Kathleen Boyer suspects the mailman. She said she could not think of anyone else in her neighborhood who would have complained about the two beehives she kept under a pine tree in her front yard in Flatbush, Brooklyn, leading the city’s health department to fine her $2,000 last fall. “I was kind of surprised,” said Mrs. Boyer, an art director with a media company. “People see us in our bee suit and they’d bring...