Location: Insect Behavior and Biocontrol Research2020 Annual Report
Objective 1. Develop new transgenic conditional lethal strains for sexing and sterility in tephritid and drosophilid fruit flies to be used in the sterile insect technique, produce redundant lethality systems for ecological safety, and transgenic technology for emerging pest species such as the Asian citrus psyllid. Objective 2. Develop paratransgenic strains that eliminate the ability of host populations to vector plant disease by using Wolbachia cytoplasmic incompatibility to drive pathogen immunity throughout populations of key pests such as Asian citrus psyllid, glassy-winged sharpshooter, and potato/tomato psyllid. Objective 3. Develop automated acoustic methods for improved surveillance and detection of hidden and invasive pests such as red palm and citrus root weevils and Asian long-horned beetle that will facilitate more rapid information collection/processing by use of big data technologies. Objective 4. Develop improved visual-cue trap systems for surveillance of invasive and outbreak insect pests such as Asian citrus psyllid and corn silk fly, and improve strategies for detecting and predicting the dispersal of these pests by understanding the role of visual and other stimuli in affecting their behavior. Objective 5. Develop predictive models for fall armyworm migration pathways that are shifting due to climate change, and improve area-wide landscape management tactics for these pests by developing cover crop and biological control strategies to control them. Sub-objective 5.A. Develop genetic methods to monitor fall armyworm population behavior and air transport models to describe and predict its migration pathways and potential changes in infestation patterns due to climate change. Sub-objective 5.B. Improve area-wide landscape management tactics by developing cover crop and other strategies to mitigate pest populations such as fall armyworm, and attract or support natural enemies and pollinators.
The experimental approaches to achieve these objectives is multidisciplinary and integrates genetics, ecology, behavior, and engineering to address various stages of control, from molecular genetics leading to autocidal strain development to predicting changes in pest migration in response to global climate change. These approaches will apply, initially, to high priority invasive fruit flies, beetles, psyllids, fall armyworm and corn silk flies, and will include studies for development of molecular genetics methods for gene discovery and manipulation to develop genetically-modified pest strains to suppress wild populations, or eliminate their ability to vector pathogens of plant disease; development of detection and surveillance methods for optimization of acoustic, chemical and visual-cue detectors for detection and surveillance of hidden, invasive and outbreak pests; and biological control studies to develop predictive models to target shifting migrations of noctuid pests in response to climate change, and development of improved area-wide landscape management tactics to mitigate pest populations and attract natural enemies and pollinators.
The ARS lab in Gainesville, Florida, research efforts resulted in significant progress towards the five objectives and subobjectives for this project. Major progress was made under Objective 1 to understand the stability of genetic sterile male strains created for Sterile Insect Technique (SIT). The natural breakdown of genetic elements used to create tetracycline-suppressible sterile males was characterized as a critical step in determining the long-term usage of these strains. After screening 1.2 million zygotic progeny under non-permissive conditions for embryonic lethality (tetracycline-free diet), heritable survival to adulthood was discovered demonstrating breakdown of the genetic elements. Additionally, an initial transcriptome analysis of early embryos Oriental fruit fly was completed along with an analysis of the role of the micro-RNAs in early embryonic male sex-determination. Under Objective 2, in vitro cultured insect cells infected with the endosymbiotic bacterium Wolbachia were microinjected into larvae of the fall armyworm and the Mediterranean flour moth to establish infected strains to be tested for use in Incompatible Insect Technique. The bacteria persisted to the adult stage and were vertically transmitted from the females to offspring. Gene editing was used to create mutations that disrupted and tagged toxin-transporter genes with introduced fluorescent protein markers. Decreased sensitivity to bio-toxins was found in these mutant strains. Under Objective 3, a prototype acoustic-based mating-disruption trap for the Asian citrus psyllids was constructed incorporating multiple yellow sticky traps containing green light-emitting diode (LED) lights highly attractive to the psyllids and strung on a mating disruption vibration exciter system and is ready for testing in orchards. Under Objective 4, studies on the relative importance of intensity versus the hue of reflected light on attraction of Asian citrus psyllids and corn silk flies were field tested to examine enhancement of responses to the colors. Electrophysiological studies were conducted on the Asian citrus psyllid and two species of corn silk flies to identify photoreceptors contributing to the vision of these insects. Detailed laboratory assays revealed attraction of the Asian citrus psyllid to ultraviolet light-emitting diodes (LEDs) as well as ultraviolet-reflecting pigments which led to using ultraviolet pigments to enhance an attract-and-kill application. An optimal yellow paint and addition of odor were used to enhance visual traps as well. Traps using multiple modes of stimuli are being prepared for field deployment. Major contribution was made under Objective 5A where the previously developed systems to monitor fall armyworm migration were coupled with biological and physical processes for the agricultural and invasive pest fall armyworm by modeling its seasonal migration, and comparing simulated migrations to observed captures, and population genetic markers, on a continental scale. Simulations corroborated the spatial distribution and mixing of Texas and Florida source populations defined by genetic haplotypes. Air transport modeling was also used to project fall armyworm movements in Africa, southeastern Asia, the Caribbean, and South America, with the results used in combination with field sampling and genetic analysis to better understand fall armyworm migration behaviors to assess the recent introduction of fall armyworm into sub-Saharan Africa and its subsequent spread in Asia. In this study an international collaboration of scientists provided genetic analysis information on the migratory potential, strain behavior, and invasion history of the pest in Africa, which is critical for future efforts to monitor, predict, and control the spread of this invasive pest in the Eastern Hemisphere. The findings provide insights into invasive moths relevant to understanding similar events in the United States. Under Objective 5B a pheromone blend with novel components for fall armyworm was assessed that demonstrated increased attraction of fall armyworm adult males to pheromone traps which will lead to increase trap capture and improve monitoring. Additionally, field assessments of the establishment of a fall armyworm specific parasitoid were made for use as biocontrol agents of this pest moth.
1. Genetic breakdown of a Tet-off conditional lethality system for insect population control. The availability of genetically modified insects presents an attractive alternative to conventional pest control methods especially with regard to Sterile Insect Technique (SIT). One concern for the use of genetically modified insect strains is the potential for genetic breakdown or developed resistance to the genetic modification when billions of insects are produced for an Integrated Pest Management Program. The genetic stability of introduced genetic modifications that produced lethality was examined and found that, when extremely large numbers of insects are produced, there can be genetic breakdown of the system. From these results, ARS researchers at Gainesville, Florida, estimated that for 100 million genetically modified fertilized eggs deposited in the field, several hundred adults may survive from a breakdown in the introduced lethal genetic construct and then contribute to a lethality resistant population. In order to avoid the development of such a resistant population, recommendations are made for the use of a secondary redundant lethality system that would prevent insects resistant to either one of the systems to survive.
2. Southeastern Asia fall armyworms are closely related to populations in Africa and India, consistent with common origin and recent migration. The fall armyworm is the primary pest of corn production in the Western Hemisphere. Severe outbreaks of fall armyworm have now been reported throughout sub-Saharan Africa India, and southeast Asia posing a significant threat to global agriculture. This makes understanding the migratory behavior of fall armyworm critical to controlling the spread of this pest. Moth specimens from southeastern Asia were collected and genetically characterized by ARS researchers at Gainesville, Florida. These studies represent the first genetic description of fall armyworm from Myanmar, which is a likely source population for migration into China and the rest of northern Asia. The fall armyworm from Myanmar, China, India, and Africa were found to be closely related suggesting a common origin for these geographically distant populations and consistent with a single recent incursion into the Eastern Hemisphere. The data demonstrate the capacity of migratory moths for rapid and long-distance dissemination through some combination of natural and human-assisted migration. The genetic studies further indicate that the fall armyworm subpopulation most likely to be a threat to rice and millet, major crops in Asia, is not present in significant numbers in Myanmar and southern China.
3. Modeling of fall armyworm migration for areawide and regional pest management. Coupled biophysical air transport-based migration models have the potential to identify regions at risk for pests capable of long-distance flight and, in combination with future climate scenarios, project the consequences of climate change on pest migration. Fall armyworm can be used as a model for projections of migratory moths. This work by ARS researchers at Gainesville, Florida, confirmed and expanded on the model first published in 2016 by testing fall armyworm flight projections to information from a national network of trap captures and the analysis of population genetic markers on continental scale. ARS researchers at Gainesville, Florida, demonstrated that the model simulations corroborated the spatial distribution and mixing of Texas and Florida source populations defined by genetic haplotypes. The model will inform conceptual designs for areawide or regional pest management programs by enabling estimates of the geographic potential of pest suppression that could be achieve with earlier pest suppression in smaller source regions.
4. Odor enhances attraction of psyllids to visual traps. Asian citrus psyllids are invasive insects that negatively impact the citrus industry as a pest but also more significantly as a vector of Huanglongbing/citrus greening. ARS researchers at Gainesville, Florida, monitored the population levels of Asian citrus psyllids which is critical for management of these pest insects and concomitantly citrus greening. Monitoring is typically conducted using yellow sticky traps. The use of different trap colors in combination with plant volatile odors, either individually or in blends, or central visual targets, was assessed to determine if specific combinations would increase attraction to the sticky traps. One shade of yellow paint on the traps in combination with a single volatile chemical were found to increase the attraction of the psyllids to the sticky traps. These results establish a foundation for potential future field trails to determine if these combined trap color/components will increase the efficacy of low population surveillance of the Asian citrus psyllids under field conditions and lead to better control of these pest insects.
5. Gene editing used to tag toxin transporter genes in the Indian meal moth. Resistance to toxin-based insecticides have become a major issue for biologically engineered crops. ARS researchers in Gainesville, Florida, used gene editing to introduce a fluorescent gene marker into the Indian meal moth and the fall army worm to create mutations in genes that are important in acquisition of toxin resistance. Gene editing of these transporter genes resulted in cultured insect cell lines and white eyed moths that produced a fluorescent protein marker and effected Bt resistance. Using this gene editing system, various pesticide resistance genes can be mutated, and the effects studied to find mechanisms to avoid or reverse pesticide resistance.
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