A Novel Mosquitocidal Bacterium as a Biocontrol Agent in Saudi Arabia: II - A Promising Larvicide Against Culex pipiens Mosquito
, Ahmed, A. M.; Abdel Megeed, A. M. and Al-Qahtaney, H. M. . 2014
Abstract.- This study was conducted to test the toxicity of a novel bacterial product against the filaria vector, Culex pipiens, mosquito in Saudi Arabia for the first time. This bacterial product was extracted from the soil bacterium, Pseudomonas frederiksbergensis isolated from the contaminated Saudi soil that was proved to be eco-friend and safe to living organisms. P. frederiksbergensis extract identified as glycolipid that afforded a potent mosquito larvicide and has surface and histological activities against 3rd instar larvae of Cx. pipiens. Larvicidal bioassay showed that the LC50 and LC90 against larvae of Cx. pipiens were 434.45 μl/l, and 767.50 μl/l, respectively, 24 hr post-treatment. Scanning electron microscopy revealed morphological symptoms of the toxic effect of P. frederiksbergensis extract. External shrinking of larval cuticle was clearly noted compared to untreated control which may be attributed to the surface activity characteristic P. frederiksbergensis extract. Moreover, a significant shrinkage in the whole body size was detected in treated larvae compared to control ones 24h post-treatment. In addition, the histological studies with the light microscopy showed P. frederiksbergensis extract destructive effects on the treated larvae midgut epithelial cells. Epithelial cells first appeared with cytoplasmic extensions followed by cellular and nuclear degradation, as well as peritrophic membrane devastation that lead to septicemia. Starting from 8 h post-treatment, larvae ceased feeding resulting in starvation and death at 24 h post-treatment. The current study introduces P. frederiksbergensis bacterial extract may a safe bio-larvicide candidate for use in the battle against Cx. pipiens mosquito. This may help in reducing the spread of this mosquito vector, that could limit mosquito-borne diseases in Saudi Arabia.
