Summer populations of the cereal aphid Metopolophium dirhodum (Walker) on winter wheat: three contrasting years.
The summer populations of the aphid Metopolophium dirhodum were monitored in a field of winter wheat in Bedfordshire, England, in 1978-80. The population growth rates, density, age structure and immigration for each year are compared. The percentage of tillers infested was found to be a sigmoid function of aphid population density, a relationship that was constant from year to year. The seasonal changes in the distribution of feeding sites are given for 1979. The highest percentage of the total population occurred on flag leaves. Dislodgement of aphids by gusts of wind appeared to be an important mortality factor, but rainfall by itself was not. Parasitism was greatest in 1978, but did not appear to control population size. Predation by the coccinellids Coccinella septempunctata, Adalia bipunctata and Propylea quattuordecimpunctata appeared to limit population growth in 1978, and to reduce population density severely in 1980. The maximum densities varied greatly and were determined by temperature-regulated growth rates, as opposed to mortality caused by wind or natural enemies.