How can neonicotinoids affect the immune systems of honeybees?

Neonicotinoids are suspected of contributing to colony collapse disorder by suppressing the immune function of honeybees. While no definitive causal link has been established, exposure to specific neonicotinoids, such as imidacloprid and clothianidin, has been associated with weakened immune systems in these insects.12

This suppression of the immune system is significant because it may make honeybees more susceptible to disease-carrying parasites, such as the varroa mite, and allow preexisting pathogen infections to worsen. For instance, research suggests that exposure to these chemicals may promote the proliferation of the deformed wing virus in infected bees. By weakening the bees' natural defenses, neonicotinoids may act as a stressor that, in combination with other pathogens or environmental factors, contributes to the sudden colony death characteristic of the disorder.123