The No. 1 challenge Massachusetts employers face is their need for skilled employees. On Thursday, Lt. Gov. Karyn Polito met with leaders from local government, education and industry to recruit more of those employers to host high school and college interns in the STEM -- science, technology, engineering and math -- fields. She also announced that Columbia Gas of Massachusetts will now host interns. "Today's discussion is really about talent," said David Cruise, president of the Hampden County Regional Employment Board. "Talent is the differentiator."