Development of Wuchereria bancrofti in Culex quinquefasciatus that survived the exposure of sub-lethal dose of Bacillus sphaericus as larvae

Development of Wuchereria bancrofti in Culex quinquefasciatus emerged from the larvae that survived the exposure of sub-lethal dose of Bacillus sphaer icus was examined in the laboratory. Third instar larvae of Cx. quinquefnsc iatus were treated with B. sphaericus at a sub-lethal dose of 11.35 mu g/25 0 mi. The female mosquitoes that emerged from the survived larvae were fed on microfilaraemic human blood and parasite development was monitored in th e fed mosquitoes. Both treated and untreated mosquitoes could ingest microf ilaria (mF) equally as there was no significant difference in mF density be tween them. But, density of developmental stages of the parasite in treated group was significantly lower. Since, there was no mortality of mosquitoes , the lower density of the developmental stages could be attributed to the loss of parasites in the treated mosquitoes. Consequently, the proportion o f mosquitoes with infective larvae (L3) and number of L3 were also signific antly lower in treated females. Delay in parasite development was also noti ced in treated mosquitoes. The present study indicates that B. sphaericus, when applied at sub-lethal dose kills larvae, and in addition, inhibits dev elopment of the filarial parasite and consequently reduces L3 yield in adul t mosquitoes that emerged from the survived larvae. (C) 2000 Elsevier Scien ce B.V. All rights reserved.