Coexistence of Aphis fabae Scop. predators on broad bean growing on soil pollution with heavy metals

Abstract

The investigations were conducted to determine the effect of soil contamination with heavy metals (cadmium, copper, nickel, lead and zinc) on the level corresponding to 3rd pollution degree in the IUNG classification on interactions between individual aphidophagous groups and their stages of development occurring in Aphis fabae Scop. colonies on broad beans. The following were analysed: the occurrence and number of individual stages of predator development (eggs, larvae, pupae and adult specimens). The Agrell’s index of coexistence were computed from the achieved results. The values of the Agrell’s index for broad bean were low for individual predator groups and their development stages. Among the investigated predator groups, the best mutual tolerance was observed for Syrphidae and Coccinellidae. Co-existence of individual aphidophagous groups seems to be strongly conditioned by food resources, i.e. aphid availability. Heavy metals, by affecting the host plant, modified the degree of its colonization by aphids and their number, hence changes in the incidence of predators. Thus, soil pollution with zinc and nickel contributed to limiting the extent of broad bean colonization by aphids and predators, and consequently to a decrease in the values of their coexistence indices; on the other hand, soil contamination with cadmium and lead favours plant colonization by aphids and predators and therefore the presence of individual aphidophagous groups was noted more frequently on the same plants.