UTTAR PRADESH JOURNAL OF ZOOLOGY

In the deficiency of advanced immune mechanism in insects, the most common and one of the efficient methods used by insects in recognising pathogens or foreign non-self substances is the melanisation process. The primary enzyme involved in melanin biosynthesis by phenoloxidase (PO) thus plays a vital role in insect immunity. In the present study, larval haemolymph of the blowfly, (Hemipyrellia tagaliana) were used to demonstrate the presence of prophenoloxidase and its activating system. The haemolymph showed favourable results in the oxidation assays carried out to test the presence of prophenoloxidase using phenolic substrates. This PO activity was shown to be repressed by phenylthiourea, an inhibitor of PO activity, while the activity was increased when exposed to microbial components such as laminarin, LPS from various bacterial species and zymogen. The results indicated that this enzyme (PO) existed in zymogen state and was activated by proteolytic cleavage when exogenous proteases and detergents were introduced in the assay system. An increased PO activity in the presence of Ca²⁺ showed its calcium-dependent nature. These results conclude that a zymogen of phenoloxidase is found in the larval haemolymph of the H. tagaliana, which is activated by proteolytic cleavage when exposed to foreign non-self-substances and pathogens.