SUMMARYPlants are the nature's biochemical factories. They bio-synthesize a diverse array of different natural products, such as alkaloids, terpenes and terpenoids, phenolic compounds, flavonoids and coumarins through their structural mechanisms to reduce insect attacks, both constitutive and inducible, while insects have evolved strategies to overcome these plant defenses.There is a widespread effort to find new pesticides, and currently it is focused on natural compounds such as flavonoids, coumarins, terpenoids, and phenolics from diverse botanical families from arid and semi-arid lands. Algeria by the diversity of its habitats has a very diverse flora. Some of these plants have very interesting insecticidal properties. The aim of this study is to evaluate the insecticidal effect of the plant Artemisia judaica L. (Asteraceae). The crude ethanol extract of the plant A. judaica was tested on the black bean aphid Aphis fabae Scop. Four doses (12.5, 6.25, 3.12 and 1.56 mg mL -1 ) were tested on contact wingless adults. The results have showed that the tested extract has been very powerful to aphids. At the highest dose 12.5 mgmL -1 , the 100% of mortality were recorded 2 hours after treatment, and for the lowest dose (1.56 mgmL -1 ) it was after 96 hours. The LD50 calculated 2 hours after treatment from the regression lines Probit = ƒ (doses) shows that it is 2.75 mgmL -1 . This powerful insecticidal activity of the tested crude extract could be due to the richness of the plant on phenolics compounds known for their bio-insecticide action.

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Halocnemum stobilaceum (Chenopodiaceae) is one of many halophyte plants from Algerian Sahara. In this study, we investigate the phytochemical composition and the insecticidal activity of the crude ethanolic extract of this plant against adults of the red flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae). Te effect of this extract on the detoxification enzyme Glutathione S-transferase (GST) and the neuroenzyme Acethylcolinesterase (AChE) was also investigated. The repellent effect was evaluated, at the concentration of 1000 μg/ insect, using the preferential zone method on blotting paper. The insecticidal effect was investigated by testing 5 doses: 100, 200, 400, 800 and 1000 μg/insect. The obtained results show that H. stobilaceum is very rich in saponins, gallic tannins, flavonoids, antocyans, coumarins and alkaloids. The plant is poor in irridoids. On insecticidal level, the extract tested at dose 1000 µg/insecte has a good repellent effect on adults of T. castaneum. The repulsively rate calculated after two hours of exposure was 60%. The extract was toxic too. Indeed, the five tested doses caused mortalities of 15, 33.3, 41.6, 48.3 and 70%, respectively, after 6 hours of exposure. The highest dose (1000 μg/insect) generated 100 deaths after 96 h of exposure. The LD 50 calculated 24 h after treatment was 225.4 μg/insect. Furthermore, the extract of this plant, at the concentration of 1000 µg/insect, inhibited acetylcholinesterase (AChE) activity. The obtained results suggest that extracts of this plant can be used to protect the stored products against insect secondary pest.

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