The population dynamics of the aphids, macrosiphum avenae, metopolophium dirhodum, and rhopalosiphum padi on oats, Avena sativa CV Fraser

Fraser oats were used to study populations of cereal aphids in 1972,1973 and 1974. The most commonly found species were Macrosiphum avenae (F.) (the English grain aphid), Metopolophium dirhodum (Wlk.) (Rose-grain aphid) and Rhopalosiphum padi (L.) (Oat bird-cherry aphid). Aphid density was highest in 1972, lower in 1973 and lowest in 1974. Generally M. avenae had the highest population with M. dirhodum slightly lower. Rhopalosiphum padi was found infrequently with low numbers. Fecundity trials, used to examine whether the difference between numbers of species was because of a difference in fecundity, did not substantiate field results but instead indicated that R.padi should have produced the highest population. Differences were not found in the population dynamics when the oats were planted in solid blocks instead of rows. A one month delay in the planting date did not change the total aphid population but did result ira higher proportion of M. avenae than found in any other plot. Coccinellid numbers in two out of the three years were considered negligible. In 1972 rain was thought to destroy many coccinellid before they reached large enough numbers to greatly affect the aphid population. No direct samples were taken of hymenopterous parasites but any found were collected and identified. Water experiments were conducted to study the effect of water on the fecundity of R. padi. It. was concluded - that R. padi definitely preferred wet conditions. Temperature and rainfall readings were used to show the effect of weather on aphid numbers. Weather was shown to be a major regulatory factor in the population dynamics of cereal aphids. Considerations were made for aphid mortality caused by sparrows.Land and Food Systems, Faculty ofGraduat