Genes, gene flow and adaptation of Diabrotica virgifera virgifera

1  Diabrotica virgifera virgifera has emerged as a major pest of cultivated maize, due to a combination of its high capacity to inflict economic damage, adaptability to pest management techniques and invasiveness.
2 This review presents a survey of the current state of knowledge about the genetics of D.   v.   virgifera . In addition, the tools and resources currently available to Diabrotica geneticists are identified, as are areas where knowledge is lacking and research should be prioritized.
3 A substantial amount of information has been published concerning the molecular phylogenetic relationships of D.   v.   virgifera to other chrysomelids.
4 There is a growing literature focused on the population genetics and evolution of the species. Several adaptations to anthropogenic selection pressure have been studied, with resistance to synthetic insecticides providing some particularly well-characterized examples.
5 A notable deficiency is a lack of studies directed toward the formal genetics of D.   v.   virgifera .     

Comparative flight behavior of Diabrotica virgifera virgifera and Diabrotica barberi in the laboratory

A tethered flight system was used to characterize and compare the flight behavior of western, Diabrotica virgifera virgifera LeConte (WCR), and northern, Diabrotica barberi (Smith and Lawrence) (NCR), corn rootworms in the laboratory. Distributions of flight durations were skewed towards short flights for both species regardless of sex or age and there was high variability in flight durations and frequency in individual beetles. Flight distributions for WCR were distinctly bimodal, reflecting a dichotomy between short trivial flights and much longer sustained flights. Trivial flight performance did not vary with age but did differ between species. In comparison to WCR, NCR took shorter flights but had a higher frequency of flights over a 23-h period. Overall, WCR beetles logged substantially more flight time in the same period of time. The proportion of individual WCR undertaking sustained flight was relatively low (<24%) and, for females, declined along with sustained flight durations as a function of age. Periodicity of trivial flight did not differ betweer the species. In general, flight activity was greatest during early morning and early evening hours. No correlations were found between any feature of flight performance and body size or wing loading ratios.

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Résumé Un système de vol captif a été utilisé pour caractériser et comparer au laboratoire les comportements de vol de D. virgifera virgifera et D. barberi. La distribution des durées de vol est nettement biaisée avec la grande majorité des vols durant moins d'une minute quels que soient le sexe et l'âge. Il y a une grande variabilité interindividuelle tant en durée qu'en fréquence de vol. Les distributions des durées de vol en fonction du sexe sont bimodales chez D. virgifera virgifera, mais pas chez D. barberi, ce qui reflète la séparation entre vols brefs ordinaires et long vols prolongés. Les vols brefs ordinaires ne dépendent pas beaucoup de l'âge ou du sexe mais diffèrent suivant l'espèce. D. barberi a eu des vols plus brefs, mais en a effectué plus pendant une période de 23 heures. Au total, D. virgifera virgifera a consacré nettement plus de temps au vol pendant la même période; mais, chez cette espèce la proportion d'individus effectuant des vols soutenus était relativement faible (<24%), avec une diminution de leur nombre avec l'âge chez les femelles; le nombre le plus élevé étant chez les jeunes femelles. La périodicité des vols ordinaires n'a dépendu ni du sexe, ni de l'espèce; l'activité de vol a été en général plus importante tôt le matin et en début de soirée. Aucune corrélation n'a été trouvée entre une quelconque performance de vol et la taille du corps ou la charge alaire.

     

Constructing life-tables for the invasive maize pest Diabrotica virgifera virgifera (Col.; Chrysomelidae) in Europe

Abstract: The western corn rootworm (Diabrotica virgifera virgifera LeConte, Col.; Chrysomelidae) is an alien invasive species in Europe. It is a univoltine species with eggs that overwinter in the soil and larvae that hatch in spring. Three larval instars feed on maize roots, which can cause plant lodging and yield loss of economic importance. Adults emerge between mid‐June and early August and can reduce yields through intensive silk feeding. In order to provide a thorough understanding of the population dynamics of this invasive pest species in the invaded European region, complete age specific life‐tables were constructed in two maize fields in southern Hungary assessing the significance of natural mortality factors acting on D. v. virgifera populations. This information provides a rational basis for devising sustainable integrated pest management programmes, in particular, by enabling the identification of vulnerable pest age intervals for the timely application of various management tools. The life‐table for D. v. virgifera in Europe resulted in a total mortality of about 99% from the egg stage in the autumn to the emergence of adult females in the following year (K_Total = 2.48), which is comparable with North America. The highest reduction of D. v. virgifera numbers resulted from the mortality in first instar larvae (94% marginal death rate) and from the unrealized fecundity (80%). However, only the variation in mortality between years can change the generational mortality and thus influence population growth. High variation in the marginal death rate between fields and years was found in the second and third instar larval stages, and in the overwintering egg stage. These mortality factors therefore have the potential to cause changes in the total generational mortality. Furthermore, the life‐table suggested that a high fecundity could compensate for a high generational mortality and would lead to population increase.     

Evolutionary directional asymmetry and shape variation in Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae): an example using hind wings

The western corn rootworm Diabrotica virgifera virgifera LeConte is a pest of maize in the USA and Europe and especially a problem in particular regions of Croatia. In the present study, patterns of variation in hind wing shape were examined. The first objective was to examine the influence of soil type on 10 populations of D. v. virgifera sampled from three regions in Croatia that differed according to edaphic factors and climate. The second objective was to investigate the potential evolutionary presence of directional asymmetry on hind wings. Geometric morphometrics was used to examine these objectives by quantifying the morphological variation within and among individuals and populations. Overall, D. v. virgifera hind wing shape changed according to major soil type classifications in Croatia. The three hind wing morphotypes found varied because of basal radial vein differences, related to landmarks 1, 3, 7, and 14. The findings of the present study show that hind wing shape in D. v. virgifera can be used to differentiate populations based on edaphic factors and may have application as a monitoring tool in the integrated management of D. v. virgifera. In an evolutionary context, the presence of directional asymmetry in the hind wings of D. v. virgifera adds to the ever growing data on the evolution of insect wings. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 110–118.     

Purification and kinetic analysis of acetylcholinesterase from western corn rootworm,Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

Acetylcholinesterase (AchE, EC 3.1.1.7) was purified from western corn rootworm (WCR, Diabrotica virgifera virgifera) beetles by affinity chromatography. The purification factor reached over 20,000-fold with a specific activity of 169.5 μmol/min/mg and a yield of 23%. The V_max values for hydrolyzing acetylthiocholine (ATC), acetyl-(β-methyl)thiocholine (AβMTC), propionylthiocholine (PTC), and S-butyrylthiocholine (BTC) were 184.8, 140.5, 150.2, and 18.8 μmol/min/mg, respectively, and K_m values were 19.7, 18.5, 14.1, and 11.0 μM, respectively. The first three substrates showed significant inhibition to the AchE at higher concentrations, whereas BTC showed inhibition at the concentrations of 0.25–2 mM but activation at >4 mM. AchE activity was almost completely inhibited by 1 μM eserine and BW284C15, respectively, but only 12% of AchE activity were inhibited by ethopropazine at the same concentration. These results suggested that the purified AchE from WCR was a typical insect AchE. Insecticides or their oxidative metabolites, chlorpyrifos-methyl oxon, carbofuran, carbaryl, malaoxon, and paraoxon, used in in vitro kinetic study exhibited high inhibition to AchE purified from WCR. However, chlorpyrifos-methyl oxon and carbofuran showed at least 36- and 4-fold, respectively, higher inhibitory potency than the remaining insecticides examined. Results from our in vitro inhibition of AchE agreed quite well with the previously published in vivo bioassay data. Arch. Insect Biochem. Physiol. 39:118–125, 1998. © 1998 Wiley-Liss, Inc.     

Spatial clustering of Diabrotica virgifera virgifera and Agriotes ustulatus in small-scale maize fields without topographic relief drift

The soil‐living larvae of Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) and Agriotes ustulatus Schaller (Coleoptera: Elateridae) can cause economic damage to maize roots, Zea mays L. (Poaceae). This study investigated the spatial clustering of both pests in four small‐scale maize fields in southern Hungary, where clustering had been observed but not expected due to the lack of topographic relief drifts and soil structuring. Between 2000 and 2002, numbers of D. v. virgifera larvae and adults and of A. ustulatus larvae were determined at four randomly chosen georeferenced maize plants in each of 24 plots per field. Soil moisture, soil bulk density, and vegetational characteristics were assessed. Moran's I test for spatial autocorrelations, semivariogram analyses, and interpolated mapping revealed that D. v. virgifera larvae and adults were spatially clustered in 67 and 50% of cases, respectively. Larvae of A. ustulatus were clustered in 75% of cases. Diabrotica virgifera virgifera larval distributions were mainly determined by increasing weed density (negative correlation), in particular with high densities of Cirsium arvense (L.) (Asteraceae), as well as by increasing soil moisture (negative correlation). Adult distributions of D. v. virgifera were mainly determined by the density distribution of flowering maize. They were moreover correlated with larval distribution and with the adult distribution of the previous year. The density distributions of male adults differed from those of females. Female density was additionally correlated with higher soil moisture and Poaceae density, e.g., with Sorghum halepense (L.) Pers. No relation was found between the larvae of A. ustulatus and D. v. virgifera. Agriotes ustulatus larval distributions were mainly determined by vegetational cover (correlation with less cover). Conclusively, male and female D. v. virgifera adults, larvae of D. v. virgifera, and larvae of A. ustulatus will display different spatial clustering even within ostensibly homogeneous habitats of flat small‐scale maize fields.     

Relationship between phenotypic traits and selected fitness components of Diabrotica virgifera virgifera

Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) is one of the most important and best-studied maize pests, yet little information is available regarding the basic relationships among its phenotypic traits, particularly those that reflect the overall fitness of this successful invader in Europe and North America. Such information is critical for studies on the invasiveness, behavioural ecology, and management of this pest. Phenotypic traits that change over the lifetime of the beetle were investigated (e.g., fresh body weight) as they can indicate changes in adult physiology or fitness of D. v. virgifera . Phenotypic traits that remain stable over the beetle's lifetime were also investigated (e.g., pronotum width, head capsule width, hind tibia length), as they most likely allow detection of genetic differences between populations. Furthermore, phenotypic traits were investigated that may best predict fecundity (e.g., fresh body weight, elytra width) and life span (e.g., elytra length), as these two factors influence the population growth of this highly invasive species. Finally, regression equations are provided for the age-specific oviposition and survival of the long-living D. v. virgifera adults, which may allow researchers to reduce the duration of their bioassays without losing information.     

European populations of Diabrotica virgifera virgifera are resistant to aldrin,but not to methyl‐parathion

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a major pest of cultivated corn in North America and has recently begun to invade Europe. In addition to crop rotation, chemical control is an important option for D. v. virgifera management. However, resistance to chemical insecticides has evolved repeatedly in the USA. In Europe, chemical control strategies have yet to be harmonized and no surveys of insecticide resistance have been carried out. We investigated the resistance to methyl‐parathion and aldrin of samples from nine D. v. virgifera field populations originating from two European outbreaks thought to have originated from two independent introductions from North America. Diagnostic concentration bioassays revealed that all nine D. v. virgifera field populations were resistant to aldrin but susceptible to methyl‐parathion. Aldrin resistance was probably introduced independently, at least twice, from North America into Europe, as there is no evident selection pressure to account for an increase of frequency of aldrin resistance in each of the invasive outbreaks in Europe. Our results suggest that organophosphates, such as methyl‐parathion, may still provide effective control of both larval and adult D. v. virgifera in the European invasive outbreaks studied.     

Western corn rootworm (Diabrotica virgifera virgifera LeConte) population dynamics

1 The western corn rootworm Diabrotica virgifera virgifera LeConte is a major insect pest of field maize, Zea mays L. Larvae can cause substantial injury by feeding on maize roots. Larval feeding may destroy individual roots or root nodes, and reduce plant growth, stability, and yield. Costs associated with managing corn rootworms in continuous maize are annually one of the largest expenditures for insect management in the United States Corn Belt.
2 Even though D. virgifera virgifera has been studied intensively for over 50 years, there is renewed interest in the biology, ecology, and genetics of this species because of its ability to rapidly adapt to management tactics, and its aggressive invasive nature.
3 This article provides a comprehensive review of D. virgifera virgifera population dynamics, specifically: diapause, larval and adult development, seasonality, spatial and temporal dynamics at local and landscape scales, invasiveness in North America and Europe, and non-trophic interactions with other arthropods.
4 Gaps in current knowledge are identified and discussed especially within the context of challenges that scientists in North America and Europe are currently facing regarding pest dynamics and the need to develop appropriate management strategies for each geographic area.     

Flight activity of Diabrotica spp. at the borders of cornfields and its relation to ovarian stage in D. barberi

Flight activity of corn rootworm beetles, the northern (NCR), Diabrotica barberi (Coleoptera: Chrysomelidae), and western (WCR), D. virgifera virgifera, was monitored using malaise traps placed at the edges of two small cornfields. Populations of beetles in the fields peaked while corn was flowering, but capture in malaise traps remained low until silks had dried. Capture of NCR and (to a lesser extent) WCR then increased and remained high through the season. Malaise traps were constructed to permit separate collections of beetles that entered on each of two opposite sides. Female NCR that were captured in sides that faced toward corn tended to contain fewer mature eggs than those in sides facing away from corn. These findings support the hypothesis that female NCR emigrate from cornfields to feed when fresh silk and corn pollen (favored foods) become unavailable, but that egg-laden NCR actively seek corn when searching for oviposition sites.

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Résumé Les activités de vol de D. barberi (NCR) et D. virgifera virgifera (WCR) ont été contrôlées par l'utilisation de pièges malais placés en lisière de deux petits champs de maïs. Les populations de ces coléoptères sont maximales quand le maïs fleurit, mais leurs captures sont restées faibles jusqu'à ce que les barbes du maïs aient été sèches. Les captures de NCR et, dans une plus faible mesure, celles de WCR ont alors augmenté et sont restées importantes pendant toute la saison. Les pièges malais ont été conçus pour que les adultes pénétrant par les côtés opposés soient récoltés séparément. Les femelles de NCR capturées face au champ de maïs avaient tendance à contenir moins d'ovocytes mûrs que celles capturées du côté opposé. Ces observations appuient l'hypothèse que les femelles NCR émigrent des champs de maïs pour s'alimenter, quand les barbes et le pollen de maïs, aliments préférés, deviennent indisponibles, mais que les femelles NCR pleines d'ovocytes mûrs recherchent le maïs quand elles sont en quête de lieux de ponte.

     

Seasonal and diel activity patterns of generalist predators associated with Diabrotica virgifera immatures (Coleoptera: Chrysomelidae)

The diel and seasonal activity of epigeal predators associated with pre-imaginal Diabrotica virgifera was described. Due to its duration, the egg stage was exposed to more predators than the larval stage. Most predators were easily categorized into day- and night-active guilds. Seasonal and diel niche partitioning may contribute to the maintenance of this diverse and abundant predator community.     

How to measure the food utilization of subterranean insects: a case study with the western corn rootworm (Diabrotica virgifera virgifera)

To date, nutritional studies on subterranean insects have focused on qualitative aspects due to experimental limitations. We have developed a method of studying insect–plant interactions quantitatively in subterranean environments. The initial and final weights of larvae of Diabrotica virgifera virgifera LeConte (Chrysomelidae, Galeruncinae) and those of maize roots, which served as food items were determined. The difference between initial and final weight of larvae and roots allowed for the calculation of the food conversion efficiency. This can be used to portray differences in food quality and its impact on larval performance and development.     

Development and economic evaluation of spatial sampling plans for corn rootworm Diabrotica spp. (Col., Chrysomelidae) adults

Abstract  To develop spatial sampling plans for corn rootworm ( Diabrotica spp.) adults, their spatial distributions were characterized and economics of sampling plans were evaluated by comparing sampling costs between spatial and conventional (non-spatial) sampling plans. Semivariogram modelling and spatial by with distance indices showed that corn rootworm adults were significantly (P < 0.05) aggregated at peak population densities and any two samples were spatially correlated within approximately 45 m, with 39–90% of the variability explained by spatial dependence. Sampling costs for spatial sampling plans linearly increased as the sampling distance decreased and exponentially increased as the field size increased. Although sampling costs for non-spatial sampling plans were generally lower, spatial sampling plans could be more economical when the mean insect density became lower and the field size became smaller. This study demonstrated that spatial sampling plans could be optimized to minimize the sampling costs and maximize the spatial resolution.     

Spatio-temporal dynamics of corn rootworm, Diabrotica spp., adults and their spatial association with environment

Multiyear and multilocation studies were conducted to investigate the within‐ and the between‐year spatial dynamics of corn rootworms Diabrotica spp. (Coleoptera: Chrysomelidae), adults and their spatial associations with environmental factors in cornfields. Grid‐based spatial sampling was conducted by trapping adults emerging from the soil (i.e., ‘emergence‐trap counts’) and by counting the number of adults in the ear zone of corn plant (i.e., ‘ear‐zone count’). Spatial analysis with distance indices (SADIE) was used to determine spatial distribution patterns and to investigate spatial associations. Ear‐zone counts and emergence‐trap counts were spatially dynamic within a year and more frequently aggregated in the middle of growing seasons and random early and late in the season. However, during the peak population periods, spatial distribution of ear‐zone counts and emergence‐trap counts were significantly consistent between years, indicating predictability of future spatial distributions. Spatial distribution of emergence‐trap counts and ear‐zone counts were positively associated with soil moisture and presence of corn plants with silks, respectively. This study demonstrated that within‐year spatial distribution patterns were dynamic and that there was between‐year spatial consistency of corn rootworm adult distributions. Such information can be used to improve preventative management of corn rootworms.     

Polymorphic microsatellite loci from the western corn rootworm (Insecta: Coleoptera: Chrysomelidae) and cross‐amplification with other Diabrotica spp

Corn rootworms (Diabrotica spp.) make up the major insect pest complex of corn in the US and Europe, and there is a need for molecular markers for genetics studies. We used an enrichment strategy to develop microsatellite markers from the western corn rootworm (Diabrotica virgifera virgifera). Of 54 loci isolated, 25 were polymorphic, and of these, 17 were surveyed for variability in 59 wild individuals. In addition, the potential for cross‐amplification of these microsatellites was surveyed for Mexican, northern, and southern corn rootworms. Nine microsatellite loci showed Mendelian inheritance and are likely to be useful in population genetics studies.     

Performance of a model for egg hatching of the western corn rootworm,Diabrotica virgifera virgifera LeConte,using measured and modelled soil temperatures as input

A model for egg hatching of the western corn rootworm,Diabrotica virgifera virgifera LeConte, was tested at several locations in Ontario, Canada, during the 1989 and 1990 seasons. The model required soil temperatures as input and was tested using measured and modelled data. Modelled soil temperatures at 5 and 10 cm depths were obtained from empirically and physically based models. The physically based model provided better estimates of soil temperatues, but both models slightly underestimated the temperatures. Predicted egg hatching, using measured and modelled soil temperature at 5 and 10 cm depths for all locations, compared reasonably well with the observations of egg hatching. When using modelled soil temperatures, the egg developmental model performed better using soil temperatures from the physically based model. However, both soil temperature models provided sufficiently accurate temperature values for use in the egg developmental model. Unlike the empirically based model, the physically based model was not site-specific and its application to larger areas appeared feasible.     

Estimation of efficacy functions for products used to manage corn rootworm larval injury

Maize, Zea mays L., is an economically important crop grown throughout the world. Corn rootworm, Diabrotica spp. (Coleoptera: Chrysomelidae), larvae constitute a significant economic threat to maize production in the United States, where yield losses and management costs associated with corn rootworm species exceed $1 billion annually. Furthermore, the introduction of the western corn rootworm, D. virgifera virgifera LeConte, into maize‐producing regions of Europe has made managing corn rootworm larval injury an international concern. Larvae injure maize plants by feeding on root tissue and are the primary target of management activities. Products commonly used to protect root systems from injury include chemical insecticides (seed or soil applied) and genetically modified maize hybrids expressing toxins derived from Bacillus thuringiensis Berliner (Bt). The confirmation of field‐evolved resistance to various Bt toxins in populations of the western corn rootworm presents a significant management challenge. We performed a meta‐analysis to provide a broad understanding of the relative efficacy of the primary products currently being used to manage corn rootworm larval injury, including insecticidal seed treatments, soil insecticides and Bt hybrids (with and without the addition of soil insecticide). Our analysis is unique in the breadth of locations and years included – we analysed 135 individual trials conducted from 2003 through 2014 at multiple sites in both Illinois and Nebraska. Panel data were produced by pairing the mean node‐injury rating for each treatment of a given trial with the mean node‐injury rating for untreated maize. Linear regression models were developed to estimate the relationship between the potential for corn rootworm larval injury and product performance. For a given level of injury potential, the parameters estimated reveal differences in the degree of root protection offered by the various product categories analysed. Implications for developing long‐term, integrated, and sustainable practices for managing this important pest of maize are discussed.