I have never seen a more low-maintenance feeder in my life; I once misplaced a culture, and found them going strong 6 months later. In return though, these are very slow growers, but the adults, funny enough, can live for years. These feeders are extremely dense in lipids, and should not be used as a primary feeder, but your ants will very much enjoy them as a secondary source of food.
Confused flour beetles are a low-maintenance, fatty feeder insect that can be kept in cultures of flour-yeast mixtures. They are relatively slow-growing, and stay at around 5mm in length, but can help provide the variety your ants will benefit from.