Graduate Thesis Or Dissertation
 

An evaluation of biological control of Linaria dalmatica with Mecinus janthinus in Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/h702q865c

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  • Dalmatian toadflax (Linaria dalmatica) has become a prolific invasive plant of rangelands in Oregon since its arrival in the early 20th century. In 2001, the Oregon Department of Agriculture initiated a release program promoting the distribution of the stem-boring weevil, Mecinus janthinus as classical biological control agent to reduce densities of Dalmatian toadflax and improve ecological integrity. This retrospective study sought to answer [1] What impact has M. janthinus had on reducing densities of Dalmatian toadflax, [2] Is M. janthinus spreading naturally to new sites, [3] Should ODA still facilitate spread of the agent, [4] If the program is successful, what is the long-term benefit acquired from this biological control program? These questions were answered using historical biological release forms and monitoring data, and a 2013 state-wide survey of Dalmatian toadflax and M. janthinus. The results show that M. janthinus has reduced average Dalmatian toadflax densities from 9.45 ± 1.34/m² prior to release, to 5.5 ± 1.1/m² after release. It was also found that the weevil has naturally migrated beyond their original release sites, and that there was no correlation between distance from release site and abundance of the weevil. These results indicate that ODA and its partners no longer need to distribute M. janthinus. Predictive modeling indicates that the current infestation of Dalmatian toadflax has reached 1% of its mean biological potential, while further expansion will be limited by the presence of M. janthinus. Reduction of plant density through biocontrol is of particular benefit to cattle production in Oregon where conventional control strategies of Dalmatian toadflax could reduce the annual value per acre of grazed land could be reduced by 6.5%.
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