In April, our speaker Steve McDaniel mentioned that it is suspected that one culprit of honeybee die-off is the use of systemics on our ornamentals. Systemics work to poison the plant such that the pest dies from eating it. Unfortunately, we learned that it also affects the flowers which is where the honeybees will be gathering pollen and nectars.
Recommended systemics to control the Iris Borer include: Imidacloprid (Merit/Marathon) and Orthene or Isotox Formula 4. These are known to be implicated in bee deaths. So, the markings on those system treated Iris, indicating a bee path to the goodies, are just leading pollinators to their death.
Carol Warner indicated digging the fans and plopping them into a bucket of plain water will drown the buggers. It may be more time consuming than the systemics but is infinitely kinder to our pollinators. You can also order special nematodes that will go after the borers as an organic approach.