Mar 23, 2012 – Carpenter Bees – They Dig It!

QUESTION:

I have a customer with a severe problem with carpenter bees, this year more than tripled over last years, and I need some help. I have replaced and painted trim boards.

ANSWER:

This problem speaks directly to the current issue with new restrictions on the use of Synthetic Pyrethroids, as these have been a mainstay for deterring carpenter bees that excavate the wood of structures for their living quarters. The microencapsulated formulations in particular, such as Demand CS, have worked well when applied over outside walls where carpenter bees were chewing into the wood, but with the new labeling soon to be on every pyrethroid Label this general application will no longer be permitted. Finding non-pyrethroid products with the same general labeling does not appear to be an easy thing to do, and their effectiveness on carpenter bees for this use is untested. 

Surface coatings of paint and clear finish are considered to be "deterrents" to carpenter bees, meaning they'd rather not chew through paint or varnish, but if push comes to shove they certainly can and will. If those trim boards are in just the perfect place and are the proper kind of wood then chewing through a thin layer of paint is not difficult. Since it is unlikely that you can eliminate all carpenter bees around an area we have to expect them to investigate all that wood on the structure as potential nesting sites. This leaves us with two options - treating each hole directly as it is discovered or treating the surface prior to the hole being dug to kill the adult bees that attempt it. 

The general life cycle of carpenter bees is for the adult bees to overwinter in their galleries. These adult bees are the ones that emerged in summer to early fall, were active for awhile, and then settled into their chambers for the winter. They emerge in the spring to further excavate the burrows and then supply them with eggs and a food supply for their own offspring. Existing holes you find right now could be treated with a contact dust insecticide and then firmly plugged to keep the bees inside, where they should die once they contact the insecticide. This will at least prevent these overwintering bees from continuing the problem at that location, as they were likely to do. But, Nature hates a void, and if these bees are eliminated others are going to come at some point in time, and this is going to be a regular problem to deal with. 

With the new labeling on pyrethroids I believe that we still have the option of treating generally UNDER the eaves of a structure, as this falls under the "exceptions" to the requirement for crack and crevice or spot treatment only on exterior surfaces. For trim around windows or for exterior surfaces where these bees are active the best you can do is to spot treat, and this means a "spot" no larger than 2 square feet. For a trim board 4 inches wide this isn't so bad, as that "spot" 4 inches wide could be 6 feet long. If you do opt for doing this preventive treatment to susceptible wood it should be done when you first begin to see adult bee activity, as this would indicate males and females now out of hibernation and ready to mate and start the digging process again. 


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