Bees are fundamental to ecosystems and agricultural productivity, ensuring the reproduction of countless plant species. Roughly one-third of the global food supply, including fruits, vegetables, and nuts, depends on bee pollination. Bees also contribute to biodiversity by supporting wild plants. However, these pollinators are currently facing numerous threats.
Chemical Contaminants
Chemical contaminants, particularly pesticides, pose a significant danger to bee populations. Neonicotinoids, a class of systemic insecticides, are absorbed by plants and can persist in pollen and nectar, exposing foraging bees. Even at low concentrations, neonicotinoids can affect the development of honeybee larvae. These chemicals can cause direct toxicity and mortality, or have sublethal effects that impair navigation, taste sensitivity, and learning in adult bees, compromising foraging ability and hive productivity.
Organophosphate insecticides also contribute to bee mortality, often through direct exposure. Herbicides, while not directly targeting bees, can indirectly harm them by eliminating wildflowers and other nectar-producing plants, reducing food sources. Fungicides can weaken bees’ immune systems or synergistically increase the toxicity of other pesticides, making bees more susceptible to pathogens. The widespread use and persistence of these chemicals mean bees are frequently exposed, accumulating toxins that can lead to colony losses.
Loss of Foraging and Nesting Sites
The destruction of natural habitats contributes to bee mortality by limiting access to food and shelter. Urbanization and infrastructure development often replace natural areas with impervious surfaces, reducing diverse floral resources and safe nesting locations. Monoculture farming, growing a single crop over large areas, offers limited nutritional diversity for bees, providing pollen and nectar for only a short period. This lack of continuous forage can lead to starvation and nutritional deficiencies, weakening colonies and making them more susceptible to other stressors.
Deforestation further reduces the natural landscapes where bees forage and nest. Many bee species rely on undisturbed habitats for reproduction and overwintering. When these sites are lost, bees struggle to build up their populations and survive seasonal changes. The scarcity of diverse food sources and secure nesting sites increases stress on bee colonies, reducing reproductive success and making them more vulnerable to disease.
Diseases and Parasites
Biological threats, including diseases and parasites, severely weaken and can eliminate bee colonies. The Varroa destructor mite is a destructive external parasite that feeds on adult and larval bees, suppressing their immune systems. Beyond direct harm, Varroa mites act as vectors for various viruses, most notably Deformed Wing Virus (DWV). DWV can cause symptoms such as twisted wings, bloated abdomens, and reduced body size in adult bees, making them unable to fly and shortening their lifespan.
Bacterial diseases also pose a serious threat. American Foulbrood (AFB), caused by Paenibacillus larvae, is highly contagious and fatal to honey bee larvae. Infected larvae die after their cells are capped, decaying into a ropy mass, and the spores can remain viable for decades. European Foulbrood (EFB), caused by Melissococcus plutonius, is another bacterial disease that infects the digestive tract of young larvae, causing them to starve and die. While EFB is less virulent than AFB, severe infections can still lead to colony collapse.
Fungal diseases, such as Nosema, caused by Nosema apis and Nosema ceranae, infect the digestive cells of adult bees. These parasites multiply in the mid-gut, impairing food digestion and debilitating the bees. Nosema ceranae is more damaging, affecting more cells and causing faster mortality. Infected bees may experience reduced lifespan, decreased foraging ability, and weakened immune function, contributing to a decline in colony strength and productivity.
Environmental Disruptions
Environmental factors, particularly those linked to climate change, jeopardize bee populations. Extreme weather events, such as prolonged droughts, excessive heat, and unseasonal cold snaps, directly impact bees. Droughts reduce the availability of floral nectar and pollen, leading to food scarcity and starvation for colonies. High temperatures can cause dehydration and stress within hives, forcing worker bees to cease foraging to cool the colony, which reduces resource collection and honey production.
Altered seasonal patterns, including earlier spring arrivals, can lead to a mismatch between bee emergence and floral bloom. If flowers bloom earlier than bees are ready to forage, pollinators may find insufficient food sources, affecting their nutrition and disease resistance. Conversely, unseasonal cold snaps or severe storms can destroy foraging opportunities, disrupt flowering cycles, or directly kill bees and damage their hives. These environmental changes exacerbate existing pressures on bee populations, making it harder for them to thrive.