Cross-pollination in seed-blended refuge and selection for Vip3A resistance in a lepidopteran pest as detected by genomic monitoring.

The evolution of pest resistance to management tools reduces productivity and results in economic losses in agricultural systems. To slow its emergence and spread, monitoring and prevention practices are implemented in resistance management programs. Recent work suggests that genomic approaches can identify signs of emerging resistance to aid in resistance management. Here, we empirically examined the sensitivity of genomic monitoring for resistance management in transgenic Bt crops, a globally important agricultural innovation. Whole genome resequencing of wild North American Helicoverpa zea collected from non-expressing refuge and plants expressing Cry1Ab confirmed that resistance-associated signatures of selection were detectable after a single generation of exposure. Upon demonstrating its sensitivity, we applied genomic monitoring to wild H. zea that survived Vip3A exposure resulting from cross-pollination of refuge plants in seed-blended plots. Refuge seed interplanted with transgenic seed exposed H. zea to sublethal doses of Vip3A protein in corn ears and was associated with allele frequency divergence across the genome. Some of the greatest allele frequency divergence occurred in genomic regions adjacent to a previously described candidate gene for Vip3A resistance. Our work highlights the power of genomic monitoring to sensitively detect heritable changes associated with field exposure to Bt toxins and suggests that seed-blended refuge will likely hasten the evolution of resistance to Vip3A in lepidopteran pests.

Rapid Adaptation and Interspecific Introgression in the North American Crop Pest Helicoverpa zea.

Insect crop pests threaten global food security. This threat is amplified through the spread of nonnative species and through adaptation of native pests to control measures. Adaptations such as pesticide resistance can result from selection on variation within a population, or through gene flow from another population. We investigate these processes in an economically important noctuid crop pest, Helicoverpa zea, which has evolved resistance to a wide range of pesticides. Its sister species Helicoverpa armigera, first detected as an invasive species in Brazil in 2013, introduced the pyrethroid-resistance gene CYP337B3 to South American H. zea via adaptive introgression. To understand whether this could contribute to pesticide resistance in North America, we sequenced 237 H. zea genomes across 10 sample sites. We report H. armigera introgression into the North American H. zea population. Two individuals sampled in Texas in 2019 carry H. armigera haplotypes in a 4 Mbp region containing CYP337B3. Next, we identify signatures of selection in the panmictic population of nonadmixed H. zea, identifying a selective sweep at a second cytochrome P450 gene: CYP333B3. We estimate that its derived allele conferred a ∼5% fitness advantage and show that this estimate explains independently observed rare nonsynonymous CYP333B3 mutations approaching fixation over a ∼20-year period. We also detect putative signatures of selection at a kinesin gene associated with Bt resistance. Overall, we document two mechanisms of rapid adaptation: the introduction of fitness-enhancing alleles through interspecific introgression, and selection on intraspecific variation.

Genome evolution in an agricultural pest following adoption of transgenic crops.

Replacing synthetic insecticides with transgenic crops for pest management has been economically and environmentally beneficial, but these benefits erode as pests evolve resistance. It has been proposed that novel genomic approaches could track molecular signals of emerging resistance to aid in resistance management. To test this, we quantified patterns of genomic change in Helicoverpa zea, a major lepidopteran pest and target of transgenic Bacillus thuringiensis (Bt) crops, between 2002 and 2017 as both Bt crop adoption and resistance increased in North America. Genomic scans of wild H. zea were paired with quantitative trait locus (QTL) analyses and showed the genomic architecture of field-evolved Cry1Ab resistance was polygenic, likely arising from standing genetic variation. Resistance to pyramided Cry1A.105 and Cry2Ab2 toxins was controlled by fewer loci. Of the 11 previously described Bt resistance genes, 9 showed no significant change over time or major effects on resistance. We were unable to rule out a contribution of aminopeptidases (apns), as a cluster of apn genes were found within a Cry-associated QTL. Molecular signals of emerging Bt resistance were detectable as early as 2012 in our samples, and we discuss the potential and pitfalls of whole-genome analysis for resistance monitoring based on our findings. This first study of Bt resistance evolution using whole-genome analysis of field-collected specimens demonstrates the need for a more holistic approach to examining rapid adaptation to novel selection pressures in agricultural ecosystems.

The Efficacy of Entomopathogenic Nematodes Plus an Adjuvant against Helicoverpa zea and Chrysodeixis includens in Aboveground Applications.

In the southern United States, corn earworm, Helicoverpa zea (Boddie), and soybean looper, Chrysodeixis includens (Walker) are economically important crop pests. Although Bt crops initially provided effective control of target pests such as H. zea, many insect pests have developed resistance to these Bt crops. Alternative approaches are needed, including biological control agents such as entomopathogenic nematodes (EPNs). However, the effectiveness of EPNs for aboveground applications can be limited due to issues such as desiccation and ultraviolet radiation. Effective adjuvants are needed to overcome these problems. Ten strains of EPNs were tested for virulence against eggs, first to fourth instars, fifth instars, and pupae of H. zea and C. includens in the laboratory. These 10 EPN strains were Heterorhabditis bacteriophora (HP88 and VS strains), H. floridensis (K22 strain), Hgkesha (Kesha strain), Steinernema carpocapsae (All and Cxrd strains), S. feltiae (SN strain), S. rarum (17c+e strain), and S. riobrave (355 and 7-12 strains). EPNs could infect eggs of H. zea or C. includens in the laboratory, but the infection was low. The mortality caused by 10 EPN strains in seven days was significantly higher for the first to fourth instars of H. zea compared to the control, as was the fifth instars of H. zea. Similarly, for the first to fourth and fifth instars of C. includens, the mortality was significantly higher compared to the controls, respectively. However, only S. riobrave (355) had significantly higher mortality than the control for the pupae of H. zea. For the pupae of C. includens, except for H. bacteriophora (HP88), S. rarum (17c+e), and H. floridensis (K22), the mortality of the other seven strains was significantly higher than the control. Subsequently, S. carpocapsae (All) and S. riobrave (7-12) were chosen for efficacy testing in the field with an adjuvant 0.066% Southern Ag Surfactant (SAg Surfactant). In field experiments, the SAg Surfactant treatment significantly increased the mortality and EPN infection for S. carpocapsae (All) on first instars of H. zea in corn plant whorls. On soybean plants, with the SAg Surfactant, S. carpocapsae (All) was more effective than S. riobrave (7-12) on fifth instars of C. includens. This study indicates that EPNs can control H. zea and C. includens, and SAg Surfactant can enhance EPN efficacy.

Reduced toxin binding associated with resistance to Vip3Aa in the corn earworm (Helicoverpa zea).

IMPORTANCE: Helicoverpa zea is a major crop pest in the United States that is managed with transgenic corn and cotton that produce insecticidal proteins from the bacterium, Bacillus thuringiensis (Bt). However, H. zea has evolved widespread resistance to the Cry proteins produced in Bt corn and cotton, leaving Vip3Aa as the only plant-incorporated protectant in Bt crops that consistently provides excellent control of H. zea. The benefits provided by Bt crops will be substantially reduced if widespread Vip3Aa resistance develops in H. zea field populations. Therefore, it is important to identify resistance alleles and mechanisms that contribute to Vip3Aa resistance to ensure that informed resistance management strategies are implemented. This study is the first report of reduced binding of Vip3Aa to midgut receptors associated with resistance.

Helicoverpa zea-Associated Gut Bacteria as Drivers in Shaping Plant Anti-herbivore Defense in Tomato.

Insect-associated bacteria can mediate the intersection of insect and plant immunity. In this study, we aimed to evaluate the effects of single isolates or communities of gut-associated bacteria of Helicoverpa zea larvae on herbivore-induced defenses in tomato. We first identified bacterial isolates from the regurgitant of field-collected H. zea larvae by using a culture-dependent method and 16S rRNA gene sequencing. We identified 11 isolates belonging to the families Enterobacteriaceae, Streptococcaceae, Yersiniaceae, Erwiniaceae, and unclassified Enterobacterales. Seven different bacterial isolates, namely Enterobacteriaceae-1, Lactococcus sp., Klebsiella sp. 1, Klebsiella sp. 3, Enterobacterales, Enterobacteriaceae-2, and Pantoea sp., were selected based on their phylogenetic relationships to test their impacts on insect-induced plant defenses. We found that the laboratory population of H. zea larvae inoculated with individual isolates did not induce plant anti-herbivore defenses, whereas larvae inoculated with a bacterial community (combination of the 7 bacterial isolates) triggered increased polyphenol oxidase (PPO) activity in tomato, leading to retarded larval development. Additionally, field-collected H. zea larvae with an unaltered bacterial community in their gut stimulated higher plant defenses than the larvae with a reduced gut microbial community. In summary, our findings highlight the importance of the gut microbial community in mediating interactions between herbivores and their host plants.

Caterpillar Salivary Glucose Oxidase Decreases Green Leaf Volatile Emission and Increases Terpene Emission from Maize.

Caterpillar salivary glucose oxidase (GOX) can function as both an elicitor or as an effector of plant defense responses depending upon the system. Treatment with GOX reduces the stomatal aperture of tomato and soybean leaves, thereby reducing the emission of volatile organic compounds (VOCs), that are important indirect defense responses of plants by attracting natural enemies of the caterpillars. Here we examined the effect of fungal GOX (fungal glucose oxidases have been used to determine specificity in defense response elicitation) on stomatal closure of maize leaves and on the volatile emission pattern whole maize plants. We also used salivary gland homogenate from wild-type and CRISPR-Cas9 Helicoverpa zea mutants deficient in GOX activity to determine the effect caterpillar saliva with and without GOX had on maize volatile emission. Collecting volatiles at 2-hour intervals allowed us to examine the changes in emission over time. Fungal GOX reduced the stomatal aperture in maize leaves, which may have influenced the observed significant reduction in total green leaf volatile (GLV) emission. Furthermore, fungal GOX significantly increased the emission of several key terpenes: linalool, DMNT, and Z-ß-farnesene from maize, while salivary gland homogenate from wild type (WT; GOX+) H. zea increased the emission of α-pinene, ß-pinene, and ocimene compared to H. zea unable to synthesize GOX. This study addressed a significant knowledge gap about the effect of GOX on maize volatiles and provides a baseline for further research on the effect of GOX on the regulation of terpene synthase genes and their relation to terpene volatile emission.

Extended investigation of field-evolved resistance of the corn earworm Helicoverpa zea(Lepidoptera: Noctuidae) to Bacillus thuringiensis Cry1A.105 and Cry2Ab2 proteins in thesoutheastern United States.

Previous studies have reported that the corn earworm/bollworm, Helicoverpa zea (Boddie), has developed field resistance to pyramided Bacillus thuringiensis (Bt) Cry1A/Cry2A maize and cotton in certain areas of the southeastern United States. The objective of the current study was to determine the current status and distribution of the resistance to Cry1A.105 and Cry2Ab2 in H. zea. In the study, 31 H. zea populations were collected from major maize planting areas across seven southeastern states of the United States during 2018 and 2019 and assayed against the two Bt proteins. Diet over-lay bioassays showed that most of the populations collected during the two years were significantly resistant to the Cry1A.105 protein. Most of the populations collected during 2019 were also resistant to Cry2Ab2, while significant variances were observed in the susceptibility of the populations collected during 2018 to Cry2Ab2. The results showed that Cry1A.105 and Cry2Ab2 resistance in H. zea is widely distributed in the regions sampled. The resistance to Cry1A.105 appeared to have plateaued, while selection for Cry2Ab2 resistance is likely still occurring. Thus, effective measures for mitigating the Cry1A/Cry2A resistance need to be developed and implemented to ensure the sustainable use of Bt crop biotechnology.

Fluorescent analyses of Bacillus thuringiensis Cry1Fa and Cry1Ab toxin binding sites on brush border membrane vesicles of Ostrinia nubilalis (Hübner), Diatraea grandiosella (Dyar), and Helicoverpa zea (Boddie) larvae.

Bacillus thuringiensis (Bt) Cry1Fa and Cry1Ab proteins are important Cry toxins due to their high, selective toxicity against a number of lepidopteran species, including important pests of corn and cotton. Competition binding assays are a classical tool for investigating Cry toxin interactions with target pest insects. We developed a fluorescence-based binding assay and assessed Cry1Fa and Cry1Ab toxin binding to brush border membrane preparations from lepidopteran corn pests including Ostrinia nubilalis (European corn borer, ECB), Diatraea grandiosella (south western corn borer, SWCB), and Helicoverpa zea (corn earworm, CEW). Homologous and heterologous competition binding assays with fluorophore-(Alexa488)-labeled Cry1Fa toxin showed that Cry1Fa shares binding site(s) with Cry1Ab toxin in ECB, and SWCB for which Cry1Ab has higher affinity than Cry1Fa. Apart from the shared binding sites, Cry1Ab and Cry1Fa bind an additional site(s) in ECB and SWCB. In CEW, Cry1Fa and Cry1Ab each, has a high affinity binding site(s), which binds the heterologous toxin with low affinity. The Cry1Ab-Cry1Fa toxin binding models for ECB, SWCB and CEW based on our results are considered in the context of what is known about acquired cross-resistance against Cry1Ab and Cry1Fa toxins.

Multiple Known Mechanisms and a Possible Role of an Enhanced Immune System in Bt-Resistance in a Field Population of the Bollworm, Helicoverpa zea: Differences in Gene Expression with RNAseq.

Several different agricultural insect pests have developed field resistance to Bt (Bacillus thuringiensis) proteins (ex. Cry1Ac, Cry1F, etc.) expressed in crops, including corn and cotton. In the bollworm, Helicoverpa zea, resistance levels are increasing; recent reports in 2019 show up to 1000-fold levels of resistance to Cry1Ac, a major insecticidal protein in Bt-crops. A common method to analyze global differences in gene expression is RNA-seq. This technique was used to measure differences in global gene expression between a Bt-susceptible and Bt-resistant strain of the bollworm, where the differences in susceptibility to Cry1Ac insecticidal proteins were 100-fold. We found expected gene expression differences based on our current understanding of the Bt mode of action, including increased expression of proteases (trypsins and serine proteases) and reduced expression of Bt-interacting receptors (aminopeptidases and cadherins) in resistant bollworms. We also found additional expression differences for transcripts that were not previously investigated, i.e., transcripts from three immune pathways-Jak/STAT, Toll, and IMD. Immune pathway receptors (ex. PGRPs) and the IMD pathway demonstrated the highest differences in expression. Our analysis suggested that multiple mechanisms are involved in the development of Bt-resistance, including potentially unrecognized pathways.

Differential heliothine susceptibility to Cry1Ac associated with gut proteolytic activity.

The Cry1Ac protein is the most active insecticidal toxin from the bacterium Bacillus thuringiensis (Bt) to members of the heliothinae subfamily in Lepidoptera, which includes some of the most devastating pests of corn and cotton worldwide. However, there are wide discrepancies in susceptibility among members of this subfamily in the US. Specifically, susceptibility to Cry1Ac in Helicoverpa zea (Hz) is >100-fold lower when compared to Heliothis virescens (Hv) larvae. The biochemical properties and Cry1Ac protoxin processing activity of gut digestive fluids from larvae of Hz and Hv were compared to test their role in differential susceptibility to Cry1Ac. Comparatively lower protease activity, associated with slower Cry1Ac proteolytic processing, was detected in digestive fluids of Hz compared to Hv. Moreover, Cry1Ac toxin processed by Hz digestive fluids displayed significantly lower toxicity in vitro against cultured insect cells compared to toxin activated by Hv proteases. These data support a contributing role for gut proteases in differential susceptibility to Cry1Ac in heliothine larvae.

Predator-prey interaction reveals local effects of high-altitude insect migration.

High-altitude nocturnal insect migrations are ubiquitous and represent significant pulses of biomass, which impact large areas and multiple trophic levels, yet are difficult to study and poorly understood. Predation on migratory insects by high-flying bats provides potential for investigating flows of migratory insects across a landscape. Brazilian free-tailed bats, Tadarida brasiliensis, provide valuable ecosystem services by consuming migratory pests, and research suggests migratory insects are an important resource to bats in autumn. We sequenced insect DNA from bat feces collected during the 2010-2012 autumn migrations of insects over southern Texas, and tested the utility of predator-prey interactions for monitoring migratory insect populations by asking: 1) how extensively do bats consume migratory insects during autumn? (2) does the prey community reflect known drivers of insect migrations, e.g. cold fronts? and (3) are migratory insects increasingly important to bats when local food resources decline in autumn? Bats consumed at least 21 species of migratory insects and 44 species of agricultural pests. Prey community richness increased with cold front passage. Bats consumed migratory moths over the entire autumn season, and the proportion of migratory moths in the bat diet increased over the course of the autumn season in all 3 years. This study confirms extensive consumption of migratory insects by bats, links patterns in prey communities to mechanisms driving insect migration, and documents a novel approach to tracking patterns of migratory insect movement. As an important resource for T. brasiliensis in autumn, migratory insects provide stabilizing effects to the local animal community.

Herbivore-Induced Defenses in Tomato Plants Enhance the Lethality of the Entomopathogenic Bacterium, Bacillus thuringiensis var. kurstaki.

Plants can influence the effectiveness of microbial insecticides through numerous mechanisms. One of these mechanisms is the oxidation of plant phenolics by plant enzymes, such as polyphenol oxidases (PPO) and peroxidases (POD). These reactions generate a variety of products and intermediates that play important roles in resistance against herbivores. Oxidation of the catecholic phenolic compound chlorogenic acid by PPO enhances the lethality of the insect-killing bacterial pathogen, Bacillus thuringiensis var. kurstaki (Bt) to the polyphagous caterpillar, Helicoverpa zea. Since herbivore feeding damage often triggers the induction of higher activities of oxidative enzymes in plant tissues, here we hypothesized that the induction of plant defenses would enhance the lethality of Bt on those plants. We found that the lethality of a commercial formulation of Bt (Dipel® PRO DF) on tomato plants was higher if it was applied to plants that were induced by H. zea feeding or induced by the phytohormone jasmonic acid. Higher proportions of H. zea larvae killed by Bt were strongly correlated with higher levels of PPO activity in the leaflet tissue. Higher POD activity was only weakly associated with higher levels of Bt-induced mortality. While plant-mediated variation in entomopathogen lethality is well known, our findings demonstrate that plants can induce defensive responses that work in concert with a microbial insecticide/entomopathogen to protect against insect herbivores.

Evaluation of some potential target genes and methods for RNAi-mediated pest control of the corn earworm Helicoverpa zea.

In this study, we explored the efficacy of knockdown four genes required for proper nervous system function by RNAi, in the corn earworm Helicoverpa zea (Boddie). Three of these genes encode components of validated insecticide target sites. We synthesized cDNA sequences orthologous to the Drosophila melanogaster genes Para (paralyticts), TipE (temperature-induced paralysis locus E), GluCl (glutamate-gated chloride channel), and Notch, and used these fragments to synthesize double-stranded RNAs (dsRNAs). We then performed experiments in an attempt to induce RNAi-mediated effects on gene expression and viability using three modes of delivery of the dsRNAs: microinjection of eggs, soaking of eggs and feeding of larvae. Microinjection of dsRNAs into eggs induced reduced hatch rates and knockdown of target gene expression for GluCl, para and TipE, but not for Notch. However, neither feeding nor soaking eggs in dsRNA solutions resulted in discernable RNAi effects. These results demonstrated the susceptibility to RNAi effects of the expression of H. zea genes encoding insecticide target sites, which suggests future avenues of research toward practical applications.

Helicoverpa zea gut-associated bacteria indirectly induce defenses in tomato by triggering a salivary elicitor(s).

Insect gut-associated microbes modulating plant defenses have been observed in beetles and piercing-sucking insects, but the role of caterpillar-associated bacteria in regulating plant induced defenses has not been adequately examined. We identified bacteria from the regurgitant of field-collected Helicoverpa zea larvae using 16S ribosomal RNA (rRNA) gene sequencing and matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry. A combination of biochemical, molecular, and confocal electron microscopy methods were used to determine the role of caterpillar-associated bacteria in mediating defenses in Solanum lycopersicum (tomato). Laboratory-reared H. zea inoculated with one of the bacteria identified in field-collected H. zea, Enterobacter ludwigii, induced expression of the tomato defense-related enzyme polyphenol oxidase and genes regulated by jasmonic acid (JA), whereas the salicylic acid (SA)-responsive pathogenesis-related gene was suppressed. Additionally, saliva and its main component glucose oxidase from inoculated caterpillars played an important role in elevating tomato anti-herbivore defenses. However, there were only low detectable amounts of regurgitant or bacteria on H. zea-damaged tomato leaves. Our results suggest that H. zea gut-associated bacteria indirectly mediate plant-insect interactions by triggering salivary elicitors. These findings provide a proof of concept that introducing gut bacteria to a herbivore may provide a novel approach to pest management through indirect induction of plant resistance.

Multifaceted effects of host plants on entomopathogenic nematodes.

The success of parasites can be impacted by multi-trophic interactions. Tritrophic interactions have been observed in parasite-herbivore-host plant systems. Here we investigate aspects of multi-trophic interactions in a system involving an entomopathogenic nematode (EPN), its insect host, and host plant. Novel issues investigated include the impact of tritrophic interactions on nematode foraging behavior, the ability of EPNs to overcome negative tritrophic effects through genetic selection, and interactions with a fourth trophic level (nematode predators). We tested infectivity of the nematode, Steinernema riobrave, to corn earworm larvae (Helicoverpa zea) in three host plants, tobacco, eggplant and tomato. Tobacco reduced nematode virulence and reproduction relative to tomato and eggplant. However, successive selection (5 passages) overcame the deficiency; selected nematodes no longer exhibited reductions in phenotypic traits. Despite the loss in virulence and reproduction nematodes, first passage S. riobrave was more attracted to frass from insects fed tobacco than insects fed on other host plants. Therefore, we hypothesized the reduced virulence and reproduction in S. riobrave infecting tobacco fed insects would be based on a self-medicating tradeoff, such as deterring predation. We tested this hypothesis by assessing predatory success of the mite Sancassania polyphyllae and the springtail Sinella curviseta on nematodes reared on tobacco-fed larvae versus those fed on greater wax moth, Galleria mellonella, tomato fed larvae, or eggplant fed larvae. No advantage was observed in nematodes derived from tobacco fed larvae. In conclusion, our results indicated that insect-host plant diet has an important effect on nematode foraging, infectivity and reproduction. However, negative host plant effects, might be overcome through directed selection. We propose that host plant species should be considered when designing biocontrol programs using EPNs.

The Impact of Inter-Kernel Movement in the Evolution of Resistance to Dual-Toxin Bt-Corn Varieties in Helicoverpa zea (Lepidoptera: Noctuidae).

Seeds or kernels on hybrid plants are primarily F(2) tissue and will segregate for heterozygous alleles present in the parental F(1) hybrids. In the case of plants expressing Bt-toxins, the F(2) tissue in the kernels will express toxins as they would segregate in any F(2) tissue. In the case of plants expressing two unlinked toxins, the kernels on a Bt plant fertilized by another Bt plant would express anywhere from 0 to 2 toxins. Larvae of corn earworm [Helicoverpa zea (Boddie)] feed on a number of kernels during development and would therefore be exposed to local habitats (kernels) that varied in their toxin expression. Three models were developed for plants expressing two Bt-toxins, one where the traits are unlinked, a second where the traits were linked and a third model assuming that maternal traits were expressed in all kernels as well as paternally inherited traits. Results suggest that increasing larval movement rates off of expressing kernels tended to increase durability while increasing movement rates off of nonexpressing kernels always decreased durability. An ideal block refuge (no pollen flow between blocks and refuges) was more durable than a seed blend because the refuge expressed no toxins, while pollen contamination from plants expressing toxins in a seed blend reduced durability. A linked-trait model in an ideal refuge model predicted the longest durability. The results suggest that using a seed-blend strategy for a kernel feeding insect on a hybrid crop could dramatically reduce durability through the loss of refuge due to extensive cross-pollination.

Survival of Corn Earworm (Lepidoptera: Noctuidae) on Bt Maize and Cross-Pollinated Refuge Ears From Seed Blends.

Refuge is mandated in the United States where genetically modified maize (Zea mays L.) expressing insecticidal proteins derived from Bacillus thuringiensis Berliner (Bt) are cultivated. Currently, refuge is deployed in different ways including blocks, field strips, or seed blends containing Bt and non-Bt maize. Seed blends provide practical advantages for refuge implementation. However, concerns related to the movement of insect larvae, potential differential survival of heterozygous resistant larvae, reduction in insect production, and cross-pollination of ears resulting in sublethal selection, have delayed seed blend use for Lepidoptera in the southern United States, where maize plantings are used as refuge for Helicoverpa zea (Boddie). In this study, we evaluated the relative survival of H. zea in Bt events and in seed blends compared with pure stand refuge and the relative survival of H. zea on the individual components of the pyramid 1507xMON810xMIR162. The results showed variation on the production of H. zea in refuge plants from seed blends compared with pure stand refuge plants. The relative survival of H. zea on the events 1507, MON810, MIR162, and 1507xMON810xMIR162 ranked similarly across the three locations tested. These results can be used in computer simulation modeling efforts to evaluate the feasibility of seed blends as a refuge deployment strategy with the pyramid 1507xMON810xMIR162. Because the reduction on survival of H. zea due to blending was variable, a sensitivity analysis that includes all possible scenarios of reduction in survival should be considered.

Weather-driven dynamics in a dual-migrant system: moths and bats.

Animal migrations generate large spatial and temporal fluctuations in biomass that provide a resource base for many predator-prey interactions. These interactions are often driven by continent-scale weather patterns and are difficult to study. Few studies have included migratory animals on more than a single trophic level or for periods spanning multiple entire seasons. We tracked migrations of three species of agricultural pest noctuid moths over the 2010-2012 autumn seasons as the moths travelled past a large colony of migratory Brazilian free-tailed bats (Tadarida brasiliensis) in Texas. Increases in moth abundance, mass of bats and duration of bat activity outside of the cave were correlated with passage of cold fronts over the study area and related increases in northerly wind. Moth responses to weather patterns varied among species and seasons, but overall moth abundances were low in late summer and spiked after one or more cold front passages in September and October. Changes in bat mass and behaviour appear to be consequences of bat migration, as cave use transitioned from summer maternity roost to autumn migratory stopover sites. Weather-driven migration is at considerable risk from climate change, and bat and moth responses to that change may have marked impacts on agricultural systems and bat ecosystem services.

The Impact of Simulated Corn Earworm (Lepidoptera: Noctuidae) Damage in Indeterminate Soybean.

Field experiments were conducted in Starkville and Stoneville, MS, during 2012 and 2013 to evaluate fruit removal level and timing on soybean growth, crop maturity, and yield. Fruit removal treatments consisted of 0, 50, and 100% of all fruit removed at specified growth stages (R2, R3, R4, and R5.5). Plant heights were determined at least biweekly from the time damage was imposed until R7. The impact of fruit removal level and timing on crop maturity was determined by estimating the percentage of naturally abscised leaves at 137 days after planting (DAP) when control plots were ∼10-15 d from harvest and the percentage of nonsenesced main stems at 139 DAP. There was no significant impact of fruit removal timing or fruit removal level on plant height or canopy width. Significant delays in crop maturity were observed when fruit removal was imposed at the R5.5 growth stage. Significant reductions in yield and crop value were observed as early as R3 and R4 when 100% of fruit was removed. Both fruit removal levels at R5.5 resulted in a significant reduction in yield and crop value compared with the nontreated control. Indeterminate soybeans appear to have the ability to compensate for some fruit loss during the early to middle reproductive growth stages without delaying maturity. However, severe fruit loss causes increasingly more yield loss as the plant approached maturity. Thresholds and economic injury levels therefore need to be adjusted accordingly to account for the dynamic nature of yield losses and crop maturity delays.