THE EFFECT OF PLANT-QUALITY ON THE ABUNDANCE OF METOPOLOPHIUM-DIRHODUM (HOMOPTERA, APHIDIDAE) ON MAIZE

In 1989-1991, populations of Metopolophium dirhodum (Walker) on maize in western Czechoslovakia were investigated. Aphid abundance was follo wed on plants subject to water stress and weed competition and of diff erent ages, sown between late March-late June. Shoot size, growth rate and leaf nitrogen content of the plants affected the performance of a phid populations. Aphids colonized maize stands in early June, after 4 00 to 500 day degrees (dd), above a 5-degrees-C threshold, had accumul ated since January 1. Initial abundance varied annually and with host plant size, between 0.1 and 9.9 aphids per plant. Population peak was attained in late June-early July (700-750 dd), after 190-300 dd of exp onential population growth. The growth rate of aphid populations was s ignificantly correlated with the growth rate and leaf nitrogen content of maize. Maximum aphid numbers varied annually and were greater on v igorous than on stunted plants. The differences in aphid abundance per sisted when recalculated per unit host plant weight. Aphids colonized the lower leaves of maize. The main difference with the population dev elopment of M. dirhodum on winter wheat was the greater initial number s per plant. Rate of population growth varied more and its duration wa s shorter on maize than on wheat. Maximum numbers per unit plant weigh t were similar on both crops.