Leek moth. Try spray, but my mum's a dab hand with her veg, and she's figting a losing battle. Every year one pest or another has a field day with some of the garden. This year its leek moth, and vine weevil. Fleece the leeks when planted to prevent the moths getting at them, and (for next year now) in autumn clear away all leaf debris in which the adult moths overwinter. Phil J

you could try spraying them in a soapy solution, so that it not only washes onto the leaves but also lays in the leaf joints. that is what i do and it does seem to keep them down to a manageable level