Location: Pest Management and Biocontrol Research
2015 Annual Report
Objectives
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.
1A: Quantify interactions among prey & predators occupying different trophic levels using molecular & gut content assays.
1B: Define impacts of Bt crops on non-target arthropod abundance, community diversity & biological control function.
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.
2A: Evaluate insecticide susceptibility of Bemisia tabaci in relation to temperature & host plant condition.
2B: Genetically characterize in-house Cry2Ab-resistant Pectinophora gossypiella; determine inheritance & whether in-house strain shares a genetic locus with the Univ. of Az Cry2Ab-resistant strain.
2C: Establish whether P. gossypiella cadherins & ABCC transporters function as Bt Cry-1Ac & Cry2Ab toxin receptors.
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.
3A: Evaluate sex ratio variability in the haplodiploid whitefly B. tabaci.
3B: Identify semiochemicals of B. tabaci.
3C: Optimize sex pheromone doses & components to attract Lygus hesperus.
3D: Investigate responses of male L. hesperus to myristyl acetate & anti-mating activity of surface-applied myristyl acetate.
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.
4A: Quantify influences of variable temperatures on development & survival of L. hesperus stages, & on eggs & nymphs of key predators.
4B: Determine effects of mating & temperature on reproduction & longevity of L. hesperus.
4C: Define key aspects of L. hesperus diapause.
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.
5A: Describe transcriptional & biological responses of L. hesperus to stressors.
5B: Develop methods to knockdown L. hesperus & B. tabaci gene targets using dsRNA.
Approach
Interactions among key prey and predator species will be quantified using molecular marking and gut content assays in laboratory, greenhouse and field experiments. Meta-analyses of updated databases will examine the impacts of transgenic Bt crops on non-target arthropod abundance, community diversity, and biological control services. Insecticide susceptibility of whitefly in relation to host and environmental conditions will be determined using laboratory assays of field-collected insects. Results of field studies will guide controlled experiments to determine mechanisms by which host condition, population density, and temperature influence susceptibility to insecticides, including expression of detoxification enzymes. Inheritance, dominance, and allelism of Cry2Ab resistance in the pink bollworm will be determined using crosses among laboratory strains of the insect. Roles of pink bollworm cadherin and ABC transporter protein as functional receptors of Cry-toxins will be examined by fluorescent imaging of cell cultures transfected with tagged clones of the target cDNA. Cytotoxicity of Cry-proteins will be determined for each putative receptor. Seasonal patterns in whitefly sex ratios will be documented in the field and association of symbionts with sex ratio shifts will be examined using PCR. Respective roles of male availability and copulation interference in determining sex ratios will be evaluated in greenhouse studies. Potential insect- and plant-derived semiochemicals for manipulating or monitoring whitefly will be identified by GC and screened using olfactometry. Attractiveness of the recently identified sex pheromone of Lygus hesperus will be optimized using electro-antennographic detection followed by field trap studies and experiments to determine the diel pattern of pheromone emission. Influences of male lygus reproductive phenology, time since mating, and concentration of a chemical inhibitor of mating on mating frequency will be determined in laboratory assays. Also, potential of the mating inhibitor as a mating disruptant will be evaluated based on responses of insects to treated substrates. Influences of environmental extremes on development and survival of lygus and selected predators, and on mating, reproduction, and longevity of lygus adults, will be examined in controlled studies incorporating constant and variable temperature regimes. Stage-specific sensitivity of the lygus diapause response will be examined in photoperiod-switching and controlled environment experiments. Companion studies will examine hemolymph protein and transcript profiles to identify potential molecular markers indicative of diapause. Molecular responses of whitefly and lygus to xenobiotic and environmental stressors, especially temperature, will be assessed based on transcriptomic responses to experimentally induced stress, and links between stress responses and susceptibility to insecticides will be examined in bioassays. dsRNA will be used against selective targets to silence genes important to biological fitness in lygus and whitefly.
Progress Report
This is a new project initiated July 1, 2015 and continuing research from the previous project, 2020-22620-021-00D, "Sustainable Pest Management Strategies for Arid-land Crops." Please see this report for additional information.
Objective 1: Research continues to characterize the intercrop dispersal patterns of lygus bugs, invasive pests, and natural enemies in a wide variety of desert agroecosystems using protein mark-capture methods. Progress was made on the initial global Bt crops non-target database, focusing on Bt corn. Preliminary meta-analyses were conducted to verify database integrity, inclusion of appropriate field parameters, and screening data for independence.
Objective 2: Studies of differences among insecticide detoxification mechanisms between phloem- and xylem-feeding insect pests continued. Studies of toxicity of ten insecticides against four key species of beneficial insects were initiated, along with experiments to identify correlations between insecticide use patterns and resistance to insecticides in the sweetpotato whitefly. Efforts to clone sequences for receptors of the Cry2A insecticidal protein in pink bollworm continued.
Objective 3: Collaborative efforts to define relationships between whitefly and selected endosymbionts were continued.
Objective 4: Studies of Lygus bug reproductive adult lifespan and lifetime fecundity under controlled conditions were continued. A study was initiated to estimate the age distribution of a field population of Lygus using lifespan under controlled conditions in a demographic model. Studies of Lygus bug egg development under constant and variable temperatures were completed and studies of daily periodicity of egg hatch were started.
Objective 5: Study of Lygus bug thermal-response genes continued, and candidate genes for expression knockdown were cloned. Also, development of systems to silence Lygus genes through oral administration of double-stranded DNA continued.
Accomplishments
