Graduate Thesis Or Dissertation

The biology and seasonality of the parasitiod Trioxys pallidus Haliday in western Oregon

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  • Seasonal synchrony between the filbert aphid, Myzocallis coryli (Goetze) and its newly introduced parasitoid Trioxys pallidus Haliday was examined in the field to evaluate the effectiveness of parasitoid based biological control in filbert orchards of Oregon. Fieldemergence observations showed that 50% eclosion of the aphid occurred 14 days before that of the parasitoid. Winter mortality of the parasitoid was 61.6% in 1986, and 55.3% in 1987. Host depression by the parasitoid was limited in early spring and steadily increased throughout the season. A post release study showed that aphid numbers diminished by greater that 62% during the peak point of the pest season. Time from ovipostion to 50% eclosion for nondiapause T. pallidus in the field ranged from 248.0 to 373.6 degree days above a base temperature of 6.0°C. Time from oviposition to mummy formation represents 64% of the time to adult eclosion. Four generations of T. pallidus were produced in a controlled field experiment in one growing season although based on heat unit calculations it would be possible to produce 6 generations in the field. The parasitoid population declined during the summer months accounting for fewer generations in the season. Diapause type individuals are present in the T. pallidus population throughout the filbert growing season but are not dominant until October-November. Diapause development continued as winter progressed as demonstrated by the decrease in the number of days to eclosion. In 1987 a total of 2,645 adult and 1,900 mummy T. pallidus were released in western Oregon filbert orchards. A 1988 survey of 12 of the 13 release sites showed 4 of the sites to have established populations that survived the winter.
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