Pollen Beetle Research Articles

Selection of floral resources to optimise conservation of agriculturally-functional insect groups

Non-crop vegetation in agricultural landscapes can provide a means of conserving insects in farmed landscapes and optimising on-farm ecosystem services as a result. Inclusion of floral resources may be particularly useful in conserving many beneficial insects, where groups including pollinators and pest natural enemies often rely on nectar and pollen during (at least part of) their life-cycle. As not all flowers are equally suited to all beneficial insects, selection of appropriate flowering plants is key to ensuring that conservation targets are met and benefits to ecosystems services realised as a result. This short paper describes an experiment conducted to assess the ‘total temporal attractiveness’ of a range of British wildflowers to selected functional insect groups. The results obtained demonstrate that flowering period alone is a poor indicator of plant suitability to insects, where no relationship existed between this and attraction to insects overall. Data also suggest that, based on attraction over a season, certain flowering plants are more likely to be of general insect conservation value and/or benefit to functional insect groups than others. Attraction to pest insects was also considered, with relatively high catches of thrips and pollen beetles observed in flowering stands of some plants.

Target-site resistance to pyrethroids in European populations of pollen beetle, Meligethes aeneus F.

Pollen beetle, Meligethes aeneus F. (Coleoptera: Nitidulidae) is a major univoltine pest of oilseed rape in many European countries. Winter oilseed rape is cultivated on several million hectares in Europe and the continuous use of pyrethroid insecticides to control pollen beetle populations has resulted in high selection pressure and subsequent development of resistance. Resistance to pyrethroid insecticides in this pest is now widespread and the levels of resistance are often sufficient to result in field control failures at recommended application rates. Recently, metabolic resistance mediated by cytochrome P450 monooxygenases was implicated in the resistance of several pollen beetle populations from different European regions. Here, we have also investigated the possible occurrence of a target-site mechanism caused by modification of the pollen beetle para-type voltage-gated sodium channel gene. We detected a single nucleotide change that results in an amino acid substitution (L1014F) within the domain IIS6 region of the channel protein. The L1014F mutation, often termed kdr, has been found in several other insect pests and is known to confer moderate levels of resistance to pyrethroids. We developed a pyrosequencing-based diagnostic assay that can detect the L1014F mutation in individual beetles and tested more than 350 populations collected between 2006 and 2010 in 13 European countries. In the majority of populations tested the mutation was absent, and only samples from two countries, Denmark and Sweden, contained pollen beetles heterozygous or homozygous for the L1014F mutation. The mutation was first detected in a sample from Denmark collected in 2007 after reports of field failure using tau-fluvalinate, and has since been detected in 7 out of 11 samples from Denmark and 25 of 33 samples from Sweden. No super-kdr mutations (e.g. M918T) known to cause resistance to pyrethroids were detected. The implications of these results for resistance management strategies of pollen beetle populations in oilseed rape crops are discussed.

Discordant patterns in the genetic, ecological, and morphological diversification of a recently radiated phytophagous beetle clade (Coleoptera: Nitidulidae: Meligethinae)

Molecular analyses on the Brassicogethescoracinus species complex (pollen beetles associated with Brassicaceae) were performed to explore genetic and ecological diversification, and robustness of the current morphologically based classification. Complete COI sequences (1,542 bp) were obtained from 69 individuals assigned to 10 recognized species and from 5 individuals of the designated outgroup (B. aeneus). Mean interspecific divergence within the clade varied from 0.005 to 0.283. The species B. epeirosi, B. subaeneus and B. cantabricus were associated with the tribe Arabideae and found to occupy basal most positions in the phylogeny, whereas all other species, mostly associated with the tribe Hesperideae, grouped together. In the latter group, B. erysimicola and B. coracinus occupied a basal position adjacent to a wider cluster of mixed haplotypes, likely, due to incomplete lineage sorting or past hybridization events. New data based on nuclear genetic markers are currently being collected to pursue a multilocus analysis.

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.

Pollination activity affects selection on floral longevity in the autumnal-flowering plant, Narcissus serotinus L.

Flower longevity, the period of time that a flower remains open, is a crucial factor in plant reproductive fitness. Though longevity varies substantially among angiosperm species, longer flower longevities may be a selective advantage under unpredictable or scarce pollination activity. This study examined this hypothesis in Narcissus serotinus L. (Amaryllidaceae), a small Mediterranean geophyte that blooms during the autumnal rainy season. Field experiments performed in three natural populations through 3 consecutive years shows that N. serotinus has the ability to expand flower longevity when pollination has not occurred. Flowers that were open longer to pollination have higher reproductive fitness than younger flowers. As N. serotinus flowers age, there was a shift in pollination patterns since flower visits by butterflies became scarcer and are replaced by one small pollen beetle. Given that there was evidence of pollen limitation and that this species produces one single flower, we suggest that extended flower longevity is selected because it assures pollination success under scarce insect visits.

Using landscape indicators to predict high pest infestations and successful natural pest control at the regional scale

Designing multifunctional landscapes requires accurate indicators to assess the effect of landscape structure on the provision on ecosystem services. Biological pest control relying on natural enemies is an important ecosystem service considered as a sustainable alternative to chemical control. The aim of this study was to measure and compare the accuracy of landscape indicators computed at various spatial scales to predict pollen beetle infestations and successful biological control in northwestern France. The sensitivity, specificity, and probability of correctly ranking fields were estimated for each indicator based on a survey of 42 fields using the receiver operating characteristic procedure. For pest infestation, the proportion of woodland and the proportion of semi-natural habitats were found to be informative indicators with good discriminatory abilities. For biological control, the proportion of woodland, the proportion of semi-natural habitats and the proportion of the previous year's oilseed rape fields with reduced soil tillage were found to be informative indicators with good discriminatory abilities. By using indicator values and optimal thresholds we were able to compute maps of areas at risk for pest infestation and those displaying successful biological control at the regional scale. This study provides tools that could help extension services, landscape planners, and policy makers in optimizing landscape structure according to the provision of a key ecosystem service. The results of this study also provide new grounds for understanding trophic interactions at the regional scale as well as the ambivalent effect of landscape complexity on pest and natural enemy populations.

The effect of a piperonyl butoxide/tau‐fluvalinate mixture on pollen beetle (Meligethes aeneus) and honey bees (Apis mellifera)

Previous work has characterised pyrethroid resistance in pollen beetle (Meligethes aeneus F.) as principally an oxidative mechanism. Piperonyl butoxide (PBO) can synergise this resistance in the field, but its effects on the honey bee are thought to be unacceptable. A field trial in Poland was conducted to show that a mixture of PBO and tau-fluvalinate at the registered rate gave increased and longer-lasting control of resistant pollen beetle. Four days after spraying with tau-fluvalinate, only 20% of pollen beetles were controlled, compared with 70% if the tau-fluvalinate/PBO mixture was used. No detriment to honey bee health was observed using the same mixture. PBO, if used in conjunction with a pyrethroid of relatively low bee toxicity, can successfully overcome pyrethroid resistance in pollen beetle without incurring an increased loss of honey bees, even if they are present at the time of spraying.

Diversity of Beauveria spp. isolates from pollen beetles Meligethes aeneus in Switzerland

Pollen beetles Meligethes aeneus were collected in oilseed rape fields at different sites in Switzerland in spring 2004–2005 and 32 isolates of the fungal genus Beauveria occurring as latent infections in the beetles were obtained and molecularly characterized. Three major clades, Beauveria bassiana sensu stricto (Clade A: n=13), Beauveriabrongniartii (Clade B: n=1) and Beauveria Clade C (n=18) were identified among the isolates based on sequences of the ITS region and the 5′ end of EF1-α. B. bassiana s.s. was further separated in the two clades, Eu_1 (n=10) and Eu_4 (n=3). The intergenic region Bloc provided best resolution of the individual clades B. bassiana s.s. Eu_1, Eu_4 and B. brongniartii. No specific clade of Beauveria appeared to be associated with adult M. aeneus populations. However, data suggested high relative abundance of Beauveria Clade C among the fungal entomopathogens infecting M. aeneus. Characterization of the isolates by simple sequence repeats (SSR) revealed further genotypic diversity within the clades except B. bassiana s.s. Eu_4 which appeared to be clonal. However, the individual SSR markers were differentially amplifiable from isolates of the different clades. It is therefore important to identify the underlying phylogenetic affinity of Beauveria isolates to interpret results based on SSR markers. The data suggest that not all available SSR markers are suitable for reliable characterization of diversity within Beauveria Clade C.

Local and landscape determinants of pollen beetle abundance in overwintering habitats

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. 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. 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. 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.

Description and taxonomic position of a new genus and species of southern African pollen beetle (Coleoptera: Nitidulidae: Meligethinae)

The pollen beetle Restiopria biondii gen. nov., sp. nov., from Western Cape, South Africa, is described. The taxonomic position of Restiopria is discussed. The new genus is not noticeably related to any other known Meligethine, although it exhibits a few shared characters with Pria Stephens 1830. Larval host plants of the single known species are male flowers of two species of the monocot family Restionaceae.

A note on the insecticide sensitivity status of Meligethes species (Coleoptera: Nitidulidae) in Luxembourg

Adult pollen beetles, Meligethes spp. (Coleoptera: Nitidulidae), were sampled from 27 and 35 oilseed rape (Brassica napus subsp. oleifera) fields scattered over Luxembourg in 2008 and 2009, respectively. Ten well-developed and active individuals from each field were transferred into 40-ml glass vials (4 replicates) with their interior surface being coated with the pyrethroid deltamethrin at rates corresponding to 0%, 0.8%, 4%, 20%, 100%, or 500% of the recommended field application rate. The percentage of dead insects was recorded at 0 h, 1 h, 5 h, and 24 h, and increased with time to a maximum. The application rate required to obtain a mortality of 50% (LC50) after 24 h of exposure was estimated by logistic regression models. The overall median LC50 calculated for all locations and years was 1.15 ± 0.29% of the field rate. The median LC50 for 2008 was 0.79 ± 0.40% of the field rate and 1.80 ± 0.40% in 2009. In 2008, no population with an LC50 below the overall median LC50 was found in the north-eastern part of the country, whereas an approximately homogeneous spatial distribution of populations with LC50s below the overall median was found in 2009, suggesting a spread of less sensitive Meligethes spp. from southwest to northeast within the period of observation. Pollen beetles from four locations were additionally tested for their sensitivity towards bifenthrin and chlorpyri- fos-methyl. The period of time until 50% of the individuals were affected (LT50) decreased exponentially with rate and differed significantly among insecticides (P = 0.005), but not among locations (P = 0.753). The average LT50 at 4% of the field rate was 9.3 ± 2.2 h, 5.4 ± 0.3 h, and 2.9 ± 0.1 h for deltamethrin, bifenthrin, and the organophosphate chlorpyrifos-methyl, respectively.

Effect of crop management and landscape context on insect pest populations and crop damage

Understanding the determinants of insect–plant interactions and pest population dynamics at multiple spatial scales is a pre-requisite for developing innovative crop protection strategies and increasing the sustainability of agroecosystems. In a two-year study, we investigated the relative influence of local crop management and landscape context on pollen beetle (Meligethes spp.) abundance and damage at 8 different spatial scales around 42 oilseed rape fields using a multi-model inference approach. We found that pest abundance was mainly determined by the proportion of grassland and woodland in the landscape at scales ranging from 1500m to 2000m. Pollen beetle damage was affected both by local management and landscape predictors at scales ranging from 1500m to 2000m. Indeed, damage was negatively correlated with the nitrogen nutrition index of the plants and positively correlated with the proportion of woodland in the landscape at a large scale. Our multi-scale approach revealed that landscape complexity determines pollen beetle abundance in the spring and that nitrogen nutrition of the plants influences crop ability to compensate bud abortions resulting from pest attacks. The results are discussed in relation to crop management, pest dispersal ability and landscape structure.

Cytochrome P450 mediated pyrethroid resistance in European populations of Meligethes aeneus (Coleoptera: Nitidulidae)

Pollen beetle, Meligethes aeneus (Coleoptera: Nitidulidae) is a major pest on several million hectares in European winter oilseed rape cultivation. Synthetic pyrethroids have been successfully used for many years to keep them under economic damage thresholds. Recently wide-spread resistance development to pyrethroids in pollen beetle populations was described in many European countries, including Germany, France, Poland, Denmark and others. Resistance monitoring is conducted by incubating beetles for 24 h in glass vials coated with different concentrations of lambda-cyhalothrin. Using such an assay format we were able to show cross-resistance to other pyrethroids, such as deltamethrin, cypermethrin, and to a somewhat lower extent bifenthrin, etofenprox and tau-fluvalinate. Here we also investigated in more detail in 27 different populations the biochemical mechanism of pyrethroid resistance. Synergism experiments revealed a high synergistic potential for piperonyl butoxide in vivo, whereas other compounds such as S,S,S-tributylphosphorotrithioate and diethylmaleimide failed to suppress pyrethroid resistance. Incubating microsomal fractions of pollen beetle with deltamethrin and subsequent LC–MS/MS analysis revealed 4-OH-deltamethrin as the major metabolite. Metabolite formation in vitro and pyrethroid resistance in vivo is correlated and inhibition trials with piperonyl butoxide, tebuconazole and aminobenzotriazole suggest the involvement of cytochrome P450′s. Furthermore we were able to show cross-resistance to tau-fluvalinate which is supported by the competitive inhibition of 4-OH-deltamethrin formation by increasing concentrations of tau-fluvalinate in microsomal hydroxylation assays. Although we provided clear experimental evidence for an oxidative mechanism of resistance in numerous populations, other mechanisms might be involved based on the data discussed.

Exploring local borders of distribution in the shrub Daphne laureola: Individual and populations traits

Biogeographic models predict that marginal populations should be more geographically isolated and smaller than central populations, linked to more stressful conditions and likely also to a reduction in density of individuals, individual growth, survival and reproductive output. This variation in population features could have important consequences for different aspects of plant ecology such as individual reproductive success, population genetic structure or plant-animal interactions. In this study, we analyze if individuals of the evergreen shrub Daphne laureola at disjunt populations in a local border of its distribution area in southern Iberian Peninsula differ in individual size, shoot growth, reproductive output and the pollination environment from central continuous populations within the area. Plants of central continuous populations were larger and produced more flowers and fruits than plants of marginal disjunct populations suggesting more optimal conditions, although they had lower annual shoot growth. In contrast, fruit set was higher in plants at the local border, suggesting a more efficient pollinator service in these populations where the main pollinator in central continuous populations, the pollen beetle Meligethes elongatus, was not present. Our results do not support strong differences in the ecological stress between marginal disjunct and central continuous populations of D. laureola in the south of the Iberian Peninsula but indicate some changes in plant-pollinator interactions that could be relevant for the sexual polymorphism in this gynodioecious species.

Insecticidal and repellent activity of selected essential oils against of the pollen beetle, Meligethes aeneus (Fabricius) adults

The essential oils from 9 aromatic plants were tested on repellency and mortality of Meligethes aeneus adults. All the tested essential oils caused high mortality of M. aeneus adults in the tarsal tests. The lethal doses after 6 h exposure were ranged between 197 and 1508 μg cm −2. Essential oils obtained from Carum carvi and Thymus vulgaris were most efficient where LD 50 was estimated as 197 and 250 μg cm −2, respectively. Repellency declined in all the essential oils as a function of time. The longest persistence time was determined for essences obtained from C. carvi and T. vulgaris where significantly the highest repellent index of 65.6% and 63.8%, respectively, was determined. Repellent index lower than 15% was determined for the remaining essential oils.

Effect on radish pests by application of insecticides in a nearby spring oilseed rape field

Chemical control of insect pests is often necessary to ensure high yields of field crops. The aim of the present study was to study whether field pesticide use influences amount of pest damage in neighbouring garden crops. Spring oilseed rape, OSR (Brassica napus L.), was established in Southern Sweden as an example of an agricultural field crop. One half of the OSR field was treated with insecticides to control flea beetles (Phyllotreta spp., Chrysomelidae) and pollen beetle (Meligethes aeneus Fab., Nitidulidae). Radish (Raphanus sativus L.) was used as an example of a common garden crop and it was sown as four replications at three different distances and on four occasions during the season. Care was taken to protect the radish plots from pesticide due to wind drift during applications. Damage to the radish by flea beetle and cabbage root fly (Delia radicum L., Anthomyiidae) along with unspecified leaf damage was recorded. Significantly lower damage by flea beetles was found on cotyledons of radish adjacent to the insecticide treated side of the OSR field compared to the untreated side in radishes from the first sowing. Unspecified damage to true leaves was also less abundant on radishes at the treated side of the OSR field as compared to the untreated side, in all three of the radish harvests analysed. However, radish plot distance from the OSR field did not influence leaf damage. Root fly damage rates in radish did not differ significantly between those adjacent to the treated and untreated sides of the OSR. Damage rates were, however, higher in the radish plots closest to the OSR field in the first sowing, which coincides with the appearance of the first ovipositing females after overwintering as pupae elsewhere. Generally, insecticide treatment in the agricultural field appeared to influence overall damage in the neighbouring garden crop, despite the fact that the garden crop was protected against wind drift of the insecticides during applications.

Pyrethroid resistance and thiacloprid baseline susceptibility of European populations of Meligethes aeneus (Coleoptera: Nitidulidae) collected in winter oilseed rape

Pollen beetle, Meligethes aeneus F. (Coleoptera: Nitidulidae), is a major pest in European winter oilseed rape. Recently, control failures with pyrethroid insecticides commonly used to control this pest have been reported in many European countries. For resistance management purposes, the neonicotinoid insecticide thiacloprid was widely introduced as a new mode of action for pollen beetle control. A number of pollen beetle populations collected in Germany, France, Austria, Great Britain, Sweden, Denmark, Finland, Poland, Czech Republic and Ukraine were tested for pyrethroid resistance using lambda-cyhalothrin-coated glass vials (adult vial test). Most of the populations tested exhibited substantial levels of resistance to lambda-cyhalothrin, and resistance ratios ranged from < 10 to > 2000. A similar resistance monitoring bioassay for the neonicotinoid insecticide thiacloprid was developed and validated by assessing baseline susceptibility data for 88 European pollen beetle populations. A variation of less than fivefold in response to thiacloprid was detected. The thiacloprid adult vial bioassay is based on glass vials coated with an oil-dispersion-based formulation of thiacloprid, resulting in a much better bioavailability compared with technical material. Analytical measurements revealed a > 56 and 28 day stability of thiacloprid and lambda-cyhalothrin in coated glass vials at room temperature, respectively. No cross-resistance between thiacloprid and lambda-cyhalothrin based on log-dose probit-mortality data was detected. Pyrethroid resistance in many European populations of M. aeneus was confirmed, whereas all populations are susceptible to thiacloprid when tested in a newly designed and validated monitoring bioassay based on glass vials coated with oil-dispersion-formulated thiacloprid. Based on the homogeneous results, it is concluded that thiacloprid could be an important chemical tool for pollen beetle resistance management strategies in European winter oilseed rape.

Organic Control of Oilseed Rape Pests through Natural Pesticides and Mixed Cultivation with Turnip Rape

A mixed cropping system of rapeseed and 10 % turnip rape as trap crop was compared with oilseed rape in pure stand to demonstrate the reduction of infestation by insect pests. Furthermore the application of bio-pesticides like pyrethrum/rape oil (Spruzit® Neu), spinosad (SpinTor), diatomeen earth (SiO~2~) /sunflower-oil and rock powder/water was tested. Oilseed rape showed a higher infestation by stem weevils (Ceutorhynchus spp.) in the mixed cropping system compared to rapeseed in pure stand. The reduction of the pollen beetle (Meligethes aeneus) on the rapeseed buds resulted from higher attractiveness of turnip rape as a consequence of advanced growth. The faster development of turnip rape seems to be the important key of successful pollen beetle regulation. The application of pyrethrum and spinosad against Ceutorhynchus spp. had no effect, spinosad was the only agent that caused a reduction of the pollen beetle.

Organic Control of Oilseed Rape Pests through Natural Pesticides and Mixed Cultivation with Turnip Rape

AbstractA mixed cropping system of rapeseed and 10 % turnip rape as trap crop was compared with oilseed rape in pure stand to demonstrate the reduction of infestation by insect pests. Furthermore the application of bio-pesticides like pyrethrum/rape oil (Spruzit® Neu), spinosad (SpinTor), diatomeen earth (SiO~2~) /sunflower-oil and rock powder/water was tested. Oilseed rape showed a higher infestation by stem weevils (Ceutorhynchus spp.) in the mixed cropping system compared to rapeseed in pure stand. The reduction of the pollen beetle (Meligethes aeneus) on the rapeseed buds resulted from higher attractiveness of turnip rape as a consequence of advanced growth. The faster development of turnip rape seems to be the important key of successful pollen beetle regulation. The application of pyrethrum and spinosad against Ceutorhynchus spp. had no effect, spinosad was the only agent that caused a reduction of the pollen beetle.

Experimental environmental change and mutualistic vs. antagonistic plant flower–visitor interactions

Abstract Habitat modification and human-induced climate change are having a severe impact on ecosystems. Plant–insect interactions in particular might become disrupted due to species-specific responses of plants and insects towards these changes. We investigated how environmental change affects flower visitation and pollination with a field study simulating pollinator habitat loss (distance to semi-natural habitat), phenological shift (anticipated flowering) and environmentally induced growth (enhanced flower height). We established 16 habitat islands of potted plants of Sinapis arvensis L., recorded all flower visitors (mainly bees, flies and pollen beetles) and quantified the seed set. Experimentally elevated flowers were less often visited by flies, while visitation by bees was not affected. Further, plants distant from calcareous grassland were less often visited by bees but visitation by flies did not decrease. Anticipated flowering reduced the number of both pollinators and herbivorous pollen beetles and increased the reproductive success (seeds per plant) of S. arvensis, showing that the loss of mutualists was compensated by an escape from antagonists. During the natural flowering period more seeds were produced close to grasslands, especially by plants of natural height, presumably due to the higher bee visitation rate. However, seed production appeared to be relatively tolerant to multiple environmental changes due to complementary patterns among the different flower visitor guilds. Our results suggest complex interactions of environmental change with responses of mutualists and antagonists, making general predictions difficult.