**1. Introduction**

Alternative methods of suppressing harmful organisms are gaining ground, and greater attention is paid to natural resistance of plants, which is conditioned by morphological and

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chemical factors. By exploiting natural resistance of plants, we can reduce the use of insecti‐ cides and thus avoid the pertaining resistance of harmful insects. Different factors are in‐ volved in defence of Brassicas against harmful organisms. It has been established that more solid (more compact heads) cabbage [1] and higher content of epicuticular wax [2] diminish the extent of damage done to cabbage by onion thrips (*Thrips tabaci* Lindeman). Thicker layer of epicuticular wax can negatively influence also the feeding of cabbage flea beetles (*Phyllotreta* spp.) and cabbage stink bugs (*Eurydema* spp.) [2].

In our research, whose results are briefly presented on the following pages, we focused on the study of glucosinolate content in different species of Brassicas and their effects on the target group of harmful organisms, cabbage flea beetles and cabbage stinkbugs.

Before the research, we made the following hypotheses:

