Biology studies of Macrosiphum avenae (Fabr.), Acyrthosiphon dirhodum (Walker), and Rhopalosiphum padi (L.) on Gramineae in western Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8s45qd088

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  • Field biology studies of three grain aphids, Macrosiphum avenae (Fabr.), Acyrthosiphon dirhodum (Walker), and Rhopalosiphum padi (L.) were conducted near Corvallis, Oregon, from 1961 to 1964. Populations of M. avenae were found on grain plants, and alatae entering spring barley may have been from wheat fields. Specimens were found more commonly on plants taller than six inches. Orchardgrass supported the largest numbers of A. dirhodum during the winter. Many grain and grass plants were inhabited by R, padi during mid-winter, and this species survived temperatures below freezing. Aphids of these three species were not found during August and September. Aphid flight was sampled using sticky traps which caught aphids from March 3 to November 14; the major flights of M. avenae and A. dirhodum occurred during July and R. padi during June. M. avenae populations appeared on spring barley in May, peaked in July and declined to zero by July 31. The first appearance of M. avenae was related to planting dates of the barley. A. dirhodum appeared in the barley fields two weeks later than M. avenae and the populations reached less distinct and lower peak numbers. R. padi appeared later in the spring and in lower numbers than the other two species. The number of aphids per infested plant increased as the number of plants infested increased. M. avenae was found on all 200 plants for only one of 40 sampling dates. In conjunctionwiththe abundance study, six life stages of M. avenae and A. dirhodum were recorded for all samples. Aphid populations consisted of progressively smaller numbers of specimens from the first to the fourth nymphal instar. There were more apterous aphids than fourth instar nymphs and the alate group was the smallest. The instar data were used to estimate the reproductive rate under natural field conditions. An estimate of 14.99 young were produced per adult M. avenae and surviving births averaged from 8.08 to 10.69 per adult. It was estimated that adults reproduced for 75% of the expected time and that 50% of the second, third, and fourth instar nymphs died under field conditions. Four areas of the barley plants were sampled; M. avenae frequented the upper growing areas of the plant and migrated to the heads, A. dirhodum inhabited three areas of the plant, and R. padi occurred on the subterranean shoot and lower senescent leaves. Statistical analysis indicated several distribution patterns. All aphids, species combined, were found to infest plants at random for most sampling dates. M. avenae and R. padi were randomly distributed from plant to plant for most samples, and A. dirhodum infested the plants at random in all samples. Specimens of M. avenae were randomly distributed across four quadrants of the fields during most samples. They were clumped within the quadrants, as were the A. dirhodum during 1963. The distribution of aphids per plant area, the number of aphids in each of six life stages, and the interaction of these two classifications showed M. avenae populations unequally distributed on the plant areas, and the number of specimens for each life stage was dissimilar. Estimates of 30, 895 to 16, 266, 718 aphids per acre along with the confidence limits were given. The larger the means the smaller were the confidence ranges relative to the mean. Coccinella trifasciata subversa LeConte and Hippodamia sinuata spuria LeConte were the most abundant Coccinellidae found and Scaeva pyrastri (L.) was the most common Syrphidae associated with the grain aphid populations, primarily M. avenae. From 100 parasitized aphids, 54 Aphidius obscuripes Ashmead emerged and 33 hyper-parasites. An undetermined entomophagus fungus was seen attacking A. dirhodum on orchardgrass.
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