Evolution Question: Why Haven't Bumble Bees Learned?

to pollinate fruit trees? I read that the native N. American bee (the “Bumblebee”) does not fly high enough to pollinate fruit trees. Consequently, farmer use the services of domesticated (Italian) honeybees, which do a fine job of pollinating trees and other crops. Before the Europeans came to this continent, the native Americans couls only grow crops like maize, that are self-pollinating. Why (in 400+ years) haven’t the bumblebees adapted to flying higher? Seems like a rather slight evolutionary modification.
Plus, can bumblebees breed with italian bees?

Why should they? They’re not lacking food in their own eco-niche, so there’s no incentive to horn in on another insect’s.

You ever see a bumblebee? They’re not exactly the most agile or swift of the bees out there. Besides, why do bumblebees need to adapt to flying higher? There’s a lot of nectar/pollen on plants close to the ground.

Why haven’t humans adapted to eating tree bark?

We don’t need to.

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Where you are getting your information from? Most of it is wrong.

There’s not just one species of “native American bee,” there are more than 3500 of them. Many of them pollinate native tree species.

And Native Americans grew lots of bee-pollinated crops, including squash, beans, tomatoes, and potatoes. Maize is not normally self-pollinating, but is wind-pollinated.

Bumblebees (which include many species) haven’t changed their foraging because they’re well-adapted to their present niche, and there’s no strong selection to change it.

Learned behavior has nothing to do with evolved behavior, which is probably what got the OP confused on the time scales involved. Bees, or any other animals, don’t “learn” to do something and then pass that knowledge on to their descendants.

Evolution would consist of some bee being born with the inherent desire to fly higher than where its food source would normally be found and then discovering a new food source there. If this access to new food significantly improved its survival rate, it might have more “descendants”. The situation here is complicated by the indirect breeding habits of bees - a bee flying around doesn’t have any direct descendants. So we’re actually talking about a queen bee giving birth to high fliers.

Four hundred years is the blink of an eye as far as evolution is concerned.

Got a cite for that? I was just at a tour yesterday of a University of Wisconsin Experimental Agriculture site and the tour guide – also the site’s director – said that bumblebees were major pollinators of their fruit trees, and they had some advantages over honeybees. Bumbley-bees, with a larger body, carried more pollen, and being mostly solitary rather than social, weren’t as subject to diseases that might infect an entire hive.

I might be wrong here, but it is my understanding of evolution that, even for seemingly minor changes, these processes take millennia for any differences to be discernible.

It depends on the intensity of selection and on how genetically “hard-wired” a particular feature or behavior is. Strong selection on a small population can have discernable effects within a relatively short period of time. Weak and variable selection on a large population will take a long time to have any effect.

Not always. Changes can occur rapidly under extreme environmental pressures, especially under patricide conditions (when a small population of an extant species is cut off from the main population). This is, in part, a function of breeding cycle; obviously a species which breeds quickly and proliferates widely is going to undergo evolutionary change rapidly. And given an artificial and directed selection process, as with, say, the breeding of dogs, measurable change can occur in only a few generations.

However, with bumblebees, there is no such pressure; they’re already well adapted to their existing habitat and sympathetic relationship with native plants in which they obtain nectar “in exchange” for delivering pollen, so they have no need to “learn” new habits for success. Indeed, the bumblebee is very well co-adapted with plants like red clover (Trifolium pratense) which is dependent upon the bumblebee’s long proboscis for effective pollination

However, the claim that bumblebees can’t fly high enough to pollinate flowering trees is bogus, as already noted by Colibri and Musicat. Aside from having personally observed bees flying at sufficient height, it is also true that the bumblebees are an important pollinator of cultivars due to their less developed social communications and diversity of pollination.

So the o.p.'s basic premise is bogus. As for “learning” in an evolutionary context, instinctive behavior modification occurs only when subjected to unbalanced environmental pressures.