The choice of host plants by the phytophagous insects depends on a number of factors, including secondary metabolites which as “specific plant substances” have a significant influence not only on the physiology and behaviour of plant-eating insects but also on the chemism of plants’ defense. The present paper determined the effect of the feeding of Acrobasis advenella caterpillars on the content of flavonoids, phenolic acids and tannins in the inflorescences of two species of host plants, namely Aronia melanocarpa and Sorbus aucuparia. The content of flavonoids and phenolic acids in the extracts of both plants where caterpillars were feeding was lower as compared to the extracts from control plants. It was found out that the content of tannins in the plant material of S. aucuparia where caterpillars were feeding increased in comparison to the control material. In 2009, their content was found to be more than 1.5 times higher, reaching over 13% of DW. A reverse reaction was observed in the case of A. melanocarpa, where the content of tannins dropped significantly. The value of that parameter in 2009 decreased more than 1.5 times and it was 5.42% of DW, while in 2010 the decrease was 2-fold, reaching 2.61% of DW.

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