Honey bees?
He's in good company. They are dying all over the world. You've probably heard of CCD (Colony Collapse Disorder).
Pesticides (especially a class called neonicitinoids), mono-cropping (90 miles of corn), parasitic mites, and other reasons including poor management and other pests... unfortunately their time is almost up. Their decline started in the late 1940's.
We only notice because we steal their honey. Many other insects are passing silently because we don't interact with them, so nobody notices.
Your dad is doing OK with only 50 percent lost. Many people lose them all, year after year. Pesticides are everywhere they eat.
OK, +1 for bringing mew down. Waaaah! :-)