Project : USDA ARS

ARS Home » Southeast Area » Gainesville, Florida » Center for Medical, Agricultural and Veterinary Entomology » Insect Behavior and Biocontrol Research » Research » Research Project #439207

Research Project: Improved Biologically-Based Methods for Management of Native and Invasive Crop Insect Pests

Location: Insect Behavior and Biocontrol Research

2024 Annual Report

Objectives
Objective 1: Develop genetically modified (GM) strains by transposon and CRISPR/Cas-mediated transgenesis for improved SIT in fruit fly pests, and new DNA delivery systems to apply this technology to a wider range of insect, including emerging pest species (e.g., caribfly, mexfly, medfly, spotted-winged drosophila). Objective 2: Develop strains of moths transinfected with Wolbachia that produce males with strong cytoplasmic incompatibility for use in the Incompatible Insect Technique (IIT) to reduce pest populations of fall armyworm and corn earworm. Objective 3: Develop CRISPR gene editing in pest moths (e.g., Indian meal moth, fall armyworm, gypsy moth) that target genes critical for acquired biopesticide resistance using both whole insects and cultured insect cells. Objective 4: Develop improved surveillance and detection methods for hidden and invasive pests (e.g., red palm and citrus root weevil, Asian long-horned beetle, Asian citrus psyllid, and stored product insect pests) that incorporate automated collection, processing, and analysis of insect acoustic signals and behavioral activity. Objective 5: Develop improved surveillance of invasive and outbreak insect pests (e.g., corn silk flies and kudzu bug) using visual-cue traps, and improve strategies for detection and prediction of such dispersing pests by understanding the role of visual and other stimuli affecting specific behaviors. Objective 6: Improve area-wide landscape management tactics by developing conservation biological control strategies to mitigate pest populations and attract or support natural enemies (e.g., against fall armyworm). Objective 7: Combine genetic methods with air-transport and climate modeling to describe and predict the distribution and behavior of agricultural pests to facilitate the mitigation of migratory source populations and to identify locations at high risk for infestations by invasive species such as fall armyworm, corn silk fly, soybean looper, Old World bollworm, and corn earworm.

Approach
Research conducted by the Behavior and Biocontrol Research Unit at the Center for Medical, Agricultural and Veterinary Entomology has historically been focused on the development of novel technologies that improve the cost-efficiency of traditional pest control strategies as well as provide environmentally benign alternatives to the use of chemical pesticides. The goals are to improve crop productivity while reducing the environmental impact and costs of pest management. The proposed research integrates different levels of biology that range from the genetic modification of pest insects to generate novel and improved variations of Sterile Insect Technique (SIT) strategies, the manipulation of pest endosymbionts to develop Insect Incompatibility Technique (IIT) strategies, the optimization of acoustic, olfactory, and visual cues to improve pest surveillance and disrupt pest behavior, the application of climate and air transport models to project pest distribution and migration patterns, and the development of landscape strategies for sustainable mitigation of pest populations. This multidisciplinary structure encourages innovation and facilitates synergism between projects. Anticipated accomplishments will initially apply to the control of high priority invasive fruit flies, beetles, psyllids, moths, and corn silk flies through new biologically based methods for pest control, improved capability to monitor pests, and better projections of pest movements to more effectively target the time and place of treatments. The impact will be higher productivity at lower cost for domestic agriculture and new and improved tools to detect and control emerging native and invasive pests.

Progress Report
Substantial progress was made by ARS researchers at Gainesville, Florida on the project objectives that fall under the NP 304 Action Plan, Component 3–Insects and Mites and Component 4–Protection of Postharvest Commodities, Quarantine, and Methyl Bromide Alternatives. In regard to Objective 1, promoters for several fruit fly genes were characterized and verified to be able to induce embryonic gene expression in genetically modified insects. Using state-of-the-art molecular techniques, these promoters were manipulated to now control the expression of a protein, a tet-Transactivator, that can turn on artificial genes that induce sterility in either male or females or both. A gene-editing method (CRISPR/Cas9) was used to induce mutations a sperm producing gene (wampa) in the fruit flies Drosphila suzukii and Anastrepha suspensa for use in constructing lines that can be used for Sterile Insect Technique (SIT). Genetically modified lines of A. suspensa were generated that can induce female-specific lethality in a temperature dependent manner. These will be developed for use in improving SIT techniques by allowing the rapid elimination of unwanted female flies. No progress was made for Objectives 2 and 3 due to a scientist's retirement. For Objective 4, field testing was conducted on signal capture and broadcasting for use of several devices capable of detecting insects within structures such as trees. Optimization of signal filtering enhanced detection capabilities greatly. Field evaluation of signal emission for mating disruption of mole crickets was continued. In regard to Objective 5, laboratory and field studies on the role of visual cues with two corn silk fly species indicated that while species differ to some degree with visual preferences, the greatest response in the field was to yellow and lime green traps. Attraction assays with kudzu bugs continued for examination of visual and olfactory attractants. A new parasitoid species from corn silk flies was discovered and host range studies initiated with several corn silk fly species as well as other tephritid and fruit fly species. Continued assays are evaluating the potential efficacy as a biocontrol agent. Under Objective 6, Laboratory studies were continued with the parasitoids Telenomus remus and Cotesia marginiventris and the earwig predator Doru taeniatum against fall armyworm. Parasitism by the two wasp species was tested with different flowers to determine if they can get adequate amounts of carbohydrates than with just honey. The earwig predator was collected from sweet corn in southern Florida and was colonized in the laboratory. Tests showed that both males and females individually consumed over 55 eggs in a 24-hour period, which resulted in over 50% of the eggs in a mass removed. In a field study, the automated Trapview® traps were placed in two field locations and monitored overnight. Moths that arrived in the early evening were genetically compared to moths that arrived later in the evening. This study is duplicated in Texas. Additionally, collections of moths in traditional pheromone-baited traps are being conducted before solar midnight and during the next morning to compare the genetics of early and late-active moths. A third field study was initiated this year to compare capture of fall armyworm moths in traditional traps with just the pheromone or in traps with the pheromone and a floral lure composed of phenylacetaldehyde plus beta-myrcene. Preliminary results suggest that when fall armyworm populations are high, more moths are attracted to the pheromone-only traps; however, when there are low populations, the pheromone-baited and pheromone-baited plus floral-baited traps catch equal numbers of moths. Under Objective 7, approximately 550 fall armyworm moths from Mexico and Texas were analyzed for patterns of genetic variation and these were correlated with modeling of climate suitability, the locations of major corn production, and wind-dependent dispersal projections. The results were used to assess the frequency and magnitude of interactions between fall armyworm from Texas, which is the migratory source for infestations in central North America, and those from Mexico. The data identify environmental factors influencing fall armyworm dispersion patterns that impact the likelihood of genetic exchanges between populations in the two American continents across the Mexico-Central America land corridor. Another 133 specimens from Arizona were analyzed and used to demonstrate that only the population associated with corn infestations was present. The absence of the other population associated with turf, pasture, millet, and alfalfa infestations likely reflects unexpected differences in migration behavior between the two groups or differences in fitness, the latter of which could have important consequences for fall armyworm control. Genetic surveys of fall armyworm from multiple locations in the U.S. identified novel patterns of population structure, linkage, and selection across the genome. The data confirms the identity of two genetically distinct strains of fall armyworm in North America, with the Z-chromosome driving divergence between strains. The results indicate that fall armyworm is a pest dyad with differences in population structure and genomic signatures of selection in response management history that should be separately considered when devising and implementing management strategies. Finally, the techniques developed for fall armyworm were applied to the soybean pest, soybean looper with over 700 specimens analyzed. Evidence of two genetically distinct populations were found and a preliminary description of soybean looper migration patterns in the southeastern United States were described.

Accomplishments
1. Identification of genes and promoters to induce male sterility for Sterile Insect Technique (SIT). Sterile Insect Technique (SIT) is a major element in Integrated Pest Management to eliminate introduced populations of dipteran and lepidopteran pests on an area-wide basis. The major disadvantage of SIT is its high cost due to the need to release overflooding numbers of sterile insects to compensate for the reduced fitness in irradiated males, and the need to rear and release sterile females in the absence of male-only strains. ARS researchers at Gainesville, Florida, characterized and genetically modified the wampa and Prosalpha6T genes from drosophilid and tephritid fruit fly pest species to generate genetic constructs capable of inducing male sterility for use in precision-guided SIT methods. The promoter sequences of the genes have been shown to drive sperm-specific fluorescent protein marking that can be used to identify the females mated to field released males. This will facilitate field studies designed to validate the effectiveness of the SIT method.

2. Mexico is a barrier restricting the introduction of invasive pests and traits into the US.. Fall armyworm is a major agricultural pest that is controlled in the US primarily by chemical pesticides and GMO Bt-crops. Resistance to several forms of Bt and other pesticides have been reported in South America generating concern that these traits could move into US populations. Genetic studies led by ARS researchers at Gainesville, Florida, in an international collaboration with scientists from the Mexican institutes of ECOSUR, the Biotecnología Genómica del Instituto Politécnico Nacional, and the Universidad Autónoma de Tamaulipas demonstrated that the geography and climate of Mexico substantially reduces population movements and gene flow of fall armyworm across the Central American land corridor. This makes the transcontinental spread of deleterious traits by natural migration less likely. These conclusions for fall armyworm are likely to be generalizable to other migratory moth pests and should inform policies designed to protect US agriculture from invasive pests and the introduction of negative genetic traits.

3. Soil factors affect pupation depth of corn silk flies. One of the major pests of fresh market sweet corn production in tropical and semi-tropical regions are corn silk flies. These flies target developing ears of corn for larval development and result in secondary fungal and bacterial infections. Insecticides are used heavily to protect developing ears, however, lapses in treatment or pest resistance can result in sufficient damage to render the cobs unmarketable. To provide better insight into the development of alternative management strategies, a scientist at Gainesville, Florida, conducted research to examine the pupation behavior of two major species of corn silk flies. In a laboratory study, three soil types were tested across six different levels of moisture to evaluate pupation behavior of the flies. Both soil and moisture levels impacted pupation depths with pupation at greater depths with moderate moisture levels and in organic muck soils. These factors are important for optimizing management strategies such as tilling or the use of parasitoids as biological control agents.

4. Crop specificity for the fall armyworm is determined by the Z-chromosome. Fall armyworm is a major agricultural pest that impacts corn and many other economic crops. This broad host range is due to two fall armyworm populations that are morphologically identical but differ in the crops they infest. Extensive genetic studies led by ARS scientists at Gainesville, Florida, in collaboration with scientists from the University of Texas A&M combined mitochondrial and Z-chromosome markers with whole genome sequencing analysis to map host plant preference to the Z-chromosome. These results defined the genetic markers that most accurately identify the strains. The markers are being applied to invasive fall armyworm populations in Africa and Asia to determine what crops in those regions are at risk as part of a continuing interaction with international groups that include the IITA, the European Union Food Safety Authority, and CIMMYT, studying the invasion of fall armyworm into the Eastern Hemisphere.

5. Two genetically distinct populations of soybean looper in the southeastern US.. Soybean looper is a major pest of soybeans and can be difficult to control because of resistance to several broad-spectrum insecticides. Understanding the population complexity of this species will facilitate the development of more targeted mitigation strategies. ARS researchers at Gainesville, Florida, led a team of university and corporate cooperators from Louisiana State University, Mississippi State University, Bayer Crop Science US, FMC Agricultural Solutions, and Corteva Agriscience. Genetic markers for soybean looper were developed and used to genetically analyze hundreds of specimens from multiple locations and time periods in the southeastern U.S. Evidence was found for two distinct soybean looper populations that exhibit limited ability to cross-hybridize. The migratory behavior of the species was also found to be significantly different from that of fall armyworm, a migratory moth with similar physical characteristics but different host specificity. There is evidence that this difference in migration behavior reflects differences in the timing of when the preferred host plants are available in quantity. The genetic markers developed here is serving as the foundation for population studies of soybean looper, in particular the mapping of the pesticide resistance traits to different regional populations. Such information will facilitate efforts to control the dissemination of pesticide resistance within the species.

6. Visual factors affecting attraction of corn silk flies. Corn silk flies are one of the primary pests threatening fresh market sweet corn production in south Florida. Flies deposit eggs on corn silk and the developing larvae feed and damage corn ears. While pesticides are used to control adult flies, precision timing of application is critical for maximum protection of ears. Surveillance of flies is hampered by the lack of sensitive trapping systems. In this study, a scientist at Gainesville, Florida, evaluated a range of visual attributes to determine the most attractive visual cues for these flies. Color, shape, background, patterns and ultraviolet reflectance influenced collections of flies on traps with differences between the two species evaluated. Both yellow and lime green strongly attracted flies and have potential as components of a visual trap.

7. Pheromone and floral attractant lures for fall armyworm. Moths can be attracted to traps in the field using several volatile chemicals. The pheromone blend released by female moths to attract male moths has been identified for most pest species and is commercially available as lures. Other volatiles, such as those produced by flowering plants, can also be used to capture moths and has the advantage of attracting both male and female moths. Flowering plants offer a range of chemicals to attract pollinators, especially phenylacetaldehyde and beta-myrcene. Although trapping studies have been conducted with one or the other lure, comparative studies with both pheromone and floral lures together have not been tested with fall armyworm. A scientist at Gainesville, Florida, conducted a trapping study in north central Florida (Marion County). Preliminary results suggest that when fall armyworm populations are high, more moths are attracted to the pheromone-only traps; however, when there are low populations, the traps catch equal numbers of moths. Therefore, the addition of floral compounds for monitoring fall armyworm appears to be advantageous. A curious result of this study was that there was no period from December through March where at least one fall armyworm moth wasn’t captured. This suggests that populations are active throughout the year further north than where overwintering populations were thought to exist.

8. Only the fall armyworm population associated with corn is present in Arizona. The fall armyworm is a major pest of corn in the Western Hemisphere and periodically causes significant economic damage in crops such as alfalfa, turf and pasture grasses, millet, and rice. The species is divided into two populations called host strains with different host preferences. ARS scientists at Gainesville, Florida, led a collaboration with researchers from Texas A&M University, the University of Nebraska, and the University of Arizona that found only the host strain that is the primary pest of corn was found in Arizona farm sites. This informs what crops are at risk in this location. Of potentially greater impact will be understanding the reason for the absence of the other strain, in particular whether it is due to differences in migratory behavior or fitness. Identifying the reason for why this host strain is absent could facilitate efforts to control this population in other locations.

U.S. DEPARTMENT OF AGRICULTURE

Insect Behavior and Biocontrol Research: Gainesville, FL