Western corn rootworm, Diabrotica virgifera virgifera LeConte, biology is tied to the continuous availability of its host (corn, Zea mays L.). Annual rotation of corn with a nonhost, like soybean (Glycine max (L.) Merrill) was a reliable tactic to manage western corn rootworm. Behavioral resistance to annual crop rotation (rotation resistance) allowed some eastern U.S. Corn Belt populations to circumvent rotation by laying eggs in soybean and in cornfields. When active in soybean, rotation-resistant adults commonly consume foliage, in spite of detrimental effects on beetle survival. Rotation-resistant beetle activity in soybean is enabled by the expression of certain proteinases and an adapted gut microbiota that provide limited protection from soybean antiherbivore defenses. We investigated the effects of corn and soybean herbivory on rotation-resistant female survival and initiation of flight using mortality assays and wind tunnel flight tests. Among field-collected females tested with mortality assays, beetles from collection sites in a cornfield survived longer than those from collection sites in a soybean field. However, reduced survival due to soybean herbivory could be restored by consuming corn tissues. Field-collected beetles that fed on a soybean tissue laboratory diet or only water were more likely to fly in a wind tunnel than corn-feeding beetles. Regardless of collection site and laboratory diet, 90.5% of beetles that flew oriented their flights upwind. Diet-related changes in the probability of flight provide a proximate mechanism for interfield movement that facilitates restorative feeding and the survival of females previously engaged in soybean herbivory.

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is the primary insect pest threatening corn, Zea mays L., production in many areas of the United States and is capable of inflicting substantial yield loss. In Illinois and bordering states, managing this pest is complicated by populations exhibiting resistance to crop rotation, historically an effective strategy to prevent larval injury caused by this corn specialist. Rotation resistance is characterized by ovipositional infidelity to corn accompanied by various adaptations promoting prolonged residency in soybean, Glycine max (L.) Merr. We conducted an analysis using survey data to estimate densities of western corn rootworm adults in Illinois soybean fields and compared those estimates for two discrete time periods: (1) 1997–2003 and (2) 2011 and 2013–2015. Annual surveys during each time period were conducted from late July through late August by visiting a number of randomly selected soybean fields in counties distributed throughout Illinois. Adults were sampled using sweep nets. Mean densities were determined for each United States Department of Agriculture crop reporting district and interpolated values were estimated to produce statewide contour plots. Our findings reveal a substantial decline in adult abundance in soybean fields throughout much of Illinois. Where significant differences were observed between the two survey periods, recent densities were 88% lower on average than those observed during 1997–2003. Potential factors contributing to the declines we observed and implications for managing this adaptive pest of corn are discussed.

Two species of Diabrotica have evolved resistance to crop rotation that involves planting the same primary crop every second year in the same location. Diabrotica barberi has been adapted by extending egg diapause for more than one winter. Diabrotica virgifera virgifera has lost its fidelity for corn, Zea mays, during the ovipositional period; eggs are laid in most fields of vegetation in the crop landscape. Both adaptations permit eggs to hatch in cornfields. D. v. virgifera has also evolved resistance to most other integrated pest management (IPM) tactics over the past 60 years, including all currently commercialized insecticidal corn hybrids. This chapter explores the diverse approaches to IPM and the role of insect behavior in resistance management.

The northern corn rootworm, Diabrotica barberi Smith & Lawrence (Coleoptera: Cbrysomelidae) is an agricultural pest that ranges from the eastern Dakotas to Kansas and east to the Atlantic coast. The endosymbiotic bacteria Wolbachia has been detected in northern corn rootworm populations from east of the Mississippi River. Using the Wolbachia 16S rDNA,ftsZ and wsp genes a boundary was identified in central Illinois, between infected and uninfected populations with the infected populations found to the east of the boundary. Sequences of portions of the Wolbachia fts Z and wsp genes have been obtained from four geographic locations of northern corn rootworm. Within infected northern corn rootworm populations, two strains have been detected. The 1,058-bp ftsZ sequences from northern corn rootworm indicate that both strains belong to the Wolbachia super-group A. NCR Type 1 Wolbachia was found from eastern Illinois to Pennsylvania. NCR Type 2 Wolbachia occurs in central Illinois. The approximate to 600-bp wsp sequences from the two strains are also dramatically different. Strain differences in restriction fragment length polymorphism, patterns of the Wolbachia-specific amplicons were used to determine the distribution of the strains. The boundary between these two strains of Wolbachia in native populations of northern corn rootworm correlates with a previously observed mitochondrial DNA genetic boundary in eastern Illinois, suggesting that the two Wolbachia strains are incompatible and little if any introgression occurs between the two infected populations. The results demonstrate that Wolbachia can influence the genetics of a major insect pest over a wide geographic area and that it may be driving reproductive isolation between populations of northern corn rootworm.

In Illinois and Indiana, the western corn rootworm, Diabrotica virgifera virgifera LeConte, circumvents crop rotation as a control measure by ovipositing in soybean (Glycine max L. Merr.) fields and in other crops in rotation with corn (Zea mays L.). A means of distinguishing between rotation-resistant and wild-type behavioral phenotypes is the first step in determining the genetic basis of rotation resistance. The time between release into and departure from a bioassay arena was used as a measure of beetle activity to distinguish between behavioral phenotypes. Results from these assays indicate that D. v. virgifera females from regions where crop rotation is no longer effective are more active than females from regions where rotation remains effective. The geographic source of the beetle population was a main significant effect in trials done in both 2004 and 2005. Behavioral differences were more easily observed in a cornfield rather than in the laboratory. Results were consistent with the hypothesis that a loss of fidelity to corn rather than any particular attractant is the cause of rotation resistance. Behavioral differences between populations of beetles in similar environments suggest that there is a genetic difference between rotation-resistant and wild-type D. v. virgifera, although no specific gene or genes have yet been identified.

This chapter discusses topics on Western corn rootworm (WCR), Diabrotica virgifera virgifera, biology and history, resistance to crop rotation (in maize and soyabean fields), WCR movement, movement and the WCR life cycle, factors influencing movement, measuring movement, diet and movement, and diet and mechanisms of rotation resistance.

A variant of the western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), that circumvents crop rotation by flying out of cornfields to lay eggs in fields planted to other crops is presenting new management challenges to producers in the eastern Corn Belt. The rotation-resistant variant was first noted in east central Illinois and quickly dispersed to northern Indiana, southern Michigan, and northwestern Ohio. The spread of this variant throughout this region seems to be a result of high-altitude daytime flight. In this study, measurements of beetle flight activity at 10 m above ground level and meteorological factors are analyzed to evaluate the influence of atmospheric conditions on high-elevation flight of western corn rootworm. Collections of beetles from 72 d in July and August 2000-2002 reveal two pronounced peaks in high-elevation western corn rootworm flight, the first between 0645 and 1100 hours and the second between 1700 and 2030 hours. Low temperatures, high wind speeds, and darkness were found to limit beetle flight activity; however, within the range of weather conditions conducive to aerial movement, the level of flight activity was not strictly related to the values of individual environmental factors. Instead, peaks in western corn rootworm flight activity at 10-m elevation corresponded to predictable transitions in atmospheric conditions above the fields.

Western corn rootworms, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) I with resistance to crop rotation, frequently move between fields of corn, Zea mays L., and soybean, Glycine max L. Merril, laying eggs in both crops. By comparing the behavioral and reproductive responses of beetles experiencing mixed corn and soybean diets to those provided with a continuous corn diet, the cost of mixing diets was measured. Larvae were collected near Urbana, IL (rotation-resistant population), and Monmouth, IL (typical rotation-susceptible population), and reared to adults in the laboratory. Females from each population were assigned to alternating corn and soybean diets of different durations. Beetles were more likely to feed on corn if it followed soybean than if they had continuous access to corn. The cost of a mixed corn and soybean diet was minimal; the fecundity of females given alternating diets of corn and soybean was similar to that of beetles given daily access to corn diets. Females laid more eggs on days when they bad access to soybean than on days with access to corn, suggesting dietary stress can induce oviposition. The only behavioral difference between the populations was a greater sensitivity to daily alternation of corn and soybean diets among beetles from the rotation-susceptible population. We found no evidence that rotation-resistant adult D. v. virgifera have any greater inclination or capacity to feed on soybean tissue than rotation-susceptible adults. Instead, periodic exposure to soybean results in nutritional stress that increases oviposition rate, lowers the threshold for feeding, and increases beetle activity.

Journal Article Mitochondrial DNA and ITS1 Differentiation in Geographical Populations of Northern Corn Rootworm, Diabrotica barberi (Coleoptera: Chrysomelidae): Identification of Distinct Genetic Populations Get access Richard L Roehrdanz, Richard L Roehrdanz USDA–ARS, Red River Valley Agricultural Research Center, Biosciences Research Laboratory, Fargo, ND 58105 (roehrdar@fargo.ars.usda.go) Search for other works by this author on: Oxford Academic Google Scholar Allen L Szalanski, Allen L Szalanski Department of Entomology, University of Arkansas, 320 Agric. Bldg., Fayetteville, AR 72701 Search for other works by this author on: Oxford Academic Google Scholar Eli Levine Eli Levine Center for Economic Entomology, Illinois Natural History Survey, Champaign, IL 61820 Search for other works by this author on: Oxford Academic Google Scholar Annals of the Entomological Society of America, Volume 96, Issue 6, 1 November 2003, Pages 901–913, https://doi.org/10.1603/0013-8746(2003)096[0901:MDAIDI]2.0.CO;2 Published: 01 November 2003 Article history Accepted: 14 July 2003 Published: 01 November 2003

A behavioral change in some western corn rootworm (Diabrotica virgifera virgifera LeConte) populations is threatening the effectiveness of crop rotation, a successful management strategy for controlling this pest. We created a set of simple meteorologic and behavioral models that can be used to predict the spread of the beetle infesting soybean (Glycine max (L.)) throughout the midwestern United States. We used data collected in Illinois, IN, MI, and Ohio to create maps of observations to evaluate the model. We displayed data on the maps using detection thresholds for western corn rootworm in soybean fields of 10 or 20 beetles per 100 sweeps and one or two beetles per yellow sticky trap per day. Counts greater than a detection threshold represent populations with a lack of fidelity to corn (Zea mays L.) and adapted to circumvent corn-soybean rotation. Some of the models invoked a landscape-diversity function that included the proportion of noncorn, nonrotated soybean vegetation on farmland in each county (i.e., extra vegetation). The best model for the period from 1997 to 2001 is based on heavy-storm data, with distance that beetles spread each year reduced by the proportion of extra vegetation in a county. This version is superior to a previously published model and to two new models that do not consider landscape diversity. Most of the models predicted spread at too high a rate between 1997 and 2001, compared with observations, but a few new models with rates of spread reduced by a landscape-diversity function matched the observations relatively well. Results suggest that the conclusions based on a linear model using proportion of extra vegetation as the key parameter are likely to be robust. Thus, we hypothesize that as the landscape diversity represented by the proportion of noncorn and nonrotated soybean vegetation in a geographic region increases, the rate of regional spread of the rotation-resistant western corn rootworm decreases over several years.

Western corn rootworm, Diabrotica virgifera virgifera LeConte, has overcome crop rotation in several areas of the central United States. We expanded a simple model of adult behavior and population genetics to explain how rotation resistance may have developed and to study ways to manage the western corn rootworm in a landscape of corn, soybean, and winter wheat where evolution of resistance may occur. We modeled six alternative management strategies over a 15-yr time horizon, as well as a strategy involving a 2-yr rotation of corn and soybean in 85% of the landscape, to investigate their effectiveness from both a biological and economic perspective. Generally, resistance to crop rotation evolves in fewer than 15 yr, and the rate of evolution increases as the level of rotated landscape (selection pressure) increases. When resistance is recessive, all six alternative strategies were effective at preventing evolution of rotation resistance. The two most successful strategies were the use of transgenic rotated corn in a 2-yr rotation and a 3-yr rotation of corn, soybean, and wheat with unattractive wheat (for oviposition) preceding corn. Results were most sensitive to increases in the initial allele frequency and modifications of the density-dependent survival function. Economically, three alternative strategies were robust solutions to the problem, if technology fees were not too high. Repellant soybean, attractive rotated corn, and transgenic rotated corn, all in 2-yr rotations, were economically valuable approaches. However, even the currently common 2-yr rotation was economical when resistance was recessive and the actual costs of resistance would not be paid until far in the future.

Bean leaf beetles (BLB; Cerotoma trifurcata) were collected in soybean (Glycine max) fields in 58 and 99 Illinois counties surveyed during the 2000 and 2001 growing seasons, respectively. In 2000, BLB counts were highest in the central portion of the state. BLB counts were lower the following year, but were more uniformly distributed throughout the state. BLB tested positive for Bean pod mottle virus (BPMV) in 37 of 41 counties assayed in 2000. In 2001, BLB tested positive for BPMV in 86 of 99 counties sampled. In 2000 and 2001, western corn rootworm (WCR; Diabrotica virgifera virgifera) adults were abundant in soybean fields only in east central Illinois. WCR adults tested positive for BPMV in 21 of 21 east central Illinois counties in 2000 and 20 of 24 sampled in 2001. BPMV was detected in soybean plants in 38 of 46 counties sampled in 2000. Field-collected WCR adults transmitted BPMV to potted soybean plants at low rates either directly from BPMV-infected soybean fields or with prior feeding on BPMV-infected plants. This is the first report of the distribution of BLB, WCR adults, and BPMV in Illinois and of BPMV transmission by adult WCR.

The western corn rootworm, Diabrotica virgifera virgifera LeConte, has adapted to crop rotation in parts of Illinois and Indiana with females now laying eggs in soybean, Glycine max L., fields in addition to corn, Zea mays L., fields. The electroantennogram (EAG) responses of females from the rotation-adapted population (Illinois) were not significantly different than the EAG responses of females from the ‘normal’ population (Missouri) for any of nine individual volatile treatments evaluated except to (E,Z)-2,6-nonadienal. However, females from the rotation-adapted population had nominally greater EAG responses than females from the ‘normal’ population for eight of nine treatments. This difference was significant when volatile treatments were combined to analyze the main effect of corn rootworm populations. Differences between populations were consistent across volatile treatments, and the volatile treatments × populations interaction was not significant for the analyses of data from females or males. The EAG responses of males from the rotation-adapted corn rootworm population were not significantly different than the EAG responses of males from the ‘normal’ population for any of the individual volatile treatments evaluated or in the combined analysis.

Abstract A simulation model of the population dynamics and genetics of the western corn rootworm, Diabrotica virgifera virgifera LeConte, was created for a landscape of corn, soybean, and other crops. Although the model was created to study a 2-locus problem for beetles having genes for resistance to both crop rotation and transgenic corn, during this first phase of the project, the model was simulated to evaluate only resistance management plans for transgenic corn. Allele expression in the rootworm and toxin dose in the corn plant were the two most important factors affecting resistance development. A dominant resistance allele allowed quick evolution of resistance to transgenic corn, whereas a recessive allele delayed resistance >99 yr. With high dosages of toxin and additive expression, the time required to reach 3% resistance allele frequency ranged from 13 to >99 yr. With additive expression, lower dosages permitted the resistant allele frequency to reach 3% in 2–9 yr with refuges occupying 5–30% of the land. The results were sensitive to delays in emergence by susceptible adults and configuration of the refuge (row strips versus blocks).

Crop rotation has traditionally been a valuable method for managing pests, but now a serious insect pest of maize (Diabrotica virgifera virgifera LeConte [Coleoptera: Chrysomelidae]) has developed behavioral resistance to rotation. A simple model of adult behavior and population genetics can explain how this resistance may have developed. This general model indicates that evolution may be caused by selection on a single gene for adult movement and that behavioral resistance only develops at high levels of rotation (> 80% of plant landscape). In less diverse landscapes, crop rotation selects for the expansion of host preferences (polyphagy) by adults. More diverse landscapes may delay the evolution of resistance to crop rotation depending on the fitness costs and the nature of the genetic system.

Abstract Two recently released, Mexican bean beetle, Epilachna varivestis, Mulsant, resistant soybean, Glycine max (L.) Merrill, germplasm lines, HC95–15MB and HC95–24MB, were examined for foliar and pod feeding resistance to adult bean leaf beetles, Cerotoma trifurcata (Förster), western corn rootworms, Diabrotica virgifera virgifera LeConte, and Japanese beetles, Popillia japonica Newman. Both lines were planted along with a susceptible control cultivar in 18 by 30-m plots and separate 0.8-ha size fields. Insects were sampled on a weekly basis with a sweep net. In late summer, defoliation ratings were recorded along with data on percentage pod feeding. Although a few significant differences in insect densities were obtained among the soybean lines on some sampling dates, no specific trends were observed in the ability of the resistant germplasm to reduce insect numbers. Insect population densities were similarly on all lines. However, both resistant lines were able to reduce defoliation during the growing season. Conversely, percentage pod feeding was similar among all the soybean lines, with no differences observed. The resistant germplasm lines appear able to lower levels of defoliation, and thus, offer a potential management tactic where leaf feeding, i.e., defoliation, is of concern. However, their ability to greatly reduce beetle population densities, and for the bean leaf beetle, to reduce pod feeding, appears limited.