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.

The effects of a microbial inoculant (Thervelics®: a mixture of cells of Bacillus subtilis C-3102 and carrier materials) on rice (Oryza sativa cv. Milkyprincess) and barley (Hordeum vulgare cv. Sachiho Golden) were evaluated in four pot experiments. In the first and second experiments, the dry matter production of rice and barley increased significantly by 10–20% with the inoculation of the mixture at a rate of 107 cfu ⋅ g–1 soil compared with the non-inoculated control. In the third experiment, the growth promoting effects of the mixture, the autoclaved mixture and the carrier materials were compared. The dry mater production of rice grains was the highest in the mixture, and it was significantly higher in the three treatments than in the control, suggesting that the carrier materials may also have a plant growth promoting effect and the living cells might have an additional stimulatory effect. To confirm the efficacy of the living cells in the mixture, only B. subtilis C-3102 cells were used in the fourth experiment. In addition, to estimate the mechanisms in growth promotion by B. subtilis C-3102, three B. subtilis strains with similar or different properties in the production of indole-3-acetic acid (IAA), protease and siderophore and phosphatesolubilizing ability were used as reference strains. Only B. subtilis C-3102 significantly increased the dry matter production of rice grains and the soil protease activity was consistently higher in the soil inoculated with B. subtilis C-3102 throughout the growing period. These results indicate that the microbial inoculant including live B. subtilis C-3102 may have growth promoting effects on rice and barley.