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.

A Diagnostic Loop-Mediated Isothermal Amplification Method to Distinguish Helicoverpa armigera (Lepidoptera: Noctuidae) From Other Related Species in the New World

Helicoverpa armigera (Hübner) is a notorious agricultural pest native to the Old World. Recently, its invasion into South and Central America has become a serious problem in the New World. The rapid detection of invasive pests is essential to eradicate them and prevent establishment. However, an extremely similar species, H. zea (Boddie) distributed in the New World makes identification difficult. Helicoverpa armigera and H. zea have only minor differences in male genitalia to separate them morphologically. Both species are attracted to the same pheromone lure, and it takes considerable time and effort to identify them from bulk samples obtained during trap monitoring. Although several molecular approaches based on PCR have been reported, these methods require expensive equipment and are unsuitable for onsite diagnostics. Here, we developed a rapid and convenient diagnostic method based on the loop-mediated isothermal amplification to distinguish H. armigera from related species: H. zea, H. assulta (Guenée), H. punctigera (Wallengren), and Chloridea virescens (Fabricius). The diagnostic method makes it possible to detect H. armigera within 90 min only using simple equipment. The method also worked with mixed DNA templates containing excess DNA from H. zea at the ratio of 1:999 (H. armigera:H. zea). This method can be an effective tool for onsite diagnostics during monitoring surveys for invasive H. armigera.

The Corn-Cotton Agroecosystem in the Mid-Southern United States: What Insecticidal Event Pyramids Should be Used in Each Crop to Extend Vip3A Durability

Recent studies suggest that resistance in Helicoverpa zea (Boddie) (Lepidoptera, Noctuidae) to Cry1A(b/c) and Cry2Ab2 toxins from the bacterium Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) has increased and field efficacy is impacted in transgenic corn and cotton expressing these toxins. A third toxin, Vip3A, is available in pyramids expressing two or more Bt toxins in corn hybrids and cotton varieties, but uncertainty exists regarding deployment strategies. During a growing season, H. zea infests corn and cotton, and debate arises over use of Vip3A toxin in corn where H. zea is not an economic pest. We used a three-locus, spatially explicit simulation model to evaluate when using Vip3A in corn might hasten evolution of resistance to Vip3A, with implications in cotton where H. zea is a key pest. When using a conventional refuge in corn and initial resistance allele frequencies of Cry1A and Cry2A were 10%, transforming corn with Vip3A slowed resistance to these toxins and delayed resistance evolution to the three-toxin pyramid as a whole. When Cry resistance allele frequencies exceeded 30%, transforming corn with Vip3A hastened the evolution of resistance to the three-toxin pyramid in cotton. When using a seed blend refuge strategy, resistance was delayed longest when Vip3A was not incorporated into corn and used only in cotton. Simulations of conventional refuges were generally more durable than seed blends, even when 75% of the required refuge was not planted. Extended durability of conventional refuges compared to other models of resistance evolution are discussed as well as causes for unusual survivorship in seed blends.

Egg Albumin as a Protein Marker to Study Dispersal of Noctuidae in the Agroecosystem

Knowledge of dispersal and spatial dynamics of pest populations is fundamental for implementation of integrated pest management and integrated resistance management. This study evaluated 1) the effectiveness of egg white albumin protein to mark larvae and adults of two polyphagous and highly mobile pests, Spodoptera frugiperda (J.E. Smith) (fall armyworm) and Helicoverpa zea (Boddie) (corn earworm) (Lepidoptera: Noctuidae), and 2) the sensitivity of polyvinylidene difluoride membrane (dot blot) in detecting albumin on marked insects. Laboratory and field experiments tested egg albumin as a protein marker, which was detected using two enzyme-linked immunosorbent assay (ELISA), microplate, and dot blot. In the laboratory, 100% of the moths sprayed with 20% egg white solution acquired the albumin marker, which was detected through the last time point tested (5 d) after application. Egg albumin was not effective at long-term marking of larvae, detected only prior the molting to the next instar. Albumin application in field cages resulted in a high percentage of moths detected as marked at 24 h and 5 d for both species. Egg albumin applied in the open field resulted in 15% of the recaptured corn earworm moths marked with most of them collected 150 m from the application area, although some were captured as far as 1,600 m within approximately 6 d after adult emergence. The results indicated egg albumin is a suitable marker to study the dispersion of fall armyworm and corn earworm in the agroecosystem and dot blot was as effective to detect egg albumin as was indirect ELISA.

Identification of Heliothine (Lepidoptera: Noctuidae) Larvae Intercepted at U.S. Ports of Entry From the New World

Heliothine larvae, especially early instars, are difficult to identify, and determinations sometimes rely on indirect information such as origin and host data. The introduction of Helicoverpa armigera (Hübner) into the New World has undermined the reliability of host and origin data to identify intercepted Helicoverpa larvae, and suspect Heliothinae/Helicoverpa larvae intercepted at U.S. ports of entry are now screened for H. armigera and Helicoverpa zea (Boddie) using molecular methods. Here, we analyze heliothine larvae intercepted during 2014-2106 to identify nontargets and evaluate morphological characters traditionally used to separate taxa. In total, nine species were identified, with Chloridea virescens (Fabricius) making up the bulk of interception records. The majority of heliothine suspects originate from Mexico and Peru on pigeon pea, chickpea, tomatillo, pea, and corn. Helicoverpa armigera is commonly intercepted from Peru on pea. Chloridea virescens is recorded from every country where interceptions were identified for this study except Guatemala and is found on multiple hosts. Identification issues and specific host/origin associations are discussed in detail.