The Structural Conservation of Panel Paintings

sunken ships in fresh or saline waters is usually severely affected by bac-

teria that erode cell walls or produce cavities or tunnels within the

secondary walls (Fig. 5a, b). Other forms of bacterial attack include species

that degrade membranes covering pit apertures but do not affect the cell

wall. All of these bacterial degradation patterns are distinct from those

produced by fungi and can be readily identified by examination with ultra-

structural techniques (Fig. 5a, b). The exceedingly high moisture content

and long exposure necessary for bacterial degradation suggest that this

type ofdegr adation would not typically be found in wooden panel paint-

ings. Conservators who encounter waterlogged cultural properties may

obtain additional information from writings by Blanchette and coworkers

(1990), Blanchette and Hoffmann (1994), and Singh and Butcher (1991).

General life cycle of insects

Damage to wood by wood-boring beetles (Fig. 6) results from the feeding

stage of larvae (commonly referred to as woodworms) that bore circular

tunnels ranging in size from 1 mm to 10 mm in diameter. The larvae feed on

the wood, leaving fecal pellets and fine particles of wood in the frass. The

common furniture beetle (Anobium spp.) adult lays numerous ellipsoidal

eggs in surface cracks or along the rough end grain of wood (Fig. 7). After

three to five weeks, larvae emerge from the eggs and eat their way into

the wood with their strong mandibles. As the larvae tunnel through the

wood, frass is often tightly packed into the gallery behind them. The larval

period may last years, and a number of instar stages and molts occur

before the larvae reach the pupal stage (Bravery et al. 1987; Creffield 1991;

Hickin 1975). The size of the tunnels reflects the size of the growing lar-

vae (Fig. 8a–c). Before pupation occurs, the larvae tunnel to the surface of

the wood and form achamber free ofwood fragments and fecal pellets.

Adults emerge after several weeks of pupation by boring an emergence

hole out to the wood surface. The size of the tunnels, orientation within

wood, and characteristics of the frass vary among the different beetle

species (Table 2). The type of wood also may govern which wood-boring

insect may attack. Some wood-boring beetles, such as powderpost beetles,

require sapwood for successful larval development and do not infest heart-

wood. The Lyctuspowderpost beetles have even stricter requirements that

Insect Damage to Wood

62 Blanchette

a b

Figure 5a, b
Transverse sections of wood with bacterial
degradation from the hull of the Uluburun, a
late Bronze Age (1400 B.C.E.) shipwreck offthe
coast of Turkey: (a) and (b) Minute cavities
caused by tunneling bacteria are present
within the secondary cell walls. The residual
wall matrix is porous and lacks integrity. The
degraded wall material is disrupted during
drying and is often pulled away from the
middle lamella. Scanning electron micro-
graphs; bar 5 10 μm.