The effect of seeds of different chickpea and cowpea cultivars on digestive proteolytic activity of Helicoverpa armigera (Lep.: Noctuidae)

Proteases are considered as major digestive enzymes in alimentary canals of most insects، which are responsible for providing amino acids and energy from nutrients for insects’ growth. The substrate azocasein was used for measuring general proteolytic activity of midgut extracts from Helicoverpa armigera (Hübner) larvae reared on different chickpea cultivars (Arman، Azad، Binivich and Hashem) and a cowpea cultivar (Mashhad) when incorporated into artificial diets at different pH values (6 to 12). The experiments were preformed at 25 ± 1Cº، 65 ± 5% RH and a photoperiod of 16:8 (L: D) h. The results showed that the lowest general proteolytic activity of the third، fourth and fifth instar larvae was on Arman، Binivich and Arman (4. 31، 4. 26 and 4. 31 U/mg، respectively)، while the highest rate was in the larvae fed on Mashhad، Azad and Mashhad (6. 68، 6. 31 and 6. 67 U/mg، respectively)، respectively. The general proteolytic activity in H. armigera larvae on all examined cultivars had an increasing trend in pH from 6 to 12. The optimum pH value of proteolytic activity in the larvae fed on different cultivars was 12، suggesting the maximum proteolytic activity of H. armigera larvae at high alkaline pH. Mashhad and Arman cultivars were the most and the least suitable hosts for H. armigera، respectively.