I’ve been watching dogbane patches for dogbane beetles for a few weeks – I saw my first one yesterday:
They spend the full lifecycle on the dogbane plant or muching the roots. I believe the plant has toxins that gives the insect chemical protection, just as milkweed does to various bugs. Such an attractive beetle, but small and hard to photograph. They’re so reflective that you must have overcast lighting, or they overexpose.