Invasive species introduced to Canada can cause pathogen spread or ‘spillover’. This means that when commercial bumble bees (used in greenhouses to pollinate tomatoes and other plants), often imported from countries over seas, interact with closely-related wildlife populations and infect them . The commercially used bumblebees are used in greenhouses for pollination, but often escape and interact with flowers that wild colonies forage on . Commercially-produced bumble bees used in greenhouses often have higher levels of various pathogens than wild bumblebees . A study conducted in southwestern Ontario, Canada, showed that bees collected near commercial greenhouses were more frequently infected by those pathogens (Crithidia bombi and Nosema bombi) than bees collected at sites away from greenhouses . Higher pathogen prevalence is a realistic predictor of the patterns of decline in the species Bombus in North America .
Non-native honey bees (Apis mellifera) can have negative implications on their interaction with native bumblebee species. Honey bees can carry Varroa mites (Varroa destructor), which are relatively large parasites that feed on the bee’s hemolymph (bee blood) causing catastrophe in hives, tracheal mites (Acarapis woodi) which attach to the bees’ trachea and suck out its hemolymph while injecting the bees with bacteria that weaken and kill the bee. Furthermore, they can carry two species of microsporidia, Nosema apis and Nosema ceranae. These microsporidia can infect a bee’s gut, damaging its digestive tract, exposing it to numerous bacteria and viruses, and; thus, shortening its lifespan. North American queen bees were exported to Europe, where they were infected by European bumblebee parasites, and then were reimported into North America for the greenhouse pollination of different plants. Robbin Thorp,bee expert and professor of entomology at the University of California, believes that the introduction of European bee diseases into the North American bumblebee population was responsible for the loss of short-tongued species of bumblebees. 
Commercially reared bumble bees colonies of B. impatiens and B. occidentalis from the United States have a greater prevalence of protozoan pathogens such as C. bombi, N. bombi, as well as, the tracheal mite Locustacarus buchneri compared to wild colonies . Studies indicate that the transportation of bumblebee colonies will cause overseas migration of parasitic mites of different origins .
Competition for resources between native and non-native species
Many bee species have been introduced to non-native countries. Possible negative consequences of these introductions include: competition with native pollinators for floral resources, competition for nest sites, introduction of pathogens, pollination of exotic weeds, and disruption of pollination of native plants . In Japan, B. terrestris is now naturalized and there are concerns that there may be possible competitive effects of this species on native bumble bees. Studies have shown that B. terrestris, in comparison to native species, has four times the reproductive output and have substantial overlap in forage use and forage timing. Recent studies suggest that honeybees can have a negative effect on bumble bees. Thomson experimentally introduced honeybees and found that their proximity to hives significantly reduced the foraging rates and reproductive success of B. occidentalis colonies. Deformed wing virus, a viral honey bee pathogen, found in commercial colonies of B. terrestris, has been transmitted between honey bee workers and bumble bee queens who have been put together in order to help induce colony founding .
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