There are a couple of contenders for the title of biggest eater in the insect world:
Caterpillars: These fast-growing machines can consume five times their body weight in leaves every day [1]. Their rapid growth spurt before metamorphosis into butterflies or moths requires a massive amount of fuel.
Mosquitoes: While not quite reaching their own weight, female mosquitoes seeking to lay eggs can drink one to three times their body weight in blood during a single feeding [2].
So, depending on what kind of "eating" counts, either caterpillars or mosquitoes could be the insect champion