Project : USDA ARS

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Research Project: Improved Biologically-Based Methods for Insect Pest Management of Crop Insect Pests

Location: Insect Behavior and Biocontrol Research

2019 Annual Report

Objectives
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.

Approach
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.

Progress Report
The research efforts by the Insect Behavior and Biocontrol Research Unit 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 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 element. Under Objective 2, in vitro cultured insect cells infected with Wolbachia were microinjected into larvae of the fall armyworm and persisted to the adult stage and were vertically transmitted from the females to offspring. Under Objective 3, in collaboration with University researchers, acoustic technology was used to disrupt the mating of the Asian citrus psyllid. Movement of males towards disruptive signals is minimal and high-energy disruptive signals reduced mating activity in treated trees. Under Objective 4, studies on the relative importance of intensity vs 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. 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 employed to assess the recent introduction of fall armyworm into sub-Saharan Africa and its subsequent spread. In this study an international collaboration of scientists led by researchers at USDA-ARS (Gainesville) 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, field assessments of the establishment of a fall armyworm specific parasitoid were made for use as biocontrol agents of this pest moth.

Accomplishments
1. Migration of pest and invasive insects. The introduction of invasive pest species and/or deleterious traits (i.e., pesticide resistance) into domestic pest populations poses a continuing threat to agriculture. This is exemplified by the recent introduction of fall armyworm into Africa, India and Asia. The subsequent spread throughout most of sub-Saharan Africa of the fall armyworm pose a significant threat to African agriculture and potent problem for the Eastern Hemisphere because it is a voracious feeder and has long-distance flight behaviors. ARS researchers in Gainesville, Florida, led an international collaboration of scientists to investigate the migratory potential, behavior, and invasion history of the fall armyworm in Africa, information critical to monitor and control the spread of this pest in the Eastern Hemisphere. The findings provide insights into invasive moths relevant to understanding similar events in the United States.

2. Genetic breakdown of embryonic conditional lethality systems. The stability of genetic sterile male strains for Sterile Insect Technique (SIT) must be validated before long-term usage of these strains. ARS researchers in Gainesville, Florida, collaborated with those at national and international universities to assess the natural breakdown of genetic elements used to create tetracycline-suppressible sterile males. Heritable survivability was discovered in offspring by screening 1.2 million zygotic progeny under non-permissive conditions for embryonic lethality. DNA sequence deletions were found in both the primary-site and in second-site maternal effect genetic modifiers. We expect that descendants of the primary-site mutations should remain susceptible to control by the lethality system; however, the second-site modifier lines are likely to be resistant to further conditional lethal control resulting in a resistant population in the field. This new knowledge indicates that use of a conditional lethality system in the field may require the use of a secondary redundant lethality system to prevent survival of individuals resistant to either system.

3. Enhanced attraction of Asian citrus psyllids to visual targets. The Asian citrus psyllid which serves as a vector of the pathogen causing citrus greening disease or Huanglongbing, is one of the most serious citrus pests worldwide with particularly devastating impacts on the Florida citrus industry. While yellow sticky traps are the standard surveillance method and critical for guidance of pest management strategies, they are not effective when psyllid populations are low. ARS researchers in Gainesville, Florida, have determined optimal paint pigments that enhance attraction of Asian citrus psyllids in the laboratory. One pigment enhanced psyllid attraction over the yellow sticky traps in the field when used by ARS researchers at Ft. Pierce, Florida. These results provide potential for enhancement of current surveillance capabilities for this vector species.

4. Acoustic disruption of Asian citrus psyllids mating. The Asian citrus psyllid which serves as a vector of the pathogen causing citrus greening disease or Huanglongbing, is one of the most serious citrus pests worldwide with particularly devastating impacts on the Florida citrus industry. The males of the Asian citrus psyllid are attracted to sounds produced by females. ARS researchers in Gainesville, Florida, in collaboration with University researchers, assessed acoustic technology to disrupt the mating of the Asian citrus psyllids. Movement of males towards disruptive signals is minimal and high-energy disruptive signals reduced mating activity in treated trees. Widespread use of such devices could help reduce the use of pesticides for management of Asian citrus psyllids.

5. Gene editing of toxin transporter genes in the Indian meal moth. Resistance to toxin-based insecticides has become a major issue for biologically engineered crops. ARS researchers in Gainesville, Florida, used gene editing in the Indian meal moth and the fall armyworm to create mutations in genes that produce transport proteins that are targets of toxin resistance. Gene editing of these transporter genes resulted in white eyed moths 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.

6. Egg parasitoids reduce fall armyworm populations. The fall armyworm moth is a major pest of corn and grass in North America. The moth must overwinter in the most Southern regions and then migrate each spring to repopulate the Northern regions. ARS researchers in Gainesville, Florida, have assessed the distribution and use of an exotic parasitoid attacking fall armyworm egg masses. Collections of the parasitoid were successful in north central and central Florida, but currently the parasitoid has not been found in south Florida. Egg masses that were 24 hours old and attached to corn leaves had the highest parasitism rate. New techniques to attach egg masses to survey flags has the potential to search for the parasitoid in habitats without corn production.

U.S. DEPARTMENT OF AGRICULTURE

Insect Behavior and Biocontrol Research: Gainesville, FL