Nematodes???should i and how to use to control sawfly on gooseberry bushes

Second year i have been hit by those dam Sawfly,last year lost every leaf because i just couldnt see the buggers,their colour is so similar to the leaves...This year managed to catch them a bit earlier and managed to save the leaves for the most part..have read a small bit about nematodes as a pest control, and was wondering if anybody has used them..?? Also any down side to using them ???