The decline of colonies of honey bees across the world is threatening local plant biodiversity and human food supplies. Neonicotinoid pesticides have been implicated as a major cause of the problem and are banned or suspended in several countries. Other factors could also be lowering the resistance of bees to opportunist infections by, for example, new resistant strains of the Varroa mite and by the parasite Nosema. Intensive agricultural practices and modern beekeeping practices may also be implicated.