Graduate Thesis Or Dissertation
 

Toxicity of some commonly used pesticides to Trioxys Pallidus and its establishment in filbert orchards of Willamette Valley

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  • A parasitic wasp, Trioxys pallidus Haliday (Hymenoptera: Aphidiidae) was imported from Europe and initially released against the filbert aphid Mvzocallis coryli (Goetze) in hazelnut (filbert) orchards of the Willamette Valley, Oregon beginning in 1984. In the present study, I investigated the establishment rates of this parasitoid. A total of 13 orchards in 1987 and 30 orchards in 1988 were sampled twice per year. Five to ten trees were selected at random in each orchard and these trees were sampled by collecting and examining ten twigs per tree and counting the number of aphids and aphid mummies on four leaves per twig. The rate of parasitization was calculated by Total No. of mummies / Total No. of aphids + mummies X 100. Data show that the parasitoid has established in many commercial orchards and out of the total of 3 0 orchards studied eleven had breeding population of Trioxys pallidus and that is rapidly moving to adjoining orchards. The parasitoid appears to have survived the standard insecticide applications in commercial orchards. The level of resistance of a field collected population of Trioxys pallidus to the most commonly used pesticides in the filbert system including Metasystox-R, Pydrin, Zolone, Diazinon, and Lorsban was determined. Adult parasitoid populations continuously exposed to Pydrin (2 sprays per year) and carbaryl (1 spray per year) since 1985, were collected near Corvallis, Benton County, Oregon and their response to various insecticides was assessed. Similar data were collected from a laboratory reared susceptible population which was never exposed to insecticides. Comparasion of LC50 and LC95 values showed no significant differences in the susceptibility of these two populations to test insecticides, although build up of some tolerance against Pydrin was evident. The field population required 1.9 times higher rate than the laboratory population for 50% mortality. Metasystox-R was highly toxic to both populations with LC50 values of 1.06 ppm and Lorsban was the least toxic with LC50 of 28.3 ppm. An insecticide toxicity rating was determined. The test chemicals were rated in a decreasing order of toxicity as Metasystox-R, Pydrin, Zolone, Diazinon and Lorsban.
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