Development of innovative biopesiticides for the control of aedes albopictus mosquitoes

Objective: Determination of the larvicidal activity of bacteria belonging to the genera Xenorhabdus and Photorhabdus and bioactive compound/s against Aedes albopictus mosquito which is capable of serving as vector of over 20 different arboviruses of major global public health concern. Material and Method: The efficacy of cell-free supernatant (CSF), growth culture and re-suspended bacterial pellet against late 3rd-4th stage Ae. albopictus larvae was evaluated in wells of a 24-well plates. Larval mortality was assessed after 24 and 48 h. The ovicidal effects of these bacteria CFS on mosquito eggs were also evaluated. Supernatants of the most effective Xenorhabdus spp. ∆hfq promoter exchange mutants were used to identify the bioactive compound/s. Results: Three Photorhabdus spp. and 13 Xenorhabdus spp. release larvicidal compounds in CSF. Cell growth culture of nearly all tested species exhibited larvicidal activity. Bacterial cells exhibited oral toxicity (59-91%) against exposed larvae. Considering ovicidal activity, overall, bacterial CSF were ineffective against mosquito eggs but after hatching, >75% of emerged 1st instar larvae died in treatments. Using the easyPACId approach, the larvicidal compounds were identified as Fabclavine and Xencoumacin. Fabclavines were as effective as commercial Bacillus thuringiensis subsp. israelensis and spinosad products within 5dpa in distilled and field collected water. Discussion: An extensive number of Xenorhabdus and Photorhabdus display larvicidal activity as cells or by producing secondary metabolites with larvicidal activity. The bioactive compounds, Fabclavine and Xenocoumacin, can be developed in novel biolarvicides or can be used as a model to design and synthesize other compounds.