Location: Pest Management and Biocontrol Research2011 Annual Report
1a. Objectives (from AD-416)
Develop knowledge and control tactics based on the physiology, biochemistry, genetics and vector-pathogen interactions of insect pests. Characterize and exploit interactions among plants, insect pests and natural enemies; investigate the role of arthropod predators and trophic interactions for improved biological control. Characterize flight behavior and dispersal of insect pests and natural enemies; elucidate relationships among landscape structure, pest and natural enemy biology and dispersal behavior. Refine sampling strategies for insect pests and their associated natural enemies; develop and refine economic thresholds for sucking pests in cotton that incorporate biological control potential; support post-eradication detection of pink bollworm populations. Refine insecticide-based management strategies; characterize factors influencing resistance to chemical insecticides and insecticidal proteins in transgenic crops; evaluate insecticide selectivity; support post-eradication pink bollworm resistance monitoring in Bt cotton.
1b. Approach (from AD-416)
Research will build a solid foundation of fundamental tactics for avoiding pest problems and will strengthen prescriptive pest control through refinement of monitoring, decision aids and effective treatment options. Research will explore and exploit the molecular and chemical basis of male-derived factors on female mating inhibition and hormonal factors regulating reproduction and diapause in Lygus. hesperus, the molecular basis of water channel proteins in Bemisia tabaci, the impact of plant virus and plant allelochemical mediated changes on B. tabaci fitness and insecticide resistance, respectively, and the molecular basis of Bt resistance in Pectinophora gossypiella. Further research will exploit semiochemicals and tri-trophic interactions for enhanced biological control, and identify insect and plant based semiochemicals enabling mating disruption and improved monitoring of B. tabaci and L. hesperus. Flight behavior and inter- and intra-crop dispersal of L. hesperus, and source-sink relationships for arthropod predators inhabiting the agro-ecosystem will be quantified, facilitating IPM at the landscape scale. Selective insecticides and improved decision aids that account for natural enemy abundance will be evaluated and developed for B. tabaci in cotton. Research will further support P. gossypiella post-eradication efforts through refinement of pheromone-based monitoring systems and detection of resistance to Bt cotton. Replaces 5347-22620-017-00D, 5347-22620-018-00D and 5347-22620-020-00D (10/10).
3. Progress Report
Plant bugs, Lygus spp., readily feed on the reproductive tissue of 4 new industrial crops (camelina, guayule, lesquerella, vernonia). Behavior did not differ among life stages or sexes and insects fed less on camelina. Flight assays for Lygus adults at high (30C) and low (16C) temperatures show the insect has a narrow physiological range for flight. Research determined Lygus bug hormonal dynamics regulating sexual maturation, gametogenesis and metabolism. The source and nature of Lygus male derived compounds that regulate female reproductive behavior were explored. The properties and composition of a Lygus male-derived antiaphrodisiac regulating female attractiveness was elucidated. Progress was made in understanding the metabolic rate and activity levels of diapausing and non-diapausing males and females and the efficacy of an external color classification system for non-invasively identifying the diapause status. Lygus bug odor receptors similar to the Drosophia sex peptide receptor and odorant receptor were identified. In addition, 39 Lygus odorant binding proteins were identified with many selectively expressed in the adult antennae and 1 up-regulated in response to female mating. These receptors are localized on the cell surface. The Lygus sex peptide receptor expression profile is consistent with a role in mediating sexual behavior. Research discovered a novel water channel protein from the Bemisia tabaci (whitefly) gut where it plays an important role in water balance. A whitefly strain discovered in 2004 from an Arizona retail store possessed high levels of resistance to insecticides and was confirmed as the first detection of the exotic Q biotype in the U.S. No Q biotype B. tabaci have ever been recovered from Arizona field crops indicating that the Q biotype may thus far be restricted to retail or wholesale ornamentals. Proteins are being used to mark insects for dispersal studies. Collaborative research is being conducted to monitor insect dispersal in conventional crops and biofuel crops. Protein markers are being applied with a broadcast sprayer. In turn, field-collected insects are examined for the presence of the marks. This technique provides a tool to mark insects over entire landscapes to study insect dispersal patterns. Studies were initiated to estimate the concentration of different marking materials that need to be applied in the field in order to mark a consistent proportion of the insect population and to estimate the rate of potential mark transfer during sampling operations. Landscape-scale spatial analyses are being conducted to estimate source and sink relationships for natural enemies of Lygus and whitefly in the cotton ecosystem. Studies were initiated to examine the efficacy of natural enemy attractants for improved biological control in cotton. Comparative honeybee colony fitness was examined in hives near imidacloprid-treated cantaloupes and hives near untreated cantaloupes to evaluate the potential link between neonicotinoid insecticide exposure and colony collapse disorder. Spirotetramat was superior to all other insecticide treatment regimens against vine mealybug infestations in table grapes.
1. Release of sterile insects suppresses resistance to Bt in transgenic Bt cotton. The introduction of Bt cotton - transgenic cotton that makes insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) - greatly reduced pink bollworm populations in Arizona. But the invasive moth remains one of the world’s most destructive cotton pests and lab tests and international field collections show that it can develop resistance to Bt in Bt cotton. To slow resistance by the pest, growers in Arizona had been required to set aside “refuges” of conventional cotton that promote survival of pink bollworm caterpillars susceptible to Bt. But due to the expense and crop losses associated with refuges, in 2006 the US Environmental Protection Agency granted permission to dispense with refuges in favor of releasing sterile pink bollworms over Arizona’s cotton fields. In this multi-agency cooperative project, ARS research scientists in Maricopa, AZ, and Parlier, CA, and scientists from the University of Arizona found for the first time that the release of sterile insects can be used to effectively suppress pest resistance to Bt in Bt cotton over a very large area. This information benefits government, academic, and industry researchers as well as regulators and administrators of insect control and resistance monitoring programs and provides new information regarding possible benefits of large-scale sterile insect release.
2. Pollinator movement between conventional and genetically modified (GM) crops. One concern in deploying transgenic plants in the environment is the spread of transgenes to other related crops in the region through pollen flow. ARS research scientists at the Arid-Land Agricultural Research Center, Maricopa, AZ, and researchers at the University of California at Davis mass marked honey bees exiting from 112 colonies over a five mile area in order to track pollinator movement between conventional and herbicide tolerant alfalfa. The honey bee dispersal data along with alfalfa seed sampling data estimate gene spread via pollen (pollen mediated gene flow). The distances traveled by marked bees ranged from a minimum of 45 m to a maximum of 5,983 m, with an average flight distance of 800 m from their apiary of origin. Gene flow averaged 1.7% at 50 m, 0.2% at 1600 m, and was not detectable at 8,050 m. These results are being utilized by seed certification agencies to develop isolation distances, and mapping and stewardship programs to be employed during the production of seed for markets that are sensitive to the presence of transgenic traits. The results are valuable to producers and regulators in terms of understanding the required distances for isolating biotech and conventional seed alfalfa production.
3. Landscape level dynamics of plant bugs in cotton. Lygus bugs affect multiple crops in arid-land agricultural systems and are major pests of cotton in Western U.S. ARS research scientists from the Arid-Land Agricultural Research Center, Maricopa, AZ, and researchers at the University of Arizona and the University of California developed predictive methods for estimating Lygus abundance in specific cotton fields. Abundance in a given cotton field can be accurately predicted by knowing the area of cotton, uncultivated habitats and seed alfalfa within 2.75m of the cotton field. This provides growers with valuable information on how they can manipulate the planting of various crops on their farms and potentially cooperate with neighboring growers to reduce the impact of pest insects regionally.
4. Flight behavior, metabolism and survivorship of lygus bugs. Lygus is a multicrop pest in the western USA, which may be more sensitive to control measures when it is overwintering. To take advantage of any potential susceptibility, more information is needed about seasonal variation in movement and metabolism. ARS research scientists at the Arid-Land Agricultural Research Center in Maricopa, AZ, showed that diapause status reduced flight activity of females but not males and that diapause increased survivorship in males but not females. These results benefit producers and pest managers in terms of understanding insect movement in the landscape during winter and spring when the pest is potentially easier to control.
5. Insecticide residues in plant guttation fluid. Identifying ways by which insecticide exposure occurs in a crop environment is important not only for effective targeting of a pest insect, but also for conserving beneficial insects by limiting exposure to pollinators, predators and parasitoids. Imidacloprid is a neonicotinoid insecticide that is taken-up by roots and systemically distributed throughout treated plants, and thus is generally considered to be selectively toxic only to plant feeding insects. ARS research scientists at the Arid-Land Agricultural Research Center, Maricopa, AZ, recovered relatively high concentrations of imidacloprid in the guttation fluid on field grown cantaloupes that were soil-treated with imidacloprid. Honeybees and other beneficial insects commonly imbibe free sources of water such as guttation droplets on leaf margins and are potentially at risk where guttation occurrences are common. Awareness of this potential source of toxicity to honeybees could help growers mitigate exposure by altering the timing of imidacloprid applications in crops or by relying on alternative insecticides.
6. Methods for calculating optimal trap height for monitoring pest insects. The abundance of many pest insect populations is monitored by placement of attractive traps with pheromone lures at the mean flight height of the particular pest. Over 60 previous studies have placed traps at several heights on a pole to catch insects at these heights above ground. However, most of these studies have not calculated the mean flight height of species in order to find the optimal trap height for monitoring. Researchers at the Arid-Land Agricultural Research Center, Maricopa, AZ, developed mathematical analysis methods to determine mean flight height and standard deviation from catch data on three or more trap placement heights for over 100 insect species reported in the literature - many pests of agriculture. Computer simulations verified the analysis methods, which will allow future studies to accurately determine the optimal height for monitoring traps that delineate pest population abundance and their distribution in the cropland.
7. Lygus impacts on the new oil-seed crop Lesquerella. Lygus bugs affect multiple crops in arid-land agricultural systems, including the new crop lesquerella that is being considered as a substitute for castor in production of industrial oils and resins. Researchers at the Arid-Land Agricultural Research Center, Maricopa, AZ, and the University of Arizona conducted long term field studies to quantify the impact of Lygus bugs on Lesquerella yield. Studies found no significant limits in seed yield or seed oil content when the crop is managed in an optimal fashion. Results will benefit growers in arid production regions who are considering Lesquerella as an alternative crop or a rotational crop in their production systems.
8. Diapause status affects external body color of Lygus. Elucidating the regulation of Lygus life cycles is essential for developing new approaches for targeted control, but such research is constrained by a lack of clear external markers that can accurately and non-invasively differentiate between bugs in different metabolic and developmental states. ARS research scientists at the Arid-Land Agricultural Research Center, Maricopa, AZ, showed that the extent and color of sub-cuticular fat creates distinct color variants that provides a non-invasive technique for quickly differentiating between diapausing (dormant) and non-diapausing individuals. Diapausers have a ventral abdomen that is light yellow to light green in color while non-diapausers have a dark green color. This color diagnostic will permit rapid assessment of field populations by growers and researchers, and will facilitate laboratory studies of development and reproduction regulation.
9. Development of an easy-to-use predator gut assay. The development of antibody and DNA probes for the study of predation is time consuming, costly, and may not be feasible for many biological control researchers. Researchers at the Arid-Land Agricultural Research Center, Maricopa, AZ, developed an easy, cost effective, and quantifiable molecular gut content assay for studying predation on insect pests. Recent research has shown that this method is more accurate and reliable than DNA based gut content assays. Predation rates on Lygus (a major pest) by the entire cotton predator complex were quantified using this method. This methodology provides a new tool for researchers to study many types of predator/prey interactions.
Naranjo, S.E., Castle, S.J. 2010. Sequential sampling plans for estimating density of glassy-winged sharpshooter, homalodisca vitripennis (Hemiptera: Cicadellidae) on citrus. Crop Protection Journal.29:1363-1370.