Saturday 1 June 2013

Beetle

Beetle
The female beetle lays her eggs in the pores (vessels) and checks of hardwood timbers, and larvae feed upon starch and other nutrients in the sapwood. Therefore, if the sapwood has insufficient starch, or its pores are too narrow for the female’s ovipositor, the hardwood should be immune to attack.
An iodine test for starch is often used at sawmills to determine the susceptibility of timber. This spot test is described in Australian Standard 1604.1.
As attack by lyctine borers is restricted to sapwood (the trees outer band of living, sap-containing tissue), and as the sapwood band in most eucalypts is thin (25 mm or less), rectangular timber beams sawn from circular logs often lack sapwood, or include it along just one edge or corner.
Therefore, while many houses in the southern regions of Australia (Victoria, South Australia, Tasmania, Perth) have hardwood bearers, joists and scantling timbers, the extent of attack is normally inconsequential, and traditionally, treatment has been considered unnecessary.
The need to treat or immunise sapwood from lyctine beetles is greater in appearance grade products (for example, floor boards and architrave).
Also, the timber cut from plantation and regrowth forests tends to have higher proportions of sapwood, so that the need for immunisation in the southern states is increasing.
Lyctines can cause serious structural weakening to timber that has high proportions of sapwood.
In Queensland and New South Wales, local species such as spotted gum (Corymbia maculata) and many of the rainforest timbers have wide sapwood bands.
Legislation was enacted some 50-60 years ago making it illegal to sell untreated lyctine susceptible sapwood in those states.
Immunisation from lyctines is most often achieved using boron treatments.
Other preservatives being used include the pyrethroids or low concentrations of the copper-based preservatives. The timber treatments accepted for the control of lyctines are described in AS 1604 under the H1 (hazard level 1) category.
Kiln drying usually kills any wood borers inhabiting timber, but does not prevent lyctines from re-infesting after the timber is removed from the kiln.
As with the other beetle borers, lyctines go through four main stages of development, from egg, to larva or grub, pupa and adult beetle. The adult beetle is dark brown, and 2-6 mm long.
In the cooler southern regions, lyctine beetles emerge from the timber and fly during spring and summer. In warmer regions, lyctine adults may emerge throughout the year.
The C-shaped, white-coloured larvae cause most damage to sapwood, as the adult beetle does not feed on wood, other than to emerge from its pupa.
To further its escape, the beetle may also bore through plasterboard or other linings attached to the wood. Emergence holes are round (not oval as for longicorn borers), 1-3 mm in diameter and lack the dark stain typical of pinhole and ambrosia borers (borers that attack live or freshly felled unseasoned timber).
The frass (chewed wood/faeces) of lyctines is like a fine flour or talc (unlike the gritty feel of Anobium frass). It can collect as small conical piles under infested timbers.
Larval galleries mostly follow the grain and are tightly packed with frass. The adult’s emergence hole is essentially empty of frass.
Susceptible timber is usually attacked within one or two years of felling. Activity normally continues for up to five years (sometimes longer) until starch and sapwood integrity is exhausted. However, frass may continue to be discharged from the attacked timber due to vibration (for example, while walking on floorboards) for many years.
Beetle
Beetle


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