Insects are constantly adapting to human-driven landscape changes; however, the roles of their gut microbiota in these processes remain largely unknown. The western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte) (Coleoptera: Chrysomelidae) is a major corn pest that has been controlled via annual rotation between corn ( Zea mays ) and nonhost soybean ( Glycine max ) in the United States. This practice selected for a “rotation-resistant” variant (RR-WCR) with reduced ovipositional fidelity to cornfields. When in soybean fields, RR-WCRs also exhibit an elevated tolerance of antiherbivory defenses (i.e., cysteine protease inhibitors) expressed in soybean foliage. Here we show that gut bacterial microbiota is an important factor facilitating this corn specialist’s (WCR's) physiological adaptation to brief soybean herbivory. Comparisons of gut microbiota between RR- and wild-type WCR (WT-WCR) revealed concomitant shifts in bacterial community structure with host adaptation to soybean diets. Antibiotic suppression of gut bacteria significantly reduced RR-WCR tolerance of soybean herbivory to the level of WT-WCR, whereas WT-WCR were unaffected. Our findings demonstrate that gut bacteria help to facilitate rapid adaptation of insects in managed ecosystems.

The use of mixtures of transgenic insecticidal seed and nontransgenic seed to provide an in-field refuge for susceptible insects in insect-resistance

To ensure food security, maize (Zea mays) is a model crop for understanding useful traits underlying stress resistance. In contrast to foliar biochemicals, root defenses limiting the spread of disease remain poorly described. To better understand belowground defenses in the field, we performed root metabolomic profiling and uncovered unexpectedly high levels of the sesquiterpene volatile β-selinene and the corresponding nonvolatile antibiotic derivative β-costic acid. The application of metabolite-based quantitative trait locus mapping using biparental populations, genome-wide association studies, and near-isogenic lines enabled the identification of terpene synthase21 (ZmTps21) on chromosome 9 as a β-costic acid pathway candidate gene. Numerous closely examined β-costic acid-deficient inbred lines were found to harbor Zmtps21 pseudogenes lacking conserved motifs required for farnesyl diphosphate cyclase activity. For biochemical validation, a full-length ZmTps21 was cloned, heterologously expressed in Escherichia coli, and demonstrated to cyclize farnesyl diphosphate, yielding β-selinene as the dominant product. Consistent with microbial defense pathways, ZmTps21 transcripts strongly accumulate following fungal elicitation. Challenged field roots containing functional ZmTps21 alleles displayed β-costic acid levels over 100 μg g⁻¹ fresh weight, greatly exceeding in vitro concentrations required to inhibit the growth of five different fungal pathogens and rootworm larvae (Diabrotica balteata). In vivo disease resistance assays, using ZmTps21 and Zmtps21 near-isogenic lines, further support the endogenous antifungal role of selinene-derived metabolites. Involved in the biosynthesis of nonvolatile antibiotics, ZmTps21 exists as a useful gene for germplasm improvement programs targeting optimized biotic stress resistance.

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 simple meteorological and behavioral model that can be used to predict the spread of the beetle infesting soybean, Glycine max (L.), throughout the Midwest. We used data collected in Illinois, Indiana, Michigan, and Ohio to create maps of observations to evaluate the model. We displayed data on the maps using thresholds of 10, 20, and 40 western corn rootworm beetles per 100 sweeps. Counts above a threshold represent populations searching for plants other than corn, Zea mays L., and adapted to the soybean–corn rotation. According to our model, the population adapted to soybean spreads 10–30 km per year depending on the directions of the prevailing storms and winds. The model underestimates the observed spread to the south. The model fits the Illinois data best when a threshold of 10 adults per 100 sweeps is used to visualize data and test the model. The model fits the Michigan data better with a threshold of 20 beetles, but is insensitive to the visualization and evaluation threshold for other areas. Model results support the hypothesis that the origin of the population of western corn rootworm infesting soybean is Ford County, IL. We predict that populations of western corn rootworm will be infesting soybean in much of Ohio, lower Michigan, and southern Wisconsin during the next 5 yr and eastern Iowa within the next 10 yr.

A simulation model of the population dynamics and genetics of the western corn rootworm, Diabrotica virgifera virgifera LeConte, was created for a la