Two species of aphids, Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer) (Homoptera: Aphididae) were the only ones which developed populations on processing tomato in a two year study conducted in central Greece. The aphid population structure showed that M. euphorbiae was much more abundant than M. persicae in both years. The former species peaked in August whilst the latter did not show any particular peak over the two successive years. Some species of natural enemies were recorded. Onus niger Wolff was found in low numbers scattered over a long period but mainly towards the end of the growing season, and it did not correlate with the aphid population. The rate of parasitism of M. euphorbiae by Aphelinus abdominalis Dalman and Praon volucre (Haliday) was very low and it seemed that these two parasitoid species did not have any particular effect on the aphid population suppression. Macrolophus pygmaeus Rambur was the key natural enemy and the most abundant and effective among the predators found. Its highest numbers occurred towards the end of the growing season following the aphid population peak, suggesting a numerical response of this species to its prey. A proportion of the population of M. pygmaeus occurring on tomato plants after fruit harvesting, might be collected and subsequently released in crops such as tomato, pepper and eggplant to biologically control pests in greenhouses, like aphids and whiteflies, thus contributing to the production of healthy vegetable products.

Aphid monitoring was conducted by means of yellow Moericke water traps placed in tomato fields in two different localities in Co Boiotia during the growing seasons in 1992 and 1993. Additionally, aphid population densities were estimated by plant sampling. Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer) were the only species which developed populations on plants. Regression analysis between the number of alates from traps with either the number of alates or the total aphid population on plants showed that there was no correlation in the case of M. persicae for both localities and years. However, there were significant relationships between the number of alates in traps and either the number of alates on plants (r2=0.83) or the total aphid population on plants (r2=0.69) for M. euphorbiae in 1992. In 1993, such significant relationships were not found for the latter species, most probably due to extremely low trap catches. Significant relationships were also found between alates in traps, during their immigration period, with either alates on plants (r2=0.93) or the total population on plants (r2=0.80) in M. euphorbiae in 1992.