No 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.

The efficacy and persistence of 2 bacterial larvicides, Vectobac-DT (Bacillus thuringiensis israelensis [Bti]) and CulinexCombi (Bti and Bacillus sphaericus [Bs]), were tested against Anopheles gambiae and Culex quinquefasciatus in temporarily unused swimming pools with rainwater in Malindi, Kenya. Pre- and posttreatment larval densities were recorded by sampling with the standard WHO dipping technique for 8 consecutive days. The larvicides were applied to the pools with a knapsack sprayer. The data showed that Vectobac-DT was highly effective against early instars of An. gambiae with 89% reduction within 24 h but not as effective against the early stages of Cx. quinquefasciatus with reduction of only 46%. CulinexCombi resulted in high mortalities to early instars of both species with over 97% reduction within 24 h, but showed a drastic reduction 48 h after application. Both Vectobac-DT and CulinexCombi were highly effective against late instars of both species, whereby Vectobac-DT persisted much longer than CulinexCombi. Anopheles gambiae was found to be more susceptible to both larvicides than Cx. quinquefasciatus. By their high efficacy and good persistence against mosquito larvae, both Vectobac-DT and CulinexCombi can be recommended for use in integrated mosquito control programs.

Ten monoclonal antibodies were produced against a k-l-type crystal protein of Bacillus thuringiensis subsp. kurstaki. Eight of the antibodies belong to the immunoglobulin GI (IgGI) subclass, with pl values ranging from 5.5 to 8.6, one could be assigned to the IgG2b subclass, and one could be assigned to the IgM class. Competitive antibody-binding assays and analysis of antibody specificity indicated that the 10 antibodies recognized at least nine distinct antigenic determinants. Eight antibodies bound to both protoxin and toxin, whereas the other two interacted with protoxin only. One antibody completely inhibited the biological activity of the delta-endotoxin, five antibodies reduced it by 15 to 82%, and four antibodies did not affect it at all. Based on cross-reaction studies, homologies and differences in the crystal protein structures of different B. thuringiensis subspecies were revealed. All of the monoclonal antibodies strongly cross-reacted with crystal proteins from strains of B.

Different ecosystems were probed in the vicinity of the city of Bhubaneswar in the Indian state of Orissa for the presence of bacterial spore-formers with activity against mosquito larvae. The most productive sites were places that were flooded during the monsoon season, including roadside ditches and shorelines of ponds. Among 630 isolates screened, 44 (7%) showed larvicidal activity against larvae of Aedes aegypti. The specific activity of the bacterial spore-formers varied greatly. Isolates were found with specific activities superior to the Bacillus thuringiensis israelensis reference strain of the Pasteur Institute. All mosquitocidal strains produced crystal proteins, and based on the biochemical analyses could be classified into the species B. thuringiensis. Such strains possess the potential for the development of new microbial products for mosquito control in India.