RESEARCH TRIANGLE PARK, N.C. (AP) — The top makers of some of the globe's most common pesticides are pushing back against critics who tie tobacco-derived chemicals to declining bee populations.

Bayer CropScience is the world's top maker of neonicotinoid pesticides and Syngenta is No. 2. They control about half of a worldwide market estimated to be worth about $3 billion. The companies are fighting pressure from regulators in the U.S. and Europe with publicity campaigns and lobbying aimed at telling people that neonics are beneficial and safe when used correctly.

Bayer CropScience spent $12 million and built visitor's centers on corporate complexes in North Carolina and Germany to show its dedication to bees. A trade magazine honored Bayer's publicity campaign for shifting blame for declining bee populations from a focus on pesticides to include other factors.