How to Treat Carpenter Bees
Carpenter bees bore holes into wood and lay eggs. When the eggs hatch, they become larvae, which turn into pupae, and then adult bees. The tunnels that the bees create are usually about four to six inches long, but over time, future generations can work on the same tunnel, so they have been known to get as long as 10 feet. So, to treat the problem, you need a pesticide that will get into all areas of those tunnels.
To do this, you need to buy a fipronil foam, an imidacloprid foam, or a combination of the two, and shoot it into all the holes, until it is coming back out at you, or the other holes. The foam will expand to several times its original size and get into all those tunnels that were created by the bees, thereby killing the bees, larvae, and pupae. This will not kill the eggs, but the foam residual should last at least 90 days, and the eggs should hatch withing six weeks. Therefore, the foam will kill the larvae as the eggs hatch. There is a link below for an imidacloprid foam that is the most cost-effective product that I have found.
Now that you have treated the larvae, it's a good idea to seal up the holes with wood filler, caulk, Bondo, or whatever works best in your case. After you have the damage repaired, you need to make sure that you do not get anymore carpenter bees. There are a couple of ways of doing this, and which method you choose will depend upon the kind of wood you are dealing with.
If you have wood that has NOT been treated with anything, like a sealer, stain, or paint, then you can use Bora-Care. This is a permanent treatment, but you do need to finish the wood with something, like a sealer or paint, about 48 hours after the product is applied. I will give you a link to the product and a link to a video on how to use it. Always mix it one to one with water. The label says that you can mix it one to five, but one to one works better.
If the wood has already been treated with a sealer, stain, or paint, then you need to apply a pesticide to all the wooden surfaces every 60 days. I have a video on how to do this and I will give you the link. The video shows how to treat for a variety of pests that may enter your house, but it's the same treatment for carpenter bees. The only thing different is that you only need to do the treatment on the areas where you are seeing the activity. That being said, I recommend that you treat all the areas shown in the video because that will prevent a lot of other pests as well, and it does not take long to do. You can use a tank sprayer or a hose end sprayer. The video covers both methods. Personally, I just use the hose end sprayer to treat all of these areas because it is way faster than using a tank sprayer and I can reach areas that are high up, like the fascia boards where carpenter bees usually attack. Both the tank sprayer or hose end sprayer will have the same result, but you need to use a different product for each method. Please note that in the video, I recommend diluting the Bifen XTS in the hose end sprayer 1 part product to 14 parts water, or 2 ounces of product to 28 ounces of water. For carpenter bees, I recommend that you mix it 1 part product to 10 parts water, or 2 ounces of product to 20 ounces of water.
Imidacloprid foam: Amazon.com: BioAdvanced Termite and Carpenter Bee Killer Plus, Foam, 18 oz : Patio, Lawn & Garden
Bora-Care: https://www.domyown.com/boracare-p-100.html
Video on how to use Bora-Care: https://www.youtube.com/watch?v=Rmr_aEodyhg
Video on how to prevent carpenter bees and other pests from entering your home: https://youtu.be/Yozv3s-Qwlw