Justincase, it's amazing and pretty cool what you have investigated I always thought the reason was human interference as well and I believe is also the cause of many other issues with insects/animals problems.
Are Agriculture's Most Popular Insecticides Killing Our Bees
Neonicotinoids are pesticides widely used to coat the seeds of agricultural plants, especially corn. But some evidence suggests these chemicals may also be poisoning bees. A tell-tale clue: reports of massive bee die-offs that all took place during corn-planting season.
Source: Science
EPA finds common insecticide is threatening bees
An EPA study found the commonly used insecticide imidacloprid, found in some 188 products in California and used on vegetables, fruit and other crops, is threatening honeybees. The finding could lend impetus to efforts to ban the chemical. Ref. Source 3g
Old Data May Provide New Insights On Honey Bee Populations
Science Related News
There has been a lack of useful, long-term datasets on the size of honey bee populations, making it difficult to quantify actual changes in honey bee abundance, and to determine what causes population declines. But researchers have studied long-term datasets from the USDA and from US states to see how they can be used together.
Source
Biologists discover sophisticated 'alarm' signals in honey bees
Bees can use sophisticated signals to warn their nestmates about the level of danger from predators attacking foragers or the nest, according to a new study. Biologists found that an Asian species of honey bee can produce different types of vibrational 'stop signals' when attacked by giant Asian hornets. Ref. Source 8t.