Abstract The effect of feeding by the grain aphid Sitobion avenae (Fabricius) (Homoptera: Aphididae) on chlorophyll, carotenoid and flavonoid content was studied in waxy and waxless triticale genotypes. On both sampling dates (5 and 10 days after infestation), seedlings of infested waxy and waxless plants had lower chlorophylls and carotenoids and higher flavonoids than in uninfested plants.

Abstract The electrical penetration graph (EPG) method was used to quantify the effect of surface waxes on probing behaviour of the grain aphid Sitobion avenae F. (Hemiptera: Aphididae). The experiments showed that wax removal significantly affected probing behaviour of S. avenae. Generally, the aphids feeding on the plants without wax had a shortened non-probing (EPG-pattern np) and prolonged penetration of peripheral tissues – epidermis and mesophyll (EPG-pattern C). The EPG tests also showed that the three tested extracts of surface waxes from waxy plants RAH 122 were active as aphicides against the grain aphid.

We studied the effect of qualitative and quantitative variation of saponin content in foliar tissues of four European alfalfa (Medicago sativa L.) cultivars (Radius, Sapko, Sitel, Radius line 1) on pea aphid (Acyrthosiphon pisum Harris) development, and the effect of aphid infestation on alfalfa saponin content. Aphids (adult apterae, larvae, and adult alatae) were counted on 3-, 6- and 9-month-old plants (before the first, second and third cutting). Thin-layer chromatography was used to detect and estimate the quantity of the following saponins: 3GlcA, 28AraRhaXyl medicagenic acid; 3Glc, 23Ara, 28AraRhaXylApi zanhic acid (zanhic acid tridesmoside); and 3RhaGalGlcA soyasapogenol B (soyasaponin I). Radius, Sapko, and Sitel contained all three saponins but Radius line 1 did not contain zanhic acid tridesmoside or medicagenic acid glycoside. Saponin content was highest in Radius and lowest in Radius line 1. Regardless of the cultivar, saponin content was higher in aphid-infested than uninfested plants. For all sampling dates, aphid numbers were highest on Radius line 1 and lowest on Radius; that is, aphid numbers were inversely related to saponin content. Alfalfa has a herbivoreinduced defense. Saponin levels increase in the foliage of infested alfalfa. Attempts of plant breeders to reduce saponin content in order to increase alfalfa digestibility for livestock might make the plants more susceptible to aphids and other pests.