Graduate Thesis Or Dissertation
 

Classical biological control of the filbert aphid, Myzocallis coryli (Goetze) (Homoptera:Aphididae) in western Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/tx31qm110

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  • A classical biological control project was undertaken against the filbert aphid, Myzocallis coryli (Goetze), in western Oregon. Hazelnut orchards in Spain, France, and Italy were searched for natural enemies of the aphid, and a parasitic wasp, Trioxys pallidus Haliday, was imported, quarantined, mass-reared, and released in Oregon orchards. The wasp successfully attacks and completes its development on the Oregon race of the filbert aphid. A greenhouse culture of the parasitoid has been maintained continuously for over 50 generations, and approximately 30,000 adult wasps have been released in the Willamette Valley. Overwintering survival has been documented in at least eight different locations. In three commercial orchards, the parasitoids reduced aphid populations by 26-32%. The newly imported biotype of T.pallidus attacking the filbert aphid was compared with the previously established biotype attacking the walnut aphid. The two races are morphologically indistinguishable, and were shown to freely hybridize in reciprocal crosses, producing viable, fertile offspring. However, the races showed distinct differences in host suitability, with the newly imported biotype having greater reproductive succes:3 on filbert aphids than the previously established (walnut) biotype. Bionomics of both M.coryli and T.pallidus were studied in the laboratory. Data indicate a higher developmental threshold for overwintering parasitoid pupae (7.4° C.) than for overwintering aphid eggs (3.3° C.). Based on a common threshold of 6.0° C., thermal requirements for time-to-adult are ca. 240 and 265 degree days for summer generations of aphids and parasitoids, respectively. Diapause termination in aphids is more strongly influenced by winter chilling than is diapause termination in parasitoids.
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