Bertram Larvan and an unnamed scientists needed some extra funds. Times were tough, after all. Hence they adopted the aliases of the Bug-Eyed Bandit and Insect Master. Their goal was to obtain money necessary to continue their research in automated insect technology. To that end, they employed their minature armies already developed in initial research.
The Bandit attempted to steal to supplement his research, and that research aided him in stealing more. In the form of tiny mechanized insects, he sent them throughout Ivy Town drawing the attention of Earth-One's Mighty Mite, the Atom. Atom proved the superior scientist and costumed crusader.
Insect Master was initially a threat to the citizens of Metropolis, until he faced Earth-Two's Superman who was more than a match for this malevolent madman. While Bug-Eyed Bandit would return a couple more times after his initial appearance, Insect Master perished after his first outing.