Abstract

Our current knowledge on the key molecular mechanisms and cognate signaling transduction, by the d-endotoxin-mediated mosquitoticidal effects, associated with exposure to Bacillus thuringiensis (Bt) and Bacillus sphaericus (Bs), is limited. Moreover, this observed mosquitocidal activity that is related to program cell death is largely unknown. Therefore, in an attempt to answer this question, the current study was primarily sought to provide evidence as to the molecular mechanism of mortality in Bt/Bs infected Aedes caspius mosquito larvae. Thus, the impact of Btand Bs treatment on the expression of some selected apoptosis-related caspase genes in A. caspius mosquito larvae was investigated, via quantitative reverse-transcriptase PCR (qRT-PCR). Mosquito larvae were collected from natural water niches. Larvae were grown to adult stage and were subsequently identified as A. caspius at Natural History Museum, London, UK. Remarkably, light and transmission electron microscopy studies of the midgut epithelial tissues revealed that both Bt and Bs brought about significant histopathological effects. Moreover, this treatment resulted in severe destruction at the sub-cellular organelle level for the mitochondria. Interestingly, qRT-PCR studies revealed that the treatment of A. caspius mosquito larvae with both Bt and Bs caused a significant up-regulation in the transcription level of all caspase genes under study, namely: CASPS17,CASPS18, CASPS19, CASPS20 and CASPS21. The results are discussed in the light of our current understanding of the signaling transduction pathway of apoptosis in insects and mosquitoes and the putative role of caspases gene expression in response to the treatment of A. caspius mosquito larvae with larvicidal bacteria.

Key words: Aedes caspius, Bacillus thuringenesis, Bacillus sphaericus, apoptosis, caspase, larvicidal bacteria.

Abbreviation

Abbreviations: Bt, Bacillus thuringiensis; Bs, Bacillus sphaericus; PCD,programmed cell death.