Effet des biopesticides sur la faune aquatique

Abstract

Mosquitoes, particularly Culex pipiens, represent a major public health concern due to their role in the transmission of numerous vector-borne diseases. This study aimed to evaluate the biocidal potential of the essential oil of Juniperus phoenicea against different developmental stages of this species, as well as to identify its mechanisms of action. Bioassays revealed significant ovicidal, larvicidal, and nymphicidal activities. The LC25, LC50, and LC90 values recorded for eggs after 72h of exposure were 105,4; 130,5 and 200 µL/L, respectively. For larvae after 24h of exposure, the corresponding values were 37,22; 56,56, and 130,6 µL/L, where as for pupae they reached 75,86; 106,8, and 211,9 µL/L. These results demonstrate that the larval stage is the most sensitive to the action of the essential oil. Chemical analysis by gas chromatography–mass spectrometry (GC–MS) led to the identification of 101 compounds, among which α-pinene (21.12%), trans-calamenene (4.87%), and 1,10-di-epi-cubenol (3.69%) were the major constituents. The observed insecticidal effect may be attributed to the synergistic action of these compounds. The study of biochemical parameters revealed a significant disruption of larval metabolism. Protein and carbohydrate contents increased during the first hours of exposure (p = 0,007; p = 0,00) and (p = 0,00; p = 0,001), respectively, before decreasing after 24h (p = 0,002; p = 0,007), respectively. Lipid levels showed a significant increase after 1h, 2h, and 24h of exposure (p = 0,02; p = 0,00; p = 0,00), respectively. Histopathological analyses of the midgut revealed severe structural alterations, including disorganization of the intestinal epithelium, cellular swelling, separation of the basement membrane, and marked nuclear modifications. Furthermore, molecular docking analysis indicated that Manooloxide exhibited the highest affinity toward acetylcholinesterase, with a binding energy of −8.2 kcal/mol, suggesting a potential inhibitory effect on this enzyme, which is essential for the proper functioning of the insect nervous system. Finally, the essential oil exhibited very low toxicity toward non-target aquatic organisms, particularly Daphnia sp., (13,33% and 26,66%) and Cloeon dipterum (0%), exposed to the LC25 and LC50 concentrations. These findings highlight its biological selectivity and its potential as a natural biopesticide for use in integrated vector management programs.