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.     

The effects of non-host plant essential oil volatiles on the behaviour of the pollen beetle Meligethes aeneus

The use of semiochemicals for manipulation of the pollen beetle Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae) is being investigated for potential incorporation into a push‐pull control strategy for this pest, which damages oilseed rape, Brassica napus L. (Brassicaceae), throughout Europe. The response of M. aeneus to non‐host plant volatiles was investigated in laboratory assays to establish whether they have any effect on host plant location behaviour. Two approaches were used. First a novel, moving‐air bioassay using air funnels was developed to compare the response of M. aeneus to several non‐host plant essential oils. The beetles avoided the host plant flowers in the presence of non‐host volatiles, suggesting that M. aeneus uses olfactory cues in host location and/or acceptance. The results were expressed as ‘repellency values’ in order to compare the effects of the different oils tested. Lavender (Lavendula angustifolia Miller) (Lamiaceae) essential oil gave the highest repellency value. In addition, a four‐arm olfactometer was used to investigate olfactory responses, as this technique eliminated the influence of host plant visual and contact cues. The attraction to host plant volatiles was reduced by the addition of non‐host plant volatiles, but in addition to masking the host plant volatiles, the non‐host volatiles were avoided when these were presented alone. This is encouraging for the potential use of non‐host plants within a push‐pull strategy to reduce the pest colonisation of crops. Further testing in more realistic semi‐field and field trials is underway.     

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.     

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.     

Host plant selection by the pollen beetle Meligethes aeneus

A simple bioassay is described for the response of Meligethes aeneus F. (Coleoptera: Nitidulidae) to different plants and plant parts. Assays with non-hibernated beetles showed that (1) cruciferous buds and stamens were greatly preferred to petals and leaves; (2) stamens were most preferred when the quantity of mature pollen was at maximum; (3) anthers were preferred to filaments; (4) stamens from five different spring cultivars of Brassica napus were preferred at significantly different degrees; (5) stamens from four B. campestris cultivars were preferred to B. napus cv. Guilliver, but only when the preferences per mm² were compared; (6) stamens from B. carinata and Sinapis alba were preferred to stamens from B. napus and B. campestris; (7) stamens from Compositae (Cirsium arvense, Leontodon nudicaulis, Sonchus arvensis and Taraxacum sp., Vulgaria group) were much less preferred than B. napus stamens (Cruciferae), but more preferred than stamens from Rosa pimpinellifolia (Rosaceae), whereas stamens from Papaver dubium (Papaveraceae) were not preferred to B. napus leaves; (8) chemical stimuli, including odours, were the most important stimuli in the bioassays. the use of equal crude areas for comparisons is briefly discussed.

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Le choix de plantes-hôtes de méligèthe des cruciferes

Résumé Une méthode simple et rapide, est signalée pour l'épreuve de la réponse de Meligethes aeneus vis-à-vis des plantes différentes et des organs différents de plantes. Des épreuves avec des insectes non-hibernés ont indiqué que (1) des étamines et des boutons sont beaucoup plus préférées que les pétales et les feuilles; (2) la préférence des étamines est au maximum en même temps que le nombre de pollens mûrs; (3) des filaments (sans pollens) sont moins préférés que les anthères; (4) les préférences des étamines de cinq variétés différentes de Brassica napus diffèrent significativement; (5) les préférences des étamines de quatre variétés de B. campestris surmontent celle de B. napus var. Gulliver, mais seulement quand les préférences par mm² sont comparées; (6) les préférences des étamines de B. carinata et Sinapsis alba dépassent celles de B. napus et B. campestris; (7) des étamines de Compositae (Cirsium arvense, Leontodon nudicaulis, Sonchus arvensis et Taraxacum sp., group de Vulgaria) sont beaucoup moins préférées que des étamines de B. napus (Cruciferae), et plus préférées que celles de Rosa pimpinellifolia (Rosaceae), tandis que les étamines de Papaver dubium (Papaveraceae) ne sont pas préférées à les feuilles de B. napus; (8) des stimuli chimiques, les odeurs incluses, étaient les stimuli les plus importants dans les épreuves. La nécessité d'appliquer des étendues standardisées dans les comparaisons est brièvement discutée.

     

Supercooling ability and cold hardiness of the pollen beetle Meligethes aeneus

Supercooling point (SCP) and cold‐hardiness of the pollen beetle Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae) were investigated. Mature eggs from the oviduct were supercooled on average to ?28.0 °C and from oilseed rape buds to ?24.4 °C; first instars were supercooled to ?21.0 °C and second instars to ?16.8 °C. Despite their high supercooling ability, none of the eggs survived 24 h exposure to ?2.5 °C. The supercooling ability of adults varied significantly among feeding and non‐feeding beetles: high SCPs prevailed during the whole warm period, being about ?12 °C; low values of SCP of ?20 °C dominated in non‐feeding beetles. In spring and autumn, beetles displayed the same acclimation efficiency: after 1 week of exposure at 2.0 °C with no access to food their SCPs were depressed equally by about 3 °C. Meligethes aeneus beetles have a different response to low temperatures depending on the season. The lowest tolerance was found in reproductively active beetles after emergence from overwintering sites; the time needed to kill 50% of individuals (Ltime₅₀) was 56.2 h at ?7 °C and the lower lethal temperature needed to kill 50% (Ltemp₅₀) after 24 h exposure was ?8.6 °C. Cold hardiness increased from midsummer to midwinter; Ltime₅₀ was 80 h in August, 182.8 h in September, and 418.1 h in January. Lethal temperature after 24 h exposure was ?9.1 °C in August and ?9.8 °C in September. In February, after diapause, the beetles started to loose their cold tolerance, and Ltemp₅₀ was slightly increased to ?9.5 °C. Hibernating beetles tolerated long exposure at ?7 °C well, but mortality was high after short exposure if the temperature dropped below ?9 °C for 24 h. Despite the season, the beetles died at temperatures well above their mean SCP; consequently, SCP is not a suitable index for cold hardiness of M. aeneus.     

Migration to and dispersal from oilseed rape by the pollen beetle,Meligethes aeneus,in relation to wind direction

1 Host‐plant‐odour‐induced upwind anemotaxis is accepted as the main mechanism by which herbivorous insects find their host plant within an heterogenous environment, but field data supporting this hypothesis are scarce. 2 The flight directions of the pollen beetle Meligethes aeneus to and from a plot of winter oilseed rape and the direction of the wind were recorded concurrently. The beetles were sampled by eight double‐sided window traps encircling the plot. Distal sides of the traps, relative to the plot, sampled the beetles as they flew towards the plot, whereas the proximal sides of the traps sampled them as they flew away from the plot. Paired data on daily catch of beetles in distal or proximal traps and the volume of air impacting each trap were compared. 3 Correlations between daily catch of M. aeneus into distal traps and trap wind volume were negative, indicating that flights by both overwintered‐ and new‐generation insects towards the plot were upwind. 4 Correlations between daily catch of M. aeneus into proximal traps and trap wind volume varied with generation. Catch of overwintered‐generation M. aeneus was negatively correlated with trap wind volume, indicating that flight was upwind. Proximal trap catch of the new‐generation M. aeneus was weakly/modestly positively correlated with trap wind volume, indicating that flights were downwind or crosswind. 5 Understanding the effect of wind direction on flight of M. aeneus holds potential for improving the forecasting of their arrival and spatial distribution on the crop for integrated pest management.     

Species-specific primers for predation studies of the pollen beetle, Meligethes aeneus (Coleoptera, Nitidulidae)

Species‐specific primers were developed for the pollen beetle (a pest in oilseed rape) for studies of predation by natural insect predators. Two forward and three reverse primers were designed within the mitochondrial COI gene and used in combination to amplify fragments in the size range of 163–290 bp. Remains of pollen beetle DNA were consistently detected in Pardosa spiders up to 24 h after ingestion but dropped drastically at 48 h. These primers will facilitate studies on biological control of this oilseed rape pest. Detection time was not correlated with fragment length as might be expected as the DNA gradually degrades into progressively shorter fragments over time.     

The spatial dynamics of pollen beetles in relation to inflorescence growth stage of oilseed rape: implications for trap crop strategies

Semi‐field‐scale arrays of oilseed rape (Brassica napus L.) (Brassicaceae) plants were used to observe the development of distributions of pollen beetles (Meligethes aeneus Fabricius) (Coleoptera: Nitidulidae) in a simulated trap crop system where inflorescence growth stage alone was used to manipulate the pest. Over two successive years, pairs of 1 m spaced square arrays of 100 glasshouse‐grown plants were placed 40 m apart in the field in May, and were subject to natural infestation by pollen beetles. The test plot of each pair had a simulated trap crop, with an outer row of plants at early flowering stage intended to protect more susceptible inner plants at late bud stage, and the control plot had all plants at the late‐bud stage, simulating a standard crop situation. Pollen beetles were counted daily on each plant for 10–13 days. The spatio‐temporal development of plot infestation was analysed in relation to the distribution of racemes in bud and raceme in flowers using Spatial Analysis by Distance IndicEs (SADIE), and tests of edge and centre distribution. Inflorescence growth stage characteristics were shown to be important in determining the spatial distributions of pollen beetles. In control plots, the numbers of racemes in bud and in flower were never edge or centre distributed. In test plots, racemes in flower were always edge distributed, and racemes in bud began edge distributed and became centre distributed. Pollen beetle numbers were usually spatially associated with the abundance of racemes in bud and/or in flower. In control plots, pollen beetles were neither edge nor centre distributed, but in test plots they maintained a significant edge distribution for 7–10 days. At the end of the experiments, females were more centre distributed in the test plots than males, and were more closely associated with racemes with buds, whereas males were more associated with racemes with flowers. In early flowering stage plants, the number of racemes in flowers were a good indicator of the abundance of racemes in buds, but this relationship was lost as flowering progressed. Although flowering racemes provide strong cues for immigrating pollen beetles, the abundance of buds may be a more important determinant of residence time, particularly for females, and is therefore a critical determinant of trap crop effectiveness.     

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.     

Do pollen beetles need pollen? The effect of pollen on oviposition,survival, and development of a flower‐feeding herbivore

Abstract.  1. Pollen is considered to be an important dietary component for many species of flower-feeding herbivores. Its influence on oviposition site selection by the pollen beetle Meligethes aeneus , and on the development of its larvae was investigated.
2. The effects of pollen presence and absence on adult, egg, and larval incidence in the field, and on larval development in the laboratory were compared through the use of Synergy, a composite hybrid oilseed rape Brassica napus variety comprising male-fertile (with pollen) and male-sterile (without pollen) plants.
3. In the field, adult females were more abundant on male-fertile plants during flowering, and a greater proportion of male-fertile than male-sterile buds were accepted for oviposition. These data indicate a possible role of pollen in oviposition site selection by female pollen beetles.
4. The numbers of first instar larvae on the two plant lines did not differ; however, more second instars were found on male-fertile than on male-sterile flowers. This suggests a greater larval survival on male-fertile plants, possibly due to the more readily available food resources and better nutrition afforded by the presence of pollen.
5. Laboratory experiments confirmed that a diet which included pollen improved survival to adulthood and resulted in heavier pupae and adults; however, pollen was not obligatory for larval survival and development.
6. The pollen beetle, previously thought to be an obligate pollen feeder, is therefore more generalist in its requirements for development. These findings may relate to the nutritional and behavioural ecology of other flower-feeding herbivores.     

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.     

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.     

Characteristics of oviposition behaviour of the pollen beetle, Meligethes aeneus on four different host plants

Oviposition behaviour of Meligethes aeneus F. (Coleoptera: Nitidulidae) is characterised and quantified on four different plant species. Six behavioural components are identified: W—walking, WA—walking with abdomen on surface, R—resting, B—biting, AOH—placing abdomen over the bite hole and OVI—oviposition. Comparison of host acceptance behaviours on Brassica napus L., Brassica juncea (L.) Czern, Brassica nigra (L.) Koch and Sinapis alba L. showed that S. alba was accepted as a host only after a long exposure to the plant. Behaviour on the Brassica species was similar, however on B. nigra beetles spent a high proportion of time actually ovipositing. We conclude that important cues for oviposition are located both on the bud surface and inside the bud.     

Orientation of Colorado potato beetle to natural and synthetic blends of volatiles emitted by potato plants

1 Behavioural responses of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), to volatiles emitted from solanaceous host plants (potato and tomato), a non‐host legume (soybean), and 13 synthetic blends or three individual chemicals emitted by potato plants were investigated in laboratory bioassays. 2 Both male and female CPB were attracted to volatiles emitted by mechanically damaged potato foliage, but not to mechanically damaged tomato foliage; CPB offered a choice between the two damaged solanaceous plants did not show a preference. 3 Among 16 odourous blends or individual chemical components of potato plant emissions tested, six blends were attractive, two were repellent, and eight elicited no preference in laboratory bioassays. Volatile blends containing relatively high amounts of the green leaf volatiles (E)‐2‐hexen‐1‐ol and (Z)‐3‐hexen‐1‐ol, or the sesquiterpene β‐ caryophyllene, were unattractive or repellent. Minimal blends attractive to CPB were comprised of (Z)‐3‐hexenyl acetate (±)‐linalool and methyl salicylate: the combination of all three chemicals elicited sexually dimorphic attraction of males; two component blends comprised of (Z)‐3‐hexenyl acetate and either (±)‐linalool and methyl salicylate attracted both sexes. Individual compounds were inactive. No significant difference was noted between two attractive blends, or an attractive synthetic blend vs. mechanically damaged potato foliage. 4 These results show that CPB are attracted to blends of specific chemicals emitted by their host plants and provide a basis for the use of plant attractants as a component of integrated management of pestiferous populations.     

Establishment of the Amplified Fragment Length Polymorphism (AFLP) technique for genotyping of pollen beetle (Meligethes aeneus) - a noxious insect pest on oilseed rape (Brassica napus)

In order to conduct studies concerning genetic variability of pollen beetles (Meligethes aeneus), a genotyping protocol was established. No genome information is available for pollen beetles so the amplified fragment length polymorphism (AFLP) technique was chosen since it does not depend on any prior sequence information of the samples and also is a sensitive and robust technique. However, several modifications were needed in order to adapt the method for analysis of pollen beetles. Basic modifications included (i) alterations of DNA purification, (ii) use of two six-cutter restriction enzymes, (iii) and modified PCR conditions. This protocol resulted in a favourable number of fragments of an appropriate size range for standard gel analysis by a DNA sequencer applicable to a single insect and even body parts enabling different assays to be conducted on a single specimen. Pollen beetles from different areas of Sweden were analysed to verify the reproducibility and efficacy of the protocol as well as for phenetic analysis. The high reproducibility of the modified AFLP protocol allows it to be used as a reliable tool for genotype analysis of pollen beetles.     

Effects of Metarhizium anisopliae on the pollen beetle Meligethes aeneus and its parasitoids Phradis morionellus and Diospilus capito

The efficacy of two Finnish strains of Metarhizium anisopliaeagainst the rape blossom beetle Meligethes aeneus (Coleoptera:Nitidulidae) and the effect on its parasitoids Phradismorionellus (Hymenoptera: Ichneumonidae) and Diospilus capito(Hymenoptera: Braconidae) were studied in laboratory and semi-fieldexperiments. Several bio-assays were performed using either directexposure of the host beetle to the pathogens, or pots containing soilinoculated with M. anisopliae conidia at a rate of 2 ×10⁸ per ml soil. Parasitised and unparasitised M. aeneuslarvae were collected in the field and were placed for pupation in thetest soil. The effect of treatment on M. aeneus andD. capito was estimated after adult emergence, and the effecton P. morionellus was estimated by dissecting hibernating pupae.While both of the M. anisopliae strains were highly pathogenicto M. aeneus adults and larvae upon direct exposure, soiltreatment resulted in no significant difference between the number ofinsects emerging (or found) from the treated and untreatedpots. However, the treated insects appeared to be latently infectedand the actual infection rate had to be estimated after their deathand incubation in a moist chamber. The mortality of the beetles causedby direct exposure to the fungus was 85% (range 70–88%). The rateof latent infection following indirect exposure via treated soil indeep pots in laboratory was 80% (range 49–100%), while that inP. morionellus was only 17% (range 0–85%), and inD. capito significantly higher, 76% (range 72–100%).The results indicate that M. anisopliae is a potentially usefulcandidate to be used as a bio-insecticide to control the pollenbeetle, and that at least the most abundant parasitoid, Phradismorionellus, is less affected than the target pest itself. Thepossible ecological role of latent infections in the host as well asin some of the parasitoids needs to be clarified.     

Effects of host plant species on the interaction between the parasitic wasp Diospilus capito and pollen beetles (Meligethes spp.)

1 Field studies were conducted in central Sweden to establish whether two host plants with high and low suitability for pollen beetles (Meligethes aeneus Fabr. [Coleoptera: Nitidulidae] and Meligethes viridescens Fabr.) affected the parasitoid Diospilus capito Nees [Hymenoptera: Braconidae]. 2 Samples of larvae were taken from fields with plots of white mustard, Sinapis alba L. and spring rape, Brassica napus L. in 1997 and 1998. Levels of parasitism and the survival and size of D. capito were measured to determine any influence of the host plant species. Survival and weights of pollen beetles from S. alba and B. napus were also measured. 3 Levels of parasitism between 8% and 29% were recorded. There was a significantly higher likelihood of being parasitized by D. capito for beetle larvae developing on S. alba than on B. napus. We argue that semiochemical or morphological properties of plant species could be responsible for differential parasitism by D. capito. 4 Neither survival of D. capito nor parasitoid size differed from hosts developing on S. alba or B. napus. Pollen beetle emergence was the same for both plant species, but beetles that developed on S. alba weighed less than those from B. napus. Results suggest that the partial resistance of S. alba to the pollen beetle will have no negative effects on the parasitoid D. capito.     

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.     

Thuja occidentalis: identification of volatiles and electroantennographic response by the invasive cedar bark beetle,Phloeosinus aubei

Recently, the distribution of the Mediterranean cedar bark beetle, Phloeosinus aubei Perris (Coleoptera: Scolytidae), has expanded to Central Europe. Reported mostly on cypress in the Mediterranean area, potential host plants in the invaded range include other scale‐leafed conifers, such as cultivars of arborvitae, Thuja occidentalis L. To reveal potential kairomonal cues for P. aubei, volatiles of T. occidentalis were collected and analysed by gas chromatography with electroantennographic detection (GC‐EAD). Assignments of chemical structures of antennally active components were carried out by gas chromatography linked to mass spectrometry (GC‐MS) using authentic reference samples. Antennal responses to synthetic samples of the identified compounds were studied by electroantennography (EAG), with antennae of female and male P. aubei. GC‐EAD analysis of head space volatiles of T. occidentalis revealed 22 antennally active compounds, of which 21 were identified. The most abundant components were α‐ and β‐thujone, fenchone, camphor, terpinen‐4‐ol, bornyl acetate and α‐terpinyl acetate, all of which are oxygenated monoterpenes. When EAG activities of synthetic samples were compared, the most intensive responses from female antennae were elicited by a mixture of α‐ and β‐thujone, followed by (–)‐terpinen‐4‐ol, (+)‐camphor, cis‐4‐thujanol, (+)‐sabina ketone, (+)‐terpinen‐4‐ol, isopulegone, (–)‐fenchone, borneol, (3Z)‐hexen‐1‐ol, (–)‐1‐octen‐3‐ol and (+)‐sulcatol. Male antennae responded the most to (–)‐terpinen‐4‐ol and cis‐4‐thujanol followed by the mixture of α‐ and β‐thujone. The next highest responses were elicited by (+)‐camphor, borneol, (+)‐terpinen‐4‐ol, (+)‐sulcatol and (+)‐sabina ketone. Striking differences were found between responses to the enantiomers of fenchone, sulcatol and 1‐octen‐3‐ol, whereas responses to the enantiomers of terpinen‐4‐ol did not differ significantly from each other. Several antennally active volatiles of T. occidentalis have also been reported from cypress and various other members of the Cupressaceae, suggesting that the sensory apparatus of P. aubei may recognize the shared components, which may enable rapid adaptation to new hosts in the invaded areas.