The effect of azadirachtin on Blastocrithidia triatomae and Trypanosoma cruzi in Triatoma infestans (Insecta, Hemiptera)

The effect of azadirachtin on Blastocrithidia triatomae and Trypanosoma cru zi, which colonise the intestinal tract of the blood-sucking bug Triatoma i nfestans, was investigated. In established infections of controls without a zadirachtin treatment, the small intestine of fifth-instar T. infestans con tained up to 7 x 10(6) B. triatomae and the rectum 3 x 10(6). In comparison to this homoxenous flagellate, the population densities of T. cruzi in the respective regions were 99.3 and 76% lower. Treatment with azadirachtin (1 mu g ml(-1)) via a blood meal and a concurrent infection with B. triatomae resulted in an increase of the population density (3 weeks p.i.), caused m ainly by the mastigote stages in the rectum. In an established B. triatomae infection (12 weeks p.i.), feeding of azadirachtin did not affect the popu lation density and composition. In an optimal T. cruzi-vector system, i.e, parasite and bug originate from the same locality, the treatment with azadi rachtin at 20 weeks p.i. strongly reduced the population density in the sma ll intestine of all bugs up to 100 days after treatment. but only in a mino r percentage of the bugs in the rectum. Trypanosoma cruzi incubated for up to 24 h in faeces of azadirachtin-treated bugs were not affected, indicatin g that the rectum of these bugs contained no toxic substances. The importan ce of these findings is that investigations of the mechanisms of action of azadirachtin offer a possibility to identify vector-derived compounds, whic h are necessary for the development of T. cruzi. thereby, giving us a possi ble new strategy to combat Chagas' disease. (C) 1999 Australian Society for Parasitology. Published by Elsevier Science Ltd. All rights reserved.