SALIVARY-GLAND APYRASE IN BLACK FLIES (SIMULIUM-VITTATUM)

Apyrase enzyme activity was demonstrated in the salivary glands of a colonized strain of Simulium vittatum. Activity was maximum (8.5 +/- 0.7 mU/pair of gland equivalents) at pH 8.0, with ADP as substrate and Ca2+ as the divalent cation. Activity was minimal in newly emerged females (1.6 +/- 0.5 mU/pair of gland equivalents) but increased by 48 h. Activity in male salivary glands was marginally detectable (0.7 +/- 0.8 mU/pair of gland equivalents), even 72 h after emergence. When newly emerged females were maintained at 4-degrees-C, salivary apyrase activity accumulated at a slow rate. Transferring females to warmer temperatures increased the rate of apyrase accumulation, but 27-degrees-C did not yield greater activity than 20-degrees-C. Apyrase activity was decreased when females engorged on whole bovine blood or on a simulated blood meal. Activity remained low 6 h after feeding, but increased to prefeeding levels by 48 h. During the second, anautogenous gonotrophic cycle, apyrase activity was not greater than during the first, autogenous gonotrophic cycle. Apyrase activity was not related to long term colonization as total salivary gland apyrase activity and pH profile in wild S. vittatum was not different from colonized S. vittatum.