You can buy a feeder with bee guards. However, those tend to be the drippiest feeders available (Perky-Pet "Four Flowers," etc.), and once they start dripping the bee guards are useless, since puddles form in the flowers outside of the bee guards, an easy meal for insects.
Bees tell each other about good nectar sources using pheromones, so it may help to clean the feeder daily with vinegar. It may also help to rub a clove of garlic around the ports. I don't recommend using Pam or other oils or greases on hummingbrd feeders.
The only sure defense against bees and wasps is to absolutely deny them access to the syrup. In June 1997 I replaced my Perky-Pet 210-P with a HummZinger, which is inherently wasp-proof because the syrup level is too low for insects to reach, but easily in range of the shortest hummingbird tongue. I also bought a Perky-Pet Oasis feeder, a copy of the HummZinger with several design flaws, but just as effective against bees. Basin feeders are also available from Opus and other companies, and all are effective in denying food to bees and wasps. All are also easy to clean.
If you choose not to try a new feeder and wasps persist, first try moving the feeder, even just a few feet; insects are not very smart, and will assume the food source is gone forever. They may never find it in its new location, while the hummers will barely notice that it was moved. If that doesn't work, take the feeder down for a day, or until you stop seeing wasps looking for it. You'll see hummers looking for it, too, but they won't give up nearly as soon as the wasps. Also, reducing the sugar concentration to 1 part sugar in 5 parts water will make it less attractive to insects, but probably won't make the hummingbirds lose interest.
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