Abstract
In this study, laboratory assessment was made with a water-dispersible toxin solution formulation of Pseudomonas frederiksbergiensis bacterium. The study was conducted to determine the activity of an isolated extract formulation of P. frederiksbergiensis toxin against 3rd stage larvae of the Rift Valley Fever vector, Aedes caspius, mosquito in Saudi Arabia for the first time. This bacterium was isolated from the contaminated Saudi soil and proved to be safe to living organisms and environment. This P. frederiksbergiensis extract, identified as glycolipid, has afforded a potent mosquito larvicidal activity against 3rd instar larvae of Ae. caspius. Larvicidal bioassay showed that the LC50 and LC90 against larvae were 253.91 or 441 mu l/l respectively at 24 hours post-treatment. Cessation of feeding was noticed starting from 6h post-treatment with the LC50. Moreover, the histological studies with the light microscope showed destructive effects for the P. frederiksbergiensis extract on the midgut epithelial layer of treated larvae. Epithelial cells appeared degenerated with degenerated nuclei in treated larvae compared to those of control ones. Transmission electron microscopy showed degenerated nuclei, mitochondria and microvelii in treated larvae compared to control ones. These gut epithelial destructions may have caused septicemia which may have resulted in death. This might be the reason of stopping feeding by larvae at 6 hours post-treatment prior to death that started from 12 h post-treatment. Based on these data, P. frederiksbergiensis bacterial extract could be suggested as a suitable biolarvicide for use in the battle against Ae. caspicus in Saudi Arabia. This bio-pesticide may help in reducing the spread of this serious vector and that, may limit mosquito-borne diseases in the country.