I just fermented some blackberry and the closet I have that stuff in has a gnat or two. Those fermenter caps let the gas out that attracts them, but they can't get in the jars. I used some on the plants and it didn't attract anything. You're using about 4-8ml in a gallon which is 3800ml.
From Duke Diamond I also got that you can use pure cane sugar (tsp/g) for organics as a "finisher". The science is that it distracts the microbes from attacking the soil NPK's and focuses them on the sugars and carbs. Who knows?
I make Fermented Plant Juice for the flower stage out of banana flowers and raw sugar. Works great and you won't have a pest issue if you use it correctly