Location: Pest Management and Biocontrol Research
Project Number: 2020-22620-023-000-D
Project Type: In-House Appropriated
Start Date: Jul 1, 2020
End Date: Jun 30, 2025
1: Improve biological control of key pests by quantifying interactions between prey & generalist predators, including predators occupying different trophic levels, using molecular marking & gut content assays in the field & defining impacts of transgenic crops on non-target species through meta-analyses. Sub-objective 1A though 1B: See uploaded project plan. Sub-objective 1C: Examine temporal and spatial dynamics of whitefly, Lygus, predator and pollinator movements between cotton and Vernonia, a new industrial crop.(New, May, 2018) Sub-objective 1D: Assess the risk of disruption of biological control of whiteflies by the introduction of a new Bt cotton with activity against Lygus bugs and thrips.(New, May, 2018) 2: Refine resistance management strategies based on improved knowledge of host (species & phenology) & environmental (temperature) influences on inducible mechanisms of stress response in whitefly & lygus & of Cry-toxin binding & mechanisms of Bt (Bacillus thuringiensis) toxin resistance in pink bollworm. Sub-objective 2A through 2C: See uploaded project plan. 3: Refine knowledge of factors regulating mate-finding & the dynamics of reproduction in lygus & whitefly by optimizing lygus sex pheromone doses & component ratios, defining insect phenology-dependent roles of short-range cues of lygus mating receptivity, & quantifying impacts of host, environmental, & population density-based factors on whitefly sex ratios. Sub-objective 3A through 3D: See uploaded project plan. 4: Define key life history parameters including the development & survival strategies of lygus & key species of beneficial insects in relation to the environment by quantifying consequences of extreme thermal environments & defining insect stage- dependent & environment-dependent diapause responses & associated transcriptional- based & endocrine-based patterns in lygus. Sub-objective 4A through 4C: See uploaded project plan. 5: Describe molecular genetic responses, facilitating survival & adaptation in pest insects by identifying lygus & whitefly transcripts responsive to xenobiotics & environmental (thermal, water, oxidative) stressors, identify molecular targets for disruption by chemical or genetic agonists or antagonists, & develop methods to deliver dsRNA for functional disruption of aquaporins or other targets essential to maintain homeostasis. Sub-objective 5A through 5B: See uploaded project plan. Sub-objective 5C: Examine the potential of an ornamental plant to disrupt the osmotic water permeability of B. tabaci aquaporin water channel proteins using cage studies and in vitro heterologous insect cell expression functional assays(New, May, 2018).
Objective 1: Biological control-informed thresholds, which determine pesticide treatment using the density of pests and their predators, will be developed for L. hesperus in cotton using experimental field research and data mining. Densities of L. hesperus and natural enemy communities will be manipulated and monitored to identify key predators of L. hesperus. Predictions of ratios that enable biological control will be tested and compared to conventional threshold models. Companion plantings of vernonia and marigold will be tested, with lab and field approaches, for their efficacy in protecting cotton by drawing pests away from the crop and towards areas with high predator density. Protein marking will be used to track movement and predator feeding patterns on all life stages, and to determine whether the impact of drought-tolerant cotton isolines on pest colonization and predator success. Objective 2: Cotton engineered to express the Bacillus thuringiensis (Bt) toxin selective for L. hesperus will be tested for non-target effects on natural enemies. Field studies will compare Bt and non-Bt cottons with and without additional insecticides. Sweep net sampling and sticky cards will measure the abundance of common predators of L. hesperus and B. tabaci. Biological control function will be assessed using established thresholds for B. tabaci and direct measures of predation. The impact of insecticidal seed treatments on the natural enemies of B. tabaci and L. hesperus in cotton will be assessed using field-based inclusion cage studies with young cotton plants containing whitefly eggs exposed to adult and immature thrips. To assess early-season and season-long efficacy and non-target impacts of cotton seed-treatments, field studies will compare population densities of B. tabaci, thrips, and other arthropods exposed to cotton with and with seed treatment. Objective 3: The efficacy of oral RNAi will be assessed in L. hesperus by feeding or injecting dsRNA for genes involved in ovary function. To determine if digestive tract nucleases destroy dsRNA before it can be effective, luminal contents and gut homogenates will be assessed for enzymatic activity. To identify genes involved in dsRNA uptake from the gut, homologs of endocytotic pathway genes will be identified then silenced by RNAi to determine function. The role of parental RNAi will be tested by injecting adult L. hesperus females with dsRNA targeting the eye pigmentation genes and examining embryo eye color. Sex determination gene homologs in L. hesperus will be identified, their expression measured, and function determined by RNAi. CRISPR/Cas gene driver methods will be optimized for L. hesperus, using injections and electroporation to modify embryos. Bt toxin resistance mechanisms in pink bollworm and corn earworm relying on mutations in the ABC transporter and midgut cadherin genes will be examined by toxicity screening and cellular localization. Determination of whether a fitness tradeoff occurs in the corn earworm with Bt toxin resistance will be made in susceptible and resistant strains fed toxic and non-toxic diets by comparing life history traits and flight performance.