Progress 08/15/10 to 08/14/11
Outputs
OUTPUTS: Amblyseius swirskii (Athias-Henriot) predatory phytoseiid mites quickly leave the foliage of plants that lack both leaf hairs (leaf trichomes) and a supplemental food source (pollen). Our first set of experiments in objective 1 sought to identify materials which could serve as artificial leaf hairs (low densities of tiny fibers) when applied to floral crops lacking leaf trichomes, thereby enhancing phytoseiid persistence and egg production. Ten adult female A. swirskii were released onto individual bean seedlings or small potted impatiens plants onto which various trichome mimic materials had been applied to the top surface of leaves. Fibers were applied with or without a light dusting of field-collected cattail pollen. The number of mites remaining on plants was assessed after 1 to 7 d and compared to untreated control plants. Phytoseiid oviposition performance on various pollens was evaluated by comparing 6 commercially purchased pollens to our cattail standard in a leaf disc assay. Objective 2 evaluated the influence of artificial leaf trichomes and pollen on A. swirskii and western flower thrips at the scale of a single plant with an exact number of predatory mites applied once. Ten adult female A. swirskii were released onto small flowering potted impatiens plants with a natural thrips infestation. Plants receiving predatory mites were treated with 1) very finely cut acrylic yarn fibers and cattail pollen, 2) fibers only, 3) pollen only, or 4) no fibers and no pollen. A no fiber and no pollen treatment without predatory mites was also included to monitor thrips levels on untreated plants. Thrips and predatory mites were counted in destructive sampling after either 5 or 19 d. The influence of fibers and pollen on both predatory mite density and thrips abundance was determined. Objective 3 evaluated the impact of fibers and pollen on A. swirskii and western flower thrips populations in large patches of impatiens with phytoseiids sprinkled onto the plant canopy from the shipping container to mimic a commercial application process. Thrips were released into the plants and the one meter square patches of impatiens were 1) left completely untreated as a control, 2) treated with very finely cut acrylic yarn fibers, cattail pollen, and A. swirskii, 3) treated with only fibers and A. swirskii, 4) treated with only pollen and A. swirskii, or 5) treated with only A. swirskii. The predatory mites were applied weekly for 3 weeks with the release density of mites estimated at each application by counting adult and immature phytoseiids in samples of the bran carrier material. Fibers and pollen were reapplied weekly. Foliage and flower samples were removed from patches weekly for 4 weeks and the number of thrips and phytoseiid mites counted. Results of this work are being presented at the Entomological Society of America annual meeting in Reno, NV in November 2011. PARTICIPANTS: Dr. Jan Nyrop: Dr. Nyrop provided overall supervision of the project and provided expertise on experimental design, data analysis, phytoseiid behavior and predator-prey interactions. He is also responsible for final reports and final editing of scientific manuscripts. Dr. Rebecca Loughner: Dr. Loughner had primary responsibility for completing the experiments that assessed phytoseiid response to trichome mimics and experiments that assessed the overall impact of trichome augmentation on the effectiveness of biological control. These responsibiliies include oversight of other personnel, execution of experiments, data analysis and preparation of report drafts. She was responsible for oversight of staff that maintained plants and mite and thrips colonies. Dr. John Sanderson: Dr. Sanderson provided expertise on greenhouse management and ensured that the longer-term experiments designed to verify that commercial-scale trichome augmentation improves thrips biological control were conducted well. He played a key role in making sure that the developed application technology is feasible for use in greenhouses. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Overall, adding tiny fibers as trichome mimics does affect predatory mite abundance. Our hypothesis was that fibers would enhance mite populations; the fibers that yielded early success on beans actually appear to have a negative impact on mites when applied to impatiens. Mite abundance clearly increased when both fibers and pollen were added to beans compared to either fibers or pollen alone. The relationship of fibers and pollen was not as straightforward on impatiens, with no clear benefit to providing both fiber and pollen over either alone. Specific outcomes for objectives are as follows beginning with objective 1 in which we identified a fiber material and pollens which could be used to enhance the suitability of plant habitat for mites. These tiny fibers must be in close contact with the leaf surface to mimic the mite habitat provided by leaf trichomes. The leaf texture of plants including impatiens, pepper, basil, and pansy was sufficiently smooth that application of an adhesive (dilute white glue) was necessary for the applied fibers to remain attached. On beans fibers with glue approximately doubled the retention of A. swirskii compared to fibers without glue. None of our originally proposed fiber materials (cellulose, jute, paper pulp) were sufficiently effective at increasing mite retention. The material that most consistently produced results was an acrylic yarn that had been pulled apart into strands and hand cut into very small lengths. Achieving an even distribution of any of the fiber materials required breaking up clumps of the raw fibers. The system ultimately used in objectives 2 and 3 consisted of shaking over the plant canopy a plastic cup with wire mesh covering the opening and several wingnuts dropped into the fiber material. Of the pollens tested, apple, cherry, and plum pollens are commercially available in quantities suitable for orchard applications and are promising for use along with the fiber technology. As the pollens are somewhat stickier than cattail pollen, we continued using cattail for our remaining objectives. Objectives 2 and 3 were conducted simultaneously using plants from the same lot. Results from the two experiments differed in A. swirskii effectiveness but not in the impact of fibers. On the individual impatiens in objective 2, the A. swirskii decreased the abundance of thrips relative to the no phytoseiid control. There was however, no consistent, clear impact of fibers and/or pollen on the abundance of A. swirskii or thrips. The densities of A. swirskii after 19 d were 2.5 to 3.5 times greater than the original 10 mites released. In objective 3 with large patches of impatiens, the A. swirskii failed to reduced thrips abundance compared to the untreated control. Although fibers alone and with pollen were associated with decreased thrips abundance, there was no impact of fibers or pollen on A. swirskii. We have not yet found a fiber material that reliably replicates the natural structure of leaf hairs when observed under a microscope and it is clear that the application of fibers is an inappropriate strategy for increasing mite densities after plants are heavily flowering.
Publications
- Loughner, R., Nyrop, J., Wentworth, K., Sanderson, J. 2011. Towards enhancing biocontrol of thrips: effects of supplemental pollen and fibers on foliar abundance of Amblyseius swirskii. Page 105-109 in IOBC/wprs Bulletin, Vol. 68 Working Group Integrated Control in Protected crops, Temperate Climate. Sutton Scotney, United Kingdom.
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