Field-Evolved Resistance: Assessing the Problem and Ways to Move Forward

"Field-evolved resistance” is defined as a "genetically based decrease in susceptibility of a population to a toxin caused by exposure to the toxin in the field.” The key component of "field-evolved” resistance is that it does confer decreased susceptibility to an insecticide in the field. Another key component is that the decrease in susceptibility to the insecticide is because of previous exposure of the target insect to the toxin in the field. Several studies have reported field-evolved resistance to crops engineered to express proteins from the bacterium, Bacillus thuringiensis (Bt). However, there has not been a consistent standard in the application of the definition of field-evolved resistance for Bt crops. The inconsistency in applying the definition arises from differences in the methods used to detect resistance, the ecology of the interaction between the pest and the Bt crop, and the effective dose the pest encounters while feeding on the Bt crop. Using case studies of reported resistance to Bt crops, it is demonstrated resistance does not come in a single form, and that in most cases, resistance can still be manage

Segregation of European Corn Borer, Ostrinia nubilalis, Aminopeptidase 1, Cadherin, and Bre5-Like Alleles, from a Colony Resistant to Bacillus thuringiensis Cry1Ab Toxins, are not Associated with F2 Larval Weights when Fed a Diet Containing Cry1Ab

Protein receptors may be required for activated Bacillus thuringiensis Cry toxins (Cry1Ab) to bind midgut epithelium prior to pore formation. Single nucleotide polymorphism markers from two Ostrinia nubilalis Hübner (Lepidoptera: Crambidae) midgut peptide receptors, cadherin (OnCad), aminopeptidase N 1 (OnAPN1), and OnBre5 (Onb3GalT5; a β-1,3-galactosyltransferase family 5 member) were used to examine segregation in F2 families derived from paired matings of Cry1Ab-resistant females and Cry1Ab-susceptible males. Genotypic frequencies for these markers did not deviate from Mendelian expectations. Analysis of F2 larvae indicate the segregation of single nucleotide pores in OnAPN1, OnBre5 (Onb3GalT5), and OnCad marker loci were independent of the segregation of logio weights of larvae feeding on Cry1Ab diet

Comparative Performance of Single Nucleotide Polymorphism and Microsatellite Markers for Population Genetic Analysis

Microsatellite loci are standard genetic markers for population genetic analysis, whereas single nucleotide polymorphisms (SNPs) are more recent tools that require assessment of neutrality and appropriate use in population genetics. Twelve SNP markers were used to describe the genetic structure of Diabrotica virgifera virgifera (LeConte; Coleoptera: Chrysomelidae) in the United States of America and revealed a high mean observed heterozygosity (0.40 ± 0.059) and low global FST (0.029). Pairwise FST estimates ranged from 0.007 to 0.045, and all but 2 populations showed significant levels of genetic differentiation (P ≤ 0.008). Population parameters and conclusions based on SNP markers were analogous to that obtained by use of microsatellite markers from the identical population samples. SNP-based FST estimates were 3-fold higher than corresponding estimates from microsatellites, wherein lower microsatellite FST estimates likely resulted from an overestimate of migration rates between subpopulations due to convergence of allele size (homoplasy). No significant difference was observed in the proportion of SNP or microsatellite markers loci that were nonneutral within populations. SNP markers provided estimates of population genetic parameters consistent with those from microsatellite data, and their low back mutation rates may result in reduced propensity for error in estimation of population parameters

Geographic and Voltinism Differentiation among North American \u3ci\u3eOstrinia nubilalis\u3c/i\u3e (European Corn Borer) Mitochondrial Cytochrome \u3ci\u3ec\u3c/i\u3e Oxidase Haplotypes

DNA sequence of European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), mitochondrial cytochrome c oxidase I (cox1) and II (cox2) genes were characterized and used for population genetic analysis. Twenty-six point mutations were identified from a 2,156 bp DNA sequence alignment. The frequency of polymorphic cox1 DdeI and HaeIII, and cox2 Sau3AI and MspI restriction sites were determined from 1,414 individuals by polymerase chain reaction restriction fragment length polymorphism. Ten haplotypes were observed. A single haplotype was present among 90% of individuals examined, and a HaeIII haplotype was not present in samples from the Atlantic coast. Significant genetic differentiation existed between Atlantic coast and midwestern United States samples, and between sympatric uni- and bivoltine ecotypes. These genetic markers identify regional and ecotype differences in the North American O. nubilalis population

Impact of Trap Design, Windbreaks, and Weather on Captures of European Corn Borer (Lepidoptera: Crambidae) in Pheromone-Baited Traps

Pheromone-baited traps are often used in ecological studies of the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae). However, differences in trap captures may be confounded by trap design, trap location relative to a windbreak, and changes in local weather. The objectives of this experiment were, first, to examine differences in O. nubilalis adult (moth) captures among the Intercept wing trap, the Intercept bucket/funnel UNI trap, and the Hartstack wire-mesh, 75-cm-diameter cone trap (large metal cone trap) as well as among three cone trap designs. Second, we examined the influence of the location of the large metal cone trap relative to a windbreak on the number of moths captured. Third, we examined the relationship between nightly mean air temperature, relative humidity, wind speed, precipitation, and the number of moths captured in large metal cone traps. The number of moths captured was significantly influenced by trap design, with large metal cone traps capturing the most moths. Wing and bucket traps were ineffective. Differences among trap captures were significant among trap locations relative to a windbreak. Under strong (\u3e14 kph) or moderate (7 \u3c 14 kph) wind speeds, traps located leeward of the windbreak captured the most moths, but when wind speeds were light (\u3c7 kph), traps not associated with windbreaks captured the most moths. The multiple regression model fitted to the relationship between number of moths captured per Julian date and nightly weather patterns was significant. Nightly mean air temperature was the most influential parameter in the model, and its relationship with moth capture was positive