"Five Reasons Honey Bees Can Be a Problem" from Xerces Society

1. Native plants need native bees. Native bees coevolved with our native plants and often have behavioral adaptations that make them better pollinators than honey bees. For example, buzz-pollination, in which a bee grasps a flower and shakes the pollen loose, is a behavior at which bumble bees and other large-bodied native bees excel, and one that honey bees lack.

2. Honey bees are sub-par pollinators. The way that honey bees interact with flowers means that they sometimes contribute little or nothing to pollination. Honey bees groom their pollen and carry it in neat pollen cakes, where it’s less likely to contact the stigma of another flower and pollinate it. They are also known “nectar robbers” of many plants, accessing their nectar in a way that means they don’t touch the pollen, often by biting a hole in the base of the flower. By contrast, many of our native bees tend to be messier, carrying pollen as dry grains, often all over their bodies where it’s more likely to pollinate the plant.

3. Hungry hives crowd out native pollinators. Introducing a single honey bee hive means 15,000 to 50,000 additional mouths to feed in an area that may already lack sufficient flowering resources. This increases competition with our native bees and raises the energy costs of foraging, which can be significant. One study calculated that over a period of three months, a single hive collects as much pollen as could support the development of 100,000 native solitary bees!

4. Honey bees can spread disease. Unfortunately, honey bees can spread diseases to our native bees—deformed wing virus, for example, can be passed from honey bees to bumble bees—and can also amplify and distribute diseases within a bee community. 

5. Urban honey bee hive densities are often too high. There is growing evidence of negative impacts in towns and cities from the presence of honey bees. A recent study from Montreal showed that the number of species of native bees found in an area decreased when the number of honey bees went up. In Britain, the London Beekeepers Association found that some parts of that city had four times as many hives as the city’s gardens and parks could support. The conservation organization Buglife recommends creating two hectares (five acres) of habitat for each hive, several times the size of an average residential lot in the United States.

"7 Reasons Honey Bees Are Bad For Native Bees" from Garden Ecology Lab

Researchers have documented at least seven different ways that honey bees may harm native bee species (summarized in Cane and Tepedino, 2016):

1. Honey bees monopolize and deplete nectar and pollen from local plant communities, which can reduce native bee reproduction.

2. By depleting local plant resources, native bee females have to devote more time and energy to fly and find new resources, which also reduces native bee reproduction.

3. Unlike honey bees, most bees are solitary, which means that they do not live in colonies and they do not have a queen. Solitary females who have access to fewer floral resources produce fewer daughters and more sons. Since female bees are needed to maintain a population, this skewed sex ratio can slow population growth and recovery in native bees.

4. When females collect less nectar and pollen, they have less food to feed their young. These bees grow up to be smaller, and are more likely to die over winter, compared to well-fed bees.

5. The longer a solitary bee mom is away from her nest, the higher risk that parasites and predators will attack her unguarded young.

6. Honey bees can physically block native, solitary bees from preferred pollen hosts.

7. Honey bees have many diseases. Some honey bee viruses have been found in native bee communities. Researchers think flowers that are visited by both native bees and honey bees are analogous to an elementary school water fountain: a place where repeat visitors can pick up a pathogen.