Effects of two purified agglutinins from Rhizoctonia solani Kuhen (Rhizoctonia solani agglutinin) were determined on larval intermediary metabolism of Pieris brassicae L. Two concentrations of Rhizoctonia solani agglutinin (RSA; 1 and 2 mg ml^–1) significantly decreased activities of both alanine and aspartate aminotransferases, but no significant activity was observed on c-glutamyl transferase. However, activity of aldolase decreased in the treated larvae by both concentrations of RSAs, but lactate dehydrogenase showed the highest activity when the larvae fed on 2 mg ml^–1 of RSAs. Activities of acid- and alkaline phosphatases significantly decreased followed by feeding on the diets containing RSAs. Similar results were observed in the amounts of high-density lipoprotein and low-density lipoprotein. The amounts of protein and triacylglycerol significantly decreased in the treated larvae, while glycogen significantly increased in the larvae fed on RSAs-containing diets. Gene expression analyses of glycerol-3-phosphate in the control and treated larvae revealed significant expression in the larvae fed on RSAI in comparison with other treatments. These results demonstrated intervening effects of RSAs on intermediary metabolism of P. brassicae larvae, further confirming their entomotoxic effects.