The Swarm (1978)

Killer bees from South America have been breeding with the gentler bees of more northern climes, slowly extending their territory northward decade after decade. Entomologist Brad Crane has discovered that something is making them come together in huge, killer swarms. He wants to keep the General Slater from using military tactics from further upsetting the balance of nature as they join to try to stop the swarms from approaching Houston.