Jan 18, 2011 - Subs And Water
QUESTION:
We are in Arizona, and subterranean termites are my concern. One of our technicians has been asked a question on the state exam that we have not been able to answer. How much moisture is required in wood before termites eat it? They give multiple choices like 13, 17, 25%, etc. Do you have a answer on this?
ANSWER:
Well that's a darned good question, and unfortunately I don't have a darned good answer. I looked in a variety of references and for the most part struck out. But, I did come across one abstract from a study of the survival of subterranean termites in woods with varying levels of moisture, where the termites were confined to the wood and could not return to soil. In this summary it was shown that at a wood moisture content of 20-24% half of the termites survived for up to 12 days, and the rest died earlier. When the moisture content was maintained at 30% the termites managed to survive for up to 6 months, and they concluded that wood with a content less than 24% was inadequate to sustain subterranean termites, and that at least 30% moisture content was necessary to keep them alive for 6 months or longer.
Now, that may or may not answer your question, since you asked about the moisture content needed for subterranean termites to "eat" the wood, and that is very different. A normal subterranean termite colony has workers maintaining contact with the soil, and replenishing their body fluids on a constant basis. This was apparently the problem for those termites in the study above that were confined to wood of 24% or less - they lost body moisture faster than it could be replaced with the low moisture content of the wood. But, when the workers can quickly return to the soil they replenish their body fluids and thus can work on wood that may be much lower in moisture content. In addition, the workers may bring moisture up to the wood to keep it wetter than it was originally, so relatively dry wood (moisture content below 20%) could very well be susceptible to attack by the termites.
We know that drywood termites can survive in very dry wood - moisture content from 5-12%, and that decay fungi generally rely on wood that has at least 20% moisture in it. We also know that the decay fungus Meruliporia (Poria) incrassata can develop a root system that also brings water from the soil below up onto otherwise dry wood, enabling it to move its destruction into areas that were not previously wet. Dampwood termites also are now known to be able to add water to their environment to keep the wood in a very damp condition.
Hopefully you can determine the correct answer from this, and depending on just how that exam question was worded the answer might be that it takes wood moisture content of 30% for long term survival of the termites, or they could attack wood with a much lower moisture content initially, as long as they can continue to move to and from the soil.
View past Ask Mr. Pest Control questions.
We are in Arizona, and subterranean termites are my concern. One of our technicians has been asked a question on the state exam that we have not been able to answer. How much moisture is required in wood before termites eat it? They give multiple choices like 13, 17, 25%, etc. Do you have a answer on this?
ANSWER:
Well that's a darned good question, and unfortunately I don't have a darned good answer. I looked in a variety of references and for the most part struck out. But, I did come across one abstract from a study of the survival of subterranean termites in woods with varying levels of moisture, where the termites were confined to the wood and could not return to soil. In this summary it was shown that at a wood moisture content of 20-24% half of the termites survived for up to 12 days, and the rest died earlier. When the moisture content was maintained at 30% the termites managed to survive for up to 6 months, and they concluded that wood with a content less than 24% was inadequate to sustain subterranean termites, and that at least 30% moisture content was necessary to keep them alive for 6 months or longer.
Now, that may or may not answer your question, since you asked about the moisture content needed for subterranean termites to "eat" the wood, and that is very different. A normal subterranean termite colony has workers maintaining contact with the soil, and replenishing their body fluids on a constant basis. This was apparently the problem for those termites in the study above that were confined to wood of 24% or less - they lost body moisture faster than it could be replaced with the low moisture content of the wood. But, when the workers can quickly return to the soil they replenish their body fluids and thus can work on wood that may be much lower in moisture content. In addition, the workers may bring moisture up to the wood to keep it wetter than it was originally, so relatively dry wood (moisture content below 20%) could very well be susceptible to attack by the termites.
We know that drywood termites can survive in very dry wood - moisture content from 5-12%, and that decay fungi generally rely on wood that has at least 20% moisture in it. We also know that the decay fungus Meruliporia (Poria) incrassata can develop a root system that also brings water from the soil below up onto otherwise dry wood, enabling it to move its destruction into areas that were not previously wet. Dampwood termites also are now known to be able to add water to their environment to keep the wood in a very damp condition.
Hopefully you can determine the correct answer from this, and depending on just how that exam question was worded the answer might be that it takes wood moisture content of 30% for long term survival of the termites, or they could attack wood with a much lower moisture content initially, as long as they can continue to move to and from the soil.
View past Ask Mr. Pest Control questions.
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