Population dynamics of three main alfalfa aphids, namely: pea aphid, Acyrthosiphon pisum (Harris), spotted alfalfa aphid, Therioaphis trifolii forma maculata (Buckton), black alfalfa aphid, Aphis craccivora Koch, and their most abundant predators and parasitoids in three sites and in two subsequent years in Isfahan, Iran, were investigated. The results revealed that frequency and temporal occurrence of alfalfa aphids and their natural enemies in different regions were varied, but aphid natural

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... nemy populations were more or less coincident with aphid populations. Populations of aphids were mainly affected by alfalfa harvesting, ambient temperature, and coccinellid predators. Hemipterous predators in contrast with coccinellids, had little effect on aphid populations. Parasitoids seem to be effective on low populations of alfalfa aphids. Air humidity and rainfall had no effect on populations of alfalfa aphids.