brussel sprouts

Question

Something is eating leaves, as tiny white flies exit each time I shake plants.

Answer 1

Probably the cabbage whitefly. These articles have advice on controlling it:

https://www.gardeningknowhow.com/plant-problems/pests/insects/whitefly-control.htm
http://eap.mcgill.ca/CPCM_7.htm

Another possibility is swede midge:

http://msue.anr.msu.edu/news/swede_midge_biology_and_management