Colour choice behaviour in the pollen beetle Meligethes aeneus (Coleoptera: Nitidulidae)

The pollen beetle Meligethes aeneus Fabricius (Coleoptera, Nitidulidae), a pest of oilseed rape (Brassica napus), is known to respond to coloured stimuli; however, current understanding of the underlying mechanisms of colour choice in this species is limited. In the present study, physiological and behavioural experiments are conducted to determine the response of the pollen beetle to colours in the field. Spectral sensitivity is measured in 10 animals using the electroretinogram technique. Light flashes (100 ms) at varied wavelengths (340–650 nm, 10‐nm steps) and at different light intensities are applied to the eye after dark adaptation. In behavioural experiments in the field, 100 water traps of varying colours (from yellow to green to blue with varying amounts of white and black added, and with known spectral reflectance) are set out on a bare soil field in May 2008. The mean spectral sensitivity curve of M. aeneus peaks at 520 nm; however, a model template fitted to the long wavelength tail of the observed curve reveals a peak at approximately 540 nm (green). A secondary sensitivity peak is observed in the ultraviolet (UV) range (370 nm). A total of 2482 pollen beetles are captured in the coloured traps. The results show that the pollen beetles' preference for yellow over other colours can be modelled as a colour opponent mechanism (green versus blue); however, further experiments are needed to specify responses to colours with higher UV reflectance. These findings may be used to optimize trap colours for monitoring to help develop integrated pest management strategies for pollen beetle control.     

Distribution of Nosema meligethi (Microsporida) in populations of Meligethes aeneus (Coleoptera: Nitidulidae) in Turkey

This is the first study on Nosema meligethi in populations of Meligethes aeneus in Turkey. In total, four of the 2020 beetles studied were infected with the parasite, giving an infection average of 0.2% in Turkey. Infection was observed in two of the eight localities investigated, and the infection rates in these localities were similar: 2.94 and 2.86%. N. meligethi infection was not observed in 1676 beetles (83% of the total studied) from five localities, including the main Brassica oleracea growing area, where chemical pesticides are commonly used. Three hundred and forty‐four beetles (17% of the total studied) were collected from three localities from uncultivated areas where there is no chemical pesticide application; infection was found in beetles from two of these localities. This study confirms that pesticide usage at sampling sites may play a role in the occurrence of N. meligethi, because the samples from which Nosema was detected originated from areas in which pesticides are not used.     

The pollen beetle, Meligethes aeneus, changes egg production rate to match host quality

Motivation-based models dominate current theory concerning host plant selection for oviposition by herbivorous insects. A female searching for a host plant will be more likely to accept a host which is of inferior quality for her offspring if motivation is high, e.g. a large eggload or long time since last oviposition. This implies that insects will accumulate eggs if exposed to hosts of low acceptability and after a time lay eggs on such hosts. An alternative strategy for insects when exposed to less acceptable hosts is to stop producing, instead of accumulating, eggs. Thus, resources would be saved until a more acceptable host is found. If this hypothesis is true, a herbivorous insect would cease egg production when exposed to hosts of low acceptability and resume egg production when exposed to hosts of high acceptability. Previous exposure should not affect oviposition rate when an insect encounters a new host of a different quality. In an earlier study pollen beetles, Meligethes aeneus (F.) (Coleoptera: Nitidulidae), did not accumulate eggs in the absence of high quality hosts. In this study we monitored the daily oviposition rate of female pollen beetles on hosts plants of low (Sinapis alba L.), intermediate (Brassica nigra Koch) or high (B. napus L.) acceptability over a 5-day period. Individuals were then switched to an oviposition resource of a different acceptability. Beetles moved from high- to low-acceptability plants reduced their oviposition rate considerably. In the opposite case, low to high acceptability, the rate of oviposition increased markedly after the switch. When M. aeneus were moved from the high-acceptability host to that of intermediate acceptability oviposition rate was modified accordingly. However, when moved to the intermediate host from a host of low acceptability oviposition on B. nigra was much less than would normally be expected. A possible mechanism for this finding is discussed. M. aeneus, by adjusting oviposition rate to host acceptability, maximizes the average host quality for offspring, even at the cost of a lower egg-laying rate. Received: 5 October 1998 / Accepted: 20 April 1999     

Low oviposition stimuli reduce egg production in the pollen beetle Meligethes aeneus

Abstract. Gravid female pollen beetles, Meligethes aeneus (F.) (Coleoptera: Nitidulidae), were exposed at different intervals to oviposition sites that varied in acceptability.The egg load of dissected individuals which had been deprived of oviposition sites was not greater than individuals which had been frequently exposed to oviposition sites.However, the egg load of individuals which had been exposed to highly acceptable host plants was greater than those exposed to a host plant of low acceptability.Over the experimental period the total number of eggs which an individual produced was lower for those that were either deprived of an oviposition site or frequently exposed to a low-quality host plant.There was no evidence of either increased oviposition probability or clutch size as the period since the last oviposition increased.It is concluded that low host quality and low host encounter rate reduce the egg production of M.aeneus. It is further concluded that the suppressed egg production reduces the accumulation of eggs, so that physiological motivation for the insect to oviposit is not increased.If low oviposition site quality acts to reduce oogenesis, as found here, then the probability of egg deposition on low-quality species may not increase over time and the effect of antixenotic resistance may be enhanced.     

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.     

Response of the pollen beetle Meligethes aeneus to volatiles emitted by intact plants and conspecifics

The response of the pollen beetle Meligethes aeneus Fab. (Coleoptera, Nitidulidae) to the volatiles of undamaged plants and conspecifics was tested in a Y-tube-olfactometer-bioassay. Beetles that had hibernated preferred significantly the volatiles emitted by their most important host plant, oilseed-rape (Brassica napus L. ‘Lorar’) in the early bud-stage. However, the odour emitted by rye (Secale cereale L.), tomato plants (Solanum lycopersicum L.), and yarrow (Achillea millefolium L.) were also attractive when tested against the corresponding growing-medium. Dock plants (Rumex obtusifolius L.) and touch-me-not (Impatiens parviflora L.) possessed no attractive properties. When tested against each other, oilseed-rape was preferred significantly by M. aeneus above all other plants, with the exception of tomato. The results indicate that M. aeneus is able to locate its host plant by olfactory stimuli in the early bud-stage, i.e. in that stage in which the infestation begins in the field and when the typical yellow colour and floral scent of oilseed-rape are absent. Female pollen beetles avoided significantly the volatiles emitted by female conspecifics and an ether extract of conspecifics of mixed sex, while volatiles from males had no significant effect on females. Furthermore, males showed no preferences when responding to conspecific odour in the olfactometer. These results suggest the existence of an epideictic pheromone for M. aeneus.     

Vitellogenin expression in the oilseed rape pest Meligethes aeneus

When investigating insecticide resistance of pest insects, for example, the pollen beetle Meligethes aeneus, it is relevant to differentiate toxicological and molecular genetic data between male and female specimens. A molecular sex determination method would allow resistance testing to be run without prior sorting of the samples. A one-step quantitative RT-PCR method for quantification of the yolk protein vitellogenin expression in the pollen beetle was established. The expression level of vitellogenin relative to tubulin was determined. Pollen beetles were tested at different time points during their development to determine if vitellogenin is a reliable molecular marker for detection of sexually mature females. The differentiation between females and males by relative expression of vitellogenin to tubulin is conditional regarding the life cycle. Sexually mature females and males could easily be distinguished, whereas immature specimens could not be seperated. Vitellogenin expression is a successful marker for identification of sexually mature pollen beetles. Females from the spring populations showed vitellogenin expression when the temperature was above 10.2°C. Further, detailed observations of vitellogenin throughout the spring indicated a strong relationship between daily temperatures and vitellogenin expression, which is an indicator of oviposition ability.     

Pollen beetle (Meligethes aeneus) oviposition and feeding preference on different host plant species

The oviposition and feeding preferences of the pollen beetle, Meligethes aeneus, were determined in choice and no-choice tests in field, semi-field and greenhouse trials. Plant species used were Brassica napus, B. campestris, B. juncea, B. nigra, B. carinata, Sinapis alba and Crambe abyssinica. With respect to number of eggs laid, S. alba and C. abyssinica were inferior to the other species. Pollen beetles laid fewer eggs on B. nigra than on the other Brassica spp. in no-choice tests, however this difference was partly due to fewer eggs laid per bud rather than fewer buds used for oviposition. Most eggs, for all plant species, were deposited in buds sized 2–3 mm. Feeding damage on all plant species was relatively similar. Pollen beetles seem to have a wider host range for feeding than for oviposition. There was good agreement in plant species ranking as oviposition hosts between the field, semi-field and greenhouse trials.     

Methodology for glutathione S-transferase purification and localization in two-dimensional gel electrophoresis performed on the pollen beetle,Meligethes aeneus (Coleoptera: Nitidulidae)

Glutathione S-transferases (GSTs) are one of the major detoxification enzymes involved in insecticide resistance. In this study, optimized methodology for GSTs purification and localization in two-dimensional gel electrophoresis is shown on the pollen beetle. Specifically, the GST proteins were purified using GSTrap 4B column, and the protein profile of the supernatant before purification was compared with the unbound fraction post-purification via two-dimensional gel electrophoresis (2D-E). The identity of these localized protein spots was confirmed by MS analysis and further analyzed by NanoLC-ESI-QUAD-TOF-MS/MS protein identification. Results indicate that 2 out of 5 protein spots were GSTs with region for class Delta and Epsilon subfamilies similar to other insects; however, the remaining 3 spots did not show any match in the current NCBInr. Both Delta and Epsilon class GSTs are specifically involved in insecticide resistance and their relatively high abundance in the 2D-E map suggests that these enzymes could play a role in the resistance of Meligethes aeneus to the most commonly used pyrethroids. The approach applied in this study for the specific localization of GSTs in 2D-E can be used for similar analyses in other organisms.     

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.     

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.     

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.     

Structure and evolution of the mitochondrial control region of the pollen beetle Meligethes thalassophilus (Coleoptera: Nitidulidae).

The organization of the mitochondrial DNA (mtDNA) control region (CR) of the pollen beetle Meligethes thalassophilus is described. This mtDNA CR represents the longest sequenced for beetles so far, since the entire nucleotide sequence ranges from approximately 5000 to approximately 5500 bp. The CR of M. thalassophilus is organized in three distinct domains: a conserved domain near the tRNAIle gene, a variable domain flanking the 12S rRNA gene, and a relatively large central tandem array made up of a variable number of approximately 170 bp repeats that is responsible for the intraspecific length variation observed. Like other CRs found in insects, the M. thalassophilus CR contains two long homopolymeric runs that may be involved in mtDNA replication. Furthermore, conserved stem-and-loop structures in the repetitive domain were identified and their possible role in generating length variation is examined. Intraspecific comparison of the tandem repeat elements of M. thalassophilus suggests mechanisms of concerted evolution leading to homogenization of the repetitive region. The utility of such an array of tandem repeats as a genetic marker for assessing population-level variability and evolutionary relationships among populations is discussed. Finally, the technical difficulties found in isolating the mtDNA CR in beetles are remarked upon.     

Enhancing rape pollen beetle parasitism within sown flower fields along a landscape complexity gradient

• 1 Sown flower habitats not only are employed in agri‐environment schemes in the European Union to enhance pollinators and birds, such as partridges, but also are hypothesized to contribute to the biological control of pests such as the rape pollen beetle Meligethes aeneus Fabr. by improving habitat and resource availability for its specialized parasitoids.
• 2 In the present study, we selected 20 sown flower fields that included one of the pollen beetles' host plants Sinapis alba L., each centred in a landscape of varying complexity, to test the influence of the surrounding landscape structure on parasitism rate and herbivory by M. aeneus. Additionally, plant cover of S. alba plants within the sown flower fields and numbers of S. alba flowers were also included in the analyses.
• 3 Landscapes with high proportions of semi‐natural habitats supported higher parasitism rates, and sown flower fields with dense S. alba plant cover hosted more parasitoids and suffered from less herbivory.
• 4 We conclude that sown flower fields are not only important for pollinators and birds, but also are long‐term undisturbed, unploughed, insecticide‐free habitats with rich food (nectar/pollen) and host resources for parasitoids, contributing to the build‐up and maintenance of large parasitoid populations, which are important biocontrol agents of rape pollen beetles.

     

Fatal attraction: search for a dead-end trap crop for the pollen beetle (Meligethes aeneus)

In sustainable pest management, orientation of insect pests can be manipulated by utilizing the relative attractiveness of different host plants. Plants attractive for oviposition but not offering a suitable resource for the development of larvae are called dead-end trap crops. In this study, the number of eggs and larvae and larval survival of Meligethes aeneus (Fab.) in the buds of Brassica napus L., B. rapa L., B. nigra L., B. juncea L., Eruca sativa Mill., Raphanus sativus Pers. and Sinapis alba L. were compared in 2011 and 2012. Overall infestation rate of buds varied from 0 to 71 %; the least attractive plants were S. alba and E. sativa. Egg clutch size per bud was greater on B. nigra and lower on S. alba and E. sativa than on B. napus. Dead larvae were found only in E. sativa and R. sativus buds. Over the two study years, 19 % of larvae on E. sativa and 35 % on R. sativus were dead. In conclusion, M. aeneus preferred to oviposit on Brassica species rather than on cruciferous plants from the other genera. In addition, R. sativus has the features of dead-end trap crop because 35 % of the larvae failed to survive.     

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.     

Development of primers to characterize the mitochondrial control region of the snow leopard (Uncia uncia)

The snow leopard (Uncia uncia) is a rare carnivore living above the snow line in central Asia. Using universal primers for the mitochondrial genome control region hypervariable region 1 (HVR1), we isolated a 411‐bp fragment of HVR1 and then designed specific primers near each end of this sequence in the conserved regions. These primers were shown to yield good polymerase chain reaction products and to be species specific. Of the 12 snow leopards studied, there were 11 segregating sites and six haplotypes. An identification case of snow leopard carcass (confiscated by the police) proved the primers to be a useful tool for forensic diagnosis in field and population genetics studies.     

Field oviposition rates and egg load dynamics of pollen beetles (Meligethes aeneus Fab.) (Colepotera: Nitidulidae)

Abstract 1 Egg loads from field collected pollen beetles (Meligethes aeneus Fab., Coleoptera: Nitidulidae) were determined by dissecting beetles caught at the beginning and end of the putative daily oviposition period. Field collected beetles were offered Brassica napus (L.) plants in cages for 8 (morning and early afternoon), 16 (overnight), and 24 h to ascertain the number of eggs laid during these time periods. 2 Most eggs were laid in the morning and early afternoon. The proportion of gravid females was higher at the beginning of the oviposition period than at the end. Most females in the morning carried two eggs, whereas one egg was more common in the afternoon. 3 We hypothesized that the number of eggs laid during the oviposition period would be equivalent to the difference between egg loads at the beginning and end of oviposition. This was not the case; differences in egg loads were significantly lower than number of eggs laid. However, the number of eggs laid was equivalent to the egg load at the beginning of the oviposition period, suggesting that eggs available in the morning are laid during the following day. 4 Population estimates of daily oviposition rates, approximately 0.7 eggs per beetle and day, were close to estimates from laboratory studies when the proportion of gravid females was taken into consideration.     

褐飞虱特异引物的设计和评估

研究稻田生态系统中天敌对褐飞虱Nilaparvata lugens( St(a)l)的捕食非常重要,但很困难.本研究设计褐飞虱的PCR特异引物,并对利用从稻田66种稻田常见节肢动物中提取的DNA进行了特异性验证,得到褐飞虱的特异引物( Lug-F1a/Lug-R1),在实验室以拟环纹豹蛛Pardosa pseudoan...     

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.