Woolly apple aphid-derived phloem sap contains small RNA. A, Woolly apple aphid stylets deposited in apple phloem. The tips of the stylets are indicated by arrowheads. B, Radio-labelled SE RNA contains a prominent small RNA band. Size markers are indicated on the right. The weak band of high molecular weight RNA is indicated by an arrow. P, periderm; Ph, phloem; X, xylem.