Azadirachtin is the most active substance separated from Azadirachta indica. It acts destructively on numerous species of insects and mites. The aim of the presented investigations was to determine the effect of azadirachtin on one of the most dangerous pests of cabbage plants, Pieris brassicae, and on its natural enemy, Apanteles glomerarus. The results of the field observations did not show any repellent effect of azadirachtin relating to laying their eggs cabbage butterflies. However, a significant effect of the azadiraehtin solution on reduction the number of cabbage butterfly caterpillars (it was more distinctly marked in respect to young larva stages) as well as on limited feeding by caterpillars. No negative influence of azadirachtin on a parasite of Pieris brassicae caterpillars, Apanteles glomeratus was distinctly shown.

Protein digestion in insects relies on several groups of proteases, among which trypsin plays a prominent role. In the current study, larvae of Pieris brassicae L. were fed radish leaves treated with 1 mM concentrations of three specific inhibitors of trypsin: AEBSF.HCl [4-(2- -aminoethyl)-benzenesulfonyl fluoride, monohydrochloride], TLCK (N-a-tosyl-l-lysine chloromethyl ketone) and SBTI (Soybean Trypsin Inhibitor) to find their potential effects on gene expression of trypsin. Initially, RT-PCR analysis revealed a gene of 748 bp responsible for synthesizing the digestive trypsin in P. brassicae larvae. Also, qRT-PCR data indicated a statistically greater expression of trypsin gene in the larvae fed 1 mM concentrations of AEBSF.HCl, TLCK and SBTI than the control. Results of the current study indicated that synthetic inhibitors can not only negatively affect the gene expression of P. brassicae trypsin, but also the insect can activate a compensatory mechanism against interruption of protein digestion by inducing more expression of the gene and producing more trypsin into the midgut lumen.

In 1993–1997 the occurrence of Lepidoptera pests: Pieris rapae L., Pieris brassicae L., Mamestra brassicae L., and Plusia gamma L. were observed on the nine different late cabbage vegetables; Savoy cabbage cv. Vertus, white cabbage cv. Amager, red cabbage cv. Langendijker, brussel sprouts cv. Maczuga, cauliflower cv. Pionier, blue kohlrabi cv. Masłowa, white kohlrabi cv. Delikates, kale cv. Zielony Kędzierzawy and broccoli cv. Piast. The field observations showed that butterflies differentiated among host-species for oviposition. The butterfly females of all species preferred for oviposition the brussel sprouts and deposited a substantially larger number of eggs on leav es of them. Plant species with green leaves were more preferred than the red leaf ones.