Graduate Thesis Or Dissertation
 

The parasite complex of the pea aphid, Acyrthosiphon pisum (Harris) on alfalfa in western Oregon

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  • This study was initiated in the Spring of 1966 for the purpose of determining the present status and effectiveness of imported parasitic wasps of the pea aphid in the Willamette Valley of western Oregon. The pea aphid is a serious pest throughout the pea and alfalfa growing regions of the United States and Canada. In the Willamette Valley of western Oregon it is common on alfalfa, red clover and vetch. Since the use of pesticides to control the pea aphid is attended by serious difficulties, it has long been felt that biological control methods are necessary. These rely on parasites to control the aphid populations. In recent years, the importation, augmentation and re. lease of small parasitic wasps belonging to the genus Aphidius has been done on a wide scale throughout the legume growing regions of North America. Beginning in 1961 several introductions were made locally in the Willamette Valley. The European species Aphidius avenae and Aphidius urticae (=Aphidius ervi ervi); and the eastern variety of the native parasite, Aphidius pisivorus (=Aphidius ervi pulcher) were released at the Hyslop Agronomy Experiment Farm near Corvallis in 1961. Recoveries of specimens identified as Aphidius pisivorus (=Aphidius ervi pulcher) were made at the Hyslop Farm in 1963. Releases of the Indian wasp Aphidius smithi were made at Dayton in Yamhill County in 1961 but no recoveries of this species were reported prior to the start of this investigation. Field data in regard to aphids, parasites, and predators were collected at weekly intervals from the experimental alfalfa plots at the Hyslop Agronomy Farm and the parasites from these collections were reared and identified. In addition to the Hyslop collections, parasites were collected and reared from other localities in the Willamette Valley which included the original release site of Aphidius smithi near Dayton. For purposes of comparison, experimental plots of alfalfa at Klamath Falls were also sampled on several occasions throughout the summer of 1966. The results of collections made in the Willamette Valley during the summer of 1966 showed that the imported Indian wasp Aphidius smithi was well established as a parasite of the pea aphid. The imported European species, Aphidius ervi ervi was also established but in much smaller numbers. The native variety, Aphidius ervi pulcher was rarely encountered and appears not to be exclusively specific on the pea aphid. In conjunction with other control factors, particularly predators, the Indian wasp is an effective control agent and has come to occupy a previously unfilled ecological niche in the pea aphid-parasitepredator complex in the Willamette Valley. A survey of the hyper-parasites indicated that they were of minor importance during the 1966 season.
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