https://edition.cnn.com/2020/01/28/us/best-flowers-for-bees-conservation-study-scn/index.html
Colony Collapse Disorder (CCD) is when all worker bees and juveniles disappear from the hive with just a single queen remaining. CCD has been predicted to be responsible for up to a 50% loss of wild honeybee species within the last 120 years. As far back as 1868, the Commissioner of Agriculture were noting a reduction in the honey bee population and yet there is still insufficient studies performed to determine the cause for this decline. It is likely climate change has been a major factor for this decline especially in boreal regions where climates are warmer due to greenhouse emmisions. Warmer climates increases the melting of ice. This increased water availability and warmer environment causes flowers to bloom earlier. Conditions at this time ie high rainfall are unsuitable for pollinators and so synchrony that took thousands of years to form is lost. This causes alterations to the phenology of pollinators and flowers at different rates. This leaves many of the plants to go unpollinated and will lower the floral diversity and so will reduce food availability and variety. It has been predicted that specialist pollinators will decrease in population and pollinators that don't discriminate will survive.
The increased use of pesticides is thought to be a major reason for this population decline. This has further reduced the floral diversity available to these pollinators. Neonicotonoids are a class of chemicals that act as a pesticide and are seen as the most responsible for the death of these pollinators out of other pesticides. These chemicals are fatal when consumed and even at non- fatal doses, it commonly causes the loss in the ability for bees to communicate and to successfully forage. The EU have banned pesticides similar to these chemical classes.
As a result of a lack of variety to the pollinators food source and exposure to pesticides has resulted in a reduction in the immune system and have made them more susceptible to infections, viruses, parasites etc. The spread of these parasites are catalyzed through the buying and selling of bees. These bees are fitted into small, enclosed boxes commonly transported from other countries who have developed partial immunities to certain diseases that the native populations are yet to establish. Blood sucking mites (Varroa destructor) is a parasite that will shorten the lifespan of the bee. These parasites are responsible for the spreading of viruses which are associated with the death of larvae. Infection of these mites are also correlated to deformities of the offspring or paralysis of infected bees. Paenibacillus are bacteria that target larvae and will often kill the larvae and decompose which will turn the larvae into liquid. Ascarpis woodi will then lay their larvae into the bee's breathing tubes which will cause suffocation. Some bees are resistant to these infections and scientists are examining the genome makeup responsible for this resistance. They are determining ways they can breed offspring containing this gene.
It is widely believed that not just a single one of these factors are responsible for such a decline in the honey bee population but instead a host of these factors commonly decrease the immunity which will then result in the death of these populations and shorten their life span (Goulson. D, et al 2015)
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