Wide-scale application of Bti/Bs biolarvicide in different aquatic habitat types in urban and peri-urban Malindi, Kenya

Abstract

Larval control is a major component in mosquito control programs. This study evaluated the wide-scale application of Bti/Bs biolarvicide (Bacillus thuringiensis var. israelensis [Bti] and Bacillus sphaericus [Bs]) in different aquatic habitats in urban and peri-urban Malindi, Kenya. This study was done from June 2006 to December 2007. The urban and peri-urban area of Malindi town was mapped and categorized in grid cells of 1 km(2). A total of 16 1-km(2) cells were selected based on presence Community Based Organization dealing with malaria control within the cells. Each of the 16 1-km(2) cells was thoroughly searched for the presence of potential larval habitats. All habitats, whether positive or negative for larvae, were treated and rechecked 24 h (1 day), 6 days, and 10 days later for the efficacy of Bti/Bs. Weekly larval sampling was done to determine the mosquito larval dynamics in the aquatic habitats during the study period. Morphological identification of the mosquito larvae showed that Anopheles gambiae s.l. Giles was the most predominant species of the Anopheles and while in the culicines, Cx. quinquefasciatus Say was the predominant species. Anopheles larvae were all eliminated in habitats within a day post-application. For culicine larvae, 38.1% (n=8) of the habitat types responded within day 1 post-treatment and all the larvae were killed, they turned negative during the days of follow-up. Another 38.1% (n=8) of the habitat types had culicine larvae but turned negative by day 6, while three habitats (14.3%) had larvae by 6th day but turned negative by 10th day. However during this Bti/Bs application studies, two habitat types, house drainage and cesspits (9.5%), remained positive during the follow-up although the mosquito larvae were significantly reduced. Both early and late instars of Anopheles larvae immediately responded to Bti/Bs application and reached 100% mortality. The early and late instars of culicine responded to the Bti/Bs application but not as fast as the Anopheles larval instars. The early instars Culex, responded with 90.8% mortality at day 1 post-treatment, and the mortality was 99.9% at day 10. Similarly, the late instars Culex followed the same trend and exhibited same mortalities. The weekly sampling in the aquatic habitats showed that there was a 36.3% mosquito larval reduction in the aquatic habitats over the 18-months study period. In conclusion, Bti/Bs biolarvicide are useful in reducing the mosquito larval densities in a wide range of habitats which have a direct impact of adult mosquito populations.

Mosquito species abundance and diversity in Malindi, Kenya and their potential implication in pathogen transmission

“…At adult stages, it would be important to advocate for proper use of LLINs and this coupled with health-promotion education at the community level in which communities are given skills on mosquito control will result in minimizing the human-vector contact. At the immature stages, communities are trained on environmental management (draining and filling) and possibly the use of larvicides such as Bacillus thuringiensis var Israelensis (Mwangangi et al 2010) which targets mostly habitats used by Anopheles and Culicines. Additionally, proper disposal of containers within the homesteads and closing the water storage containers inside the houses will tackle the aedian populations.…”

Bacillus sphaericus in the adults of Culex quinquefasciatus mosquitoes emerged from treated larvae and its effect on development of the filarial parasite, Wuchereria bancrofti

“…It has been proved to be very effective against Cx. quinquefasciatus, the vector of bancroftian filariasis, breeding in habitats prevalent in urban and peri-urban areas (Gunasekaran et al 1996;Medeiros et al 2005;Mwangangi et al 2011). After its application, the spores and crystals of the bacterium are ingested by (Gunasekaran et al 2000).…”

Insecticidal potency of bacterial species Bacillus thuringiensis SV2 and Serratia nematodiphila SV6 against larvae of mosquito species Aedes aegypti, Anopheles stephensi, and Culex quinquefasciatus

“…Several other researchers reported potential efficacy of commercial microbial formulations containing B. sphaericus (Bs), B. thuringiensis subsp. israelensis (Bti), and combination (Bti/Bs) against larval instars of Aedes, Anopheles, and Culex in laboratory as well as field conditions (Mwangangi et al 2011;Chenniappan and Ayyadurai 2011;Singh and Prakash 2009). These studies demonstrate that each mosquito species responds differently to the microbial agent and that mortalities were dependent on dose, age of larvae, time of exposure, level of insecticide resistance, and combination of active material in the treatment.…”