Phenology, Host-Plant Resistance, and Biological Control of Stephanitis pyrioides in Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/v118rh19r

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  • The azalea lace bug (Stephanitis pyrioides Scott) is a recently detected invasive pest to the Pacific Northwest and has become a major concern in Oregon. It feeds on azaleas as well as rhododendrons causing stippling on the top side of leaves. The damage is aesthetically displeasing and affects plant vigor and photosynthetic capabilities, and, in cases with severe damage, can kill plants. The objectives of this work were to: 1) monitor for the presence of potential natural enemies and life stages of S. pyrioides from 2014 to 2016 through sampling in the Willamette Valley in Oregon, 2) observe any resistant cultivars that may be present, and 3) examine biological control efficacy of S. pyrioides using a predator and pathogen. These three objectives were looked at to provide information on what natural enemies are present and what time of the year S. pyrioides control would be most effective, find potential plant characteristics that may confer resistance, and determine if biological control is a viable option to reduce S. pyrioides pest abundance. Two specialist natural enemies of S. pyrioides, Anagrus takeyanus Gordh and Stethoconus japonicus Schumacher were not found and only about 8% of all arthropods captured in sweep nets and 4% in sticky traps could potentially prey on S. pyrioides as generalist predators. From shake sampling and leaf collections, adults and eggs were found year round and a total of 8,780 S. pyrioides were collected for all stages. Over half of all collected adults were females. Nymphs were found almost exclusively during the spring and summer months. Roughly 3.5 generations, based on a total development time of 394 degree-days (DD) are estimated to have occurred using weather data from Salem, Oregon. Secondly, cultivar observations to evaluate natural resistance by assessing for infestation or damage provided a list of approximately 75 species and cultivars that had no evidence of azalea lace bug feeding. Of these 75, four cultivars, species and hybrids were tested in a laboratory for feeding and fecal deposition beside a susceptible cultivar. All four resistant rhododendrons had no feeding and resulted in mortality rates over 90%. Third, evaluations of biological control, specifically predation by a green lacewing, Chrysoperla rufilabris Burmeister, significantly reduced S. pyrioides per leaf in a nursery setting when combined with methyl salicylate in 2014. However, larger follow up studies in 2015 did not reflect these results. The pathogen Metarhizium anisopliae had a high mortality rate when sprayed, but only caused a marginally higher mortality rate when compared to water sprays. Overall, this work presents novel and valuable information on azaleas and rhododendrons and S. pyrioides in the Pacific Northwest. This work provides the framework of phenology, a mode of resistance and valuable information on biological control to consider and incorporate into future management of S. pyrioides in Oregon.
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