The ISPC-6 (LC50 4.22 × 103 spores mL−1) and ISPC-5 (LC50 6.44 × 103 spores mL−1) strains exhibited comparatively lower larvicidal activity. Monnerat et al. (2004) have compared the larvicidal activity of different Brazilian B. sphaericus strains with standard 2362 and found that some of the strains exhibited higher toxicity towards C. quinquefasciatus. Similarly, four B. sphaericus isolates from China were also reported to be two to six

times more toxic than strain 1593 against C. quinquefasciatus (Sun et al., 1996). The virulence of entomopathogenic B. sphaericus isolates is related to the serotype and the phage group (Brownbridge & Margalit, 1987). Yousten (1984) has grouped virulent strains of B. sphaericus under serotype 5a5b and phage type III. In accordance with Alectinib supplier this, isolate ISPC-8 was also shown to be highly virulent against C. quinquefasciatus and grouped

under serotype 5a5b and phage type III (Table 1), whereas ISPC-5 and ISCP-6 belong to serotype 26a26b and phage type IV exhibiting lower toxicity; a similar observation was also reported by Yousten (1984). The varying levels of larvicidal activity of the ISPC-6 strain may be due to the loss of virulence during subculturing of the organism (Rao & Mahajan, 1990). As compared with other selleck screening library isolates, ISPC-8 was found to be highly toxic. Therefore, its spectrum of larvicidal activity was studied against different mosquito species. The DCLK1 results indicated that C. quinquefasciatus was most susceptible, followed by C. tritaeniorhynchus, A. albopictus and A. aegypti. The respective LC50 values

were 0.68 × 103, 2.01 × 103, 4.91 × 103 and 9.33 × 103 spores mL−1 (Table 2). Compared with Aedes sp., Culex sp. were found to be highly susceptible to ISPC-8. These observations are in line with earlier reports which showed that the B. sphaericus is more active against Culex sp., while B. thuringiensis ssp. israelensis is more active against Aedes sp. (Lacey & Undeen, 1986). Several authors have also observed a similar larvicidal profile for B. sphaericus 2362 and other strains (Sun et al., 1996; Monnerat et al., 2004). The target spectrum of B. sphaericus is limited to mosquitoes, primarily Culex and certain Anopheles sp. (Delécluse et al., 2000), while Aedes sp. required 100-fold higher doses of ISPC-8 as compared with Culex sp. Similarly, Sun et al. (1996) reported that A. aegypti larvae (LC50 43.7 ng mL−1) required higher doses of Chinese isolates of B. sphaericus than C. quinquefasciatus (LC50 1.41 ng mL−1). Some B. sphaericus spore/crystal preparations kill A. aegypti larvae at doses 100–1000-fold higher than that required for C. quinquefasciatus (Lacey & Undeen, 1986). An explanation for this pattern has been proposed by Davidson (1989), based on the affinity that a fluorescein isothiocyanate-labeled toxin binds to the larval midgut of these mosquito species. It was shown that the toxin does not bind to the midgut of A.