Butterfly Betrayal - Ruth J. Hartman

Raising butterflies is peaceful and calm, until someone dies. 

Majestic Monarch Butterfly Farm might flitter away forever. That is, unless Seneca James acquires the property next door. She and Winifred, her costume-wearing cat, have a fight on their hands. Their land sits next to a milkweed-covered field, essential for monarchs. If she's unsuccessful in buying it, her precious, winged friends won't survive. When people end up dead on her farmland, Seneca is suspected of murder. What is it about the milkweed field that's worth killing for? And who's the murderer?