Pest population dynamics are related to a continental overwintering gradient.

Overwintering success is an important determinant of arthropod populations that must be considered as climate change continues to influence the spatiotemporal population dynamics of agricultural pests. Using a long-term monitoring database and biologically relevant overwintering zones, we modeled the annual and seasonal population dynamics of a common pest, Helicoverpa zea (Boddie), based on three overwintering suitability zones throughout North America using four decades of soil temperatures: the southern range (able to persist through winter), transitional zone (uncertain overwintering survivorship), and northern limits (unable to survive winter). Our model indicates H. zea population dynamics are hierarchically structured with continental-level effects that are partitioned into three geographic zones. Seasonal populations were initially detected in the southern range, where they experienced multiple large population peaks. All three zones experienced a final peak between late July (southern range) and mid-August to mid-September (transitional zone and northern limits). The southern range expanded by 3% since 1981 and is projected to increase by twofold by 2099 but the areas of other zones are expected to decrease in the future. These changes suggest larger populations may persist at higher latitudes in the future due to reduced low-temperature lethal events during winter. Because H. zea is a highly migratory pest, predicting when populations accumulate in one region can inform synchronous or lagged population development in other regions. We show the value of combining long-term datasets, remotely sensed data, and laboratory findings to inform forecasting of insect pests.

A Multimodal Sensing Platform for Interdisciplinary Research in Agrarian Environments.

Agricultural and environmental monitoring programs often require labor-intensive inputs and substantial costs to manually gather data from remote field locations. Recent advances in the Internet of Things enable the construction of wireless sensor systems to automate these remote monitoring efforts. This paper presents the design of a modular system to serve as a research platform for outdoor sensor development and deployment. The advantages of this system include low power consumption (enabling solar charging), the use of commercially available electronic parts for lower-cost and scaled up deployments, and the flexibility to include internal electronics and external sensors, allowing novel applications. In addition to tracking environmental parameters, the modularity of this system brings the capability to measure other non-traditional elements. This capability is demonstrated with two different agri- and aquacultural field applications: tracking moth phenology and monitoring bivalve gaping. Collection of these signals in conjunction with environmental parameters could provide a holistic and context-aware data analysis. Preliminary experiments generated promising results, demonstrating the reliability of the system. Idle power consumption of 27.2 mW and 16.6 mW for the moth- and bivalve-tracking systems, respectively, coupled with 2.5 W solar cells allows for indefinite deployment in remote locations.

Field-evolved resistance of Helicoverpa zea (Boddie) to transgenic maize expressing pyramided Cry1A.105/Cry2Ab2 proteins in northeast Louisiana, the United States.

The corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), is a major target pest of pyramided Bt maize and cotton in the U.S. In 2017 and 2018, notable ear damage and larval survival of H. zea were observed on pyramided Cry1A.105/Cry2Ab2 maize in some fields in northeast Louisiana, U.S. The objective of this study was to determine if the field control problem was due to resistance development to the Bt proteins in plants. A total of 15 H. zea populations were collected from Bt and non-Bt maize plants in 2017 and 2018 in multiple locations in Louisiana, Florida, and Georgia. Diet-overlay bioassays showed that LC50s of Cry1A.105 and Cry2Ab2 for populations collected from the areas with control problems in northeast Louisiana were as much as >1623- and 88-fold greater than that of a susceptible strain, respectively. In addition, two field trials in 2018 validated that Cry1A.105/Cry2Ab2 maize failed in managing natural H. zea populations, while Bt maize containing Vip3A was effective in northeast Louisiana. Results of the study documented that the observed field control problems of Cry1A.105/Cry2Ab2 maize against H. zea in northeast Louisiana were due to resistance development of the insect to the Bt proteins in plants. This is the first documentation of field-evolved resistance to pyramided Bt maize in a target insect species in southern U.S. However, susceptibility levels to Cry1A.105 and Cry2Ab2 varied greatly among populations collected from the three states, suggesting uneven distributions of the resistance in the region.

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.

Further Description of Helicoverpa zea (Lepidoptera: Noctuidae) Male Genitalia and New Genetic Evidence of Synonymy With Respect to the Anomalous Form, "Heliothis stombleri".

The Helicoverpa/Heliothis complex can cause serious damage to agricultural crops. Phenotypic similarity makes it difficult to discriminate between closely related Helicoverpa species. Currently, morphology of the male genitalia complemented with molecular techniques constitutes the best approach for species identification. In this work, a broad microscopic examination of adult Helicoverpa zea (Boddie) males (n = 200) captured in central Argentina was carried out in order to provide a detailed description of the valvae and the phallus. A considerable degree of variability was recorded. Both rounded and sharp valve apices were observed and valvae were not always parallel-sided. Most evident differences were detected concerning the number of cornuti on the phallus. A range of 15-21 cornuti per phallus was recorded, the mode being 18. A significant minority of the samples (3.5%) displayed an abnormal genital condition showing a constricted phallus lacking cornuti, and pointed valvae. This form was initially attributed to a distinct species, Heliothis stombleri, and later proposed as a synonym of H. zea based on additional morphological observations and molecular studies. Here, a phylogenetic analysis combining mitochondrial (cytochrome oxidase subunit I) and nuclear (elongation factor -1 alpha) genes was performed on these and other Helicoverpa specimens collected in the same geographical region, in order to further verify the taxonomic status of H. stombleri. The tree topology clearly grouped H. stombleri with H. zea, supporting the assumption that the former represents, in fact, an anomalous form of the latter. Further experiments are needed to clarify the etiology of this anomaly and its persistence over time.

Intraear Compensation of Field Corn, Zea mays, from Simulated and Naturally Occurring Injury by Ear-Feeding Larvae.

Ear-feeding larvae, such as corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae), can be important insect pests of field corn, Zea mays L., by feeding on kernels. Recently introduced, stacked Bacillus thuringiensis (Bt) traits provide improved protection from ear-feeding larvae. Thus, our objective was to evaluate how injury to kernels in the ear tip might affect yield when this injury was inflicted at the blister and milk stages. In 2010, simulated corn earworm injury reduced total kernel weight (i.e., yield) at both the blister and milk stage. In 2011, injury to ear tips at the milk stage affected total kernel weight. No differences in total kernel weight were found in 2013, regardless of when or how much injury was inflicted. Our data suggested that kernels within the same ear could compensate for injury to ear tips by increasing in size, but this increase was not always statistically significant or sufficient to overcome high levels of kernel injury. For naturally occurring injury observed on multiple corn hybrids during 2011 and 2012, our analyses showed either no or a minimal relationship between number of kernels injured by ear-feeding larvae and the total number of kernels per ear, total kernel weight, or the size of individual kernels. The results indicate that intraear compensation for kernel injury to ear tips can occur under at least some conditions.

Efficacy of Silk Channel Injections with Insecticides for Management of Lepidoptera Pests of Sweet Corn.

The primary Lepidoptera pests of sweet corn (Zea mays L. convar. saccharata) in Georgia are the corn earworm, Helicoverpa zea (Boddie), and the fall armyworm, Spodoptera frugiperda (J. E. Smith). Management of these pests typically requires multiple insecticide applications from first silking until harvest, with commercial growers frequently spraying daily. This level of insecticide use presents problems for small growers, particularly for "pick-your-own" operations. Injection of oil into the corn ear silk channel 5-8 days after silking initiation has been used to suppress damage by these insects. Initial work with this technique in Georgia provided poor results. Subsequently, a series of experiments was conducted to evaluate the efficacy of silk channel injections as an application methodology for insecticides. A single application of synthetic insecticide, at greatly reduced per acre rates compared with common foliar applications, provided excellent control of Lepidoptera insects attacking the ear tip and suppressed damage by sap beetles (Nitidulidae). While this methodology is labor-intensive, it requires a single application of insecticide at reduced rates applied ∼2 wk prior to harvest, compared with potential daily applications at full rates up to the day of harvest with foliar insecticide applications. This methodology is not likely to eliminate the need for foliar applications because of other insect pests which do not enter through the silk channel or are not affected by the specific selective insecticide used in the silk channel injection, but would greatly reduce the number of applications required. This methodology may prove particularly useful for small acreage growers.

Bt Maize Seed Mixtures for Helicoverpa zea (Lepidoptera: Noctuidae): Larval Movement, Development, and Survival on Non-transgenic Maize.

In 2012 and 2013, field trials were conducted near Rosemount, MN, to assess the movement and development of Helicoverpa zea (Boddie) larvae on non-Bt refuge corn plants within a seed mixture of non-Bt and Bt corn. The Bt corn hybrid expressed three Bt toxins-Cry1Ab, Cry1F, and Vip3A. As the use of seed mixtures for insect resistance management (IRM) continues to be implemented, it is necessary to further characterize how this IRM approach impacts resistance development in ear-feeding Lepidopteran pests. The potential for Bt pollen movement and cross pollination of the non-Bt ears in a seed mixture may lead to Bt toxin exposure to larvae developing on those refuge ears. Larval movement and development by H. zea, feeding on non-Bt refuge plants adjacent to either transgenic Bt or non-Bt plants, were measured to investigate the potential for unintended Bt exposure. Non-Bt plants were infested with H. zea eggs and subplots were destructively sampled twice per week within each treatment to assess larval development, location, and kernel injury. Results indicate that H. zea larval movement between plants is relatively low, ranging from 2-16% of larvae, and occurs mainly after reaching the second instar. Refuge plants in seed mixtures did not produce equivalent numbers of H. zea larvae, kernel injury, and larval development differed as compared with a pure stand of non-Bt plants. This suggests that there may be costs to larvae developing on refuge plants within seed mixtures and additional studies are warranted to define potential impacts.

Insect Damage, Aflatoxin Content, and Yield of Bt Corn in Alabama.

Isoline pairs of hybrid corn, similar except for presence or absence of a Bt trait, were planted at eight sites across Alabama over three years. This study evaluated insect damage, yield, and aflatoxin levels as affected by the Bt traits, YieldGard Corn Borer (expressing Cry1Ab), Herculex I (expressing Cry1F), Genuity VT Triple PRO (expressing Cry1A.105 and Cry2Ab2), Agrisure Viptera 3111 (expressing Vip3Aa20 and Cry1Ab), and Genuity SmartStax (expressing Cry1A.105, Cry2Ab2, and Cry1F). When examined over all sites and years, hybrids with any of the included Bt traits had lower insect damage and higher yields. However, insect damage was not consistently correlated to yield. Bt traits expressing multiple proteins provided greater protection from corn earworm feeding than did traits for single proteins. Yields and aflatoxin levels were highly variable among sites although irrigated sites had higher yields than nonirrigated sites. Aflatoxins commonly accumulate in corn in the southeastern United States because of prevailing high temperatures and frequent dry conditions. Aflatoxin levels were not consistently associated with any factors that were evaluated, including Bt traits.

Vertical distribution and tissue selection of Helicoverpa zea (Lepidoptera: Noctuidae) adult oviposition and neonates on soybean with an indeterminate or determinate growth habit.

Helicoverpa zea (Boddie) is a polyphagous pest that can cause serious damage to crops, including soybeans (Glycine max L.). In soybeans with both determinate and indeterminate growth habits, H. zea larvae are more commonly found on leaves compared to blooms, stems, and pods. Past research demonstrated that H. zea adults tend to oviposit near the upper part of the plant canopy in soybeans with a determinate growth habit. However, ovipositional selection on soybeans with an indeterminate growth habit is unknown. We hypothesized that H. zea would oviposit more uniformly throughout the canopy on indeterminate soybean growth habits due to more diffuse reproductive tissue. We planted field and greenhouse experiments with varieties sharing a similar relative maturity (2 maturity group [MG] 5.2 varieties and 2 MG 5.4/5.5 varieties) but with different growth habits. To test oviposition selection, adult H. zea females were allowed to oviposit under field and caged conditions. We counted the number of H. zea eggs and neonates on each plant tissue type from each of 3 equal parts in the plant canopy: upper, middle, and lower. In both experiments, eggs and neonates were most common on leaves at the top of the plant regardless of soybean growth habit. Consequently, ovipositional selection is likely independent of reproductive tissue availability, and patterns of oviposition through the canopy are similar in growth habits. An improved understanding of H. zea ecology in soybeans relative to indeterminate growth habits may improve recommendations for managing this significant pest of soybean.

Helicoverpa zea Boddie (Lepidoptera: Noctuidae) pupal success and adult eclosion across variable soil type and moisture.

Helicoverpa zea Boddie (Lepidoptera: Noctuidae) is an important pest in many crops in the southern United States. Upon reaching the final larval instar, H. zea quests for a pupation site in the soil. Pupae are vulnerable to mortality since their movement is limited. Soil type and moisture can influence H. zea emergence, but the interaction of these factors has not been demonstrated. We compared sandy and clay soils in greenhouse and laboratory experiments. In the first experiment, we evaluated the preference of larvae to choose either sandy or clay soil for pupation. In a second experiment, we set the sandy soils at different moisture levels and observed prepupae pupation preference in a choice scenario. In a third experiment, we observed prepupae pupation in different moisture levels in a no-choice scenario. In a 4th experiment, we evaluated adult emergence following pupation when we increased moisture or kept it constant. In a final experiment, we evaluated pupation behavior in sandy or clay soils with a webcam and a glass arena. We found that larvae preferred to pupate in sandy soils over clay soils and that pupal success was highest at intermediate moisture levels. In addition, elevated soil moisture levels did not impact the emergence of H. zea between sandy or clay soil. Finally, H. zea did not take longer to burrow in either sandy or clay soil, but the tunnels of the pupal burrow were larger in sandy soil compared to clay soil. Our results clarify H. zea behavior across soil moisture and soil type.

Influence of varieties of hemp, Cannabis sativa (Rosales: Cannabaceae), and fertilization rates on damage caused by corn earworm, Helicoverpa zea (Lepidoptera: Noctuidae).

Industrial hemp, Cannabis sativa L., production has been negatively impacted by larvae of corn earworm, Helicoverpa zea (Boddie), which feed on developing inflorescences. Adult H. zea oviposit on hemp once flowers develop, and late-instar larvae can cause serious loss to both quality and yield. A 2-year study to assess the influence of hemp variety and fertilization practices on damage caused by H. zea was conducted. Differences in damage ratings among varieties were observed in both years; however, the rate of nitrogen applied did not influence biomass yield or damage rating. These results indicate that increasing nitrogen fertility may not be an effective means of cultural control for mitigating damage from H. zea. Floral maturity was very influential on damage caused by H. zea as late-maturing varieties had much less floral injury than those which matured early in outdoor field trials. Some cannabinoids were also correlated to damage rating, but this relationship was due to late-maturing plants with immature flowers low in cannabinoid concentrations receiving less floral injury. Based on these results, the selection of high-yielding varieties that flower when ovipositional activity of H. zea is expected to decline should be the first step in an integrated pest management program for hemp production. This research expanded our knowledge of the role of fertility rate, varietal characteristics, cannabinoid profile, and floral maturity on damage caused by H. zea to hemp. Findings from this research will allow growers to make more informed agronomic decisions before planting to improve hemp production.

Longitudinal trials illustrate interactive effects between declining Bt efficacy against Helicoverpa zea (Lepidoptera: Noctuidae) and planting dates of corn.

Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) has evolved resistance to insecticidal toxins from Bacillus thuringiensis (Bt) Berliner (Bacillales: Bacillaceae) expressed in genetically engineered corn, Zea mays L. This study provides an overview of field trials from Georgia, North Carolina, and South Carolina evaluating Bt and non-Bt corn hybrids from 2009 to 2022 to show changes in susceptibility in H. zea to Bt corn. The reduction in kernel injury relative to a non-Bt hybrid averaged across planting dates generally declined over time for Cry1A.105 + Cry2Ab2 corn. In addition, there was a significant interaction with planting date used as a covariate. The reduction in kernel injury remained above 80% and did not vary with planting date from 2009 to 2014, whereas a significant decline with planting date was found in this reduction from 2015 to 2022. For Cry1Ab + Cry1F corn, the reduction in kernel injury relative to a non-Bt hybrid averaged across planting dates did not vary among years. The reduction in kernel injury significantly declined with planting date from 2012 to 2022. Kernel injury as a proxy for H. zea pressure was greater in late-planted trials in non-Bt corn hybrids. Our study showed that Bt hybrids expressing Cry1A.105 + Cry2Ab2 are now less effective in later planted trials in reducing H. zea injury; however, this was not the case during the earlier years of adoption of corn expressing these 2 toxins when resistance alleles were likely less frequent in H. zea populations. The implications for management of H. zea and for insect resistance management are discussed.

Competition between brown stink bug (Hemiptera: Pentatomidae) and corn earworm (Lepidoptera: Noctuidae) in field corn.

Interspecific competition is an important ecological concept which can play a major role in insect population dynamics. In the southeastern United States, a complex of stink bugs (Hemiptera: Pentatomidae), primarily the brown stink bug, Euschistus servus (Say), and corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), are the 2 most common pests of field corn, Zea mays L. (Poales: Poaceae). Stink bugs have the greatest potential for economic injury during the late stages of vegetative corn development when feeding can result in deformed or "banana-shaped" ears and reduced grain yield. Corn earworm moths lay eggs on corn silks during the first stages of reproductive development. A 2-year field study was conducted to determine the impact of feeding by the brown stink bug during late-vegetative stages on subsequent corn earworm oviposition, larval infestations, and grain yield. Brown stink bug feeding prior to tasseling caused deformed ears and reduced overall grain yield by up to 92%. Across all trials, varying levels of brown stink bug density and injury reduced the number of corn earworm larvae by 29-100% and larval feeding by 46-85%. Averaged across brown stink bug densities, later planted corn experienced a 9-fold increase in number of corn earworm larvae. This is the first study demonstrating a competitive interaction between these major pests in a field corn setting, and these results have potential implications for insect resistance management.

Continued decline in sublethal effects of Bt toxins on Helicoverpa zea (Lepidoptera: Noctuidae) in field corn.

The majority of field corn, Zea mays L., in the southeastern United States has been genetically engineered to express insecticidal toxins produced by the soil bacterium, Bacillus thuringiensis (Bt). Field corn is the most important mid-season host for corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), which has developed resistance to all Cry toxins in Bt corn. From 2020 to 2023, corn earworm pupae were collected from early- and late-planted pyramided hybrids expressing Bt toxins and non-Bt near-isolines in North and South Carolina (16 trials). A total of 5,856 pupae were collected across all trials, with 55 and 88% more pupae collected in later-planted trials relative to early plantings in North and South Carolina, respectively. Only 20 pupae were collected from hybrids expressing Cry1F + Cry1Ab + Vip3A20 across all trials. Averaged across trials, Cry1A.105 + Cry2Ab2 hybrids reduced pupal weight by 6 and 9% in North and South Carolina, respectively, relative to the non-Bt near-isoline. Cry1F + Cry1Ab hybrids reduced pupal weight on average by 3 and 8% in North and South Carolina, respectively, relative to the non-Bt near-isoline. The impact of the Bt toxins on pupal weight varied among trials. When combined with data from 2014 to 2019 from previous studies, a significant decline in the percent reduction in pupal weight over time was found in both states and hybrid families. This study demonstrates a continued decline in the sublethal impacts of Bt toxins on corn earworm, emphasizing the importance of insect resistance management practices.

Continental-scale migration patterns and origin of Helicoverpa zea (Lepidoptera: Noctuidae) based on a biogeochemical marker.

Insect migrations have ecological and economic impacts, particularly in agriculture. However, there is limited knowledge about the migratory movements of pests at the continental scale, which is an important factor influencing the spread of resistance genes. Understanding the migratory patterns of economic pests, like Helicoverpa zea (Boddie), is essential for improving Integrated Pest Management (IPM) and Insect Resistance Management (IRM) strategies. In this study, we used stable hydrogen isotopic ratios in wing tissue as a biogeochemical marker to examine migratory patterns and estimate the native origins of H. zea individuals collected across a wide latitudinal gradient in North America. Samples collected at higher latitudes (Ontario, Canada and Minnesota, USA) exhibited a greater proportion (60%-96%) of nonlocal individuals, with an increased probability of origin from the southeastern United States. Populations from mid-latitudes (Florida, North Carolina, and South Carolina) showed a blend of local and nonlocal (40%-60%) individuals. Finally, 15% of the southernmost population individuals (Puerto Rico) were classified as migratory, with some having a probability of origin at higher latitudes (>30°). Overall, our results provide evidence of a northward spring/summer migration of H. zea in North America and underscore the significance of the southeastern United States as a hub for genetic flow. In addition, based on stable hydrogen isotopic ratios, there is strong evidence of reverse (southward) migration of H. zea from the continental United States to Puerto Rico. Our study highlights the implications for IPM and IRM programs and the need for management strategies that account for both northward and southward migration patterns.

Determination of Residual Control and Concentration of Chlorantraniliprole in Soybean.

Studies were conducted in 2020 and 2021 at the Delta Research and Extension Center in Stoneville, MS to determine concentrations of chlorantraniliprole (Prevathon, FMC Corporation, Philadelphia, PA) in soybean (Glycine max L.) leaves and florets. Chlorantraniliprole was applied as a foliar spray at four rates (0.028, 0.053, 0.078, 0.103 kg ai ha-1) for leaves and two rates (0.053, 0.078 kg ai ha-1) for florets. Leaf bioassays with corn earworm, Helicoverpa zea (Boddie), were conducted concurrently to determine mortality within three plant zones to evaluate chlorantraniliprole distribution throughout the canopy. For the leaf study, plants were partitioned into three zones consisting of a top (18th node), middle (13th node), and bottom (9th node) zone. Leaf samples from each zone were analyzed for chemical concentrations and bioassays were conducted at 1, 7, 14, 21, and 28 days after treatment (DAT). Floret samples were analyzed at 4, 7, 10, and 14 DAT. Concentrations of chlorantraniliprole, though variable, provided >71% control through all sampling dates, application rates, and canopy zones tested. Chlorantraniliprole was viable up to 28 DAT. Results from the soybean floret study suggested chlorantraniliprole was detected in florets up to 14 DAT. An additional leaf bioassay was conducted using concentrations detected in the floret study. Concentrations in florets provided mortality of corn earworm up to 48% out to 14 DAT. With a long residual expected, chlorantraniliprole applications should continue to be used to control corn earworm infestations in soybean and some additional control could be expected in florets.

Susceptibilities of Helicoverpa zea (Lepidoptera: Noctuidae) Populations From the Mississippi Delta to a Diamide Insecticide.

The corn earworm, Helicoverpa zea (Boddie), is a major pest of row crops in the Southern United States. Control of this insect is dependent on preventative insecticidal transgenic crops and synthetic insecticide applications when damaging populations are encountered in the field. Recently, the use of chemicals from the diamide class of insecticides, particularly chlorantraniliprole, has been used to control unacceptable populations. Due to the increased importance of this active ingredient for control of corn earworms, populations of this insect from the Mississippi Delta have been monitored for susceptibilities annually since 2016. Overall, 58 populations of H. zea were examined for their susceptibility to chlorantraniliprole through diet-incorporated bioassays from 2016 to 2021. Based on probit analysis, there was only a 4-fold difference between the highest and lowest LC50 estimates for all populations tested. Through weights of 2nd and 3rd instar larvae, there appears to be a substantial fitness cost associated with surviving caterpillars that fed on various concentrations of chlorantraniliprole in bioassays, which is not captured through the yes or no response of typical survival analysis. Overall, there was not a detectable trend of reduced susceptibility to chlorantraniliprole over the course of the six-year study.

Factors Affecting Population Dynamics of Helicoverpa zea (Lepidoptera: Noctuidae) in a Mixed Landscape with Bt Cotton and Peanut.

In North America, weather and host-plant abundance drive the population dynamics of the migratory pest Helicoverpa zea. The objectives of this study were to (i) estimate monthly abundance of H. zea moths in Bt cotton and peanut fields, (ii) document the effects of weather on H. zea trap catches, and (iii) determine larval hosts supporting H. zea populations from 2017 to 2019. Year-round trapping of H. zea moths was conducted in 16 commercial fields in two regions of the Florida Panhandle using delta traps. H. zea moth catches were associated with temperature, rainfall, and relative humidity. Larval hosts were determined by isotopic carbon analysis. Our results showed year-round H. zea flights in both regions across two years, with the highest and lowest moth catches occurring from July to September and November to March, respectively. There was no difference in catches between traps set on Bt cotton and peanut. In the Santa Rosa/Escambia counties, weather explained 59% of the variance in H. zea catches, with significant effects of temperature, relative humidity, and rainfall. In Jackson County, weather explained 38% of H. zea catches, with significant effects of temperature and relative humidity. Carbon isotopic data showed that feeding on C3 plants, including Bt cotton, occurred over most of the year, although feeding on C4 hosts, including Bt corn, occurred during the summer months. Hence overwintering and resident populations of H. zea in the Florida Panhandle may be continually exposed to Bt crops, increasing the risk for the evolution of resistance.

Within-field spatial patterns of Helicoverpa zea (Lepidoptera: Noctuidae) and spatial associations with stink bugs and their injury in field corn.

The corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), is a cosmopolitan pest in the field crop landscape in the southeastern United States. Field corn (Zea mays L.) is the most important midseason host for H. zea where intensive selection pressure occurs for resistance to insecticidal toxins from Bacillus thuringiensis (Bt). Because spatial patterns of H. zea in field corn have not been extensively studied, field corn was sampled for H. zea larvae and injury in 2021 and 2022. Patterns of spatial aggregation were identified in a number of fields in both larval populations and injury. Aggregation of H. zea larvae was less common at R5 than at R2. Associations between the spatial patterns of H. zea and the variability in crop phenology were identified in some fields, with positive associations between plant height and H. zea larvae, indicating that ovipositing H. zea moths avoid areas with reduced plant height and delayed reproductive maturity. Additionally, negative spatial associations between stink bug ear injury and H. zea larvae and their injury were found in a small number of cases, indicating some spatial interactions between the two pest complexes and their injury. Results from these studies provide valuable insight into the spatial patterns of H. zea in field corn. An understanding of the local dispersal and population dynamics of H. zea can be used to help further improve integrated pest management and insect resistance management programs for this major polyphagous pest.