Old House Borer, Vol. 6, No. 30
Hylotrupes bajulus
Order: Coleoptera
Family: Cerambycidae
“Daddy and Uncle Okie both retired six years ago. Uncle Okie has one of those portable sawmills, and they enjoy cutting and sawing lumber off the home place. Three years ago, we walled the den with some of the boards they sawed. Now we can’t stay in there without having the TV or radio on because there’s some sort of bugs chewing in the wall. That scritch-scritch-scritching sound is hard to ignore if you are just sitting there trying to read. They have chewed holes in some boards, and we’ve found a couple of these big beetles on the windowsills. There are even more of these in the log cabin they built on the pond back home.”
Several species of large wood boring beetles can occur in lumber that has not been properly kiln-dried before use. This happens when adult beetles lay their eggs in recently felled logs or stored lumber and the resulting larvae develop inside the undried lumber. Most species take several years to emerge as adults but will not reinfest exposed lumber inside a building. Old house borers are the exception; they can and will reinfest exposed softwood lumber in buildings, especially wood with suitable moisture content.
Despite their name, old house borers are more common in new buildings, preferring wood less than 10 years old. They only attack softwoods such as pine, spruce, fir and hemlock, and prefer wood with a moisture content of 10 to 12% or higher. It is the larvae that cause damage by tunneling and eating the wood, and it is the chewing of larger larvae that produces that rasping sound. Because wood is not very nutritious, it can take two to ten years to complete a generation, with rate of growth depending on moisture content and nutritional quality of the wood. Adult beetles vary considerable in size, ranging from 1/3 inch to one inch depending on quality of the food they had as larvae. Heavy repeated infestations can seriously weaken large structural timbers, especially timbers exposed to high moisture.
Control: The best preventive treatment for wood- boring beetles is to make sure any lumber used in a building has been properly kiln dried. Kiln drying kills eggs and larva that may already be living in the lumber and reduces moisture content. Most wood-boring insects do not survive or grow well at moisture levels below 8%. However, kiln drying does not prevent subsequent infestation by old house borers if the moisture content rises to suitable levels. Keeping wood dry and sealing exposed surfaces with paint or other sealant also helps prevent infestations.
Treatment options for active infestations range from removing and replacing infested timbers to having the building tented and fumigated. A less drastic option is to treat infested boards with a borate product, such as Bora-Care. Large dimension timbers can be treated by drilling and injecting with a borate paste, such as Jecta, and by treating exposed surfaces with Bora-Care. Surface applications of Bora-Care can only be applied to unfinished wood surfaces. Borate treatments may not kill large larvae and adults that are ready to emerge within the next year or so but are more effective on smaller larvae and for preventing reinfestation.
See Bug's Eye View No. 6 of 2020 for information on powderpost beetles in hardwood floors.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
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