I guess I'm lucky I don't have any of those problems with my lettuce, but something I spray on my okra, and a number of other things, as an anti-fungal spray, is hydrogen peroxide, and it seems to kill the aphids on the okra, although they will show up again, eventually. And what you should look around for, when aphids are a problem, are ants, which often farm them! I use a cup of H2O2/gal - the 3% I buy in Dollar Tree - and don't add anything to is, as it reacts with almost anything. I use that on my cherry tomatoes, that I don't spray the Surround/potassium bicarbonate mix on, that is a prophylactic I spray on many things, both for the insects and fungal problems. But I don't spray that on greens, or other things that are a pain to get the powder off of, like the cherry tomatoes. I usually do it once a week, and if you spray the Bt, do that at least a day after the H2O2, as it will kill things like that, though it dissipates quickly.