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A complex of thrips species infests seedling stage cotton, Gossypium hirsutum (L.), in the southern United States. Preventive control tactics are recommended to manage early season infestations, but foliar insecticides may be necessary to prevent injury for the duration of seedling development. The objective of this work was to compare efficacy of spinetoram to that of spinosad and current standard products, and to define the minimum effective spinetoram rate for satisfactory control of thrips. Foliar applied insecticides were applied with and without a surfactant against varying thrips infestation levels in field plots. Results demonstrated that infestations comprised primarily of tobacco thrip, Frankliniella fusca (Hinds), were more sensitive to spinetoram than spinosad at equivalent rates of active ingredient. Spinetoram applied at 13.0 to 26.0 g a.i./ha provided control comparable to commercial standards under moderate infestation levels. Consistency and numerical increases in efficacy were observed when applying spinetoram (13.0 g a.i./ha) with a surfactant. Efficacy of spinetoram at 13.0 g a.i./ha in combination with a surfactant was confirmed against onion thrips, Thrips tabaci (Lindeman), and in commercial scale plots. Spinetoram alone was not adequate for managing extremely high (>269 fold greater than a threshold of one thrip per plant) populations of tobacco thrips. These experiments demonstrate that spinetoram, applied at 13.0 to 26.0 g a.i./ha, has utility in the management of thrips infesting cotton seedlings. [ABSTRACT FROM AUTHOR]

Feeding by insect herbivores activates plant signaling pathways, resulting in the enhanced production of secondary metabolites and other resistance-related traits by injured plants. These traits can reduce insect fitness, deter feeding, and attract beneficial insects. Organic and inorganic chemicals applied as a foliar spray, seed treatment, or soil drench can activate these plant responses. Azelaic acid (AA), benzothiadiazole (BTH), gibberellic acid (GA), harpin, and jasmonic acid (JA) are thought to directly mediate plant responses to pathogens and herbivores or to mimic compounds that do. The effects of these potential elicitors on the induction of plant defenses were determined by measuring the weight gains of fall armyworm, Spodoptera frugiperda (J. E. Smith) (FAW) (Lepidoptera: Noctuidae) larvae on four crop plants, cotton, corn, rice, and soybean, treated with the compounds under greenhouse conditions. Treatment with JA consistently reduced growth of FAW reared on treated cotton and soybean. In contrast, FAW fed BTH- and harpin-treated cotton and soybean tissue gained more weight than those fed control leaf tissue, consistent with negative crosstalk between the salicylic acid and JA signaling pathways. No induction or inconsistent induction of resistance was observed in corn and rice. Follow-up experiments showed that the co-application of adjuvants with JA failed to increase the effectiveness of induction by JA and that soybean looper [Chrysodeixis includens (Walker)], a relative specialist on legumes, was less affected by JA-induced responses in soybean than was the polyphagous FAW. Overall, the results of these experiments demonstrate that the effectiveness of elicitors as a management tactic will depend strongly on the identities of the crop, the pest, and the elicitor involved. [ABSTRACT FROM AUTHOR]

Cotton, Gossypium hirsutum (L.), plants expressing insecticidal crystal (Cry) proteins of Bacillus thuringiensis (Bt) Berliner are planted on significant acreage across the southern region of the United States. Fall armyworm, Spodoptera frugiperda (J. E. Smith), can be a significant cotton pest in some years, but this species has not been a primary target of Bt cotton technologies. The objective of this study was to quantify fall armyworm larval survivorship and fruiting form injury on transgenic cotton lines expressing Cry1Ac (Bollgard), Cry1Ac + Cry2Ab (Bollgard II), and Cry1Ac + Cry1F (WideStrike) Bt proteins. Larval survivorship and fruiting form damage of fall armyworm on Bollgard, Bollgard II, WideStrike, and non-Bt (control) cotton lines were evaluated in no-choice field studies. Fall armyworm (third instars) were placed on flower buds (squares), white flowers, and bolls, enclosed within a nylon mesh exclusion cage, and evaluated at selected intervals after infestation. Exposure of fall armyworm larvae to Bollgard cotton lines generally resulted in no significant effects on survivorship compared with larvae exposed to the non-Bt cotton line. Survivorship and plant injury by fall armyworm on Bollgard II cotton lines was variable compared with that on non-Bt cotton lines, and significant differences between treatments were inconsistent. Fall armyworm had significantly lower survivorship and caused less plant injury on WideStrike cotton lines than on non-Bt cotton lines across all plant structures. Development and survivorship of fall armyworm larvae on these cotton lines also were evaluated in no-choice laboratory assays by offering the previously described fruiting forms to third instars. Bollgard II and WideStrike cotton lines significantly reduced fall armyworm development and survivorship compared with those larvae offered non-Bt tissue. These results suggest that differences exist among selected Bt cotton technologies in their performance against fall armyworm. [ABSTRACT FROM AUTHOR]

To counter the threat of insect resistance, Bacillus thuringiensis (Bt) maize growers in the U.S. are required to plant structured non-Bt maize refuges. Concerns with refuge compliance led to the introduction of seed mixtures, also called RIB (refuge-in-the-bag), as an alternative approach for implementing refuge for Bt maize products in the U.S. Maize Belt. A major concern in RIB is cross-pollination of maize hybrids that can cause Bt proteins to be present in refuge maize kernels and negatively affect refuge insects. Here we show that a mixed planting of 5% nonBt and 95% Bt maize containing the SmartStax traits expressing Cry1A.105, Cry2Ab2 and Cry1F did not provide an effective refuge for an important above-ground ear-feeding pest, the corn earworm, Helicoverpa zea (Boddie). Cross-pollination in RIB caused a majority (>90%) of refuge kernels to express ≥ one Bt protein. The contamination of Bt proteins in the refuge ears reduced neonate-to-adult survivorship of H. zea to only 4.6%, a reduction of 88.1% relative to larvae feeding on ears of pure non-Bt maize plantings. In addition, the limited survivors on refuge ears had lower pupal mass and took longer to develop to adults. [ABSTRACT FROM AUTHOR]

Protein contamination on refuge kernels due to cross-pollination from Bt corn to non-Bt corn ears is a major concern in the use of a seed mixture refuge strategy (“RIB”) for resistance management of ear-feeding pests. In this study, occurrence, distribution, and ear damage of the corn earworm, Helicoverpa zea (Boddie), were evaluated in three planting patterns of non-Bt and Bt corn plants containing Genuity® SmartStax™ traits. The three planting patterns were 1) pure stands of 27 Bt plants; 2) pure stands of 27 non-Bt plants; and 3) one non-Bt plant in the center surrounded by 26 Bt plants. A total of six trials were conducted in open field conditions with natural infestations in 2011 and 2012. Egg populations of H. zea were distributed randomly or uniformly, and the number of eggs laid was similar between Bt and non-Bt corn ears regardless of the planting patterns, suggesting that females of H. zea have no egg-laying preference between Bt and non-Bt plants. Bt corn plants containing Genuity® SmartStax™ traits were equally effective in the control of H. zea in pure stands of Bt corn and “RIB” plantings. Occurrence of larvae and ear damage on Bt corn were significantly lower than on non-Bt plants and there were no significant differences between pure stands of Bt and “RIB” plantings across all trials. However, the limited numbers of live larvae in the pure stands of Bt plants were distributed non-randomly, suggesting a possibility of uneven expression of Bt proteins or elevated larval movement in the pure stands of Bt plants. Larval occurrence (3rd–5th instars) and ear damage on the refuge ears in “RIB” plantings were similar to or greater than found on ears of pure stands of non-Bt plants. However, more studies are needed to understand the effect of pollen movement on the full life cycle of H. zea before a final conclusion on the refuge function of RIB planting can be made. [ABSTRACT FROM AUTHOR]

A survey investigating the composition of adult thrips species and the effect of preventive, at-plant insecticides on this composition was conducted at multiple locations across the U.S. Cotton Belt in 2009 and 2010. Small-plot experiments included insecticide seed treatments containing imidacloprid (Aeris®) or thiamethoxam (Avicta Complete Cotton®), in-furrow applications of the insecticide aldicarb (Temik®), and an untreated control (no at-planting insecticide). The species composition of adult thrips varied among all locations which included trials within Arkansas, Georgia, Louisiana, Mississippi, Missouri, North Carolina, South Carolina, Tennessee, Texas and Virginia. As was the case in previous studies, tobacco thrips (Frankliniella fusca [Hinds]) was the dominant species at most locations. This species comprised an even greater percentage of the species composition in cotton not treated with insecticide. Conversely, the percent composition of other species tended to increase in cotton treated with insecticide. These observations suggest that tobacco thrips are relatively more sensitive to these insecticides. Overall, aldicarb reduced populations of adults more than other treatments, particularly imidacloprid. [ABSTRACT FROM AUTHOR]

BACKGROUND Larval movement of target pest populations among Bt and non- Bt plants is a major concern in the use of a seed mixture refuge strategy for Bt resistance management. In this study, occurrence and larval movement of the sugarcane borer, Diatraea saccharalis (F.), were evaluated in four planting patterns of non- Bt and Bt plants containing Genuity® SmartStaxTM traits in 2009-2011. The four planting patterns were: (1) a pure stand of 27 Bt plants; (2) one non- Bt plant in the center, surrounded by 26 Bt plants; (3) a pure stand of 27 non- Bt plants; (4) one Bt plant in the center, surrounded by 26 non- Bt plants. Studies were conducted under four conditions: (1) open field with natural infestation; (2) greenhouse with artificial infestations; open field with artificial infestations (3) on the center plants only and (4) on every plant. The major objective of this study was to determine whether refuge plants in a seed mixture strategy could provide a comparable refuge population of D. saccharalis to a 'structured refuge' planting. RESULTS Larvae of D. saccharalis showed the ability to move from infested plants to at least four plants away, as well as to adjacent rows, but the majority remained within the infested row. However, the number of larvae found on the non- Bt plants in the mixture plantings was not significantly reduced compared with the pure stand of non- Bt corn. CONCLUSION The results of this study show that refuge plants in a seed mixture may be able to provide a comparable refuge population of D. saccharalis to a structured refuge planting. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Diatraea saccharalis is a major corn borer pest. Midgut serine proteinases are essential for insect growth and development. Alteration of midgut proteinases is responsible for Bt resistance development in some species. To clone midgut trypsin and chymotrypsin cDNAs and to test if the Cry1Ab resistance in D. saccharalis is associated with changes in midgut proteinases, total midgut tryptic and chymotryptic activities, cDNA sequences, and gene expressions of three trypsin and three chymotrypsin genes were comparatively examined between Cry1Ab-susceptible (Cry1Ab-SS) and Cry1Ab-resistant (Cry1Ab-RR) strains. Full-length cDNAs encoding three trypsin- and three chymotrypsin-like proteinases were sequenced from Cry1Ab-SS and Cry1Ab-RR larvae. These cDNAs code for active forms of midgut serine proteinases with all functional motifs, including signal peptide, conserved His-Asp-Ser for the catalytic triad, three pairs of cysteines for disulfide bridge configurations, and conserved substrate specificity determination residues. In general, cDNA and putative protein sequences are highly similar between Cry1Ab-SS and Cry1Ab-RR strains, except for a few nucleotide and predicted amino acid substitutions, whose function need to be further clarified. Total trypsin and chymotrypsin activities were also similar between Cry1Ab-SS and Cry1Ab-RR strains. Transcriptional levels of the trypsin and chymotrypsin genes had numerical difference between Cry1Ab-SS and Cry1Ab-RR strains, but the difference was not statistically significant. Data suggest that the development of Cry1Ab resistance in D. saccharalis was not significantly associated with these trypsins and chymotrypsins. Results clarified the role of six midgut proteinases and provided a foundation for continuing examination of potential involvement of other midgut proteinases in Bt resistance development and other important biochemical processes. [ABSTRACT FROM AUTHOR]

Twospotted spider mite, Tetranychus urticae (Koch), has become a significant early season pest of cotton, Gossypium hirsutum L., in the midsouthern U.S. Sixteen experiments were conducted across the midsouthern U. S. to determine the impact of twospotted spider mite infestation timing on cotton injury, stunting, and yields. Twospotted spider mites from a greenhouse colony were used to initiate infestations at the three-leaf stage, at first flower, and at 200 heat unit intervals after first flower. Twospotted spider mite injury on a scale of zero to five (0 = no injury, 5 = severe injury), plant stunting, and final cotton yields were measured. In general, all infestation timings had higher injury ratings compared to the uninfested control. The highest injury ratings were observed for the three-leaf and first flower infestations. Additionally, infestations at the three-leaf stage caused more plant stunting than later infestation timings. In most of the experiments, the three-leaf infestation resulted in significant stunting of cotton plants. For cotton yields, early infestations caused the greatest yield losses. Significant yield losses compared to the untreated control were observed for infestations initiated up to first flower plus 800 heat units. These results suggest that cotton should be protected from twospotted spider mite infestations beyond that point in the growing season. Results from this experiment will be used to improve integrated pest management of twospotted spider mite in cotton. [ABSTRACT FROM AUTHOR]

Studies conducted during 1996 through 1998 showed that the use of an at-planting insecticide significantly reduced densities of thrips (adults and immature) compared to the non-treated control. In these studies the use of an at-planting insecticide also resulted in significantly greater lint yield compared to the non-treated. Additional studies were conducted during 1999 and 2000 to determine how thrips infestations impact yield. Thrips densities were lower during 1999 and 2000 compared to those observed during 1996 through 1998. Fewer differences in thrips densities were observed between treated and non-treated plots. Analysis of yield components using plant mapping procedures did not detect any differences between the treated and non-treated plots and there were no significant differences in total yield observed. Results from these studies and previous studies indicate that environmental conditions might influence cotton response to thrips infestations. This interaction warrants further study. [ABSTRACT FROM AUTHOR]

Sugarcane borer, Diatraea saccharalis (F.), is a major target of transgenic maize expressing Bacillus thuringiensis (Bt) proteins in South America and the US mid-south region. Resistance development in target pest populations is a major threat to the sustainable use of Bt crops. In our field trials in 2009, a significant number of live borers and plant injury from D. saccharalis were observed in an experimental SmartStax™ maize line. The objective of this study was to assess the relative susceptibility of two field populations of D. saccharalis collected from non-Bt and Bt maize plants containing SmartStax™ traits to five individual Cry proteins. The five Bt proteins included two proteins (Cry1A.105 and Cry2Ab2) that were expressed in SmartStax™ maize plants and three other common Bt proteins (Cry1Aa, Cry1Ab and Cry1Ac) that were not produced in SmartStax™. Larval mortality and growth inhibition on Bt diet of the fourth generation after field collections were evaluated 7 days after release of neonates on the diet surface. The laboratory bioassays showed that 50% lethal concentration (LC50) values for Cry1A.105 and Cry2Ab2 for the population originated from Bt plants were 3.55- and 1.34-fold greater, respectively, than those of the population collected from non-Bt plants. In contrast, relative to the population from non-Bt plants, the LC50 of the population sampled from Bt plants were 3.85-, 2.5- and 1.64-fold more sensitive to Cry1Aa, Cry1Ab and Cry1Ac, respectively. The results did not provide clear evidence to conclude that the observed field survival of D. saccharalis on Bt plants was associated with increased levels of resistance. [ABSTRACT FROM AUTHOR]

Cotton, Gossypium hirsutum (L.), plants expressing insecticidal crystal (Cry) proteins from Bacillus thuringiensis Berliner (Bt) constitute the majority of cotton acreage planted across the southern region of the United States. Fall armyworm, Spodoptera frugiperda (J. E. Smith), can be a significant cotton pest in some years, but this species has not been a primary target of Bt cotton technologies. The objective of this study was to characterize fall armyworm oviposition sites on cotton plants expressing Bt proteins. Fall armyworm adults were released into isolation cages containing cotton plants expressing either single (Bollgard®, Cry1Ac) or pyramided proteins (Bollgard II®, Cry1Ac:Cry2Ab; WideStrike™, Cry1Ac:Cry1F) or a conventional non-Bt cotton line. Following an oviposition period of two-three days, cotton plants were destructively sampled to locate egg masses. The distribution of egg masses on Bt cotton plants was not significantly different from that on non-Bt plants. Most egg masses were recorded on leaves, predominately on the abaxial surface, regardless of cotton line. Significantly more egg masses (>68%) were deposited on leaves near or emerging directly from the main stem (sympodial branch nodes 0-2) than on leaves emerging from branch nodes farther from the main stem. Fall armyworm oviposition was not influenced by Bt proteins and sampling protocols for eggs and early instars should be similar in fields of Bt and non-Bt cotton plants. [ABSTRACT FROM AUTHOR]

The sugarcane borer, Diatraea saccharalis (F.), is a major target of transgenic maize expressing Bacillus thuringiensis (Bt) proteins in South America and the mid-Southern region of the United States. During 2007-2009, a total of 986 feral individuals of D. saccharalis were collected from maize fields in six locations of Louisiana and Mississippi and examined for resistance to Cry1Ab maize using F1/F2 screens. Major resistance alleles to Cry1Ab maize in the populations sampled from non-Bt maize plants during 2007 and 2008 in Louisiana and 2009 in Mississippi were rare. From a total of 487 individuals collected from three locations in Louisiana in 2007 and 2008, only one individual was identified with major resistance alleles. In addition, no major resistance alleles were detected in 242 individuals collected from three locations in Mississippi in 2009. The frequency of major resistance alleles was estimated to be 0.002 with a 95% CI of 0.00025- 0.0057 for the Louisiana populations and < 0.0061, with 95% probability, for the Mississippi populations. The resistance frequency estimated for the Louisiana populations in 2007 and 2008 was not significantly different from those reported previously for populations sampled in 2004-2006. However, among 200 individuals sampled from non-Bt maize plants in 2009 in Louisiana, six individuals were identified to possess major resistance alleles. The estimated major resistance allele frequency for the populations sampled from non-Bt maize plants in 2009 in Louisiana was 0.0176 with a 95% CI of 0.0072 to 0.0328, which was significantly greater than those estimated for the populations collected in 2004-2008. Similarly, the frequency of minor resistance alleles to Cry1Ab maize for the Louisiana populations collected in 2009 was also significantly greater than those estimated for the populations sampled before. In addition, two out of 57 feral individuals collected from Bt maize plants in Louisiana in 2009 were identified to carry major resistance alleles to Cry1Ab maize. Since 2010, transgenic maize expressing pyramided Bt genes has been planted in the US mid-Southern region and by 2011, pyramided Bt maize has replaced Cry1Ab maize as the dominant Bt maize for managing lepidopteran pests including D. saccharalis. The timely switching from single-gene Cry1Ab maize to the pyramided Bt maize should prevent further increases in Cry1Ab resistance allele frequency and thus ensure the continued success of Bt maize for managing D. saccharalis in the region. [ABSTRACT FROM AUTHOR]

Tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is a damaging pest of cotton, Gossypium hirsutum L., grown in mid-southern U.S. states that include Arkansas, Louisiana, Mississippi, Missouri, and Tennessee. Chemical control tactics have been the primary method for managing infestations, but this strategy has become less effective due to development of insecticideresistant populations. The objective of this study was to evaluate the efficacy of sulfoxaflor against a range of tarnished plant bug infestation levels compared to acephate, the most widely utilized insecticide. Across infestation levels (12 locations, 49 trials), sulfoxaflor applied at ≥ 50 g ai/ ha provided control and yield levels similar to that observed with acephate. Against moderate infestations, single applications of sulfoxaflor (≥ 50 g ai/ha) or acephate reduced infestations below the action threshold 64 to 83% of the time through 8 d after application. Two applications of these same treatments and application timings against high infestations resulted in frequencies below the action threshold of 71 to 93%. Number of nymphs did not significantly differ between application of 50 and 75 g ai/ha of sulfoxaflor and acephate within single or sequential timings. As with any insecticide, effective tarnished plant bug control will depend on the quality of the application, pest population dynamics, and re-infestation intervals. Routine scouting practices will be necessary in determining the timing of insecticide treatments following a sulfoxaflor application. The new mode of action and efficacy provided by sulfoxaflor can be incorporated in cotton integrated pest management programs for tarnished plant bug that utilizes multiple insecticides. [ABSTRACT FROM AUTHOR]

Transgenic crops that produce Bacillus thuringiensis (Bt) toxins are grown widely for pest control, but insect adaptation can reduce their efficacy. The genetically modified Bt toxins Cry1AbMod and Cry1AcMod were designed to counter insect resistance to native Bt toxins Cry1Ab and Cry1Ac. Previous results suggested that the modified toxins would be effective only if resistance was linked with mutations in genes encoding toxin-binding cadherin proteins. Here we report evidence from five major crop pests refuting this hypothesis. Relative to native toxins, the potency of modified toxins was >350-fold higher against resistant strains of Plutella xylostella and Ostrinia nubilalis in which resistance was not linked with cadherin mutations. Conversely, the modified toxins provided little or no advantage against some resistant strains of three other pests with altered cadherin. Independent of the presence of cadherin mutations, the relative potency of the modified toxins was generally higher against the most resistant strains. [ABSTRACT FROM AUTHOR]

The sugarcane borer, Diatraea saccharalis, is a major target pest of transgenic corn expressing Bacillus thuringiensis (Bt) proteins (i.e., Cry1Ab) in South America and the mid-southern region of the United States. Evolution of insecticide resistance in such target pests is a major threat to the durability of transgenic Bt crops. Understanding the pests' resistance mechanisms will facilitate development of effective strategies for delaying or countering resistance. Alterations in expression of cadherin- and alkaline phosphatase (ALP) have been associated with Bt resistance in several species of pest insects. In this study, neither the activity nor gene regulation of ALP was associated with Cry1Ab resistance in D. saccharalis. Total ALP enzymatic activity was similar between Cry1Ab-susceptible (Cry1Ab-SS) and -resistant (Cry1Ab-RR) strains of D. saccharalis. In addition, expression levels of three ALP genes were also similar between Cry1Ab-SS and -RR, and cDNA sequences did not differ between susceptible and resistant larvae. In contrast, altered expression of a midgut cadherin (DsCAD1) was associated with the Cry1Ab resistance. Whereas cDNA sequences of DsCAD1 were identical between the two strains, the transcript abundance of DsCAD1 was significantly lower in Cry1Ab-RR. To verify the involvement of DsCAD1 in susceptibility to Cry1Ab, RNA interference (RNAi) was employed to knock-down DsCAD1 expression in the susceptible larvae. Down-regulation of DsCAD1 expression by RNAi was functionally correlated with a decrease in Cry1Ab susceptibility. These results suggest that down-regulation of DsCAD1 is associated with resistance to Cry1Ab in D. saccharalis. [ABSTRACT FROM AUTHOR]

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), has become the primary target of foliar insecticides in cotton, Gossypium hirsutum L., throughout the Midsouth over the past several years. This prompted a reevaluation of existing action thresholds for flowering cotton under current production practices and economics. A trial was conducted at 19 locations throughout the Midsouth during 2006 and 2007. Threshold treatments ranged from a weekly automatic insecticide application to a very high threshold of 10 tarnished plant bugs per 1.5 row-m on a black drop cloth. Individually, all locations reached the lowest threshold, and eight locations had a significant yield loss from tarnished plant bugs. Across all locations, lint yield decreased 0.85 to 1.72% for each threshold increase of one tarnished plant bug per 1.5 row-m. Yield loss was most closely correlated to pest density during the latter half of the flowering period. The relationship between plant bug density or damage and yield was similar for drop cloth, sweep net, and dirty square sampling methods, but the correlations among these sampling methods were not high. Incorporating actual insecticide application data from the trial and average production and economic factors for Midsouth cotton, the economic threshold, if monitoring once per week, should be between 1.6 and 2.6 tarnished plant bugs per 1.5 row-m during the flowering period. More frequent monitoring or situations where insecticide applications are more efficacious may alter this threshold. [ABSTRACT FROM AUTHOR]

Using an F1 screen, 352 feral individuals of the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), were examined for the presence of Bacillus thuringiensis (Bt)-resistance alleles. These insects represented four geographical populations collected in central and northeastern Louisiana, USA, and one field population from the Gulf Coast area of Texas, USA, during 2006. The F1 screen used various crosses between field-collected insects and a laboratory strain of Cry1Ab-resistant D. saccharalis, including both reciprocal crosses and group mating. F1 neonates of the crosses were screened for Bt resistance on Bt maize leaf tissue. One field-collected individual of D. saccharalis was shown to have a Bt-resistance allele. Based on Bayesian analysis procedures, the Bt-resistance allele frequency in the five populations of D. saccharalis was 0.0028 with a 95% confidence interval of 0.0003–0.0079. The successful identification of a resistance allele in a field collection of insects suggests that the F1 screening technique could be an effective tool for detecting and monitoring rare Bt-resistance alleles in field populations of D. saccharalis. [ABSTRACT FROM AUTHOR]

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), infestations in most of North America north of Mexico arise from annual migrations of populations that overwinter in southern Texas and Florida. A comparison of the cytochrome oxidase I haplotype profiles within the fall armyworm corn-strain, the subgroup that preferentially infests corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.), identified significant differences in the proportions of certain haplotypes between the Texas and Florida populations. These proportional differences were preserved as the populations migrated, providing a molecular metric by which the source of a migrant population could be identified. The migratory pattern derived from this method for several south- eastern states was shown to be consistent with predictions based on analysis of historical agricultural and fall armyworm infestation data. These results demonstrate the utility of haplotype proportions to monitor fall armyworm migration, and they also introduce a potential method to predict the severity of cotton crop infestations in the short term. [ABSTRACT FROM AUTHOR]

Transgenic Bacillus thuringiensis (Bt) corn, Zea mays L., has been widely used to manage a corn borer complex in the mid-southern region of the United States. The sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), has become a dominant cornstalk boring species in some areas of this region, especially in Louisiana. Therefore, management of sugarcane borer resistance to Bt corn is critical to ensure the long-term sustainability of Bt corn for the region. This study screened 280 two-parent family-lines of sugarcane borer from four geographical populations in Louisiana during 2005 to determine whether Bt resistance allele frequency in sugarcane borer is sufficiently low to meet the rare resistance assumption of the current "high dose/refuge" resistance management strategy for Bt corn. These sugarcane borer family-lines were examined for Bt resistance by using novel F2 screening procedures. No major Bt resistance alleles were detected in these four populations. The estimated frequency of major Bt resistance alleles was <0.0027, with a 95% probability and a detection power of 94%. The estimated minor resistance allele frequency was 0.0063, with a 95% CI of 0.0025-0.0117. During a previous study, a major Bt resistance allele was detected in one individual from 213 family-lines of another Louisiana population of sugarcane borer. Combining these data with the current screen, the frequency of major Bt resistance alleles across the five populations was 0.001, with a 95% credibility interval of 0.0001-0.0028 and a detection power of 95%. Major Bt resistance allele frequencies in Louisiana sugarcane borer populations seem to be low, and they should support the rare resistance allele requirement of the high dose/refuge strategy. [ABSTRACT FROM AUTHOR]

A Louisiana strain of the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), was selected for resistance to the CrylAb protein of Bacillus thuringiensis (Bt) by using an F2 screening procedure. Survival of Bt-resistant, -susceptible, and -heterozygous genotypes of sugarcane borer was evaluated on vegetative and reproductive stages of five non-Bt and seven Bt field corn, Zea mays L., hybrids in a greenhouse study. Larval survival was recorded 21 d after infestation of neonates on potted plants. Larval survival across the three sugarcane borer genotypes and five non-Bt corn hybrids after 21 d ranged from 23.6 ± 5.2% (mean ± SEM) to 57.5 ± 5.2%. Mean survival of CrylAb-resistant larvae on vegetative and reproductive plant stages was 12 and 21%, respectively. During the vegetative stages, all seven Bt corn hybrids were highly efficacious against CrylAb- susceptible and -heterozygous genotypes of sugarcane borer, with a larval survival rate of <2% for the Bt-susceptible genotype and ⩽5% for the heterozygotes. However, 8-18% of the heterozygous genotype survived on reproductive stage plants for four of the seven Bt corn hybrids tested. The variation in performance of Bt corn cultivars at vegetative and reproductive growth stages against Cry lAb resistant sugarcane borer suggests differential seasonal expression that may hasten resistance in the field. Bt corn hybrids expressing a "high dose" for European corn borer, Ostrinia nubilalis (Hübner), may not produce a sufficient high dose for the sugarcane borer. [ABSTRACT FROM AUTHOR]

The sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), strain (F52-3-R) was developed from F3 survivors of a single-pair mating on commercial Cry1Ab Bacillus thuringiensis (Bt) corn plants in the greenhouse. The susceptibility of a Bt-susceptible and the F52-3-R strain of D. saccharalis to trypsin-activated Cry1Ab toxin was determined in a laboratory bioassay. Neonate-stage larvae were fed a meridic diet incorporating Cry1Ab toxin at a concentration range of 0.0625 to 32 µg g−1. Larval mortality, larval weight, and number of surviving larvae that did not gain significant weight (<0.1 mg per larva) were recorded on the 7th day after inoculation. The F52-3-R strain demonstrated a significant level of resistance to the activated Cry1Ab toxin. Larval mortality of the Bt-susceptible strain increased in response to higher concentrations of Cry1Ab toxin, exceeding 75% at 32 µg g−1, whereas mortality of the F52-3-R strain was below 8% across all Cry1Ab concentrations. Using a measure of practical mortality (larvae either died or gained no weight), the median lethal concentration (LC50) of the F52-3-R strain was 102-fold greater than that of the Bt-susceptible insects. Larval growth of both Bt-susceptible and F52-3-R strains was inhibited on Cry1Ab-treated diet, but the inhibition of the F52-3-R strain was significantly less than that of the Bt-susceptible insects. These results confirm that the survival of the F52-3-R strain on commercial Bt corn plants was related to Cry1Ab protein resistance and suggest that this strain may have considerable value in studying resistance management strategies for Bt corn. [ABSTRACT FROM AUTHOR]

Transgenic maize, Zea mays L., expressing the Bacillus thuringiensis (Bt) CrylAb toxin has been planted to extensive areas across the United States and several other countries, but no resistance has been documented in field populations of lepidopteran target pests. This article describes the first report of resistance alleles to commercially available CrylAb Bt maize in a Louisiana population of sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae) Two hundred thirteen two-parent isolines of D. saccharalis were screened for CrylAb resistance on Bt maize leaf tissue using an F2 screening technique. Larvae representing three isolines survived >15 d on Bt tissue in the F2 generation. The second generation backcross progeny (B1F2) derived from isoline 52 completed larval development on Bt maize in the greenhouse. Segregation and resistance frequency analysis associated with isoline 52 suggested that Bt resistance is probably determined by a nearly completely recessive allele at a single locus. With this assumption, the estimated resistance allele frequency in this population is 0.0023, within a 95% confidence interval of 0.0003-0.0064. [ABSTRACT FROM AUTHOR]

A lepidopterous pest complex of southwestern corn borer, Diatraea grandiosella Dyar, and sugarcane borer, Diatraea saccharalis (F.), causes economic damage to field maize, Zea mays L., in the southern United States. Management of natural infestations was evaluated in irrigated and non-irrigated plots of Bacillus thuringiensis (Bt) transgenic maize hybrid expressing the insecticidal Cry1A(b) protein associated with the MON810 transformation event. Bt maize significantly (P ≤ 0.05) reduced the number of adult borer exit holes per plant, frequency of plants with adult exit holes in stalks, and frequency of plants with ear shank and cob tunneling compared to non-Bt maize regardless of irrigation regime. Ear length and grain yields were not significantly (P > 0.05) improved in the Bt hybrid compared to those in the non-Bt hybrid but were either similar or significantly (P ≤ 0.05) greater in irrigated than in non-irrigated maize. As stalk borer infestation persisted, a significant (P ≤ 0.05) increase was observed in the number of adult borer exit holes per stalk and in the number of plants affected with exit holes, ear shank tunneling, and cob tunneling in the irrigated non-Bt maize than in the non-irrigated, non-Bt maize. This suggests that irrigated non-Bt maize fields may offer a favorable environment for increased maize stalk borer infestation and survival. During the two-year study, sugarcane borer abundance increased compared to southwestern corn borer. Larvae removed from plants near crop maturity revealed a three to one predominance of sugarcane borer over southwestern corn borer. This might signal greater selection pressure on sugarcane borer in Bt maize in the southern United States. Current Insecticide Resistance Management (IRM) plans need to consider stalk borer species composition in an area and the differences in Bt susceptibility between sugarcane borer and other maize stalk-borer species to meet the high-dose IRM strategy. [ABSTRACT FROM AUTHOR]

The effects of late-season insect-simulated defoliation and premature harvest-aid application on cotton lint yield and physical fiber properties were evaluated in field experiments at two locations in Louisiana. Insect-simulated defoliation was accomplished by manually removing leaves with scissors, while all harvest-aids were applied with a CO2 backpack sprayer. Defoliation timings were NAWF5 + 450 heat units (HU), + 550 HU, + 650 HU, + 750 HU, and + 850 HU. Insect-simulated defoliation at NAWF5 + 450 HU reduced lint yield by 18% compared with the standard (chemical defoliation at 80% open, NAWF5 + 1050 HU); however, insect-simulated defoliation at NAWF5 + 550 HU and later developmental stages had no effect on lint yields. Chemical defoliation at NAWF5 + 450 HU, + 550 HU, and + 650 HU development stages reduced lint yield by 38,37, and 15%, respectively, below the standard. Harvest-aid applications at NAWF5 + 750 HU and + 850 HU did not affect lint yields compared with the standard. Insect-simulated defoliation did not impact fiber properties, but chemical defoliation of plants at growth stages ≤NAWF5 + 550 HU significantly lowered fiber micronaire at one location in both years. Chemical defoliation did not influence fiber strength, length, elongation, or uniformity. These results indicate that management strategies for late-season bottom defoliating insects should be terminated at plant development ≥NAWF5 + 550 HU, while chemical defoliation should not be initiated until plant development ≥NAWF5 + 750 HU. [ABSTRACT FROM AUTHOR]

One field strain each of the European corn borer, Ostrinia nubilalis (Hübner); south-western corn borer, Diatraea grandiosella Dyar; and sugarcane borer, Diatraea saccharalis (F.); were collected from cornfields in northeastern Louisiana. Susceptibilities of the field strain and a corresponding laboratory strain of the three borer species to Cry1Ab protein in DK69-70 Bacillus thuringiensis (Bt) corn hybrid were determined by exposing neonates to intact leaf tissues from whorl stage plants or by feeding neonates or third instars on a meridic diet treated with different concentrations of Cry1Ab protein extracted from Bt corn leaves. Mortality and growth of larvae were evaluated after 2 and 4 d posttreatment in the bioassays by using intact leaf tissues or after 7 din the bioassays by using diet incorporating Cry1Ab protein. D. saccharalis was the least susceptible species to Cry1Ab protein among the three species, followed by D. grandiosella, whereas O. nubilalis was most susceptible. The 2-d mortality of D. saccharalis neonates on intact Bt leaf tissues was lower than that of O. nubilalis and D, grandiosella. All neonates of O. nubilalis were killed on the diet treated with Cry1Ab protein at 0.5 and 1 mg/kg. The mortality of D. grandiosella was >75% at 1 mg/kg, but it was <6% for D. saccharalis at 1 mg/kg. The LC50 values of D. saccharalis were 3- and 11-fold higher than those of D. grandiosella and O. nubilalis, respectively. The LC50 values of D. saccharalis were 8- and 32-fold higher than those of D. grandiosella and O. nubilalis, respectively. Larval growth of the three species on Cry1Ab-treated diet was inhibited, but the inhibition was greater for O. nubilalis and D. grandiosella than for D. saccharalis. The lower susceptibility of D. saccharalis to Cry1Ab protein suggests that it is necessary to verify if a high-dose Bt corn for O. nubilalis and D. grandiosella is also a high dose for D. saccharalis. [ABSTRACT FROM AUTHOR]

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Stink bugs have become more common pests in cotton (Gossypium hirsutum L.), and the frequency of insecticides applied for their control has increased; therefore, establishing base-line insecticide mortality data is important for future resistance monitoring programs. A series of laboratory and field studies were used to characterize the susceptibility of stink bug species and selected development stages to pyrethroid and organophosphate insecticides. Stink bugs collected in the field were exposed to technical grade insecticides using the adult vial test (AVT) and to formulated products applied to cotton bolls and foliage. In the AVT, acephate was more toxic than dicrotophos to brown stink bug [Euschistus servus (Say)] adults. Brown stink bug and southern green stink bug [Nezara viridula (L.)] adults were equally sensitive to dicrotophos. Generally, brown stink bug adults were most sensitive to the pyrethroid, bifenthrin (1.8- to 6.5-fold), compared with other pyrethroids. Brown stink bug adults were significantly less susceptible than southern green stink bug adults to cyfluthrin (3.9-fold), cypermethrin (2.9- to 33.8-fold), and λ-cyhalothrin (7.6- to 66.5-fold). The LC[SUB50]S (μg/vial) for pyrethroids in the AVT ranged from 0.27 to 2.55,0.06 to 0.40, and 0.02 to 0.58 for brown stink bug adults, late-instar nymphs (of all species), and southern green stink bug adults, respectively. The order of susceptibility of stink bug species and developmental stages to insecticides from least to most susceptible was adult Euschistus spp., late-instar nymphs, and southern green stink bug adults. In field studies, acephate, dicrotophos, and high rates of bifenthrin, cypermethrin, cyfluthrin, z-cypermethrin, and λ-cyhalothrin- treated plant tissue produced significant levels of brown stink bug adult mortality (52.5 to 89.2%) compared with non-treated controls (P≤0.01). [ABSTRACT FROM AUTHOR]

In the United States, fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a target species of transgenic corn (Zea mays L.) expressing pyramided Bacillus thuringiensis proteins. In 2011, a total of 150 F2 two-parent families of S. frugiperda were established using single-pair matings of feral individuals collected from three locations in Louisiana and Florida. The objective of this study was to determine the susceptibility of these field derived families of S. frugiperda to a pyramided Bt corn hybrid containing Agrisure®Viptera™ 3111 traits. For each F2 family, 96 neonates were assayed on leaf tissue of Agrisure®Viptera™ 3111 corn in the laboratory. None of the 150 families survived for 7 days on leaf tissue of the Bt corn plants. The results demonstrate that the field populations of S. frugiperda collected from Louisiana and Florida were susceptible to the pyramided Bt corn product containing Agrisure®Viptera™ 3111 traits. The data generated in this study can be used as baseline data for resistance monitoring. [ABSTRACT FROM AUTHOR]

The article presents a letter to the editor concerning an article by Tabashnik et al. in the February 2008 issue discussing the field-evolved resistance to the toxin Bacillus thuringiensis.

The fall armyworm, Spodoptera frugiperda (J. E. Smith), is a target species of transgenic corn containing pyramided Bt genes in the United States. During 2011, a total of 149 F2 two-parental family lines were established using single-pairing of S. frugiperda collected from 3 locations in Louisiana and Florida. This study examined the susceptibility of these F2 two-parental family lines to 2 commonly used pyramided Bt corn traits, Genuity®VT Double Pro™ and Genuity®SmartStax™. Nine out of the 149 family lines showed less susceptibility to the leaf tissue of Genuity®VT Double Pro™ or Genuity®SmartStax™ plants. Larvae of these 9 family lines exhibited significant survivorship and growth on leaf tissue of the Bt corn plants. Two laboratory colonies were established from the F2 survivors of 2 of the 9 family lines. However, larvae from both colonies could not survive on whole plants of their corresponding Bt corn products in the greenhouse, suggesting these families were not resistant to the pyramided Bt corn traits. The results suggest that the pyramided Bt corn products containing Genuity®VT Double Pro™ or Genuity®SmartStax™ corn traits are effective in protecting against S. frugiperda. [ABSTRACT FROM AUTHOR]

Redbanded stink bug, Piezodorus guildinii (Westwood), is a significant soybean pest across the mid-south region of the United States. The objectives of these studies were to characterize: (1) redbanded stink bug oviposition in relationship to soybean maturity group (MG), plant structure, crop phenology, and vertical distribution within the plant canopy; and (2) redbanded stink bug adult sex ratios in relationship to soybean phenology. A total of 5645 redbanded stink bug eggs in 421 egg masses (clusters) were field collected from naturally-occurring populations in MG IV and V soybean over a three year period (2009 to 2011). The mean number of eggs within a cluster was 16.6 ± 0.3. Plant structures by MG interactions were highly significant with more egg masses oviposited on leaves in MG IV (79.4%) and more on pods in MG V (72.7%). The ratio of females to males was similar in all soybean growth stages except R5, where the sex ratio increased to 1.4:1, coinciding with peak oviposition. Only 29.9% of egg clusters in MG IV and 18.3% of egg clusters in MG V were oviposited in the upper 35 cm of the soybean canopy. Based on these results, sampling strategies and insecticide application placement for stink bugs may require modification.

The sugarcane borer, Diatraea saccharalis, is a major target pest of transgenic corn expressing Bacillus thuringiensis (Bt) proteins (i.e., Cry1Ab) in South America and the mid-southern region of the United States. Evolution of insecticide resistance in such target pests is a major threat to the durability of transgenic Bt crops. Understanding the pests' resistance mechanisms will facilitate development of effective strategies for delaying or countering resistance. Alterations in expression of cadherin- and alkaline phosphatase (ALP) have been associated with Bt resistance in several species of pest insects. In this study, neither the activity nor gene regulation of ALP was associated with Cry1Ab resistance in D. saccharalis. Total ALP enzymatic activity was similar between Cry1Ab-susceptible (Cry1Ab-SS) and -resistant (Cry1Ab-RR) strains of D. saccharalis. In addition, expression levels of three ALP genes were also similar between Cry1Ab-SS and -RR, and cDNA sequences did not differ between susceptible and resistant larvae. In contrast, altered expression of a midgut cadherin (DsCAD1) was associated with the Cry1Ab resistance. Whereas cDNA sequences of DsCAD1 were identical between the two strains, the transcript abundance of DsCAD1 was significantly lower in Cry1Ab-RR. To verify the involvement of DsCAD1 in susceptibility to Cry1Ab, RNA interference (RNAi) was employed to knock-down DsCAD1 expression in the susceptible larvae. Down-regulation of DsCAD1 expression by RNAi was functionally correlated with a decrease in Cry1Ab susceptibility. These results suggest that down-regulation of DsCAD1 is associated with resistance to Cry1Ab in D. saccharalis.

Pest resistance to pesticides is an increasing problem because pesticides are an integral part of high-yielding production agriculture. When few products are labeled for an individual pest within a particular crop system, chemical control options are limited. Therefore, the same product(s) are used repeatedly and continual selection pressure is placed on the target pest. There are both financial and environmental costs associated with the development of resistant populations. The cost of pesticide resistance has been estimated at approximately $ 1.5 billion annually in the United States. This paper will describe protocols, currently used to monitor arthropod (specifically insects) populations for the development of resistance. The adult vial test is used to measure the toxicity to contact insecticides and a modification of this test is used for plant-systemic insecticides. In these bioassays, insects are exposed to technical grade insecticide and responses (mortality) recorded at a specific post-exposure interval. The mortality data are subjected to Log Dose probit analysis to generate estimates of a lethal concentration that provides mortality to 50% (LC(50) of the target populations and a series of confidence limits (CL's) as estimates of data variability. When these data are collected for a range of insecticide-susceptible populations, the LC(50) can be used as baseline data for future monitoring purposes. After populations have been exposed to products, the results can be compared to a previously determined LC(50) using the same methodology.