not organic but a drop of washing up liquid in a little water on the surface of the soil works wonders, i had loads of these pesky blighters after the neighbour mowed her nettle patch - one dose with washing up liquid and they were gone. I think they breathe through their bodies and WUL coats...
i remember using that stuff, it's sweet and sickly smelling but f.me it literally covered the plants in crystal overnight... use some now and maybe once every week something like that. that shit works!