Taux de reproduction du puceron du pois (Acyrthosiphon pisum Harris) et teneur en acide médicagénique de la luzerne (Medicago sativa L)

Abstract

Summary — Net reproductive rate of the pea aphid (Acyrthosiphon pisum Harris) and medicagenic acid content of lucerne. Medicagenic acid, a major component of the saponin content of lucerne, has been reported by some authors as one of the possible mechanisms of resistance of lucerne to the pea aphid. We have measured the net reproductive rate of the pea aphid on 12 clones or hybrids of lucerne, derived from cultivars or lines of American (La, Res, Te) and French (12, 58, Eur) origins. The pea aphid performances were tested on plants growing under controlled conditions (temperature 20 °C, photophasis 16 h). Before the budding stage of the plants, small cages were placed at the tips of the stems and infested with five fourth-stage pea aphid larvae. Survival and fecondity of these insects were evaluated after 7 and 14 days. Dried powdered aerial parts of the 12 groups of plants were used for chemical and biological tests. High performance liquid chromatography was used to measure the medicagenic acid content. Two kinds of biological tests were carried out to assess the medicagenic acid contents. The ’yellow mealworm test’ used larvae of Tenebrio molitor and quantified the dry food assimilated; the Trichoderma viride test is a traditional biological test which estimates the growth inhibition of fungus. The reproductive rates of the pea aphids were not correlated with the medicagenic acid content of the plants, as evaluated by the biological tests or the chemical analysis. We conclude that medicagenic acid is not a factor in the resistance of lucerne to the pea aphid.