As I recall, my grandmother said citrus peels were good for the compost pile BUT you had to keep that compost longer than say traditional green scraps. Citrus peels take a little longer to decompose and so that may be why she said that. I am not sure of the pesticide factor on the peels but do know that until the peel begins to break down you do have some natural pesticide features happening in your compost pile. In fact as a child, I can recall my grandmother using citrus peels that she zested around areas she didn't want bugs to be. Please note I am going off of memories from 30+ years ago so some of the information may not be exact.