Potentials of the Extracts of Algerian Saharan Plant Cotula cinerea for the Management of Two Insect Pests, Aphis fabae and Tribolium castaneum

The insecticidal potential of the Saharan plant Cotula cinerea, was evaluated on two insect species namely Aphis fabae and Tribolium castaneum by topical application (contact toxicity) and repellency test. A crude ethanolic extract of aerial part of the plant was prepared and tested in the laboratory on adults of both species. For contact toxicity, five doses were tested on each of the two species 1.56, 3.12, 6.25, 12.5 and 25 mg/ml for A. fabae and 25, 50, 250, 350 and 500 µg/insect for T. castaneum. The repellency of the extract was studied at the dose 500 μg/insect for T. castaneum and 25 µg/ml for A. fabae. Results showed that the repellency of the extract increased with exposure time and the highest rates were observed after 4 h of exposure (72.33 ± 22% for T. castaneum and 87 ± 3.6% for A. fabae). For insecticidal activity, at the highest doses (25 mg/ml and 500 µg/ml), 100% mortality is obtained 72 h after treatment for A. fabae and after 48 h for T. castaneum. The extract of this plant was found to be more toxic against T. castaneum adults. LD50 calculated 24 h after treatment for the two species is estimated at 1.7 mg/ml for A. fabae and at 30.3 µg/insect for T. castaneum. The extract of this plant inhibited the activity of acetylcholinesterase (AChE) in both insect species. This result suggests that this plant has a neurotoxic effect on A. fabae and T. castaneum. The results of phytochemical study showed that the plant is mainly rich in flavonoids, gallic tannins, alkaloids, saponosides and glucosides. The insecticidal effect obtained in this study could be due to the synergetic action of all constituents of the extract. Results suggest the possibility of using the extracts of this plant in integrated pest management to replace the chemical insecticides.