It's an infestation if you're losing plants. I got to a point where I couldn't even sprout seeds of ANYTHING, they'd eat 'em up and gobble 'em down. I was really banging my head, too. Then, for whatever reason, I started reading the label of my
Spinosad. It treats FGs and fruit flies (I've started lacto-fermenting and the fruit flies can get seriously outta control, but I'm not sure they're fruit flies, they're so tiny!). A neighbor told me they'll breed in drains and to bleach them every few weeks, and that in combination with the
Spinosad has all but eliminated the problems I was having near and in the house.
If you're just getting some on the stickies and have no other issues, you're probably ok. Do keep in mind, however, that they can help vector some diseases so you do want to stay on top of them. :)