least partially between both life stages. It is hypothesized that this may be a result of extensive differences in diet breadth between the life stages: larvae are specialists of brassicaceous plants, whereas adults are generalists. Finally, it is suggested that the manipulation of plant quality to increase pollen beetle development time may comprise a valuable strategy for favouring biological control by natural enemies of this pest; for example, as a result of extending the vulnerability window of larvae to attack by parasitoids.     

Pollen beetles are consumed by ground‐ and foliage‐dwelling spiders in winter oilseed rape

Pollen beetles, Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), are major pests in oilseed rape (OSR), Brassica napus L. (Brassicaceae). Among the predator species in the generalist predator complex present in OSR fields, wolf spiders (Araneae: Lycosidae) are found on the ground and cobweb spiders (Araneae: Theridiidae) build webs in the foliage. Here we study the incidence of predation of pollen beetles by these two spider groups using DNA‐based molecular analysis. Wolf spiders of the genus Pardosa and the cobweb spider, Theridion impressum L. Koch, were each collected in three winter OSR fields over a period of about 3 weeks. Pollen beetle densities as well as the occurrence of predators and alternative prey were monitored. In total, 13.8% of the collected Pardosa spp. tested positive for pollen beetle DNA in the PCR analyses, whereas 51.7%T. impressum were positive. The likelihood of detecting pollen beetle DNA in the gut contents of both spider groups was positively related to pollen beetle larval density. The implications of these results for conservation biological control and future studies of food webs in OSR are discussed.     

Effects of non‐host plant odour on Meligethes aeneus during immigration to oilseed rape

The use of semiochemicals for the manipulation of the pollen beetle, Meliethes aeneus (Fabricius) (Coleoptera: Nitidulidae), is being investigated for potential incorporation into a push‐pull strategy for this pest, which damages oilseed rape, Brassica napus L. (Brassicaceae), throughout Europe. Previous laboratory behavioural studies using volatiles from non‐host plants showed that M. aeneus is repelled by the odour of lavender, Lavendula angustifolia Mill. (Lamiaceae), essential oil. This article reports on semi‐field and field trials to investigate this behaviour under more realistic conditions. Semi‐field experiments were conducted to assess the relative importance of olfaction at different points in host location behaviour by M. aeneus. The results showed that oilseed rape plants treated with lavender odour were less colonised by M. aeneus in comparison with an untreated control, but that the treatment effect was much reduced if the lavender odour was applied after colonisation. The field experiment demonstrated that lavender odour caused a significant reduction in the number of adult M. aeneus infesting the oilseed rape plants in the treatment plots compared to the control plots. Overall, these findings are very encouraging for the future development of a push‐pull pest control system.     

Baseline susceptibility and insecticide resistance monitoring in European populations of Meligethes aeneus and Ceutorhynchus assimilis collected in winter oilseed rape

Pollen beetle, Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), and cabbage seed weevil, Ceutorhynchus assimilis (Paykull) (Coleoptera: Curculionidae), are important pests in the production of European winter oilseed rape, Brassica napus L. (Brassicaceae), which is grown on several million hectares in Europe. Insecticide treatments are common to control both pests once they exceed economic damage thresholds; however, not many chemical classes are available for their control in European oilseed rape. Particularly pollen beetles recently developed high levels of pyrethroid resistance impairing field control at recommended rates in many countries, whereas no resistance is yet reported to another important insecticide, thiacloprid. The major objective of this study was to investigate the spatio‐temporal susceptibility status of pollen beetle against the recently introduced insecticide thiacloprid. From 2009 to 2012 more than 630 populations of pollen beetle collected in 13 countries were monitored for resistance to thiacloprid by using an adult vial test. No shifting to lower susceptibility of pollen beetle to thiacloprid has been observed between 2009 and 2012. Furthermore, we were able to show that pollen beetle larvae are extremely susceptible to thiacloprid, whereas within strains larvae are significantly more resistant than adults to pyrethroids such as lambda‐cyhalothrin. Dose‐response data for thiacloprid against cabbage seed weevil populations collected in 2011 in Germany, Sweden, and Ukraine showed a 10‐fold higher intrinsic sensitivity compared to pollen beetle, and showed only a low variation in response. In addition, we also tested 17 cabbage seed weevil populations collected in five countries against lambda‐cyhalothrin with low variation in response (three‐fold), suggesting full baseline susceptibility and no resistance to pyrethroids. The implications of the data presented for resistance management in coleopteran pests in winter oilseed rape are discussed.     

Effect of a turnip rape <Emphasis Type="Italic">(Brassica rapa)</Emphasis> trap crop on stem-mining pests and their parasitoids in winter oilseed rape <Emphasis Type="Italic">(Brassica napus)</Emphasis>

Concerns about the negative effects of chemical control of oilseed rape (Brassica napus L.) pests on non-target species, human safety, and development of insecticide resistance, require alternative control strategies such as the use of trap crops and biocontrol to be developed. Psylliodes chrysocephala(L.) (Coleoptera: Chrysomelidae) (cabbage stem flea beetle) and Ceutorhynchus pallidactylus (Marsh.) (Coleoptera: Curculionidae) (cabbage stem weevil) are two major stem-mining pests of oilseed rape. This study investigated the phenology of these pests and their main parasitoids in the UK, the potential use of turnip rape (Brassica rapa L.) as a trap crop to reduce oilseed rape infestation, and the effects of insecticide treatment on pest incidence and larval parasitism. Water trap samples, plant dissections and pest larval dissections were done to determine: the incidence of adult pests and their parasitoids, the level of plant infestation by the pests and percentage larval parasitism, respectively. The turnip rape trap crop borders reduced P. chrysocephalabut not C. pallidactylus infestation of oilseed rape plots. Treatment of the trap crop with insecticide had little effect on either pest or parasitoid incidence in the oilseed rape. TersilochusmicrogasterSzép. andT. obscurator Aub. (Hymenoptera: Ichneumonidae) were the main larval parasitoids of P. chrysocephalaand C. pallidactylus, respectively. Tersilochus microgasteris reported for the first time in the UK. The implications for integrated pest management are discussed.     

Crop management affects pollinator attractiveness and visitation in oilseed rape

Ecological intensification of agriculture implies managing ecological processes to improve performance of agricultural systems. However, impacts on relevant ecological functions such as insect pollination from other crop management factors are poorly explored. Pest insects and crop resources such as water availability can directly affect crop yields, but it is unknown if there are indirect effects through effects on insect pollination. With a factorial experiment, we examined how irrigation and control of pollen beetles affected crop attractiveness and pollinator visitation in an open-pollinated spring oilseed rape cultivar. We studied how irrigation and pest control modified the production of flowers and nectar in oilseed rape, and if this in turn affected the flower-visitation of honey bees and bumble bees. Pest control increased the number of oilseed rape flowers by 69%, and the amount of nectar per flower with 36%, but for the latter only in non-irrigated plots. Furthermore, we found higher pollinator densities in plots with reduced pollen beetle densities. Pest control also reduced the number of non-legitimate flower visits, suggesting higher pollination efficiency in plots with reduced pollen beetle densities. We show that crop management affects the value of mass-flowering crops as a resource for pollinating insects. Development of pest control tools that are harmless to pollinators could increase the value of flowering crops as food resources for pollinating insects.     

Laboratory and field response of the pollen beetle, Meligethes aeneus, to the odour of oilseed rape

Abstract. The behavioural response of adults of the pollen beetle, Meligethes aeneus F. (Coleoptera: Nitidulidae), to the odour of one of their host-plants, oilseed rape ( Brassica napus L.), was observed in the laboratory using a fourarmed airflow olfactometer, and under semi-natural conditions using a markrelease–recapture technique. Oilseed rape leaf and flower odour was attractive to pollen beetles in the olfactometer and they dispersed upwind from the centre of a circular array (radius 20 m) of yellow water traps, baited with extracts of oilseed rape leaves or flowers. The dispersal of pollen beetles in the absence of oilseed rape odour was predominantly downwind and crosswind. The percentage recapture of pollen beetles was significantly greater in traps baited with rape flower extracts than leaf extracts. Pollen beetles can use odour-mediated upwind anemotaxis to locate oilseed rape plants from distances of at least 20 m over open ground.     

Impact of insecticides on oilseed rape bud infestation with eggs and larvae of pollen beetle (<Emphasis Type="Italic">Brassicogethes aeneus</Emphasis> (Fabricius))

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.     

Responses of <Emphasis Type="Italic">Phradis</Emphasis> parasitoids to volatiles of lavender, <Emphasis Type="Italic">Lavendula angustifolia</Emphasis>—a possible repellent for their host, <Emphasis Type="Italic">Meligethes aeneus</Emphasis>

Hymenopterous parasitoids of herbivorous insects can be useful biocontrol agents in integrated pest management strategies. However, the potential effects on these beneficials of new components in such strategies are often neglected. Essential oil of lavender, Lavendula angustifolia (Miller) (Lamiaceae), has recently been identified as a potential repellent in new control strategies being developed for the pollen beetle Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), a major pest of oilseed rape, Brassica napus L. (Brassicaceae). We tested the electrophysiological and behavioural responses of two common parasitoids of M. aeneus: Phradis interstitialis (Thomson) and P. morionellus (Holmgren) (both Ichneumonidae) using coupled gas chromatography-electroantennodetection (GC-EAD) and olfactometry techniques. Both species elicited electrophysiological responses to lavender oil volatiles, including two compounds known to be repellent to M. aeneus. However, the parasitoids gave no significant responses to the odours of lavender oil in behavioural bioassays and there was no evidence to suggest that lavender-treated oilseed rape plants would reduce host habitat location by parasitoids of the target pest.     

Local and landscape determinants of pollen beetle abundance in overwintering habitats

• 1 The development of integrated pest management strategies requires that the semi‐natural habitats scattered across the landscape are taken into account. Particular determinants of insect pest abundance in overwintering habitats just before they migrate onto crops appear to be poorly known and of crucial importance for understanding patterns of crop colonization and pest population dynamics at the landscape scale.
• 2 The emergence of pollen beetle Meligethes aeneus F. was studied in grassland, woodland edge and woodland interior over a 3‐year survey in France using macro‐emergence traps. A suite of variables at the local and the landscape scale was assessed for each trap, aiming to identify potential relevant habitat indicators. The effects of habitat characteristics were evaluated using partial least square regressions.
• 3 It was found that M. aeneus can overwinter in all types of habitat but that particular habitat characteristics at the local and landscape scales may explain their abundance in overwintering sites more than the types of habitat: relative altitude, litter thickness, soil moisture and proximity to the previous year's oilseed rape fields appear to be positively correlated with abundance of adults over the 3 years.
• 4 Hence, the abundance of emerged pollen beetles depends on both the landscape configuration of the previous year's oilseed rape fields around overwintering sites and local habitat characteristics. Landscape configuration may determine population flow towards overwintering sites in the late summer, and local habitat characteristics may influence survival rates during the winter. The findings of the present study provide valuable insight into the role of semi‐natural habitats as a source of pests, patterns of crop colonization in the spring, and the influence of landscape on pollen beetle abundance.

     

Responses to olfactory and visual cues by over-wintered and summer generations of the pollen beetle, Meligethes aeneus

Abstract.  Behavioural responses to odours of oilseed rape in bud and flower stage and to green and yellow colours are studied for the two main phenological stages of pollen beetles, Meligethes aeneus , a major pest of oilseed rape, Brassica napus . Over-wintered individuals oviposit in buds of oilseed rape. Adults of the new generation (i.e. the summer generation) feed on flowers of different plant species before over wintering. In olfactometer experiments, the over-wintered beetles display a higher preference for odour of oilseed rape at the bud stage compared with the summer generation, both with and without colour stimuli. Flower odours are preferred in combination with yellow colour. Colour stimuli presented alone do not affect the behaviour. The summer generation beetles respond to both bud and flower odour. Adding colour stimuli changes the summer generations preference towards yellow and flower odour.     

Are honey bees' foraging preferences affected by pollen amino acid composition?

Abstract.  1. Although pollen is a vital nutritional resource for honey bees, Apis mellifera , the influence of pollen quality on their foraging behaviour is little understood.
2. In choice-test experiments, bees showed no innate pollen-foraging preferences, but preferred oilseed rape Brassica napus pollen over field bean Vicia faba pollen after previous foraging experience of oilseed rape.
3. The free amino acid content of oilseed rape and field bean pollen was compared using high-performance liquid chromatography. Oilseed rape pollen contained a greater proportion of the most essential amino acids required by honey bees (valine, leucine, and isoleucine) than field bean, suggesting that oilseed rape pollen is of greater nutritional quality for honey bees than is field bean pollen.
4. Honey bee foraging preferences appeared to reflect pollen quality. The hypothesis that pollen amino acid composition affects the foraging behaviour of honey bees is discussed.     

The relative attractiveness of Brassica napus,B. rapa,B. juncea and Sinapis alba to pollen beetles

It is often suggested that weeds from the same family as the crop plant may increase insect pest damages by providing shelter and additional oviposition opportunities. We compared the relative attractiveness of Brassica rapa L., B. juncea L., Sinapis alba L. and B. napus L. (Capparales: Brassicaceae) to the pollen beetle and its hymenopteran parasitoids in field conditions. Our results revealed that none of the investigated plants increased the pest abundance on B. napus plants. On the contrary, B. juncea and S. alba lured beetles away from B. napus during its damage-susceptible stage. The parasitism rate of pollen beetle larvae was the highest on B. juncea plants, indicating that cruciferous weeds could improve the natural control of the pollen beetle by providing additional hosts for parasitoids. Therefore, close relatives of oilseed rape might be used to trap pollen beetle adults, but also to support populations of natural enemies that could decrease the number of beetles.