Effect of soil contamination with heavy metal ions on the harmful and useful entomofauna of broad beans

Influence of some selected heavy metals applied into soil as water salt solutions (2 mg Cd, 30 mg Cu, 15 mg Ni, 80 mg Pb and 70 mg Zn/kg soil d.m.) on the growth and development of broad beans and on occurrence of harmful and beneficial insects on the plant was investigated in field conditions. The applied doses of soil contamination with heavy metals strongly affected broad beans development. Plants were characterised by a significantly lower number and length of shoots and a lesser number of pods per plant as compared to the control. Chemical analysis of individual parts of plant revealed big differences in heavy metal contents in roots of plants in contaminated soil as compared to control soil with natural contents of metal ions. In the above ground parts, i.e. leaves and shoots the differences were considerably smaller. Numbers of beetroot aphids were determined on the selected plants since its appearance to the end of its development. Simultaneously, occupation of aphid colony by predators: ladybirds, Syrphidae and Chrysophidae larvae was also assessed. The number of plants occupied by aphids at each plot was also estimated. Aphids on plants in soil with increased metal contents formed more numerous colonies, also the insects invaded a bigger number of plants. Ladybird larvae, predators for aphids, occurred in more numerous colonies on plants in contaminated soil. The numbers of other aphid predators: Syrphidae and Chrysophidae larvae did not reveal statistically significant differences.