Behaviour and ecology of the western corn rootworm (Diabrotica virgifera virgifera LeConte)

1 The western corn rootworm (WCR) is a historic pest with a legacy of resistance and behavioural plasticity. Its behaviour and nutritional ecology are important to rootworm management. The success of the most effective and environmentally benign rootworm management method, annual crop rotation, was based on an understanding of rootworm behaviour and host–plant relationships. Enthusiastic adoption of crop rotation, provided excellent rootworm management, but also selected for behavioural resistance to this cultural control.
2 Though well-studied, significant gaps in WCR biology remain. Understanding the topics reviewed here (mating behaviour, nutritional ecology, larval and adult movement, oviposition, alternate host use, and chemical ecology) is a starting point for adapting integrated pest management and insect resistance management (IRM) to an expanding WCR threat. A presentation of significant questions and areas in need of further study follow each topic.
3 The expansion of WCR populations into Europe exposes this pest to new environmental and regulatory conditions that may influence its behaviour and ecology. Reviewing the state of current knowledge provides a starting point of reference for researchers and pest management decision-makers in North America and Europe.
4 The trend toward increasing adoption of transgenic maize will place an increasing premium on understanding WCR behaviour. IRM plans designed to promote sustainable deployment of transgenic hybrids are grounded on assumptions about WCR movement, mating and ovipositional behaviour. Preserving the utility of new and old management options will continue to depend on a thorough understanding of WCR biology, even as the ecological circumstances and geography of WCR problems become more complex.     

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.     

Selection of entomopathogenic fungi for the control of the western corn rootworm Diabrotica virgifera virgifera

Abstract:  The western corn rootworm Diabrotica virgifera virgifera Le Conte (Col., Chrysomelidae), a serious pest of maize, has been recently introduced into Europe. Several approaches for its control are presently under investigation including microbial agents. During a field survey in Hungary in 2005, naturally occurring entomopathogenic fungi were found to attack this pest. These novel isolates together with standard isolates were tested for virulence against D. v. virgifera larvae and adults. Twenty strains of Metarhizium anisopliae , Beauveria bassiana and Beauveria brongniartii were used in bioassays in the laboratory. Larvae and adults were dipped into a spore suspension with a concentration of 1 × 10⁷ conidia (con.)/ml. They were kept for 14 days at 22°C (±2°C) and 70% relative humidity. The number of infected larvae and adults were counted and infection rates were calculated. Adults were significantly more susceptible to entomopathogenic fungi than larvae. The most virulent isolate infected about 47% of larvae ( M. anisopliae Ma2277), whereas the infection rate in adults was up to 97% ( M. anisopliae Ma2275). Isolates of M. anisopliae caused significantly higher mortalities than isolates of B. brongniartii and B. bassiana . Most of the adult beetles were killed within 12 days. Isolates from D. v. virgifera were more virulent than those from other hosts.     

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.     

Protease activities in the midgut of Western corn rootworm (Diabrotica virgifera virgifera LeConte)

The Western corn rootworm is one of the most economically important pests in corn. One possibility for controlling this pest is the cultivation of transgenic corn expressing Bacillus thuringiensis (Bt) toxins, such as Cry3A, Cry34Ab1/Cry35Ab1, and Cry3Bb1. However, widespread cultivation of the resulting Bt corn may result in the development of resistant pest populations. The Bt toxins are processed by proteases in the midgut of susceptible insects. Thus, protease activity studies were conducted using the midgut juice (pH 5.75) from third instars larvae of the susceptible Western corn rootworm. As a result, the activities of the serine endopeptidases trypsin, chymotrypsin, elastase, cathepsin G, plasmin, and thrombin; the cysteine endopeptidases cathepsin L, papain, cathepsin B, and cathepsin H; the aspartic endopeptidase pepsin; the metallo endopeptidase saccharolysin; the exopeptidase aminopeptidase, and the omegapeptidase acylaminoacylpeptidase were detected. These results are of basic interest but also lead to reference systems for the identification of protease-mediated resistance mechanisms in potentially resistant individuals.     

Screening of entomopathogenic nematodes for virulence against the invasive western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) in Europe

Entomopathogenic nematode species available in Europe were screened for their efficacy against both the root-feeding larvae and silk-feeding adults of the western corn rootworm, Diabrotica virgifera virgifera LeConte. Laboratory screening tests were aimed at the selection of candidate biological control agents for the management of this invasive alien pest in Europe. Steinernema glaseri, S. arenarium, S. abassi, S. bicornutum, S. feltiae, S. kraussei, S. carpocapsae and Heterorhabditis bacteriophora were studied to determine their virulence against third instar larvae and adults of D. v. virgifera in small-volume arenas (using nematode concentrations of 0.5, 0.8, 7.9 and 15.9 infective juveniles cm-2). All nematode species were able to invade and propagate in D. v. virgifera larvae, but adults were rarely infected. At concentrations of 7.9 and 15.9 cm-2, S. glaseri, S. arenarium, S. abassi and H. bacteriophora caused the highest larval mortality of up to 77%. Steinernema bicornutum, S. abassi, S. carpocapsae and H. bacteriophora appeared to have a high propagation level, producing 5970+/-779, 5595+/-811, 5341+/-1177 and 4039+/-1025 infective juveniles per larva, respectively. Steinernema glaseri, S. arenarium, S. feltiae, S. kraussei and H. bacteriophora were further screened at a concentration of 16.7 nematodes cm-2 against third instar larvae in medium-volume arenas (sand-filled trays with maize plants). Heterorhabditis bacteriophora, S. arenarium and S. feltiae caused the highest larval mortality with 77+/-16.6%, 67+/-3.5%, and 57+/-17.1%, respectively. In a next step, criteria for rating the entomopathogenic nematode species were applied based on results obtained for virulence and propagation, and for current production costs and availability in Europe. These criteria were then rated to determine the potential of the nematodes for further field testing. Results showed the highest potential in H. bacteriophora, followed by S. arenarium and S. feltiae, for further testing as candidate biological control agents.     

A novel Bacillus thuringiensis (PS149B1) containing a Cry34Ab1/Cry35Ab1 binary toxin specific for the western corn rootworm Diabrotica virgifera virgifera LeConte forms ion channels in lipid membranes

The binary Bacillus thuringiensis PS149B1 insecticidal crystal (Cry) protein is comprised of two components, Cry34Ab1, a 14-kDa protein, and Cry35Ab1, a 44-kDa protein, the combination of which forms a novel binary toxin active on western corn rootworm larvae. The permeabilizing behavior of the native binary toxin and its two individual components expressed as recombinant proteins was studied using calcein efflux determination in liposomes and by ion channel activity measurements in planar lipid bilayers (PLBs). Data obtained with solubilized native PS149B1 binary protein revealed it to be a pore-forming toxin that can permeabilize liposomes and form ion channels ( approximately 300-900 pS) in PLBs at pH 5.5 but not pH 9.0. The 14-kDa component of the toxin also formed ion channels ( approximately 15-300 pS) at pH 5.5 but did not insert easily in PLBs. While the 44-kDa moiety did seldomly form resolvable ion channels ( approximately 15-750 pS) in PLBs, it did destabilize the membranes. It showed pH-dependent truncation to a stable 40-kDa protein. The purified 40-kDa truncated product formed channels ( approximately 10-450 pS) in PLBs at pH 5.5. At that same pH, while a 3:1 molar mixture (14:44 kDa) of the individual components of the toxin induced channel activity that resembled that of the 14-kDa component alone, the 3:1 molar mixture of the 14-kDa component and 40-kDa truncated product induced channel activity ( approximately 20-800 pS) similar to that of PS149B1 in planar lipid bilayers. We conclude that the overall membrane permeabilization process of Cry34Ab1/Cry35Ab1 is a result of ion channel formation.     

Influence of adult diet on the reproductive biology and survival of the western corn rootworm,Diabrotica virgifera virgifera

Adult corn rootworm beetles,Diabrotica virgifera virgifera LeConte, were maintained on three dietary regimes which mimicked the progression of corn tissues that would be available in the field for beetles eclosing when corn was in the following growth stages: (A) after tassels had emerged but prior to silking and pollen shed; (B) while plants were silking and shedding pollen; and (C) after pollination was complete and silks had turned brown. A fourth regime (D) was established in which green corn silks, pollen, and leaves were provided throughout the study. The mean number of eggs laid per female over the 12-week duration of the study was 125, 235, 179, and 441 for regimes A, B, C, and D, respectively. Median length of life was 7.2, 7.2, 6.7, and 8.8 weeks for regimes A, B, C, and D respectively. Beetles in regime A laid a greater proportion of their eggs at an older age than did beetles from regimes B and C. To further investigate the influences on survival of changes in food quality of corn as plants and beetles aged, newly-eclosed beetles and beetles that had been maintained in caged plots of corn growing in a greenhouse for various lengths of time were caged on corn at different stages of growth, and the proportion of beetles surviving for 48 h was determined. Survival decreased as plants aged for both groups of beetles, but decreased at a faster rate for old than for young beetles.

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Influence de l'alimenation sur la reproduction et la survíe deDiabrotica virgifera virgifera

Résumé D. virgifera virgifera LeConte a été placé sur des régimes nutritifs mimant l'évolution des tissus du maïs disponsibles dans le champ lorsque les insectes éclosent est aux stades suivants du maïs: 1) après émergence de l'épi mâle, mais avant l'apparition des barbes et l'émission du pollen; 2) lors de la présence de barbes et de l'émission de pollen; 3) après la pollinisation et quand les barbes ont bruni. Un quatrième régime a été fourni pendant toute l'expérience comprenant des barbes vertes, du pollen et des feuilles. Les pontes moyennes des femelles pendant les 12 semaines de l'étude on été 125, 235, 179 et 441 pour les régimes 1, 2, 3 et 4. Les dates de mort de la moitié des adultes a été 7,2, 7,2, 6,7 et 8,8 semaines pour respectivement les mêmes régimes. Les femelles du régime 1 pondent à un âge plus avancé que les femelles des régimes 2 et 3. L'influence des changements de la qualité alimentaire du maïs au fur et à mesure du vieillissement des plantes et deDiabrotica, a été déterminée par la survie au bout de 48 heures d'insectes éclos depuis peu et d'autres maintenus en cage sur des lots de maïs à différents stades poussant en serre depuis des temps plus ou moins longs. Plus les plantes sont âgées, plus la survie des 2 groupes deDiabrotica diminue, mais plus vite chez les lots d'insectes âgés.

     

Assembly and annotation of full mitochondrial genomes for the corn rootworm species, Diabrotica virgifera virgifera and Diabroticabarberi (Insecta: Coleoptera: Chrysomelidae), using Next Generation Sequence data

Complete mitochondrial genomes for two corn rootworm species, Diabrotica virgifera virgifera (16,747 bp) and Diabrotica barberi (16,632; Insecta: Coleoptera: Chrysomelidae), were assembled from Illumina HiSeq2000 read data. Annotation indicated that the order and orientation of 13 protein coding genes (PCGs), and 22 tRNA and 2 rRNA sequences were in typical of insect mitochondrial genomes. Non-standard nad4 and cox3 stop codons were composed of single T nucleotides and likely completed by adenylation, and atypical TTT start codons was predicted for both D. v. virgifera and D. barberinad1 genes. The D. v. virgifera and D. barberi haplotypes showed 819 variable nucleotide positions within PCG regions (7.36% divergence), which suggest that speciation may have occurred ~ 3.68 million years ago assuming a linear rate of short-term substitution. Phylogenetic analyses of Coleopteran MtD genome show clustering based on family level, and may have the capacity to resolve the evolutionary history within this Order of insects.     

Molecular cloning and functional characterization of an endogenous endoglucanase belonging to GHF45 from the western corn rootworm, Diabrotica virgifera virgifera

A novel insect β-1,4-endoglucanase (DvvENGaseI) gene belonging to the glycoside hydrolase family (GHF) 45 was identified from the western corn rootworm, Diabrotica virgifera virgifera. The cDNA of the DvvENGaseI consisted of a 720 bp open reading frame encoding a 239 amino-acid protein. Analysis of the amino acid sequence revealed that DvvENGaseI exhibits 60% protein sequence identity when compared with an endoglucanase belonging to GHF45 from another beetle, Leptinotarsa decemlineata. Western blot analyses using a polyclonal antiserum developed from a partial peptide sequence revealed that DvvENGaseI expression coincided with body regions corresponding to the fore-, mid- and hindgut, although regions corresponding to the midgut and hindgut were the primary sites for DvvENGaseI expression. Functional analysis of the DvvENGaseI by RNA interference (RNAi) indicated that nearly complete knock-down of gene expression could be obtained by injection of dsRNA based on qRT-PCR and western blot analysis. However, suppression only resulted in slight developmental delays suggesting that this gene may be part of a larger system of cellulose degrading enzymes.     

Analysis of the dynamics of adaptation to transgenic corn and crop rotation by western corn rootworm (Coleoptera: Chrysomelidae) using a daily time-step model

Western corn rootworm, Diabrotica virgifera virgifera LeConte, has overcome crop rotation in several areas of the north central United States. The effectiveness of crop rotation for management of corn rootworm has begun to fail in many areas of the midwestern United States, thus new management strategies need to be developed to control rotation-resistant populations. Transgenic corn, Zea mays L., effective against western corn rootworm, may be the most effective new technology for control of this pest in areas with or without populations adapted to crop rotation. We expanded a simulation model of the population dynamics and genetics of the western corn rootworm for a landscape of corn; soybean, Glycine max (L.); and other crops to study the simultaneous development of resistance to both crop rotation and transgenic corn. Results indicate that planting transgenic corn to first-year cornfields is a robust strategy to prevent resistance to both crop rotation and transgenic corn in areas where rotation-resistant populations are currently a problem or may be a problem in the future. In these areas, planting transgenic corn only in continuous cornfields is not an effective strategy to prevent resistance to either trait. In areas without rotation-resistant populations, gene expression of the allele for resistance to transgenic corn, R, is the most important factor affecting the evolution of resistance. If R is recessive, resistance can be delayed longer than 15 yr. If R is dominant, resistance may be difficult to prevent. In a sensitivity analysis, results indicate that density dependence, rotational level in the landscape, and initial allele frequency are the three most important factors affecting the results.     

Optimum temperature for egg development of phenotypes in Haemonchus contortus cayugensis as determined by Arrhenius diagrams and Sacher's entropy function

Lejambre L. P. and Whitlock J. H. 1973. Optimum temperature for egg development of phenotypes in Haemonchus contortus cayugensis as determined by Arrhenius diagrams and Sacher's entropy function. International Journal for Parasitology3: 299–310. Oxygen uptake, maturation time and percentage hatch were determined on eggs from “wild-type” Haemonchus contortus cayugensis populations as well as those from the morph types smooth, linguiform B and linguiform A. Sacher's organizational entropy, which is essentially a sum of oxygen utilized by a system corrected for the number of viable units in the system, was used to determine the optimum temperature for development of the eggs. Although the eggs from “wild-type” H. contortus cayugensis hatched well across a broad temperature range; individual phenotypes showed a much narrower range. The optimum temperature for the development of eggs from smooth worms was approximately 30°C while linguiform A and B hatched best at 25°C. Linguiform A eggs had a broader temperature tolerance than linguiform B so that at temperatures of 17°C they hatched with a greater efficiency than did either smooth or linguiform B. It is argued that H. contortus follows a “strategy” of having many phenotypes, each one of which appears to be adapted to a different temperature. This would allow a population to maintain a broad range of optimal temperatures without the expense of maintaining the cybernetic machinery which a single individual would have to have if it were to tolerate the same range of temperature.     

The effect of application time and soil factors on the occurrence of Beauveria brongniartii applied as a biological control agent in soil

The effects of abiotic and biotic soil factors on occurrence of the entomopathogenic fungus Beauveria brongniartii after application at different times of the year were examined in Switzerland. Applications made from May to August generally resulted in an increase of 1-5 x 10(3) CFU g(-1) dry soil compared to untreated control plots. Conversely, soils treated in October and November yielded no increase. Soil temperatures between 20 and 25 degrees C, and high clay content of the soil had a positive effect on the occurrence and density of B. brongniartii whereas increased catalase activity and temperatures above 27 degrees C had a negative influence. Laboratory experiments revealed that a higher number of CFUs developed after one month of incubation at 22 degrees C than at 12 degrees C. Differences were not detected after three months of incubation, indicating that growth rate was simply slower at sub-optimal temperatures. The increase was different in three native soils, but was not correlated with different clay contents of the soil. In sterilized soil, though, the differences were not detected, suggesting that biotic factors have a greater influence rather than soil texture.     

Assessment of a rapid method,using soil cores,for estimating the amount and distribution of crop roots in the field

Summary A study was made of the relationship between the number of roots (N_r) observed on unit area of the freshly exposed, horizontal faces of soil cores, and the amounts of roots (per unit volume) present in the same cores. Soil cores, 7 cm diameter, were extracted to depths of 1 m from cereal crops in 1976 at three field sites located on clay soils. Sampling was either at the start of stem elongation, or at anthesis. Estimates of root length per unit soil volume (L) were derived from N_r by assuming random orientation of roots in the soil.Values of L were found to be highly correlated with the measured lengths of both the main roots (root axes) and the total roots (axes and laterals) washed from the soil at a given growth stage, for each of the soils. On average, L was 3.3 times the length of root axes washed from the soil, and was 0.42 times the length of total roots, but there was appreciable variation between different growth stages and field sites. Possible factors giving rise to differences between L and the measured lengths of roots are discussed. Estimates of root length from observation of soil cores may nonetheless provide a suitable basis for rapidly comparing therelative distribution of roots down the soil profile under field conditions.     

Ectomycorrhizas associated with a relict population of Dryas octopetala in the Burren, western Ireland. I. Distribution of ectomycorrhizas in relation to vegetation and soil characteristics

The distribution of ectomycorrhizas on Dryas octopetala L in grass heaths of the 450 km² karst region known as the Burren in Western Ireland was examined in relation to soil factors and vegetation type. Ectomycorrhizas were identified or characterised from 56 soil cores from 30 sites, and the occurrence of each ectomycorrhizal (EM) type was quantified by estimating the total length of mycorrhizal tips of each type. Soil organic matter, total nitrogen, extractable phosphorus, pH and depth were the soil factors determined. In total, 24 EM types were recorded. The EM community of Dryas roots was significantly more species-rich in one vegetation type—Hyperico-Dryadetum—than in others (Arctostaphylo-Dryadetum or Asperulo-Seslerietum). Multiple linear regression analyses indicated that soil organic matter and soil depth explained a significant portion of the variation in EM abundance, while soil organic matter and extractable phosphorus explained a significant portion of the variation in EM diversity. Canonical correspondence analysis showed that some individual EM types (e.g. Craterellus lutescens, Cenococcum geophilum, Tomentella sp., Boletus sp.) exhibited distinct soil preferences, most markedly in relation to soil organic matter, which, in this analysis, was the main significant soil variable distinguishing the three vegetation types.     

A stochastic development fraction model for predicting the development of the nematode parasite of sheep, Haemonchus contortus from egg to infective larvae under the influence of temperature

1. 1 Regression models for predicting the minimum, the median and the maximum period of development of the parasite H. contortus from egg to the infective stage of constant temperature were described.

2. 2. Simulations were used to study the development of the parasite to the infective stage.

3. 3. Further, an analytic Stochastic Development Fraction Model was used to reproduce the development of the parasite obtained by simulations.

4. 4. The Stochastic Development Fraction Model was compared with the Deterministic Development Fraction Model to expose its potentials for predicting the development of parasites on pasture where varying temperature prevail.

The life history of Labiostrongylus eugenii, a nematode parasite of the Kangaroo Island wallaby (Macropus eugenii): development and hatching of the egg and the freeliving stages

Smales L. R. The life history of Labiostrongylus eugenii, a nematode parasite of the Kangaroo Island Wallaby (Macropus eugenii): development and hatching of the egg and the free living stages. International Journal for Parasitology7: 449–456. Labiostrongylus eugenii (Trichonematidae) occurs in the stomach of the Kangaroo Island Wallaby. Egg morphology is similar to that of other strongyloids. When incubated at 25°C embryogenesis is completed in about 30 h. An incomplete moult occurs within the egg, and larvae hatch at a sheathed second-stage $\text{43}\text{1}\text{2}\text{–83}\text{1}\text{2}$ h later. Development occurred at all temperatures between 2° and 37°C with an optimum about 25°C and an upper limit near 37°C. The hatching process is very rapid, taking about 2 min. It is signalled by increased larval activity followed by a change in shell permeability. The larva hatches at that pole of the shell which has become plastic.The sheathed second-stage larva measures 659.50 ± 22.54 μm by 27.98 ± 1.22 μm. Its internal structures are concealed by a mass of opaque granules which were demonstrated as neutral lipid by oil red O staining. A second incomplete moult at 3–4 days results in a doubly sheathed infective larva from which the lipid gradually disappears. The mouth never appears patent and the larvae neither feed nor grow but rather decrease in size with age. Optimal temperatures for larvae range between 15°–25°C with 37°C about the upper limit. The significance of this developmental pattern is discussed.