Interactions between corn earworm, Helicoverpa zea (Boddie), and soybean, Glycine max L. (Merrill), were investigated in the Mid-South to evaluate thresholds and damage levels. Field studies were conducted in both indeterminate and determinate modern cultivars to evaluate damage, critical injury levels, and soybean response to simulated corn earworm injury. Field studies were also conducted to evaluate the response of indeterminate cultivars to infestations of corn earworm. Field studies were also conducted to investigate the relationship between pyrethroid insecticide application and corn earworm oviposition in soybean. Results of field studies involving simulated corn earworm damage indicated the need for a dynamic threshold that becomes more conservative as soybean phenology progressed through the reproductive growth stages. This suggested that soybean was more tolerant to fruit loss during the earlier reproductive stages and was able to compensate for fruit loss better during this time than at later growth stages. Results of field studies involving infestations of corn earworm indicated that current thresholds are likely too liberal. This resulted in economic injury level tables being constructed based upon a range of crop values and control costs, however, a general action threshold was also recommended for indeterminate soybean in the Mid-South. Field study results investigating the relationship of pyrethroid application and corn earworm oviposition indicated that even in the presence of an insecticide, corn earworm prefers to oviposit in the upper portion of the canopy, as well as on the leaves as opposed to all other plant parts, consistent with all previous literature.

The introduction of pyramided Bacillus thuringinesiss (Bt) in field corn, Zea mays L. has helped reduce kernel and foliar damage from caterpillar pests including fall armyworm, Spodoptera frugiperda (J.E. Smith) and corn earworm, Helicoverpa zea (Boddie). These pests can also be controlled with diamide insecticides. No compensation for manual kernel damage occurred at any section of the ear for Bt or Non-Bt corn. No consistent impacts on corn growth or yield were observed following foliar applications of diamide insecticides at various growth stages. The diamides exhibit longer residual efficacy than other insecticides available for fall armyworm management in field corn. Based on the level of mortality observed on young tissue developed after treatment with chlorantraniliprole, chlorantraniliprole translocated in corn and could therefore be more beneficial than other insecticides when applied during vegetative growth stages.

Soybean looper and corn earworm are economically damaging pests in Mississippi soybeans. Chemical control plays a large role in the control of these pests. Some producers have started applying an automatic co-application of insecticide and fungicide at the R3 growth stage. Insect growth regulators are a commonly used insecticide for this management strategy. The purpose of this research was to evaluate the impact of insect growth regulators on soybean looper and corn earworm mortality when applied with an automatic fungicide application at the R3 growth stage in soybean. Insecticide treatments included methoxyfenozide, diflubenzuron, and novaluron. These insect growth regulators showed very little control and mortality, especially when compared to chlorantraniliprole, which has become an industry standard for control of lepidopteran pest control of in soybean. The automatic application of an insect growth regulator insecticide with a fungicide at the R3 growth was not viable for economic insect management strategies.

Helicoverpa zea is one of the most costly insect pests of food and fiber crops throughout the Americas. Pyrethroid insecticides are widely applied for control as they are effective and relatively inexpensive; however, resistance threatens sustainability because alternative insecticides are often more expensive or less effective. Pyrethroid resistance has been identified since 1990 and monitoring has utilized cypermethrin in the adult vial test, but resistance mechanisms have not yet been elucidated at the molecular level. Here we examined field-collected H. zea males resistant to cypermethrin for target site and metabolic resistance mechanisms. We report the cDNA sequence of the H. zea sodium channel a-subunit homologous to the Drosophila para gene and identified known resistance-conferring mutations L1029H and V421M, along with two novel mutations at the V421 residue, V421A and V421G. An additional mutation, I951V, may be the first example of a pyrethroid resistance mutation caused by RNA-editing. We identified other specimens with significantly higher transcriptional expression levels of cytochrome P450 genes CYP6B8 and CYP6B9 compared to the susceptible, ranging from a factor of 3.7 to 34.9 and 5.6 to 39.6, respectively. In addition, we investigated if differences in insect growth stage and pyrethroid structure affect our ability to predict resistance in the adult vial test. Vial bioassays with cypermethrin, esfenvalerate, and bifenthrin were conducted on third instars and male moths from a susceptible laboratory colony and the F1 generation of a resistant field population. For the resistant population, vial assays using either growth stage gave similar resistance ratios for each of the three pyrethroids, respectively, proving the adult vial test accurately reflects larval resistance. However, resistance ratios varied considerably depending on the pyrethroid used, so values obtained with one pyrethroid may not be predictive of another. This dissertation is the first to identify molecular mechanisms associated with H. zea pyrethroid resistance. Our results suggest carefully chosen pyrethroid structures diagnostic for specific resistance mechanisms could improve regional monitoring programs and development of high throughput assays to detect the resistance mechanisms used in tandem with traditional monitoring may greatly improve our ability to identify and predict resistance and make better control recommendations.

Insecticides in the diamide class have a novel mode of action and have become a key component for management of agriculturally important lepidopteran pests since their introduction in 2008. Corn earworm, Helicoverpa zea (Boddie); and the armyworm complex including fall armyworm, Spodoptera frugiperda (J.E. Smith); and Spodoptera exigua (Hübner); are significant pests of agroecosystems in the Mid-southern and Southeastern regions of the United States. They have developed resistance to, and/or inconsistent control has occurred with most chemical classes. The objectives of this study were to establish susceptibility levels of field populations of H. zea, S. frugiperda, and S. exigua collected in the Mid-southern and Southeastern regions of the United States to flubendiamide and chlorantraniliprole. To achieve equivalent levels of mortality for each species, a higher concentration of flubendiamide was required compared to chlorantraniliprole. Furthermore, two experiments were conducted to determine the systemic and residual efficacy of chlorantraniliprole and flubendiamide against H. zea on vegetative and reproductive structures of soybean. Chlorantraniliprole moved systemically and had significantly greater control than flubendiamide in the systemic and residual study out to 31 DAT. Flubendiamide did not move systemically but provided significant residual control out to 31 DAT compared with the untreated control. Neither insecticide was detected in reproductive structures. Finally, to determine the risk of resistance development, a S. exigua colony, originating from a field collection in 2013, was separated into three cohorts that were independently selected with three concentrations (0.016, 0.020, and 0.025 ppm) of flubendiamide incorporated into a meridic diet. These concentrations were chosen from the LC30, LC60 and LC90 of the original colony. Resistance ratios never increased past 2.11old. The highest resistance ratios occurred after 18 generations for the LC30 colony, 19 generations for the LC60 colony, and 13 and 15 generations for the LC90 colony. After reaching their highest point of resistance, the colonies began to decline in egg production and larval survivability and did not recover. After 22 generations the selected colonies were terminated. The results from this portion of the study suggest that the potential for resistance development of beet armyworm to flubendiamide is unclear.

Helicoverpa zea, commonly referred to as corn earworm, has been a major pest of corn and cotton, along with many major crops grown in United States. Migration of this pest plays a major role in its distribution and successful survival. Part of the current resistance management strategy for transgenic crops, using non-Bt crops as refuges, is totally based on the movement of the adult populations between the Bt and non-Bt fields, and successful exchange of genetic material between the rare resistant and susceptible populations. To study the movement and migration patterns, and their implications in resistance management, suitable molecular genetic markers were comparatively selected, followed by a study of temporal variations in populations from north Mississippi. The dominant marker system Inter Simple Sequence Repeats (ISSR) was selected for the study based on higher polymorphism (5.0) and PIC (0.34) values compared to Simple Sequence Repeats (SSR) and Sequence Related Amplification Polymorphism (SRAP) marker systems. 53 ISSR loci were used in understanding the temporal variations in H. zea. Percent polymorphism and heterozygosity levels showed variation among the twelve collections tested. Early spring putative migrants were distinct from the rest of the generations. Population differentiation was higher in the beginning of the season and then declined by end of the season (pairwise FST = 0.341, early in March and 0.025, late in August). Average heterozygosity levels recorded were 0.11, coinciding with 1993 and 2002 data. The result of this study supports the existence of spring migration of adults and their contribution to the local gene pool. The extent of genetic exchange between the putative migrants and the local populations varied among three years. There is variation in population densities from migrants and local emergence in one of the three years. The results of this study indicate a need for continuous monitoring for genetic changes and their possible implications for resistance management in transgenic crops in Mississippi.

No description available.

Edamame (Glycine max (L.) Merr.), also known as vegetable soybean, is primarily grown and consumed in Asia. In recent years, the demand for edamame in the United States has risen due to its health benefits as an alternative, plant-based protein. Due to the lack of domestic production, most edamame is imported from Asia. In an attempt to increase domestic production, research efforts have begun in Virginia and other regions to develop cultivars and best management practices for growing edamame in the mid-Atlantic region. Beginning in 2018, edamame trials examining breeding lines and cultivars were conducted to look at their suitability for this region. These varieties were sampled and evaluated for insect and disease complexes as well as their implications on plant yield and quality. Most of the insects and diseases that were found were very similar to pest complexes commonly found in cultivated soybeans in Virginia. However, due to edamame being marketed as a vegetable, insects and diseases that caused unsightly blemishes or damage to the pods or seeds were most concerning. Multiple insects and diseases were present but some of the most important insects and diseases we observed from 2018-2020 were pod feeding stink bug (Hemiptera: Pentatomidae), as well as the diseases like purple seed stain, Cercospora kikuchii, and bacterial pustule, Xanthomonas axonopodis pv. glycines. From 2019-2021 an integrated pest management study was conducted to determine best management practices for minimizing insecticide applications while applying them at thresholds to control key pests. In three growing seasons, I was able to determine that pesticides can be limited prior to flowering while insecticide inputs will need to be increased after flowering to protect the pods from pests, specifically stink bugs. Additionally, from 2019-2021 insecticide and fungicide field trials were conducted to test different pesticides on their efficacy against pod damaging pests and diseases. The growing seasons between 2019 and 2021 resulted in varying insect and disease pressure that led to inconsistent results. However, insecticides such as cyclaniliprole and sulfoxaflor performed well compared to other treatments. Lastly in 2020-2021, corn earworm (Helicoverpa zea [Boddie], Lepidoptera: Noctuidae), an important soybean pest and most likely a major pest of edamame, was tested for pyrethroid susceptibility and resistance across the state using a bean-dip bioassay. Pyrethroid efficacy to control this pest across Virginia seemed to vary by location and year, however, the bean-dip bioassay proved to be a time-efficient strategy for further monitoring these populations in the coming years. / Doctor of Philosophy / Edamame, also known as vegetable soybean, is primarily grown and consumed in Asia. Due to the lack of domestic production, most edamame is imported from overseas. Edamame trials were conducted in Virginia beginning in 2018, to look at production practices suitable for growing this crop in the region. Scientists observed edamame to document insect and disease complexes as well as their implications on yield and quality. Most of the insects and diseases that were found were very similar to what is known to already occur in soybeans. However, due to edamame being marketed as a vegetable, insects and diseases that left blemishes or damage to the pod were most concerning. Multiple insects and disease were present but some of the most important insects and diseases we observed were pod feeding stink bug species as well as the diseases purple seed stain and bacterial pustule. In 2019-2021 a pest management study was conducted to determine best management practices for minimizing insecticide applications while applying them at thresholds to control key pests. We were able to determine that pesticide usage can be limited prior to flowering while they will need to be increased after flowering to protect the pods. Additionally, in 2019-2021 insecticide and fungicide field trials were conducted to determine the efficacy of materials against pod damaging pests and diseases. The growing seasons between 2019 and 2021 resulted in varying insect and disease pressure, however, several insecticides with reduced ecological impacts out preformed others. Lastly in 2020-2021, corn earworm, a major pest of soybean and presumable of edamame, was tested for pyrethroid susceptibility and resistance across the state using a bean-dip bioassay. Pyrethroid efficacy across Virginia seemed to vary by location and year but the bean dip bioassay method proved to be a time-effective strategy for monitoring the states corn earworm populations against insecticides.

Made available in DSpace on 2016-12-23T14:37:27Z (GMT). No. of bitstreams: 1 Thiago Gechel Kloss.pdf: 874754 bytes, checksum: ef2f39dcbc8d4a2efd94b7fd9f513851 (MD5) Previous issue date: 2011-09-02 / Among the biological control agents, Bacillus thuringiensis Berliner (1911) stands out the most and the egg parasitoid of Trichogramma Westwood (1833). Diverse factors can interfere with the effectiveness of these agents and investigations are necessary to succeed in the utilization of these agents isolated or together. In this case, the objective of this study was to select the populations of Trichogramma and the isolated or formulated of B. thuringiensis the most adequate for the management of populations of Helicoverpa zea (BODDIE, 1850) and to evaluate the influence of variation in the populations of H. zea in these agents. Moreover, the effects of interaction between them in host populations were also evaluated. In the evaluation of the Trichogramma agents, ten females population, individually received a piece of cardboard containing eggs with a determined population of H. zea. The characteristics analyzed were parasitism (%), emergence of individuals (%), sex ratio and number of adults per host egg. In the analysis of B. thuringiensis, 34 isolates and the formulated commercial Agree® and Dipel® were used and also inoculated on a diet, in a concentration 3 x 108 spores mL-1. Furthermore, lethal concentration of the isolates and more virulent formulates were estimated. In the assessment of the interaction between these agents, the cardboard with the eggs of population of H. zea were sprayed with different isolates and formulated B. thuringiensis and were offered the females of population of Trichogramma. The characteristics evaluated where the same previously described for the populations of Trichogramma, except the female longevity. The biological control agents Trichogramma and B. thuringiensis showed adequate for the management of the populations of H. zea. In addition, the use of the agents together generated few negative effects and in some cases even strengthened the parasites of Trichogramma sp., showing the use of them together which can increase the efficiency of the control of populations of H. zea. Alterations caused by the difference population of the biological characteristics of Trichogramma and in the levels of virulence of the isolates and formulated of B. thuringiensis were registered, but these variations weren t sufficient to generate undesirable levels of these characteristics in the management of the insect populations / Entre os agentes de controle biológico destacam-se a bactéria Bacillus thuringiensis Berliner (1911) e o parasitoide de ovos Trichogramma Westwood (1833). Diversos fatores podem interferir na eficiência desses agentes e investigações são necessárias para se obter sucesso na utilização deles de forma isolada ou em conjunto. Sendo assim, o objetivo deste estudo foi selecionar as populações de Trichogramma e os isolados ou formulados de B. thuringiensis mais adequados para o manejo de populações de Helicoverpa zea (BODDIE, 1850) e avaliar a influência da variação populacional de H. zea nesses agentes. Além disso, foram avaliados os efeitos da interação entre eles nas populações hospedeiras. Na avaliação do agente Trichogramma, fêmeas de dez populações receberam individualmente cartelas contendo ovos de uma determinada população de H. zea. As características analisadas foram parasitismo (%), emergência dos indivíduos (%), razão sexual e número de adultos por ovo do hospedeiro. Na análise de B. thuringiensis, foram utilizados 34 isolados e os formulados comerciais Dipel® e Agree®, que foram inoculados sobre a dieta, na concentração 3 x 108 esporos mL-1. Além disso, foi realizada a estimativa da concentração letal (CL50) para os isolados e formulados mais virulentos. Na avaliação da interação entre os agentes, cartelas com ovos das populações de H. zea foram pulverizados com diferentes isolados e formulados de B. thuringiensis e oferecidas para fêmeas de uma população de Trichogramma. As características avaliadas foram as mesmas descritas acima para as populações de Trichogramma, com exceção da longevidade das fêmeas. Os agentes de controle biológico Trichogramma e B. thuringiensis se mostraram adequados para o manejo de populações de H. zea. Além disso, o uso conjunto desses agentes gerou poucos efeitos negativos e em alguns casos até potencializou o parasitismo de Trichogramma sp., evidenciando que o uso deles em conjunto pode aumentar a eficiência de controle das populações de H. zea. Alterações ocasionadas pela diferença populacional nas características biológicas de Trichogramma e nos níveis de virulência dos isolados e formulados de B. thuringiensis foram registradas, porém essas variações não foram suficientes para gerar níveis indesejáveis dessas características no manejo das populações de insetos

Field corn, Zea mays L., has been introduced to the market with pyramided Bacillus thuringiensis (Bt) corn technologies. These technologies reduce kernel damage from ear feeding caterpillar pests, including corn earworm, Helicoverpa zea (Boddie). The first generation Bt traits in field corn demonstrated limited activity on corn earworm feeding on grain in ears. The pyramided corn technologies have greater cumulative protein concentrations and improved expression throughout the plant, so these corn traits should provide an effective management tool against these pests. In addition, reduced kernel injury may also have a direct effect on physical grain quality. The results for this trial showed no relationship between number of damaged kernels and yield was observed for corn hybrid expressing the Herculex®, YieldGard®, or Genuity VT Triple Pro® technologies. A significant relationship between both damaged kernels and test weight and damaged kernels and aflatoxin concentrations was observed in two technologies.