الفهرس 
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Abstract
The present study aimed to make the best use of botanical resources to formulate a safe, eco-friendly and potent larvicide against Cx. pipiens to be used in the programs of disease-vectors control.
1. Algae collection, purification and extraction
Six seaweeds of three different types (red, green and brown) were collected from Fayed City, Ismailia Government, Egypt, Saturday (24 April 2021), purified, taxonomically identified in the Phycology lab, Botany Department, Faculty of Science, Ain Shams University, and extracted by cold maceration till exhausted using ethanol (95%) with (1 dry powder :3 ethanol) ratio (w/v). The percentage yield of Lithothamnion fasciculatum, Chaetomorpha linum, Ulva intestinalis, Sargassum dentifolium, Acanthophora spicifera and Laurencia papilosa were (9.26, 6.99, 4.22, 2.28, 1.69 and 1.27%), respectively, of their dry weight.
2. GC-MS analysis of algal extracts.
GC-MS analysis was performed at the Central lab unit of Ain Shams University for all algae and the resulting chromatogram was analyzed depending on NIST, Wiley/NIST mass spectral database as references to identify their chemical constituents. Fatty acids represented the major group of compounds appeared specially, palmitic acid and myristic acid, they were observed in most of the extracts in different ratios, and other compounds were also detected as phytol, sterols, bicyclic carboxylic acids and sesquiterpenes. Sixty-three compounds were identified in A. spicifera, (78) in L. fasciculatum, (36) in L. papilosa, (82) in Ch. Linum, (80) in U. intestinalis and (22) in S. dentifolium. Palmitic acid was the major component detected in A. spicifera followed by oleic Acid, while 1,4-Benzenedicarboxylic acid, bis(2-ethylhexyl) ester and 1-O-hexadecylglycerol-bis-trimethylsilyl ether derivative were the major two compounds found in L. fasciculatum. palmitic acid and 13-octadecenoic acid, (E)-, TMS derivative were the main compounds in L. papilosa whereas palmitic acid and myristic acid were the widest peaks in the GC-MS analysis of Ch. linum. On the other hand, alpha-linolenic acid and palmitic Acid were the major compounds in U. intestinalis and di-n-octyl phthalate and bis(2-ethylhexyl) phthalate were recorded in S. dentifolium.
3. Larvicidal activity.
The toxicological activity of the six extracts was tested against Cx. pipiens 3rd larval instar by the immersion method with different concentrations and results were observed every 24 hours along 96 hours A direct relationship between the used concentrations, time and the percentage mortality was observed. The LC50 values recorded for A. spicifera, L. fasciculatum, L.papilosa, Ch. linum, U. intestinalis and S. dentifolium were (176.00, 193.47, 232.46, 224.45, 231.06 and 241.79 ppm), respectively, 48 hours post-treatment. Based on the toxicity index of the tested extracts, A. spicifera extract showed the highest larvicidal activity followed by L. fasciculatum and Ch. linum, while S. dentifolium showed the lowest larvicidal activity.
4. Morphological observations.
Morphological malformations were observed in treated larvae subjected to the LC50 of algal extracts, examined by binocular and light microscope. Severe alternations were observed in larvae treated with the red algae (A. spicifera, L. fasciculatum and L. papilosa) such as body distortion, head reduction, loss of segmentations, cuticle destruction, alimentary canal expelling, neck elongation and ganglia enlargement, on the other hand, the brown alga S. dentifolium showed a head reduction, seta loss, fainted cuticle and thorax malformation, and the green algae (Ch. linum, U. intestinalis) caused trunk deformation and antennal loss.
5. Histological studies.
Histological malformations induced by the tested algal extracts were studied and examined in the Faculty of Medicine, Al-Azhar University. Epithelial cell destruction, basement membrane distortion, peritrophic membrane lysis, columnar cells apical protrusion, nuclear aggregation and disintegration and cytoplasmic vacuole formations were observed in treated midgut of Cx. pipiens larvae.
6. Biochemical activity.
6.1. Determination of total main metabolite
Larvae treated with LC50 of algal ethanolic extracts were subjected to quantitative biochemical analysis to identify the changes that occurred in levels of the main metabolites (lipid, protein and carbohydrate). A great increase in total metabolites was recorded in treated larvae with both A. spicifera and L. fasciculatum extracts with different ratios comparable to untreated larvae.
6.2. Determination of enzymes activity.
(AChE, GST and α and β esterases) levels were tracked in larvae treated with LC50 of algal ethanolic extracts and it was found that A. spicifera and L. fasciculatum significantly reduced levels of all enzymes comparable to the control, while Ch. linum reduced levels of GST and α and β esterases, L. papilosa lowered levels of α and β esterases and S. dentifolium lowered levels of β esterase.
The results of this study will contribute to a great reduction in the application of synthetic insecticides, which in turn decrease environmental pollution. The results of the present study may encourage further research on using simple and inexpensive application methods for controlling mosquitoes in their breeding sites.