Water extractsfrom selected Geraniaceae plants, to which paraffin oil was added as adjuvant, were tested. It was observed that the plant extracts researched limited Colorado potato beetle feeding and development and adding adjuvant increased the effects. The highest antifeedant activity towards Colorado potato beetlesand their larvae wasobs erved in extractsobtained from Pelargonium × hortorum Bailey and Geranium pusillum L. The extract from Pelargonium × hortorum Bailey added to food showed a negative effect on the development of female reproductive organs and embryo development and showed the highest effectiveness in field conditions.

The research on impact of Cleonus piger Scop. (Coleoptera; Curculionidae) feeding and the occurrence of other pest insects on milk thistle plants grown in monoculture and crop rotation after cereals, with two different seeding dates was carried out in the years 2003–2005. The infestation and density of C. piger larvae in roots of plants grown in monoculture increased with subsequent developmental phases and subsequent years of the experiment. Feeding resulted in the decrease in crop yield by 40% compared to the crop rotation treatment. In crop rotation stands, the infestation of milk thistle roots by C. piger larvae was 4–5 times lower at the final phase than in monoculture. Postponing seeding by three weeks led to the decrease of infestation and density of C. piger larvae, but the crop yield was lower than that from the earlyseeded stands. No other phytophagous species of economic importance were found.

The study objective was to investigate the influence of microbiologically obtained surfactin on the feeding and development of Oulema melanopus and Oulema gallaeciana on spring wheat ( Triticum aestivum) and spring barley ( Hordeum vulgare). The purified bioproduct was applied to the leaves of cereal plants at a concentration of 660.5 mg · l ^–1. The tests were conducted as a no-choice test and a choice test. Pest feeding and egg-laying were analyzed. The addition of surfactin to the food reduced the feeding of female and male tested insects as compared to controls. Male pests caused less damage to plants than females. Insect feeding on surfactin-treated plants was low in the first days of the experiment. The tested insects laid fewer eggs on plants treated with the biosurfactant. In terms of food selection, both female and male Oulema spp. were much more likely to choose food to which surfactin had not been applied. It can thus be concluded that surfactin can contribute positively to the biological control of beetles of the genus Oulema under natural conditions. However, further research is needed to better understand the mechanisms by which analogues of this compound limit the development of this cereal pest in its natural environment.