u could try picking them off by hand and dropping them into a bucket of water mixed with dishsoap. its a lot of work but u dont have to use chemicals. another idea would be to try using cayenne pepper. i would just sprinkle it right onto the plant itself and see if that helps at all, maybe try doing a few to test so as to be sure it doesnt hurt the plants themselves but i really dont think that it will.
otherwise u can try organic sprays or potato dust. good luck, sockiescat.