NATIVE MOSQUITOCIDAL BACTERIA AS BIOCONTROL AGENTS 1 AGAINST THE MOSQUITO VECTOR, CULEX PIPIENS

Samples of the Bacillus thuringiensis (Bt) and Pseudomonas frederiksbergensis (Pf), both proved to be safe to living 12 organisms and environment, were isolated from rural soil of Saudi Arabia, and evaluated for entomopathogenicity 13 against 3 rd larval stage of Culex pipiens. Spore-crystal mixture of the Bt isolate showed a mosquitocidal activity 14 similar to that of the reference B. t. israelensis H14 (Bti-H14). However, toxin extract of Pf, identified as glycolipid 15 biosurfactants, showed 14 times higher toxicity than that of the Bti-H14. This significant difference in toxicity could 16 be attributed to the difference in the bacterial product used as it was the purified crude toxins of pf compared to 17 spore-crystal mixture of Bt isolate or Bti-H14. Light and electron microscopy showed destructive effects for the Pf 18 toxin extract on the midgut epithelial layer of treated larvae. Epithelial cells were first appeared with cytoplasmic 19 extensions followed by cellular and nuclear degradation. Additionally, Pf toxin extract has a devastating effect on 20 the peritrophic membrane that may have resulted in septicemia. In addition, scanning electron microscopy showed 21 body shrinkage in Pf toxin-treated larvae which was clearly noted compared to untreated control ones. This could be 22 attributed to the surface activity of characteristic to this bacterial extract. Molecular characterization of the current 23 Bt isolate, investigating the synergistic effect of combining both the Bt spore-crystal mixture (or δ-endotoxins) and 24 the Pf toxin on mosquito larvae, as well as isolating more native Bt isolates from the Saudi environment, are 25 currently under investigation. These data may be of a great help for stepping up an effective control measure against 26 mosquito vectors in Saudi Arabia 27