Digestive Tract Proteases and ?-amylase of Pistachio Green Stink Bug, Acrosternum heegeri (Hemiptera: Pentatomidae)

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Pistachio green stink bug, Acrosternum hegeeri, due to its inflicting damages on crop quantity and quality, is of a great economical importance in pistachio production. On the other hand, a knowledge of digestive enzymes, is quite indispensable in the study and application of new pest management technologies. Results of studeies have shown that midgut in this insect is divided into four sections (m1-m4) all of which are morphologically different with their pHs determined as 6.4±0.1, 6.22±0.13, 6±0.1 and 6.1±0.12, respectively. In addition, salivary gland pH value amounts to 6.04±0.1. Enzymatic assays, using hemoglobin as substrate, revealed maximum proteolytic activity in m1 and m3 at pH 3 and in m2 and m4 at a pH of 4. The specific substrates for cysteine proteases, Z-Arg-Arg-pNA, Z-Phe-Arg-pNA, were hydrolyzed by midgut extract suggesting the strong presence of the cysteine proteinases cathepsin L and a low level of cathepsin B, respectively. The presence of cysteine proteases was supported by strong enhancement (53.12%) of the midgut proteinase activity in the presence of DTT for Z-Phe-Arg-pNA and (13.5%) for Z-Arg-Arg-pNA, respectively. Hydrolyzing activity of the cathepsin L and B in midgut extract against the substrates Z-Phe-Arg-pNA and Z-Arg-Arg-pNA was inhibited by the specific inhibitor, E-64 by 90% and 66%, respectively. During the study ?-amylase in the midgut was also investigated, the enzyme optimum pH being 5. The results show that cysteine and acid proteinases should be the major proteases in the midgut of pistachio green stink bug, in consistence with the prevailing pH in the insect’s midgut. Amylolytic activity was also determined in the midgut extract of the green stink bug.

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