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.