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.

     

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 .     

Genome scan of Diabrotica virgifera virgifera for genetic variation associated with crop rotation tolerance

Abstract:  Crop rotation has been a valuable technique for control of Diabrotica virgifera virgifera for almost a century. However, during the last two decades, crop rotation has ceased to be effective in an expanding area of the US corn belt. This failure appears to be due to a change in the insect's oviposition behaviour, which, in all probability, has an underlying genetic basis. A preliminary genome scan using 253 amplified fragment-length polymorphism (AFLP) markers sought to identify genetic variation associated with the circumvention of crop rotation. Samples of D. v. virgifera from east-central Illinois, where crop rotation is ineffective, were compared with samples from Iowa at locations that the behavioural variant has yet to reach. A single AFLP marker showed signs of having been influenced by selection for the circumvention of crop rotation. However, this marker was not diagnostic. The lack of markers strongly associated with the trait may be due to an insufficient density of marker coverage throughout the genome. A weak but significant general heterogeneity was observed between the Illinois and Iowa samples at microsatellite loci and AFLP markers. This has not been detected in previous population genetic studies of D. v. virgifera and may indicate a reduction in gene flow between variant and wild-type beetles.     

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.     

Systemic RNAi in western corn rootworm,Diabrotica virgifera virgifera,does not involve transitive pathways

Western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte) is highly sensitive to orally delivered double‐stranded RNA (dsRNA). RNAi in WCR is systemic and spreads throughout the insect body. This raises the question whether transitive RNAi is a mechanism that functions in WCR to amplify the RNAi response via production of secondary siRNA. Secondary siRNA production is achieved through RNA‐dependent RNA polymerase (RdRP) activity in other eukaryotic organisms, but RdRP has not been identified in WCR and any other insects. This study visualized the spread of the RNAi‐mediated knockdown of Dv v‐ATPase C mRNA throughout the WCR gut and other tissues using high‐sensitivity branched DNA in situ hybridization. Furthermore, we did not detect either secondary siRNA production or transitive RNAi in WCR through siRNA sequence profile analysis. Nucleotide mismatched sequences introduced into either the sense or antisense strand of v‐ATPase C dsRNAs were maintained in siRNAs derived from WCR fed with the mismatched dsRNAs in a strand specific manner. The distribution of all siRNAs was restricted to within the original target sequence regions, which may indicate the lack of new dsRNA synthesis leading to production of secondary siRNA. Thus, the systemic spread of RNAi in WCR may be derived from the original dsRNA molecules taken up from the gut lumen. These results indicate that the initial dsRNA dose is important for a lethal systemic RNAi response in WCR and have implications in developing effective dsRNA traits to control WCR and in resistance management to prolong the durability of RNAi trait technology.     

Suitability of different fluorescent powders for mass-marking the Chrysomelid, Diabrotica virgifera virgifera LeConte

Abstract:  The Western Corn Rootworm, Diabrotica virgifera virgifera LeConte (Col., Chrysomelidae), is an invasive alien pest of maize, Zea mays , in Europe. The suitability of 14 fluorescent powders for mass-marking the adults was studied in laboratory and in field cages. The visual discrimination between remaining spots of each colour on the beetles was investigated under ultraviolet (UV) light, as well as their retention time and the influences of those colours on the beetle survival and flight take-off response. The two best recognizable orange colours (i.e. of Radiant Colour and of Fiesta Colours Swada) were proposed for field experiments in first priority, followed by an orange and a yellow (both Magruder Colour), another yellow (Fiesta) and a pink (Radiant), as all did not affect beetle survival and flight take-off response and were recognizable under UV light for at least 10 days in the field. In contrast, the colours yellow and green (Radiant), red and blue (Magruder), yellow (Ciba Geigy) and pink (Fiesta) were unsuitable, because they either quickly disappeared from the beetles or adversely affected beetle survival or flight take-off response. For mass releases with differently marked beetles, only the use of a single orange colour together with a single yellow colour or the use of a pink colour together with a yellow colour can be used since few spots can clearly be discriminated from each other under UV light.     

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.     

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.     

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.     

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.     

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.     

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.     

Field studies of the temporal response patterns of male Diabrotica virgifera virgifera LeConte and D. barberi Smith and Lawrence to 8R-methyl-2R-decyl propanoate

ABSTRACT. Variations in the diel response of male northern and western corn rootworms attracted to a synthetic pheromone source were examined in southwestern Ontario. Activity was measured by the number of males caught at hourly intervals in sticky traps baited with 8 R -methyl-2 R -decyl propanoate. Northern corn rootworm males were attracted to the pheromone between 22.30 and 0330 hours and were unresponsive at all other times at temperatures above 15°C. Western corn rootworm males had a bimodal response with peaks in attraction from 08.30 to 12.30 hours and again from 15.30 to 18.30 hours. While the period of peak attraction for northern corn rootworm males was well defined, the pattern for western corn rootworm males was erratic and many beetles were caught throughout the day. Evening temperatures below 15°C suppressed the activity of both northern and western corn rootworms. While the nightly period of activity for the northern corn rootworms was shifted by low temperatures to the following morning, that of the western corn rootworm was not altered substantially. As a result, peaks in the response of northern and western corn rootworm males occurred simultaneously under these conditions, suggesting strongly that temporal separation of activity periods was not an important factor in maintaining sexual isolation for these species in Ontario.     

Nutritional resources used by the invasive maize pest Diabrotica virgifera virgifera in its new South-east-European distribution range

Food utilization by adults of the invasive maize (Zea mays L.) (Poaceae) pest western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte) (Coleoptera: Chrysomelidae) was investigated in the south‐eastern part of its new European distribution range. At weekly intervals over a 10‐week period, 10 beetles per field were collected from six fields that had a high abundance of flowering weeds and six fields with a low abundance of flowering weeds, with the aim of understanding adult feeding behaviour in Europe and comparing this behaviour with North American WCR. Gut content analysis was performed to determine the use of maize tissue and weed pollen with regard to maize phenology. Furthermore, all pollen found within the gut was quantified and identified to plant species level. The use of maize tissue by adult WCR changed over time according to maize phenology. Pollen originating from plants other than maize was used more frequently as the maize matured. Adults fed on pollen from 19 of 25 different plant species found in maize fields and showed a preference for the pollen of specific weeds. Pollen from weed species was found more often in beetles from fields with a high abundance of weeds compared to beetles from fields with a low abundance of weeds. Females consumed greater amounts of pollen than males, the latter feeding on a wider diversity of host plants. The pollen resources used by adult WCR in Hungary were more diverse compared to WCR in the USA, which may contribute to the invasion success of WCR in Europe.     

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.     

The contribution of prehatch and posthatch development to protandry in the chrysomelid Diabrotica virgifera virgifera

Laboratory tests with eggs of Diabrotica virgifera virgifera LeConte showed that during a 10-day hatching period, hatch of male eggs predominated on the first and second days, eggs of mixed sex, with ca. 1:1 ratio, hatched on the third and fourth days, and eggs hatching from the fifth to the tenth days were nearly all female. Overall, female eggs hatched a mean of 2.9 days later than male eggs. Not only did female eggs hatch later, but the time for posthatch development to the adult stage was 1.8 days longer for females. The later egg hatch and longer posthatch development for females resulted in female adults emerging a mean of 4.7 days later than male adults. Total adult emergence lasted 14 days; of this, males predominated during the first 5 days, and females predominated during the last 9 days. Males of D. v. virgifera appear to have evolved protandry (the tendency for males to emerge before females) by developing both a postdiapause embryonic stage and a combined larval and pupal stage of shorter duration.

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Résumé L'observation, au laboratoire, pendant une période d'éclosion de dix jours, des oeufs de D. v. virgifera LeConte, a montré que les oeufs mâles prédominent les deux premiers jours d'éclosion, que les oeufs des deux sexes, avec des fréquences 0,5/0,5, ont éclos les troisième et quatrième jours, et que les oeufs éclos du cinquième au dixième jour étaient presque tous femelles. Globalement, les oeufs femelles ont éclos en moyenne 2,9 jours plus tard que les oeufs mâles. De plus, la durée du développement post-embryonnaire des femelles a demandé 1,8 jour en plus. Une éclosion plus tardive et un développement post-embryonnaire plus long ont entrainé une émergence des femelles en moyenne 4,7 jours après les mâles. La période d'émergence des adultes s'est étalée sur 14 jours; les mâles ayant dominé pendant les 5 premiers jours et les femelles pendant les 9 derniers. Les mâles de D. v. virgifera semblent avoir évolué vers la protandrie en acquerant, tant une diapause post-embryonnaire que des stades de développements larvaire et nymphal plus brefs.

     

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.     

Influence of corn planting date on the life stage development and phenology of Diabrotica virgifera virgifera

Under field conditions in eastern South Dakota, USA three different planting dates of corn and three times of egg infestation were used to imposed synchronous and asynchronous timing of corn growth and Diabrotica virgifera virgifera LeConte egg hatch and subsequent development. Median occurrence of each of the three larval stages and of the adult stage for each of the infestation-planting treatments was determined by relating occurrence to thermal units and to days after infestation. No significant differences were found among the treatments for median occurrence of each life stage when the thermal unit approach was used. However, significant differences were found among treatments for median occurrence when the day after infestation approach was used. Consistent parameters are needed for prediction of the occurrence of life stages of this insect. Despite the various imposed conditions, this study indicates that the least variable method of predicting life stage occurrence and adult emergence of D. v. virgifera was the use of thermal unit accumulations (base 11°C).

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Résumé Dans les conditions de l'est du Sud Dakota (USA), 3 dates de semailles de maïs et 3 dates de contamination avec des ufs de D. virgifera virgifera LeConte ont servi à imposer ou à empêcher la synchronisation des éclosions des ufs et par conséquent des développements ultérieurs. Les dates médianes d'apparition de chacun des 3 stades larvaires et des imagos ont été déterminées en relation avec les unités de température et le nombre de jours depuis la contamination. Aucune différence significative entre les dates médianes d'apparition n'a été mise en évidence par utilisation des unités de température; par contre, ces différences deviennent significatives lorsque l'on utilise le nombre de jours depuis la contamination. Des paramètres fiables sont nécessaires pour prédire la présence des différentes stades de cet insecte. En dépit des différentes conditions imposées pour cette étude, la méthode la moins capricieuse pour prédire l'apparition d'un stade larvaire et l'émergence des adultes est la somme de températures avec une base de 11°C.