Bee Help Guide
Do not use any insecticides (topical and systemic) as they may be lethal to bees.
The leading cause of bee population decline is habitat reduction. Planting flowering perennials will help to rebuild their habitat.
Remember to deadhead your flowers. This encourages the plant to produce more flowers than it would otherwise and increases the amount of pollen (food) available.
The majority of bee species are solitary and are ground nesters. Leaving exposed soil instead of using landscape fabric and mulch will help rebuild the population.