COMPARABILITY OF TWO COMMERCIAL FORMULATIONS OF BACILLUS THURINGIENSIS VAR ISRAELENSIS AND B. SPHAERICUS AGAINST LARVAE OF CULEX QUINQUEFASCIATUS (D1PTERA:CULICIDAE) IN VARIOUS ECOLOGICAL NICHES

Abstract:
A study was initiated in the laboratory to compare the effects of spore dust and sawdust formulations of Bacillus thuringiensis var israelensisand B.sphaericus on immatures of laboratory and field samples of C. quinquefasciatus. Various types of ecological niches including cesspits, cement tanks and 'U' drain which form the habitats of the mosquitoes, were selected for this study. Bacilli formulations were tested against 2nd, 3rd and 4th instar larvae of laboratory and field collected samples as mentioned above and the LC50 values were determined by computer analyses. The LC50 of B.thuringiensis were compared with those of B.sphaericus and it was concluded from this study that B.thuringiensis is highly toxic to all stages of larvae in laboratory and field habitats. Both sawdust formulations produced 80-100% mortality after 24 hrs. in all stages of larvae from three habitats and in laboratory samples at 0.005% concentration. It was concluded from these results that B.thuringiensis is a more effective biocide than B.sphaericus in moderate and tropical conditions.