If you are referring to honey bees of European descent, the answer is yes, they are in decline. I'll answer this first from observation and leave the quoting of statistics to others.
Observation 1 - The Past
When I was growing up there were honey bees everywhere. Any flowering shrub was buzzing with a host of bees as soon as it started flowering. I remember lying in my backyard in a large patch of white clover and watching bee after bee travel from one flower to the next harvesting nectar and pollen. I also remember when that clover patch bloomed I once got stung running through it with bare feet. As I picked yellow dandelion flowers for my father's bounty of one cent per flower (ones that had went to seed were worthless as the point was to get them before they spread), I often had to wait on a bee to leave before I could pick the flower.
There was this crab apple bush in a neighbor's yard behind us and down the alley. It turned a fuchsia when it bloomed and it had a cloud of bees surrounding it for three weeks. That is when I learned that if you leave bees alone they will leave you alone. I would get within the branches underneath the canopy with my face only 20 cm from the flowers and watch the bees. I could see them pack the pollen on their legs, something they didn't do with dandelion as much. I once remember trying to count the bees that visited the flowers in front of me but kept loosing track after a few hundred. Perhaps those hours sitting in Mrs. German's crab apple bush started my fascination with bees.
Without realizing it, I had my first bee lining experience. Noticing that when I set my Slurpy cup down, full of hard earned dandelion funded sugar water, the bees soon found it and landed on the edge, I watched in which direction they flew and moved that cup that way. Soon I had more bees visiting, lots of them in fact. Now finding the direction was even easier. I kept doing that and after about an hour I found myself outside the edge of town at an old elm tree on section line road watching the bees in a cloud of erratic dots entering and leaving a hole about 3m up the tree. I had found their hive. It was an awesome sight but the sound was even more thrilling. It was more than a buzz, it was a hum that came from that tree, and I imagined to myself that if I could get up there and touch the tree near the entrance I could probably feel it vibrate. A colony like that can have 60,000 bees. I visited it many times later with sugar water in hand to gather my own crowd of bees to watch. I did the same thing a week later picking a different direction and found another colony in a sugar maple in the yard of a classmate who later turned out to be the first girl I kissed (thanks bees).
Practically I could not go anywhere and get away from bees except into the many, many wheat fields surrounding my small hometown in Kansas. Even there, an errant weed often attracted them, but 10m in from the edge of a field there were no bees. It was buzz barren.
When I go visit my parents, my children run around barefoot without fear. Bees are rare and that clover patch is gone because there was nothing to pollinate it. Mom and Dad hand pollinate their squash to make sure they get enough. They don't even plant okra anymore.
Observation 2 - The Present
We, my wife and two children, moved to our ten acre farm which had a old barn and a car port but was otherwise 10 acres of bahia grass with scattered trees. Here and there were a few very small white flowers, some thistles, and dandelion which no one will pay me to pick.
We moved in mid-January, one year and were thrilled to see our brown grass turn green over the next few months. Ten whole acres of happy greenness not hot concrete. We cut our first acre of field with the old Massey-Fergusson and planted our first crop of veggies. Of course, it wasn't the best because the sandy soil had little nutrients but we did get beans, squash, corn, and tomatoes, among others. To catch rain off the barn roof I purchased five 250 gallon plastic containers that were used to ship honey from Argentina to Florida. Each and every one had 5 or 6 gallons of honey in the bottom that didn't come out at the packaging factory. I had lids for all of them but one.
That first year we didn't get much squash and the tomatoes, despite our best efforts, didn't produce many fruits per plant. We did have pollinators, in the form of a little solitary bee that were a beautiful metallic green color.
But there weren't many of them and they couldn't pollinate an acre of blooming veggies. Our first two hives were waiting for bees which we would get in May, well past the date we needed pollinators. I do remember we were amazed at a passion flower that grew near our house. They have amazing flowers.
May came and we drove to Georgia to get our bees. We hived them and made sure they had a good start. By September, each colony built about 10-12 combs in their top bar hives and we did our best to leave them alone, though like in my boyhood, I would take a water break from hoeing and go stand by the nearest hive, watching the bees go in and out, listening to the buzz and the bugs and birds. The bees would come in with pollen covered backs and pollen baskets bulging.
In Florida we had two complete planting seasons, and we started our fall crops. By then the hives were 3/4 full of comb with tens of thousands of bees. Even in our poor soil, the difference was amazing. The squash quadrupled, the tomatoes tripled, and any species that needed pollination did much better. But something else amazing happened.
We started getting calls from neighbors. They would say, "Wow, come over here. My persimmon tree is buzzing. Are these your bees?" I'd go over and sure enough the tree buzzed from 6m away and a cloud of bees tended the blossoms. Bee lining was easy, because it was a bee highway to our farm. "Yup, those are my bees, I'd say." We received another call from our direct neighbor where we had placed a hive on our side of the property line. She said, "Mick, the wind blew open the bee hive last night. Get over and help them. I've had more tomatoes then I can eat since you put those bees there." One day a elderly man stopped by with a bag full of okra. "Hey, ya don't know me but I live about half a mile south of ya. I hear ya got bees," he said. "Well I wanna to bring ya some okra because this is my best crop ever and I think it's your bees. I can't even eat it all." It was a great way to meet he neighbors. One family with three lemon trees and two limes trees (this is Florida) grew lemons and limes for the first time. At least a dozen more times we'd heard a story second hand from a distant neighbor that had grown more vegetables in their small veggie plots than ever.
I sure do wish I liked persimmons more:
Now, after years of four healthy hives on the farm, when spring comes, it's not just green. Because the bees have been pollinating year after year, everything produces more seeds, weeds or not. Our yard is dotted with little white flowers in February, then big yellow soft greeneyes, then purple phlox, then white and purple skullcap, red buckeye, violet larkspur, and indigo day flowers. In May, parts of the lawn turn absolutely pink with beardtongues. Then lavender bellflowers, woodsage, with azaleas everywhere. The back 2.5 acres is in cover crops of clover and sun hemp and it goes from a purple carpet twice as big as a football field then turns to 8' foot tall plants bursting with bright yellow flowers. We're awash in deer's tongue, spider wort, and lady lupine. We have blossoms from February straight through to November. The bees are back in town.
We've spawned at least six swarms so our bees are now someone else's bees. There are more than a hundred passion flower vines within 30m of my back door. Our passion fruit is edible and good:
And that 250 gallon honey tank without the lid? It was licked clean before I found it full of thousands of dead workers that expired when they loaded themselves with honey and were too weak to make that one last flight home. Our ladies couldn't resist and we didn't find it in time to make them hunt more naturally.
Yes, Virgina, There Are Less Bees
And while there are many reasons, the big four are:
1. Pesticides - Bees don't need to pollinate corn but they love its pollen. Corn is one of the most sprayed crops and pesticides aren't selective. Many of the new systematic type pesticides (neonicotinoids) that are taken in from the roots and become apart of the plant's biochemistry are the worst. The imidacloprid based pesticides are even killing birds. Pesticides are every where so bees are not.
2. Mono-culture - Wheat, barley, oats, and all the grasses we call grains, don't need pollination. Even corn. But with acres and acres of a single, non-flowering and non-nectar producing crops, bees don't have enough nectar available to survive in the area. That's why there are no bees in the middle of a wheat field. What about large flowering crops like almonds in California? Even in large crops, like fields of almonds, with plenty of blossoms, bees can't survive because of all the trees blooming at once and the bees don't have enough time to get enough nectar to store enough honey to survive. This forces almond growers to pay for truckloads of bees to be shipped in to pollinate the flowers in time and that weakens the bee colonies. Even if they put bee hives in the fields with the almonds it wouldn't work. Bees need continuous sources of nectar for many months and that is rarely the same plant. Plants have evolved to bloom at different times of the year just because bees prefer certain flowers over others and one way to get bee visitors if you're not so popular is to bloom when no one else does in the area.
3. Large scale hive managementCommercial apiaries are about honey, not bees. Most commercial hives are in a constant state of weakness because the hives are split to make new hives instead of old world swarm catching. It may have always been this way but the demand for bee products due to the cosmetics and body care industries have given beekeepers an additional large market, but it is stressed to produce for it. That coupled with the deadly environment we have created for bees due to #1 and #2 it is harder than ever to keep large bee yards. Constant hive moving, splitting, inspections disturb the hive and weaken it. This means the beekeeper needs to use specialty insecticides and fungicides within the hive to help them and this in turn weakens the bees even more. I can take some confectioner's sugar and dust my bees to cause them to clean each other to handle parasites but imagine doing that with 1,800 hives? It's easier to pump in some sugar water laced with antibiotics and fungicides. And speaking of that, sometimes there are so many bee hives in a single area the only way to feed them is by pumping corn syrup into the bottom of the hive, killing a lot of the hive to do so. But it's artificial nectar they will turn into honey and survive with. Here's a video showing how to do open feeding using corn syrup. Does this look normal to you? It's fitting there is no sound in this video but the calm of death.
You might see current articles stating that bees are returning. They'll quote a Maryland study showing that since 2006 we've gone from 2.4 million hives to 2.6 million. Really, only 200,000 hives in 9 years? Before 1950 and the advent of commercial chemical farming, there with 5.5 million active bee colonies in America. Commercial beekeepers accept a 33% loss of their colonies per year -- acceptable?
4. Lack of genetic diversityAll honey bees came from Europe. The native Americans called them "white bees" because the white man brought them. Most southern states have laws that require you to queen your hives from known genetic stock and if you lose a marked queen you are required to requeen it with a pedigreed queen. This is to avoid spread of "Africanized bees", so called "killer bees", the result of a little genetics experiment in Brazil. But even in the north it is considered best practice to use queens only of pure descent from a known and state certified apiary. And it is done artificially. They gas her and knock her up.
How's that for natural? Static genetics make a weak gene pool.
So yes, again, we are losing bees. But so far the Aussie's are doing well and the EU has banned certain pesticides. Maybe things will change. Maybe we can all bee happy again in the future.
Articles regarding honey bee population decline: