The Saga continues

It's late March 2014 and a new year for Death Watch Beetles. The tapping has resumed but so far I've only found 5 beetles. The tell-tale tapping resumed about 1 week ago which is earlier than last year which was mid April.

For the past 12 months I've been periodically spraying Kibosh using the long straw from a WD40 can, deep into exit wholes onto specific timbers.  I will monitor these timbers closely to see whether there is a reduction in the number of beetles I find from these this year. The rationale for spraying into the holes is that some research has shown  that  adult death watch beetles do not necessarily   emerge from the  timber and can mate in cavities. Also adult females may reenter existing flight-holes and lay their eggs deep in the  timber. Therefore by spraying into the exit holes I may be killing larvae before they transform into adults.  Spraying has shown that 80% of holes are single holes whereas 20% seem to have connections to other holes. A small percentage form a maze and the spray exits from other holes and crevices.

In addition to periodically leaving the dehumidifier running next to these timbers, I've also had a go at heat treatment.

One very expensive way to (maybe?) treat death watch beetle is to employ a specialist firm that wraps your house in a giant bubble and pumps hot air with carefully controlled low humidity air into your house to dry out the timbers and remove the vital moisture that the death watch beetles need.  It's carefully controlled to stop the beams splitting.  I havent got a clue how much this costs but looking pictures I found on the internet of what's involved, I wouldnt be surprised that a £30k+ price tag could be involved.

I opted for a simple route to see whether heat treatment works. I used a infra red heater to heat the surface of the wood on a particular beam to 60oC and left it exposed for a period of 1 hour. The theory is that death watch beetles die if they are exposed to temperatures of 55oC for more than 15 minutes.  There doesnt however seem to be a consistent view on the internet of what the temperature should be or what the exposure time should be.  Some reports say 47oC for 15 minutes whilst others suggest 55oC for 8 hours.

Unfortunately my mathematical ability to solve differential equations has long since passed - it would be useful to still be able to do this to calculate whether temperature expose has any real effect. The beetle larvae can be 1-2cm below the surface of the wood. Although the surface of the wood will reach the fatal 60oC, there's no guarantee how hot the wood gets several cm in.  Wood doesnt heat up instantly and therefore there is a temperature gradient.  The outside may be cold (one side of the wood faces the exterior) and so loses heat rapidly and another face may be laying on a brick sole plate acting like a huge heat sink so also doesnt get hot. Because of this the heat may quickly dissipate to a non fatal level.  I tried a few experiments of pieces of wood that are not part of my house and it look like  wood in free space takes over 1 hour for 5cm piece of wood to reach a similar temperature to the surface.  I therefore guessed that exposing the wood for 1 hour would penetrate 2cm for wood which is attached to the fabric of the building. Since most holes seem to be in the 1-2cm deep category, I figured this would be adequate to kill most larvae beneath the surface. 

By using a variety of techniques (including beetles munching their way through previously chemically treated wood) I am hopeful many of them will be killed off. It doesnt matter if it doesn't kill them all - by dramatically reducing the death watch beetle population, the population may naturally die off since the probably of finding a mate to keep the reduction cycle going, may be reduced.

In the coming weeks, I'll report on the quantities of beetles found.