Abstract
EFFICACY OF SELECTED MICROBIAL LARVICIDES ON FIELD-COLLECTED LARVAE OF MOSQUITOES FROM PORT HARCOURT METROPOLIS

Ekerette I. B.* and Ebere N.

ABSTRACT

The comparative effectiveness of two microbial larvicides: Bacillus thuringiensis var israelensis/Bacillus sphaericus (Bti/Bs) combined and Bacillus thuringiensis var israelensis (Bti) were determined against Culex quinquefasciatus and Anopheles gambiae complex collected from the field. Various concentrations (0.2, 0.4, 0.6, 0.8, 1.0) mg/l of the two larvicides were tested in the laboratory against third instar of the larval species, to determine their mortality rates, lethal concentration (LC) at 50% and 90%. The field diagnostic concentrations being twice the LC-99.9% value were determined. All values were evaluated using probit analysis. The dose-response lines of Anopheles gambiae complex and Culex quinquefasciatus showed lethal concentration (LC): LC50 – 0.458mg/l; LC90 – 1.470mg/l and LC50 – 0.392mg/l; LC90 1.109mg/l respectively, after 48 hours, when treated with Bacillus thuringiensis var israelensis/Bacillus sphaericus (Bti/Bs). Activity with Bacillus thuringiensis var israelensis (Bti) alone for Anopheles gambiae complex and Culex quinquefasciatus after 48 hours were LC50 – 0.684mg/l; LC90 – 3.413mg/l and LC50 – 0.622mg/l; LC90 – 2.713mg/l, respectively. Culex quinquefasciatus was non significantly more susceptible than Anopheles gambiae complex for the same concentrations of Bti/Bs and Bti alone. The diagnostic concentrations after 48 hours exposure of the larvae, had no significant difference between the species, when they were treated with the same larvicide, Bti/Bs (Culex quinquefasciatus – 5.179mg/l; Anopheles gambiae complex – 7.601mg/l); Bti alone (Culex quinquefasciatus – 18.032mg/l; Anopheles gambiae complex – 25.298mg/l). Mortality observed in the control was less than 5%. These results propose the use of Bti/Bs and Bti alone in the control of mosquito vectors of many disease agents that plague humans. The combination of Bti/Bs appear to be more effective than Bti alone in the control of Culex quinquefasciatus more than Anopheles gambiae complex.

Keywords: Efficacy, Bacillus thuringiensis var israelensis, Bacillus sphaericus, Mosquitoes, Port Harcourt.


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