Northern Corn Rootworm Research Articles

A universal artificial diet for corn rootworm (Diabrotica spp.) larval biopesticide assays.

We identified a single diet formulation that can be used for three Diabrotica species including southern (SCR), western (WCR), and northern corn rootworm (NCR) by evaluating the performance of these pests on specialized diets (F9800B diet for SCR, WCRMO-2 diet for WCR, and NCRMO-1 diet for NCR) and a larval diet (F9772 diet) widely used for lepidopteran species. After 10 days of rearing, the WCRMO-2 diet yielded better or equal larval growth and development of all three rootworm species compared to other diets. For SCR larvae, the WCRMO-2 diet outperformed other diets. Larval fresh weight, percent molt to 2nd instar, and percent molt to 3rd instar on the WCRMO-2 diet were 12-fold, 2.7-fold, and 14-fold increases, respectively compared to that of the F9800B diet. Significantly more SCR larvae survived on the WCRMO-2 diet (98.9%) than on the F9800B diet (90.6%). The WCRMO-2 diet supported WCR and NCR larvae equal to the NCRMO-1 diet and better than other diets. The F9772 diet was the worst diet of all examined species. The availability of a universal diet (the WCRMO-2 diet) for the three Diabrotica species would facilitate research programs to monitor resistance development and develop new control tactics targeting these important pests.

Corn Rootworm (CRW) Diabrotica SPP.: A Review of its Impact to Maize Production and Current and Future Control Options

Western corn rootworm (WCRW), Diabrotica virgifera virgifera (Le Conte), and Northern corn rootworm (NCRW), Diabrotica barberi, are economically significant pests of maize production in the US corn belt. Maize plants are primarily damaged via CRW beetle larvae feeding on root tissue, which impairs nutrient uptake, vertical stability, and ultimately agronomic potential. CRW species are remarkably adaptable and able to overcome many of the agricultural practices and controls developed by farmers and the crop protection industry. CRW has also developed resistance to multiple insecticide classes, both chemical and protein in nature. Modern integrated approaches utilizing agricultural best practices, chemical insecticides, and genetically modified maize varieties with pyramided trait proteins are needed to control resistant populations of CRW. Next-generation technologies that target CRW will provide farmers with effective options to combat this challenging pest.

Susceptibility of northern corn rootworm (Diabrotica barberi) populations to Cry3Bb1 and Gpp34/Tpp35Ab1 proteins in seedling and diet overlay toxicity assays.

The northern corn rootworm, Diabrotica barberi Smith & Lawrence (Coleoptera: Chrysomelidae) is a major pest of maize in the United States Corn Belt. Recently, resistance to Bacillus thuringiensis (Bt) maize was reported in North Dakota and increased use of Bt maize hybrids could facilitate resistance evolution in other maize-producing states. In this study, susceptibility to Bt proteins was evaluated in wild D. barberi populations from 8 fields collected in 5 different states (Minnesota, Missouri, Nebraska, Iowa, and North Dakota). Field populations were compared to a susceptible D. barberi colony in seedling and diet toxicity assays conducted with 3 concentrations of Cry3Bb1 (0.4, 4.0, and 40.0 µg/cm2) and Gpp34/Tpp35Ab1 (previously called Cry34/35Ab1; 1.4, 14.0, and 140.0 µg/cm2). The 2019 population from Meeker Co., Minnesota (MN-2019), exhibited the lowest mortality to Cry3Bb1 and also had nominally lowest mortality to Gpp34/Tpp35Ab1 at the highest concentrations tested in diet toxicity assays. Percent second instar was also highest for larvae of the Minnesota population surviving Cry3Bb1. In seedling assays, MN and IA-2018 populations exhibited the highest proportion survival and dry weight to both proteins expressed in corn. No significant differences in mortality, percent second instar, and dry weight were observed at the highest concentration for both proteins among the populations collected in in 2020. Most D. barberi populations were still highly susceptible to Cry3Bb1 and Gpp34/Tpp35Ab1 proteins based on diet and seedling assays, but resistance appears to be developing in some D. barberi populations. Now that methods are available, resistance monitoring may also be needed for D. barberi in some regions.

Host search behaviors of specialist and generalist root feeding herbivores (Diabrotica spp.) on host and non-host plants

Western, northern, Mexican, and southern corn rootworms (WCR, NCR, MCR, and SCR) are serious corn pests. We evaluated host search behavior of these pests on six plant species using a video tracking system. After a 5-min exposure to plant roots, behavioral parameters were automatically recorded and used to quantify the search behavior. The search behavior was not observed for sorghum since no neonates survived after contacting sorghum roots. After exposures to corn roots, all neonates exhibited the localized search behaviors (i.e., shortening total distance traveled, lowering movement speed, increasing turn angle, moving farther from origin) which are used to stay in and search within root systems. When larvae contacted roots of wheat, barley, oats, soybean, or controls, they expanded the search area by extending the travel path, increasing velocity, and reducing turn angles and total distance moved. The intensity of the search expansion is highly associated with the host preferences known for the four rootworm species and subspecies. Neonates of each corn rootworm exhibited distinct search behaviors. In fact, NCR larvae had the highest speed, the greatest travel path, and the lowest turn angle, whereas MCR larvae had the highest turn angle and moved faster than WCR and SCR larvae.

Chromobacterium Csp_P biopesticide is toxic to larvae of three Diabrotica species including strains resistant to Bacillus thuringiensis

The development of new biopesticides to control the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is urgent due to resistance evolution to various control methods. We tested an air-dried non-live preparation of Chromobacterium species Panama (Csp_P), against multiple corn rootworm species, including Bt-resistant and -susceptible WCR strains, northern (NCR, D. barberi Smith & Lawrence), and southern corn rootworm (SCR, D. undecimpunctata howardi Barber), in diet toxicity assays. Our results documented that Csp_P was toxic to all three corn rootworms species based on lethal (LC50), effective (EC50), and molt inhibition concentration (MIC50). In general, toxicity of Csp_P was similar among all WCR strains and ~ 3-fold less toxic to NCR and SCR strains. Effective concentration (EC50) was also similar among WCR and SCR strains, and 5-7-fold higher in NCR strains. Molt inhibition (MIC50) was similar among all corn rootworm strains except NCR diapause strain that was 2.5–6-fold higher when compared to all other strains. There was no apparent cross-resistance between Csp_P and any of the currently available Bt proteins. Our results indicate that Csp_P formulation was effective at killing multiple corn rootworm strains including Bt-resistant WCR and could be developed as a potential new management tool for WCR control.

Patterns of Microbiome Composition Vary Across Spatial Scales in a Specialist Insect.

Microbial communities associated with animals vary based on both intrinsic and extrinsic factors. Of many possible determinants affecting microbiome composition, host phylogeny, host diet, and local environment are the most important. How these factors interact across spatial scales is not well understood. Here, we seek to identify the main influences on microbiome composition in a specialist insect, the western corn rootworm (WCR; Diabrotica virgifera virgifera), by analyzing the bacterial communities of adults collected from their obligate host plant, corn (Zea mays), across several geographic locations and comparing the patterns in communities to its congeneric species, the northern corn rootworm (NCR; Diabrotica barberi). We found that bacterial communities of WCR and NCR shared a portion of their bacterial communities even when collected from disparate locations. However, within each species, the location of collection significantly influenced the composition of their microbiome. Correlations of geographic distance between sites with WCR bacterial community composition revealed different patterns at different spatial scales. Community similarity decreased with increased geographic distance at smaller spatial scales (~25 km between the nearest sites). At broad spatial scales (>200 km), community composition was not correlated with distances between sites, but instead reflected the historical invasion path of WCR across the United States. These results suggest bacterial communities are structured directly by dispersal dynamics at small, regional spatial scales, while landscape-level genetic or environmental differences may drive community composition across broad spatial scales in this specialist insect.

Sequences Encoding a Novel Toursvirus Identified from Southern and Northern Corn Rootworms (Coleoptera: Chrysomelidae).

Sequences derived from a novel toursvirus were identified from pooled genomic short read data from U.S. populations of southern corn rootworm (SCR, Diabrotica undecimpunctata howardi Barber) and northern corn rootworm (NCR, Diabrotica barberi Smith & Lawrence). Most viral sequences were identified from the SCR genomic dataset. As proteins encoded by toursvirus sequences from SCR and NCR were almost identical, the contig sets from SCR and NCR were combined to generate 26 contigs. A total of 108,176 bp were assembled from these contigs, with 120 putative toursviral ORFs identified indicating that most of the viral genome had been recovered. These ORFs included all 40 genes that are common to members of the Ascoviridae. Two genes typically present in Ascoviridae (ATP binding cassette transport system permeases and Baculovirus repeated open reading frame), were not detected. There was evidence for transposon insertion in viral sequences at different sites in the two host species. Phylogenetic analyses based on a concatenated set of 45 translated protein sequences clustered toursviruses into a distinct clade. Based on the combined evidence, we propose taxonomic separation of toursviruses from Ascoviridae.

Pollen Feeding Reduces Predation of Northern Corn Rootworm Eggs (Coleoptera: Chrysomelidae, Diabrotica barberi) by a Soil-Dwelling Mite (Acari: Laelapidae: Stratiolaelapsscimitus).

Simple SummaryFlowering plants are used to enhance pest control by predators and parasitoids, but insect herbivores can also use floral resources. We documented the species of adult rootworm beetles on key plants, and found that northern corn rootworm (NCR) adults were commonly associated with sunflower inflorescences while western corn rootworm adults were most abundant in corn and on squash blossoms. Consumption of sunflower and corn pollen by NCR adults did not impact predation of their eggs by an omnivorous mite, but a predatory soil-dwelling mite ate pest eggs less frequently and took longer to feed on eggs when NCR adults had fed on sunflower pollen. While increasing plant diversity can benefit natural enemies and pest control within agroecosystems, it is important to consider how floral resources alter dietary preferences of biocontrol agents.Landscape diversification with flowering plants can benefit pollinators and natural enemies, although insect pests can also use floral resources for nutrition and chemoprotection. Corn rootworms (Coleoptera: Chrysomelidae, Diabrotica spp.) are major pests of corn (Zea mays L.), and while subterranean larvae primarily feed on corn roots, adult rootworms commonly consume floral resources from other plant species. We quantified the species, density, and sex of adult corn Diabroticite rootworm beetles on wild and cultivated sunflower, corn, and squash, quantified pollen within the bodies of adult northern corn rootworms [NCR, D. barberi (Smith & Lawrence)], and investigated how consumption of sunflower and corn pollen by NCR adults impacted predation of their eggs by two soil-dwelling mites with different feeding specialization. NCR were the most common Diabroticite species on sunflower inflorescences and western corn rootworm (WCR, D. v. virgifera LeConte) were more abundant in corn and squash blossoms. Pollen feeding by NCR adults did not impact egg predation by omnivorous Tyrophagus putrescentiae (Schrank) (Acari: Sarcoptiformes, Acaridae), but predatory Stratiolaelaps scimitus (Womersley) (Acari: Mesostigmata, Laelapidae) ate eggs less frequently and took longer to feed on eggs from NCR females that had fed on sunflower pollen. This research suggests pollen feeding by adult NCR can impact predation of their eggs. While increasing plant diversity can benefit natural enemies and pest control within agroecosystems, it is important to consider how floral resources alter dietary preferences of biocontrol agents.

Development of a nondiapausing strain of northern corn rootworm with rearing techniques for both diapausing and nondiapausing strains

The northern corn rootworm, Diabrotica barberi Smith & Lawrence, has a univoltine life cycle that typically produces one generation a year. When rearing the northern corn rootworm in the laboratory, in order to break diapause, it is necessary to expose eggs to a five month cold period before raising the temperature. By selective breeding of the small fraction of eggs that hatched without cold within 19–32 days post oviposition, we were able to develop a non-diapausing colony of the northern corn rootworm within five generations of selection. Through selection, the percentages of adult emergence from egg hatch without exposure to cold treatment significantly increased from 0.52% ± 0.07 at generation zero to 29.0% ± 2.47 at generation eight. During this process, we developed an improved method for laboratory rearing of both the newly developed non-diapausing strain as well as the diapausing strain. The development of the non-diapausing colony along with the improvements to the rearing system will allow researchers to produce up to six generations of the northern corn rootworm per year, which would facilitate research and advance our knowledge of this pest at an accelerated rate.

Elucidation of the MicroRNA Transcriptome in Western Corn Rootworm Reveals Its Dynamic and Evolutionary Complexity

Diabrotica virgifera virgifera (western corn rootworm, WCR) is one of the most destructive agricultural insect pests in North America. It is highly adaptive to environmental stimuli and crop protection technologies. However, little is known about the underlying genetic basis of WCR behavior and adaptation. More specifically, the involvement of small RNAs (sRNAs), especially microRNAs (miRNAs), a class of endogenous small non-coding RNAs that regulate various biological processes, has not been examined, and the datasets of putative sRNA sequences have not previously been generated for WCR. To achieve a comprehensive collection of sRNA transcriptomes in WCR, we constructed, sequenced, and analyzed sRNA libraries from different life stages of WCR and northern corn rootworm (NCR), and identified 101 conserved precursor miRNAs (pre-miRNAs) in WCR and other Arthropoda. We also identified 277 corn rootworm specific pre-miRNAs. Systematic analyses of sRNA populations in WCR revealed that its sRNA transcriptome, which includes PIWI-interacting RNAs (piRNAs) and miRNAs, undergoes a dynamic change throughout insect development. Phylogenetic analysis of miRNA datasets from model species reveals that a large pool of species-specific miRNAs exists in corn rootworm; these are potentially evolutionarily transient. Comparisons of WCR miRNA clusters to other insect species highlight conserved miRNA-regulated processes that are common to insects. Parallel Analysis of RNA Ends (PARE) also uncovered potential miRNA-guided cleavage sites in WCR. Overall, this study provides a new resource for studying the sRNA transcriptome and miRNA-mediated gene regulation in WCR and other Coleopteran insects.

Needs Assessment for Corn Insect Pest Management in Iowa

AbstractCorn, Zea mays L. (Cyperales: Poaceae), production is essential to Iowa’s economy and provides food, feed, and fuel beyond the state. Farmers face a number of challenges in corn production, including insect pests, and understanding farmers’ perceptions and concerns is critical for extension personnel to provide adequate and relevant programming. The Iowa State University Agriculture and Natural Resources Crops Team conducted a survey of Iowa farmers and agribusiness professionals during the 2019–2020 extension season. The goal was to understand farmer perceptions of corn pests and whether farmers experienced challenges with resistance to Bt traits or insecticides. Additionally, we aimed to realize farmers’ confidence in developing resistance management plans and discussing those needs with their input suppliers and advisors. Our survey revealed that northern corn rootworm, Diabrotica barberi Smith & Lawrence (Coleoptera: Chrysomelidae), was the pest of greatest concern across the state. People were generally more concerned about belowground Bt trait performance than aboveground traits, though only 12% of respondents reported Bt trait failure for corn rootworms. In general, people were not concerned about the performance of seed treatments or soil- or foliar-applied insecticides. Farmers generally felt very confident in developing a resistance management plan and discussing their needs with their advisors. The results of this survey will be used to target extension programming throughout the state and increase confidence for farmers and agribusiness employees to discuss resistance management plans together.

RNA-based pesticides aim to get around resistance problems

The half-inch-long corn rootworm larva packs a surprising punch. It feasts on the root system of corn before pupating into a black and yellow beetle that does further damage to the plant’s leaves. Before the advent of genetically modified (GM) crops that produce insecticidal proteins to fight rootworm, these insects cost US farmers an estimated $1 billion annually in damage and control measures. As destructive agricultural pests such as the corn rootworm evolve resistance to conventional pesticides, researchers and farmers are looking to RNAi-based treatments as a promising possible alternative. Image credit: Science Source/USDA/Nature Source. But as insects such as the corn rootworm evolve resistance to the suite of traits baked into commodity crops, scientists are queuing up a new application for a biotech tool that targets the protein-making machinery of insects. First identified in 1990, RNA interference (RNAi) entails using double-stranded RNA (dsRNA) to block messenger RNA from its usual function (i.e., sending out instructions to make proteins). With impressive specificity, RNAi can potentially block nucleotide sequences that are only found in a target pest and not in friendly insects or humans. As a result, some scientists are keen on making RNAi the next big tool in agricultural science. The EPA first approved an RNAi pesticide in 2017. That product, called SmartStax Pro, is a GM corn seed that will deploy both transgenic insecticidal proteins and RNAi to fight western and northern corn rootworm. It’s expected to be released in the United States in the next few years (1), according to its maker, Bayer AG, which is headquartered in Leverkusen, Germany. But GM crops are just one of many agriculture-related applications for RNAi. As the cost of producing dsRNA has dropped precipitously, biotech companies are developing dsRNA formulations that could also serve as spray pesticides, making the technology more …

Baseline Susceptibility of a Laboratory Strain of Northern Corn Rootworm, Diabrotica barberi (Coleoptera: Chrysomelidae) to Bacillus thuringiensis Traits in Seedling, Single Plant, and Diet-Toxicity Assays

The northern corn rootworm (NCR), Diabrotica barberi Smith & Lawrence, is an economic pest of maize in the U.S. Corn Belt. The objective of this study was to determine the baseline susceptibility of a laboratory NCR strain to Bt proteins eCry3.1Ab, mCry3A, Cry3Bb1, and Cry34/35Ab1 using seedling, single plant, and diet-toxicity assays. Plant assays were performed in greenhouse using corn hybrids expressing one of the Bt proteins and each respective near-isoline. Diet-toxicity assays, consisting of Bt proteins overlaid onto artificial diet were also conducted. In both plant assays, significantly more larvae survived Cry34/35Ab1-expressing corn compared with all other Bt-expressing corn, and larvae that survived eCry3.1Ab-expressing corn had significantly smaller head capsule widths compared with larvae that survived Cry34/35Ab1-expressing corn. In seedling assays, larvae surviving eCry3.1Ab-expressing corn also had significantly smaller head capsule widths compared with larvae that survived mCry3A-expressing corn. Additionally, larvae that survived mCry3A-expressing corn weighed significantly more than larvae surviving eCry3.1Ab- and Cry34/35Ab1-expressing corn. In single plant assays, no significant differences in larval dry weight was observed between any of the Bt-expressing corn. In diet assays, LC50s ranged from 0.14 (eCry3.1Ab) to 10.6 µg/cm2 (Cry34/35Ab1), EC50s ranged from 0.12 (Cry34/35Ab1) to 1.57 µg/cm2 (mCry3A), IC50s ranged from 0.08 (eCry3.1Ab) to 2.41 µg/cm2 (Cry34/35Ab1), and MIC50s ranged from 2.52 (eCry3.1Ab) to 14.2 µg/cm2 (mCry3A). These results establish the toxicity of four Bt proteins to a laboratory diapausing NCR strain established prior to the introduction of Bt traits and are important for monitoring resistance evolution in NCR field populations.

Food/Feed and Environmental Risk Assessment of Insect-resistant Genetically Modified Maize MIR604 for Food and Feed Uses, Import and Processing under Regulation (EC) No 1829/2003 (EFSA/GMO/UK/2005/11)

Food/Feed and Environmental Risk Assessment of Insect-resistant Genetically Modified Maize MIR604 for Food and Feed Uses, Import and Processing under Regulation (EC) No 1829/2003 (EFSA/GMO/UK/2005/11)

Final Health and Environmental Risk Assessment of Genetically Modified Maize 59122

Final Health and Environmental Risk Assessment of Genetically Modified Maize 59122

Evaluation of Seed Treatment and Soil-Applied Insecticides Against Larval Western and Northern Corn Rootworm, 2020

Evaluation of Seed Treatment and Soil-Applied Insecticides Against Larval Western and Northern Corn Rootworm, 2020

Performance of Seed Treatments and Soil-Applied Insecticides Against Larval Western and Northern Corn Rootworm, 2019

Performance of Seed Treatments and Soil-Applied Insecticides Against Larval Western and Northern Corn Rootworm, 2019

Pest categorisation of Diabrotica barberi.

The EFSA Panel on Plant Health performed a pest categorisation of Diabrotica barberi (Coleoptera: Chrysomelidae), the northern corn rootworm, for the EU. D. barberi is a univoltine species occurring in mid‐western and eastern USA and Canada, where it reproduces on maize (Zea mays), the preferred larval host. A small proportion of individuals can develop to a lesser extent on spelt (Triticum spelta), rice (Oryza sativa), millet (Panicum miliaceum) and a few North American wild grasses. Eggs are laid in the soil of maize fields, where they overwinter and can enter a diapause which can extend for more than one winter. Larvae hatch in late spring and early summer. Adult emergence peaks in the summer to feed on maize tassels, silks and ear tips. Adults abandon maize fields looking for other feeding hosts and return to maize for oviposition during late summer and autumn. D. barberi is considered a key pest of maize, together with other rootworm species of the same genus. D. barberi is regulated in the EU by Directive 2000/29/EC (Annex IAI). Within this Directive, a general prohibition of soil from most third countries prevents the entry of D. barberi larvae. However, adults carried on sweetcorn or green maize are potential pathways for entry into the EU. Climatic conditions and the wide availability of maize provide conditions to support establishment in the EU. Following establishment, impact on maize yields is anticipated. Phytosanitary measures are available to inhibit entry of this pest. D. barberi satisfies the criteria, which are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. D. barberi does not meet the criteria of occurring in the EU nor plants for planting being the principal means of spread for it to be regarded as a potential Union regulated non‐quarantine pest.

Optimizing Egg Recovery From Wild Northern Corn Rootworm Beetles (Coleoptera: Chrysomelidae).

The northern corn rootworm, Diabrotica barberi Smith & Lawrence (Coleoptera: Chrysomelidae), is one of the most important insect pests in the U.S. Corn Belt. Efforts to obtain eggs from wild northern corn rootworm populations using techniques developed for other rootworm species have been unsuccessful due to lack of oviposition. In 2016, we evaluated four oviposition media in choice tests within each of three female densities in 30.5 × 30.5 × 30.5 cm BugDorm cages. The number of eggs laid per female was significantly affected by female density and the interaction of female density × oviposition media, but oviposition was relatively poor in all oviposition media (1.2 eggs per female when averaging the three female densities and all oviposition media). Single females were also evaluated in nonchoice assays in 6 cm × 6 cm × 8 cm clear plastic boxes and averaged up to 108 eggs per female depending on the oviposition media. In 2017, the cumulative number of eggs laid per female in boxes with one female was not significantly different from the number of eggs laid per female in boxes with 3 females. In 2018, the cumulative number of eggs laid per female was not significantly different between female densities of 1, 3, 5, or 10 females per box. Total egg production per box therefore increased as female density increased. More than 27,000 wild northern corn rootworm eggs were collected from just 190 females when collected relatively early in the field season. We now have an efficient and robust system for obtaining eggs from wild northern corn rootworm females.

Field-Evolved Resistance of Northern and Western Corn Rootworm (Coleoptera: Chrysomelidae) Populations to Corn Hybrids Expressing Single and Pyramided Cry3Bb1 and Cry34/35Ab1 Bt Proteins in North Dakota.

Northern, Diabrotica barberi Smith & Lawrence, and western, D. virgifera virgifera LeConte, corn rootworms (Coleoptera: Chrysomelidae) are major economic pests of corn, Zea mays L., in North America. Corn hybrids expressing Bacillus thuringiensis Berliner (Bt) toxins are commonly used by growers to manage these pests. Several cases of field-evolved resistance to insecticidal proteins expressed by Bt corn hybrids have been documented in many corn-producing areas of North America, but only for D. v. virgifera. In 2016, beetles of both species were collected from five eastern North Dakota corn fields and reared in a growth chamber. In 2017, larvae reared from those populations were subjected to single-plant bioassays to screen for potential resistance to Cry3Bb1, Cry34/35Ab1, and pyramided Cry3Bb1 + Cry34/35Ab1 Bt toxins. Our results provide the first documented report of field-evolved resistance in D. barberi to corn hybrids expressing Cry3Bb1 (Arthur problem population) and Cry34/35Ab1 (Arthur and Page problem populations, and the Ransom and Sargent populations) proteins in North America. Resistance to Cry3Bb1 was also observed in the Ransom population of D. v. virgifera. Increased larval survival on the pyramided Cry3Bb1 + Cry34/35Ab1 hybrid was observed in both species. No cross-resistance was evident between Cry3Bb1 and Cry34/35Ab1 in any of the D. barberi populations tested. Our experiments identified field-evolved resistance to Bt toxins in some North Dakota populations of D. barberi and D. v. virgifera. Thus, more effective control tools and improved resistance management strategies are needed to prolong the durability of this technology for managing these important pests.