SALIVARY APYRASE IN NEW-WORLD BLACKFLIES (DIPTERA, SIMULIIDAE) AND ITS RELATIONSHIP TO ONCHOCERCIASIS VECTOR STATUS

Salivary gland apyrase is believed to be critical to blood-feeding in arthropod vectors. This enzyme was measured in six New World blackflie s representing three taxonomic pairs of non-vectors and vectors of Onc hocerca volvulus. In Simulium (Psilopelmia) ochraceum, a highly anthro pophilic vector in Mexico and Guatemala, apyrase exhibited maximum act ivity between pH 8.0 and 9.0, mean 39.8 +/- 4.7 milli Units/pair of gl and equivalents (mU), and was enhanced when ATP was used as a substrat e. In the zoophilic non-vector Simulium (Psilopelmia) bivittatum maxim um activity was significantly less (5.1 +/- 0.7 mU) under all conditio ns examined. Preference for ADP or ATP as substrate was a function of the pH of the reaction for this species. Apyrase activity in Simulium (Simulium) metallicum Bellardi (29.5 +/- 11.5 mU), a zoophilic seconda ry vector in Mexico and Guatemala, resembled that of S. (Ps.)ochraceum (24.8 +/- 13.7 mU at pH 8.5) with ADP as substrate, but showed reduce d activity with ATP. Both these Central American vectors had higher ap yrase activity than found in Simulium (Notolepria) exiguum, a vector o f O. volvulus in Ecuador and Colombia. However, maximum apyrase activi ty, measured at pH 8.0 with ADP as substrate, was greater in S. (N.) e xiguum (10.9 +/- 0.6 mU) than in Simulium (Notolepria) gonzalezi (5.9 +/- 1.9 mU), a non-vector species widespread in Central America. There fore, for the consubgeneric species pairs examined, a positive associa tion was detected between higher concentrations of apyrase activity an d their vector status for O. volvulus.