Effect of Bacillus thuringiensis ssp. israelensis on the development of Plasmodium gallinaceum in Aedes aegypti (Diptera : Culicidae)

Adult, female Aedes aeglypti, some of which had survived a sublethal dose ( LC50) of Bacillus thuringiensis ssp. israelensis (Bti) as larvae, were fed on chickens with gametocytaemia of Plasmodium gallinaceum. Parasite develop ment was monitored by dissecting samples of the mosquitoes immediately afte r the feed and on days 1, 7 and 9 post-feed, to check for the presence of g ametocytes, ookinetes, oocysts and sporozoites, respectively. As the propor tions of batches of fed mosquitoes found positive for gametocytes and ookin etes and the density of these parasite stages in the infected flies did not differ significantly between Bti-treated and untreated mosquitoes, ingesti on of gametocytes and development of ookinetes did not appear to be affecte d by Bti exposure. However, the Bti-treated mosquitoes were significantly l ess likely to carry oocysts and those that were oocyst-positive carried sig nificantly fewer oocysts than the untreated controls, indicating Bti-induce d parasite loss during development of oocysts. Consequently, the proportion of mosquitoes with sporozoites was also significantly lower in the treated group. The study shows that mosquitoes surviving Bti treatment did not ful ly support parasite development. The implication of this effect is discusse d in terms of malaria transmission.