Helicoverpa Zea Research Articles

Hemp Microbiome Composition and Function Under Developing Pest Management Solutions

Conventional pesticides used in cropping systems prevent damage caused by pathogens and pests but may also have unintended consequences for non-target organisms associated with plants. For example, fungicide application may affect microbes such as fungal endophytes that potentially confer protective benefits to the host, such as pathogen or pest resistance. Here we investigated how fungicide application and pathogen inoculation altered the communities of pathogenic and non-target endophytic leaf microbes in hemp (Cannabis sativa L.). We found that fungicide application and inoculation with fungal pathogens affected hemp-associated microbial communities. Fungicide application altered fungal endophyte community composition, increased heterogeneity of fungal communities, reduced pathogen abundance, and decreased diversity of the endophytic fungal community. Inoculation with pathogenic fungi decreased the abundance of bacterial endophytes relative to control and fungicide-treated plants. We then investigated the potential of a common fungal endophyte isolated from this study, Ophiocordyceps sp., as a biological control agent for Helicoverpa zea, a common insect pest in hemp. Contrary to our expectations, larvae preferred food inoculated with Ophiocordyceps sp., though it did not alter growth or mortality of larvae. Together, our results indicate that hemp-associated endophyte communities are sensitive to abiotic and biotic manipulations, and that fungicide application impacts non-target microorganisms that could confer important functions for crop health. We encourage future studies to analyze the impact of biological control agents on host ecology in an integrated pest management plan and to examine ways to better utilize existing microbial associations to create biological controls.

Inheritance of Cry2Ab2 resistance in two Helicoverpa zea (Lepidoptera: Noctuidae) populations resistant to single- and dual-Bacillus thuringiensis proteins

Cry2Ab2 is a Bacillus thuringiensis (Bt) protein that has been pyramided with Cry1A.105 in transgenic maize and Cry1Ac in cotton to control some major lepidopteran pests including the corn earworm/bollworm, Helicoverpa zea (Boddie). However, the widespread occurrence of resistance of this pest to the pyramided Cry1A/Cry2A crops in the southern region of the United State has become a threat to the sustainability of the technology. In this study, multiple genetic crosses and backcrosses were developed to characterize the inheritance of Cry2Ab2 resistance in two H. zea populations resistant to the single protein, Cry2Ab2 (RR2Ab) and the dual proteins in Bt maize, Cry1A.105/Cry2Ab2 (RRVT2P). Diet-overlay bioassays with F1 hybrids from reciprocal crosses between a susceptible and the resistant populations showed that the Cry2Ab2 resistance in both RR2Ab and RRVT2P was inherited autosomally and non-recessively. Segregation tests in F2 and backcrossed generations indicated that the resistance was likely controlled by more than one locus. The effective dominance levels of the resistance estimated at each of three discriminating concentrations were similar between RR2Ab and RRVT2P, ranging from incompletely dominant to incompletely recessive. The similar inheritance observed in RR2Ab and RRVT2P suggests that the Cry2Ab2 resistance is independent from the Cry1A.105 resistance. The non-recessive inheritance of the resistance could be an important factor causing the widespread resistance of this insect to the Cry1A/Cry2A crops in the southern region. Implications of the observed inheritance properties in Bt crop resistance management are discussed.

Commodity risk assessment of Petunia spp. and Calibrachoa spp. unrooted cuttings from Costa Rica.

The European Commission requested the EFSA Panel on Plant Health to evaluate the probability of entry of pests (likelihood of pest freedom at entry), including both regulated and non-regulated pests, associated with unrooted cuttings of the genera Petunia and Calibrachoa produced under physical isolation in Costa Rica. The relevance of any pest for this opinion was based on evidence collected according to specific criteria, following the methodology used for high-risk plants adapted for the specificity of this assessment. Twenty-two EU regulated pests (beet curly top virus, Bemisia tabaci, Chloridea virescens, Eotetranychus lewisi, Epitrix cucumeris, Epitrix tuberis, euphorbia mosaic virus, Helicoverpa zea, Liriomyza huidobrensis, Liriomyza sativae, Liriomyza trifolii, pepper golden mosaic virus, potato spindle tuber viroid, Ralstonia pseudosolanacearum, Ralstonia solanacearum, Spodoptera ornithogalli, squash leaf curl virus, Thrips palmi, tomato golden mosaic virus, tomato leaf curl Sinaloa virus, tomato spotted wilt virus, tomato yellow leaf curl virus) and one pest that is not regulated in the EU (Aleurodicus dispersus) fulfilled all relevant criteria and were selected for further evaluation. For these pests, the risk mitigation measures proposed in the technical dossier from Costa Rica were evaluated taking into account possible factors limiting their efficacies. Additionally, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The estimated degree of pest freedom varies among the pests evaluated, with tomato spotted wilt virus being the pest most frequently expected on the imported cuttings. The expert knowledge elicitation indicated, with 95% certainty that between 9927 and 10,000 bags containing unrooted cuttings of Petunia spp. and Calibrachoa spp. per 10,000 would be free of tomato spotted wilt virus.

Marking Helicoverpa zea (Lepidoptera: Noctuidae) with fluorophores for use in mark-release-recapture research

Abstract Knowledge of insect dispersal and long-distance migratory flight capacity and patterns represent key factors needed for risk assessment of invasive pest species, insecticide resistance management, and more effective pest control. Having operative tools to both mark and track insect pest movement is therefore critical to achieving such goals. Here, we describe a new procedure for marking Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), one of the most economically important crop pests in the United States. Adult H. zea moths were effectively marked using the liquid fluorophore cartax green, a persistent UV-fluorescent pigment, both directly by topical application and indirectly by briefly submerging pupae in the marking solution prior to adult emergence. Regardless of the application method, the cartax mark was retained on the moths throughout their entire adult lifespan. No mortality differences were observed between cartax green-marked and water-marked (control) moths. Additionally, using rotary flight mills, we found no significant differences in several flight parameters, including total number of flights, flight speeds, flight distances, or flight durations between unmarked and cartax-marked moths. Under laboratory conditions, we did observe the lateral transfer of different colored fluorophores between moths, indicating that undesirable marking could potentially occur. Moreover, we found that not all fluorophores were equally retained on H. zea moths, with cartax green remaining intact on moths longer than did a corresponding magenta fluorophore. The results show that cartax green fluorophore could be a practical marker for H. zea and other holometabolous species targeted for large-scale mark-release-recapture research.

Hemp regulates the fitness of corn earworm (Lepidoptera, Noctuidae) and its tachinid (Diptera) parasitoids.

Pest management on hemp is still in its infancy, and biological control options are limited. Helicoverpa zea (corn earworm) is one of the key pests of hemp cultivated outdoors, especially on cultivars grown for cannabinoids and grain. In a three-year study, we assessed the effect of diet on the performance of H. zea and its tachinid parasitoids. Parasitized (bearing fly eggs) and unparasitized (without eggs) H. zea larvae were fed on hemp flowers or an artificial diet. Five tachinid species parasitized H. zea larvae, but the most abundant species were Winthemia rufopicta (68.8%) and Lespesia aletiae (28.3%). Overall, 55.2% of H. zea larvae bearing tachinid eggs died, while the mortality of unparasitized larvae reached 24.7%. The success of tachinids increased by 2-fold when the host larvae were fed on an artificial diet. Our results demonstrated that high protein food (artificial diet), intensity of parasitism, and caterpillar size play a role in the fitness of both the herbivores (H. zea) and its tachinid parasitoids. These findings have important implications for understanding biological control mechanisms and open new insights into the impact of landscape variation on plant-herbivore-parasitoid interactions. This study contains supporting evidence that makes both Winthemia rufopicta and Lespesia aletiae excellent candidates for biological control programs against H. zea, a key pest of hemp in the United States.

Effect of Blended Bt Corn Refuge on Corn Earworm (Lepidoptera: Noctuidae) Infestation and Grain Yield

Blended refuges for corn-expressing toxins from Bacillus thuringiensis (Bt) Berliner controls have been approved in the United States as an alternative resistance management approach to structured refuge. This study examined the impact of blended refuges up to 30% non-Bt seed on the corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), larval numbers, and kernel injury, and its effect on corn grain yield and test weights. The percentage of infested ears, larval numbers, and kernel injury of the 20% blend were not significantly different from the non-Bt and nonblended Bt for the Cry1A.105 + Cry2Ab + Cry1Fa2 treatment, but infested ears, larval numbers, and kernel injury of the nonblended Cry1A.105 + Cry2Ab treatment was lower than the comparable non-Bt hybrids, with the 20% blend being intermediate. The nonblended Cry1A.105 + Cry2Ab + Vip3Aa20 had virtually no larvae in ears and no kernel injury. Ear infestation, larval numbers, and kernel injury of the non-Bt blends with Vip3Aa20 were proportional to the percentage of non-Bt seed in the blend, and all infested ears were from the non-Bt refuge plants. Grain yield and test weight were not significantly different among nonblended or blended treatments of any Bt product tested. Results indicate losses of grain yield and test weight by corn earworm in seed blends up to 30% non-Bt seed are unlikely with infestation levels observed in this study.

Cultivars of corn recommended for silage in the Agreste Meridional of Pernambuco

The semiarid region of Pernambuco produces 99.5% of the forage corn, considering that 93.8% of the ruminant herd is produced in this region of the Brazilian Northeast. The Agreste Meridional is located in this region, which presents seasonality in production due to water deficit. Silage is one of the adopted roughage conservation strategies, with corn being the forage that presents the best indicators when fed to animals. Agronomic aspects are often neglected, considering that the performance of cultivars may vary with the growing environment. The objective of this research was the introduction and evaluation of corn cultivars for the production for whole-plant silage in the Agreste Meridional of Pernambuco, Brazil. The experiment was carried out in a randomized block design, with seven treatments, of which five non transgenic cultivars (‘Alagoano’, ‘Nordestino’, ‘São Luís’, ‘PV2 Viçosense’ and ‘PV1 Branca’) and two transgenic hybrids (‘LG 6030 VT PRO2’ and ‘AS 1573 YG’). It was observed that all genotypes showed susceptibility to Spodoptera frugiperda and Helicoverpa zea, except for the ‘AS 1573 YG’ hybrid, due to the Bt technology. The biometric characters of the genotypes were influenced by the environment. However, with yield of 10,537 and 10,666 kg ha-1 (dry matter), the genotypes ‘Alagoano’ and ‘AS 1573 YG’, respectively, were selected for cultivation in the Agreste Meridional region for the production of silage, which can be used in intensive production systems or family farming.

Beyond wingbeats: dispersal capacity and morphophysiological determinants in Helicoverpa zea (Lepidoptera: Noctuidae)

Abstract Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) is a polyphagous pest impacting numerous economic crops. This impact is facilitated by its long-range dispersal capacity, which can lead to the colonization of new cultivated areas in the agricultural landscape and the potential spread of insecticide-resistant populations. Despite these negative implications, it is unclear how ecological and morphological factors influence H. zea flight capacity. Here, we investigated the dispersal capacity and morphophysiological determinants of the flight performance of H. zea. Tethered flight mill experiments were conducted to examine the impact of mating status, age [young (2-day-old), middle-aged (3- to 6-day-old), or old (7- to 9-day-old)], and sex on the flight capacity of moths under controlled conditions. We found that the flight capacity was not influenced by mating status or the number of mature eggs. Males flew faster than females, and middle-aged moths’ flight had higher performance (speed, time, and distance) than young and old moths. Body size and wing-to-thorax ratio negatively influenced the moth flight time. Male’s body size was larger than females, but they had a smaller forewing area and smaller wing-to-thorax ratio. Middle-aged moths exhibited the highest likelihood of engaging in migratory movements (> 10 km). Finally, oogenesis-flight syndrome was not detected, confirming the hypothesis of facultative migration in this species. Our results enhance our understanding of the factors influencing the flight behavior of H. zea, which can be used to predict the long-range capacity of infestation of this species, and the spread of resistance genes to management tools, such as insecticides and Bacillus thuringiensis (Bt) toxins expressed in transgenic crops.

Utility of Cry1Ja for Transgenic Insect Control.

Insect control traits are a key component of improving the efficacy of insect pest management and maximizing crop yields for growers. Insect traits based on proteins expressed by the bacteria Bacillus thuringiensis (Bt) have proven to be very effective tools in achieving this goal. Unfortunately, the adaptability of insects has led to resistance to certain proteins in current commercial products. Therefore, new insecticidal traits representing a different mode of action (MoA) than those currently in use are needed. Cry1Ja has good insecticidal activity against various lepidopteran species, and it provides robust protection against insect feeding with in planta expression. For Bt proteins, different MoAs are determined by their binding sites in the insect midgut. In this study, competitive binding assays are performed using brush border membrane vesicles (BBMVs) from Helicoverpa zea, Spodoptera frugiperda, and Chrysodeixis includens to evaluate the MoA of Cry1Ja relative to representatives of the various Bt proteins that are expressed in current commercial products for lepidopteran insect protection. This study highlights differences in the shared Cry protein binding sites in three insect species, Cry1Ja bioactivity against Cry1Fa resistant FAW, and in planta efficacy against target pests. These data illustrate the potential of Cry1Ja for new insect trait development.

Species-specific evolution of lepidopteran TspC5 tetraspanins associated with dominant resistance to Bacillus thuringiensis toxin Cry1Ac

Transgenic crops producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have proven to be highly effective in managing some key pests. However, the evolution of resistance by the target pests threatens the sustainability of Bt crops. The L31S mutation in a tetraspanin encoded by HarmTspC5 (previously known as HaTSPAN1) has been shown to confer dominant resistance to the Bt protein Cry1Ac in Helicoverpa armigera, a globally damaging lepidopteran pest. However, the broader implications of the L31S mutation in the tetraspanins of other lepidopteran species remain unclear. The evolutionary analyses in this study indicate that TspC5s have evolved in a species-specific manner among the lepidopteran insects. To investigate the role of TspC5s in conferring dominant resistance to Cry1Ac, we used the piggyBac-based transformation system to generate four transgenic H. armigera strains that express exogenous TspC5 variants from three phylogenetically close species (Helicoverpa zea, Helicoverpa assulta and Heliothis virescens) and one phylogenetically distant species (Plutella xylostella). In comparison with the background SCD strain of H. armigera, the transgenic strains expressing HzeaTspC5-L31S, HassTspC5-L31S, or HvirTspC5-L31S exhibited significant resistance to Cry1Ac (10.0-, 21.4-, and 81.1-fold, respectively), whereas the strain expressing PxylTspC5-L27S remained susceptible. Furthermore, the Cry1Ac resistant phenotypes followed an autosomal dominant inheritance pattern and were closely linked to the introduced mutant TspC5s. These findings reveal the conserved role of TspC5s from Helicoverpa and Heliothis species in mediating the dominant resistance to Cry1Ac, and they provide crucial insights for assessing resistance risks related to mutant tetraspanins and devising adaptive resistance management strategies for these major lepidopteran pests.

High-throughput screening for novel Bacillus thuringiensis insecticidal proteins revealed evidence that the bacterium exchanges Domain III to enhance its insecticidal activity.

Approximately 3000 Bacillus thuringiensis (Bt) isolates were screened to discover novel three-domain (3D) Cry proteins active against Helicoverpa zea (corn earworm). From 400 active isolates found during the primary screening, Cry1Ac and Cry2A, which are known to be active against H. zea, were removed using multiplex-primer PCR and high-throughput column chromatography. This process reduced the number of active cultures to 48. DNA segments encoding Domain III of these 48 cultures were amplified by PCR and sequenced. Sequencing revealed two novel Cry1B-type Domain IIIs. Further sequencing of the flanking regions of these domains revealed that one was part of Cry1Bj (GenBank: KT952325). However, the other Domain III lacked Domains I and II. Instead, this Domain III was associated with two open reading frames, ORF1 and ORF2. ORF1 was identified as an ATP-binding protein, and ORF2 as an ATPase, suggesting that Bt exchanges Domain III among homologous Cry proteins.

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.

Homology-based characterization of the cis-regulatory elements modulate flavone induction of CYP321A1 in Helicoverpa armigera

Xenobiotic response element (XRE) to flavone was the cis- regulatory elements that mediates the induction of the allelochemical-metabolizing CYP321A1 gene from Helicoverpa zea. However, it was unknown whether the XRE-Fla element existed in other species. Recently we have identified and cloned the CYP321A1 gene with promoter region in a related species, Helicoverpa armigera. Sequence similarity of two orthologous CYP321A1 genes was 97.27%, but the promoter sequence similarity was only 56.32%. Sequence alignment showed the XRE-Fla like element owns three mutations in H. armigera compared with H. zea. Progressive 5′ deletions and internal mutation indicated that H. armigera XRE-Fla was the essential element of CYP321A1 gene in response to flavone. XRE-Fla mutations and EMSA analysis confirmed that the H. armigera XRE-Fla element binding factor was stronger than H. zea. The findings indicate the XRE element mutations mainly contribute to the differences between the flavone-induced expressions of two CYP321A1 genes, which improve the flexibility and adaptability for allelochemical response of H. armigera.

Potential for Grain Sorghum as a Trap and Nursery Crop for Helicoverpa zea and Its Natural Enemies and Dissemination of HearNPV into Cotton

Potential for Grain Sorghum as a Trap and Nursery Crop for Helicoverpa zea and Its Natural Enemies and Dissemination of HearNPV into Cotton

Functional expression and characterization of CAPA receptor in the digestive tract and life stages of Drosophila suzukii, and differential activities with insect PRXamide peptides.

Spotted-wing drosophila, Drosophila suzukii (Matsumura), is an invasive vinegar fly that is a major threat to the small fruits industries globally. Insect capa genes encode multiple neuropeptides, including CAPA-periviscerokinin (CAPA-PVK) peptides, that are specifically known to cause diuresis or anti-diuresis in various organisms. Here we identified and characterized a corresponding G protein-coupled receptor (GPCR) of the D. suzukii CAPA-PVK peptides: CAPA receptor (CAPA-R). To better characterize the behavior of D. suzukii CAPA-R, we used insect cell-based functional expression assays to evaluate responses of CAPA-RagainstD. suzukii CAPA-PVKs, CAPA-PVKs from five species in Insecta, one species from Mollusca, modified CAPA-PVK peptides, and some PRXamide family peptides: pyrokinin (PK), diapause hormone (DH), and ecdysis-triggering hormone (ETH). Functional studies revealed that the D. suzukii CAPA-R is strongly activated by both of its own natural D. suzukii CAPA-PVKs, and interestingly, it was strongly activated by other CAPA-PVK peptides from Frankliniella occidentallis (Thysanoptera), Solenopsis invicta (Hymenoptera), Helicoverpa zea (Lepidoptera) and Plutella xylostella (Lepidoptera). However, D. suzukii CAPA-R was not activated by Mollusca CAPA-PVK or the other PRXamide peptides. Gene expression analyses showed that the CAPA-R was highly expressed in the Malpighian tubules and moderately in hindgut compared to other digestive organs or the rest of body, supporting diuretic/antidiuretic functionality. When compared across life stages of D. suzukii, expression of CAPA-R was approximately 1.5x greater in the third instar than the other stages and minimally detected in the eggs, 4-day old pupae and 3-day old adults. Our results functionally characterized the D. suzukii CAPA-R and a few short peptides were identified as potential biological targets to exploit the CAPA-R for D. suzukii management.

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.

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.

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.

Anatomy of a pest control failure: introgression of cytochrome P450 337B3 alleles from invasive old-world bollworm into native corn earworm (Lepidoptera: Noctuidae).

The establishment of invasive species populations can threaten the ecological balance in naïve habitats and impact agricultural production practices. Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)(old-world bollworm, OWBW) and Helicoverpa zea (corn earworm, CEW) were geographically separated prior to the 2013 report of OWBW invasion into South America. Introgression of OWBW-specific cytochrome P450 337B3 (CYP337B3) gene into CEW was repeatedly detected across South America and the Caribbean. Two hybrids were documented from Texas in 2019. In this study, screening insects collected in Olathe, CO, USA, where a failure of pyrethroids to control CEW damage to conventional sweetcorn in 2023 detected 28.6% of insects with the OWBW-specific CYP337B3 marker. Nucleotide sequencing of the CYP337B3 gene identified 73.1% and 26.9% of insects carried CYP337B3v2 and CYP337B3v6 alleles, respectively, and 0.15 overall frequency of CYP337B3 alleles. Based on prior data for distinct phylogeographic origins of CYP337B3v2 and v6 alleles, our results indicate Olathe samples were derived from 2 different introductions: An uncertain source of the v6 allele that was initially reported in West Africa and possibly South American or Caribbean origin of the globally distributed v2 allele. One of the 1618 individuals screened also carried a ribosomal RNA internal transcribed spacer 1 derived from OWBW. Local selection pressures at the Olathe location imposed by repeated pyrethroid exposures are likely attributed to the prevalence of CYP337B3, where control practices hasten the accumulation of phenotypic resistance by adaptive introgression. Pyrethroid and other resistance factors carried by invasive OWBW may continue to impact CEW management tactics across the Americas.

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.