When do the June bugs leave?

Flies in the family Pyrgotidae are endoparasitoids of these and related beetles. The female flies pursue the beetles in flight, laying an egg on the beetle's back under the elytra where the beetle cannot reach it. The egg hatches and the fly larva enters the body cavity of the beetle, feeding on and eventually killing the host before pupating. Wasps in numerous families are parasitoids of Phyllophaga grubs, including Pelecinidae, Scoliidae, and Tiphiidae.