Validation of RNA interference in western corn rootworm Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) adults

BACKGROUND: RNA interference (RNAi) is commonly used in insect functional genomics studies and usually involves direct injection of double‐stranded RNA (dsRNA). Only a few studies have involved exposure to dsRNAs through feeding. For western corn rootworm (Diabrotica virgifera virgifera) larvae, ingestion of dsRNA designed from the housekeeping gene, vacuolar ATPase (vATPase) triggers RNAi causing growth inhibition and mortality; however, the effect of dsRNA feeding on adults has not been examined. In this research, WCR adults were fed with vATPase‐dsRNA‐treated artificial diet containing a cucurbitacin bait, which is a proven feeding stimulant for chrysomelid beetles of the subtribe Diabroticina to which rootworms belong. RESULTS: Real‐time PCR confirmed suppression of vATPase expression and western blot analysis indicated reduced signal of a protein that cross‐reacted with a vATPase polyclonal antiserum in WCR adults exposed to artificial diet treated with dsRNA and cucurbitacin bait. Continuous feeding on cucurbitacin and dsRNA‐treated artificial diet resulted in more than 95% adult mortality within 2 weeks while mortality in control treatments never exceeded 20%. CONCLUSIONS: This research clearly demonstrates the effect of RNAi on WCR adults that have been exposed to dsRNA by feeding and establishes a tool to screen dsRNAs of potential target genes in adults. This technique may serve as an alternative to target screening of larvae which are difficult to maintain on artificial diets. Copyright © 2011 Society of Chemical Industry     

RNAi as a management tool for the western corn rootworm,Diabrotica virgifera virgifera

The western corn rootworm (WCR), Diabrotica virgifera virgifera, is the most important pest of corn in the US Corn Belt. Economic estimates indicate that costs of control and yield loss associated with WCR damage exceed $US 1 billion annually. Historically, corn rootworm management has been extremely difficult because of its ability to evolve resistance to both chemical insecticides and cultural control practices. Since 2003, the only novel commercialized developments in rootworm management have been transgenic plants expressing Bt insecticidal proteins. Four transgenic insecticidal proteins are currently registered for rootworm management, and field resistance to proteins from the Cry3 family highlights the importance of developing traits with new modes of action. One of the newest approaches for controlling rootworm pests involves RNA interference (RNAi). This review describes the current understanding of the RNAi mechanisms in WCR and the use of this technology for WCR management. Further, the review addresses ecological risk assessment of RNAi and insect resistance management of RNAi for corn rootworm. © 2016 Society of Chemical Industry     

Impact of Cry3Bb1-expressing Bt maize on adults of the western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

BACKGROUND: Genetically engineered maize producing insecticidal Cry3Bb1 protein from Bacillus thuringiensis (Bt) is protected from root damage by corn rootworm larvae. An examination was made to establish whether western corn rootworm (Diabrotica virgifera virgifera) adults are affected by Cry3Bb1‐expressing maize (MON88017) when feeding on above‐ground tissue. RESULTS: In laboratory bioassays, adult D. v. virgifera were fed for 7 weeks with silk, leaves or pollen from Bt maize or the corresponding near‐isoline. Male, but not female, survival was reduced in the Bt‐leaf treatment compared with the control. Female weight was lower when fed Bt maize, and egg production was reduced in the Bt‐silk treatment. ELISA measurements demonstrated that beetles feeding on silk were exposed to higher Cry3Bb1 concentrations than beetles collected from Bt‐maize fields in the United States. In contrast to silk and pollen, feeding on leaves resulted in high mortality and low fecundity. Females feeding on pollen produced more eggs than on silk. C:N ratios indicated that silk does not provide enough nitrogen for optimal egg production. CONCLUSIONS: Direct effects of Cry3Bb1 on adult beetles could explain the observed effects, but varietal differences between Bt and control maize are also possible. The impact of Bt maize on adult populations, however, is likely to be limited. Copyright © 2011 Society of Chemical Industry     

玉米根萤叶甲的抗逆性与防治研究进展

玉米根萤叶甲（Diabrotica virgifera virgifera Leconte）在美国是最重要的玉米害虫。它不仅对一些环戊二烯、有机磷类和氨基甲酸盐类化学杀虫剂产生了很强的抗药性,还对玉米 大豆轮作和调整播期等农业防治措施产生了适应性。此外,该虫有较广的适生性和扩展性。在过去的60年内,它从美国中西部传到了东北部沿海地区,并入侵欧洲定殖为害。新近采用的防治方法主要是种植转Bt基因抗虫玉米。表达经生物工程改良并导入的某个Bt毒素基因如Cry3Bb1、Cry34Ab1/Cry35Ab1或mCry3A的转基因抗虫玉米可毒杀取食的玉米根萤叶甲。但在转Bt基因玉米使用数年后,田间观察和温室筛选研究显示,玉米根萤叶甲具有对转基因玉米的潜在抗性。本文对该叶甲与防治有关的生物学特性、抗逆性及其机制、防治措施做了综述和讨论,旨在对该害虫的检疫防除有所帮助。     

The western corn rootworm (Diabrotica virgifera virgifera): a new maize pest threatening Europe

The western corn rootworm Diabrotica virgifera virgifera is one of the most dangerous pests in maize in the USA. For many years, US growers have had to control this pest in maize fields by soil treatment or spraying. Ten years ago, this pest was also 'imported' into Europe. It was the job of the plant protection advisers and officials to inform endangered countries about the appearance of this pest, to develop control strategies for Europe and to establish research programmes to prevent further spread. This paper presents the history of this pest in Europe, its biology, the situation in 2001 and corn rootworm management scenarios for the future.     

玉米根萤叶甲在中国的潜在适生区域与检疫措施研究

玉米根萤叶甲(Diabrotica virgfera virgifera Leconte)是一种原产北美洲南部和中美洲北部并于1992年以来在欧洲快速传播扩散的危险性玉米害虫.该虫对我国玉米生产构成严重威胁.为了防范其入侵,本文在概述其生物学和传播蔓延趋势的基础上,利用基于生态位概念的GARP软件对该虫在我国的潜在适生区域进行了预测.研究显示适生区广布于黑龙江、吉林、辽宁、内蒙古、新疆、河北、北京、天津、山东、山西、陕西、宁夏、甘肃、江苏、安徽、河南、湖北、四川、云南和西藏等省区,其中最适生区主要位于东北平原的南部、华北平原的南部、渭河平原及其南北附近地区.据此结果,对其远距离传入中国的可能途径做了分析,对高危地区进行了分析判断,最终提出了检疫与防范建议.     

The socioeconomic benefits of biological control of western corn rootworm Diabrotica virgifera virgifera and wireworms Agriotes spp. in maize and potatoes for selected European countries

Journal of Plant Diseases and Protection - Innovative biological pest control of the western corn rootworm (WCR) Diabrotica virgifera virgifera and wireworms Agriotes spp. in maize and potato...     

Estimating the global area of potential establishment for the western corn rootworm (Diabrotica virgiferavirgifera) under rain‐fed and irrigated agriculture*

A CLIMEX model for Diabrotica virgiferavirgifera (western corn rootworm), was initially fitted to the known range of this pest in the USA and Mexico under rain‐fed agricultural situations. When this model was projected into Europe, it became clear that soil moisture thresholds for irrigation differed markedly between Central Europe and the USA. A second model was fitted using soil moisture parameters derived from theoretical expectations, and was found to fit the known distribution of all North American locations well, and all the European distribution records perfectly. Globally, the modelled potential range of D. v. virgifera covers approximately 64% of the global area of maize production. The highest nascent biosecurity risks to maize‐producing areas posed by the western corn rootworm are China, Japan, Argentina, South Africa and Australia. Biosecurity agencies concerned with managing D. v. virgifera invasion risks to Asia should adopt a regional approach to the problem, attempting to slow its spread through Eurasia. The sensitivity of D. v. virgifera’s modelled potential distribution to the inclusion of irrigated sites in the model training dataset highlighted the importance of carefully exploring the implications of land‐use factors that might be practised in different ways in the model training area and the area of concern.     

基于MaxEnt模型预测气候变化下玉米根萤叶甲在中国的潜在地理分布

为评估不同气候条件下玉米根萤叶甲Diabrotica virgifera virgifera在我国的潜在地理分布情况及适生区的空间格局变化趋势,通过筛选影响该虫分布的关键环境变量并基于其在全球的分布数据,运用MaxEnt模型和ArcGIS软件预测其在历史和未来气候情景下的潜在地理分布范围和适生区空间格局变化。结果表明,所构建MaxEnt模型的受试者工作特征 （receiver operating characteristic, ROC）曲线下面积（area under curve, AUC）平均为0.960,说明模型预测结果为优秀,具有较高的可信度。关键气候变量中最冷月最低温对玉米根萤叶甲的潜在地理分布具有十分重要的影响,累积贡献率为44.5%。历史气候条件下,玉米根萤叶甲的总适生区面积占我国陆地总面积的23.78%,高适生区主要分布于我国河南、湖北、陕西、甘肃、重庆、四川和云南等省市。未来气候情景下,玉米根萤叶甲在我国的总适生区面积略有减少,整体上呈现出南部收缩、北部扩张的趋势,原中南部的中、高适生区逐步转变为低适生区或非适生区。玉米根萤叶甲在我国的适生区较为广泛,适生范围涵盖多个重要玉米产区,对玉米安全生产威胁较大,应给予足够的重视,严防该虫传入我国。     

Partial purification and characterization of a methyl-parathion resistance-associated general esterase in Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

Increased hydrolytic metabolism of organophosphate insecticides has been associated with resistance among Nebraska western corn rootworm populations. In this study, resistance-associated esterases were partially purified by differential centrifugation, ion exchange, and hydroxyapatite column chromatography, with a final purification factor of 100-fold and recovery of approximately 10%. Kinetic analysis of the partially purified enzyme indicated that the K_m of the group II esterases was identical for the two populations, although V_max was consistently threefold higher in the resistant population. A putative esterase, DvvII, was further purified to homogeneity by preparative polyacrylamide gel electrophoresis. DvvII is a monomer with a molecular weight of approximately 66 kDa, although three distinct isoforms with similar pIs were evident based on isoelectric focusing gel electrophoresis. Immunoassays with the Myzus persicae E4 antiserum indicated that group II esterases from D. v. virgifera were cross-reactive and expressed at much higher titers in the resistant population relative to the susceptible counterpart. These results suggest that the resistance is likely associated with overproduction of an esterase isozyme in resistant D. v. virgifera populations.     

Differential response of male and female Diabrotica speciosa (Coleoptera: Chrysomelidae) to bitter cucurbit-based toxic baits in relation to the treated area size

Cucurbitacin-rich extracts are phagostimulants for both male and female Luperini, but field trials reveal that males are far more attracted to them than females. The sex ratio and number of beetles killed by an application of cucurbitacin-based toxic baits was assessed at two different scales: small areas of 100 m², and a larger area of 10,000 m². The small area bait applications killed mostly males (95.2%), but the 1-ha treated plot showed a lower sexual bias (57% male). An earlier study indicated point sources (sticky traps) attracted only males. Results indicate that the distance attraction to bitter cucurbit extracts is almost exclusive to males, but the wide dispersal of a toxic bait based on them should promote encounter and control of both sexes within the treated area. No significant non-target effects were observed.