Bees produce sweet honey and painful stings, but their role in food production is far more extensive as the primary pollinators of most flowering plants. Declining bee populations have been observed in many countries since 2006, leading to much speculation as to the reasons for their decline and how losing bees altogether could affect mankind. One theory is that cell phone towers interfere with their ability to navigate, while another theory involves poisoning by herbicides.
Some plants are pollinated by the wind, but most are pollinated by insects. Beetles and butterflies, among others, can pollinate plants, but bees do the job most efficiently. Nearly all fruit and most vegetable species owe their pollination to insects; without bees, we'd lose many of the plants we use for food. Some crops, like wheat and rice, don't need insect pollination, but at least 30 percent of the world's food crops and 90 percent of wild plants require insect involvement, so we would have fewer food choices -- or we'd have to find an alternate way of pollinating plants.
Animals that rely on particular plant species would become extinct if those plants ceased to exist. This means whole ecosystems would alter, eliminating some of the world's biodiversity. For example, many cattle used for milk and meat eat mainly alfalfa and lupins, both of which need to be insect-pollinated. With less food available to feed large animals, there would be less meat and milk production, so the human diet would change significantly.
Clothing and Fuel
Rapeseed, or canola, is grown to produce fuel as well as being used for cooking oil and foodstuffs. Without pollination there would be less production of biofuel, which means we'd rely more on fossil fuels and run out of them sooner. Cotton is pollinated by bees and other insects, so without bees there'd be fewer choices for clothing material; a greater reliance on man-made fabrics would further deplete fossil-fuel sources.
Many medicines are plant-based, so if bees become extinct we would lose our source of some pharmaceuticals. Morphine -- the basis of most pain-killers -- is extracted from opium poppies. Opium poppies can self-pollinate, but studies have shown there's a better yield from cross-pollinated cultivars. Many other plants used in pharmaceuticals also require pollination by insects.