Insects with wood-boring larvae

 

Magdalena Kutnik (author)

 

Insects with wood-boring larvae are a major cause of wood-degradation around the world, and within this category there are several major sub-groups which are distinct and described below:.

The house longhorn beetle Hylotrupes bajulus

(old house borer, European house borer EHB)

Monotypic genus of wood boring beetles in the family Cerambycidae (the longhorn beetles) only one species Originating from Europe

Have been spread in timber and wood products, now present in Southern Africa, Asia, the Americas, Australia

The altitude limit is considered to be 1600 m

In 2004, the species was detected in Perth, Western Australia. A containment program was set up and expanded to a full eradication campaign in 2008

Description

Adults are brown to black, hairy, 8 to 20 mm long, with long antenna

Two hairless tubercles on the pronotum are characteristic of the species

On the elytra usually there are two whitish pubescent spots

Polymorphic species, having an extreme variability both in the dimensions and in the aspect

Females have an elongated telson they use to lay eggs in wood cracks

Larvae are creamy white, up to 30 mm long. They have primitive eyes and strong mandibles they use to dig into the wood

Biological cycle

Adults are most active in the summer (June–September in the northern hemisphere)

Duration of larval stage 2 to 5 years

Larvae usually pupate just beneath the wood surface and eclose in mid to late summer

When emerging from wood, the adults cut oval exit holes 6–10 mm in diameter

Degradation

Degrade softwoods only

Powdery frass is visible in the galleries and in the vicinity of the hole

Contrary to the name old-house borer, the species is more often found in new houses - beetles might be attracted by the high resin content of wood harvested less than 10 years earlier

The damage is usually greater if old wood is attacked, as the nutrient content of wood decreases - with age the larva has to consume larger amounts of wood

Larvae are able to go through other materials (plastic, metal)

 

Trichoferus holosericeus (ex-Hesperophanes cinereus)

Description

Adults are reddish brown to black, 13 to 24 mm long, with long antenna

Larvae are creamy white, a bit bigger than EHB, 25 - 30 mm long

Biology and life cycle very similar to EHB

Occur mainly in southern Europe, low economic impact

Degradations

The galleries and exit holes are a bit bigger than EHB

Attack hardwoods only, usually sapwood (oak, black locust, poplar, beech, walnut tree, …).

 

The common furniture beetle Anobium punctatum

The furniture beetle is of European origin and is found mainly in countries with temperate climates

It occurs naturally in the wild in the temperate woodlands of northern Europe and may have colonised other similar temperate environments, particularly in New Zealand and the east coast of North America

It is perceived to be the main cause of damage to timber in the UK over the last 100 years

Description

Adults are small oval brown beetles approximately 4-6mm long

When viewed from above, the head and eyes are invisible beneath the thorax

The surface of the wing covers is covered with fine yellowish hairs and longitudinal rows of pits

The antennae have 11 segments with the last 3 segments enlarged

Larvae are greyish white in colour with a narrow dark band over the mouth parts and grow to about 6mm long

Biological cycle

Adults emerge from infected timber in the spring, generally between May and August

Clusters of up to 50 eggs are only laid on wood (in cracks, crevices, exposed end grain or previous emergence holes)

Duration of larval stage 2 to 4 years

When emerging from wood, the adults cut round hole of approximately 1-2mm in diameter

Degradation

Infest the sapwood of temperate softwoods and hardwoods, but may also infect the heartwood of timbers such as beech, birch, cherry, alder and spruce, or timbers that have been modified by fungal attack

Prefer moist wood (> 14% RH), high moisture levels shorten their life cycle and speed the development of the infestation

Most obvious sign of infestation = accumulation of powdery frass and tiny pellets underneath infested wood or streaming from exit holes

The larvae excavate tunnels approx. 1-2 mm in diameter, generally parallel to the grain of the timber

The tunnels are filled with the residues of the timber consumed, forming a cream-coloured powdery material consisting of lemon-shaped pellets when viewed with a microscope

Most obvious sign of infestation = accumulation of powdery frass and tiny pellets underneath infested wood or streaming from exit holes

 

The death watch beetle Xestobium rufovillosum

This beetle is found in Europe, including the United Kingdom, as well as North America, Corsica, Algeria, and New Caledonia

Its natural habitat is dead or decaying hardwood, or in some cases coniferous wood, especially when the timber has been softened by fungal attack

Description

Adults are brown beetles approximately 6 to 7.5 mm long

The head is largely concealed by a brown thoracic shield

The shield and elytra (wing covers) are dark brown or reddish-brown, with a patchy felting of yellowish-grey short hairs

Larvae are creamy-white with six legs, black jaws, a pair of eyespots on either side of the head, grow up to 11 mm long

Biological cycle

Adults emerge in April, May or June, in temperatures above 10 °C

o attract mates, the adult insects create a tapping or ticking sound that can sometimes be heard in the rafters of old buildings on summer nights

Batches of 40 to 80 eggs are laid in crevices in old wood inside buildings, trees, and inside tunnels left behind by previous larvae

Duration of larval stage up to 10 years

When emerging from wood, the adults cut round hole of approximately 2mm in diameter

Degradation

Degrade softwoods and hardwoods (sapwood or more)

Can develop only in humid wood already infested by fungi, decayed wood is also much easier for the larva of the deathwatch beetle to bore into which allows them to develop at a faster rate

The sapwood is more nutritious and is usually attacked first, followed by heart wood that has been softened by decay.

Oak (Quercus spp.) is the main host, with American oaks being more susceptible than European oaks

The beetle does not infest wood that has recently died; about sixty years must pass for dead oak to reach a suitable condition for attack

These beetles tend to stay on the same piece of wood for several generations until resources are used up and the piece of wood is no longer sufficient

 

Anobiids (Anobiidae)

Anobium punctatum (common furniture beetle)
Xestobium rufovillosum (death watch beetle)
Oligomerus ptilinoides (furniture beetle)
Nicobium castaneum (library beetle)
Ptilinus pectinicornis (fan-bearing wood borer)
Hadrobregmus pertinax (furniture beetle)

Cause significant damage to wood used in construction in Europe

Are the models used to evaluate the efficacy of wood preservatives according to European standards

 

The powder-post beetle lyctus (Lyctus brunneus & Lyctus linearis)

The two species are very similar, L. linearis being less common

Native from tropical areas but common everywhere in Europe since more than a century

Description

Adults are brown/reddish, 2.5 to 6 mm long, short antennae, elytra covered with short hair

Larvae are creamy-white with six legs, black jaws, grow up to 5 mm long

Biological cycle

Adults emerge between April and August, live 2-3 weeks

Batches of several dozens of eggs are laid in wooden pores (the diameter needs to be > 50 µ)

Duration of larval stage 12 to 18 months depending on the starch content (very short)

When emerging from wood, the adults cut round hole of approximately 1 to 2 mm in diameter

Degradation

Attack only the sapwood of hardwoods with large pores : oak, chestnut, ash, walnut, black locust, most of the tropical wood species

Wood-based panels can be attacked if made from these wood species

The amount of damage depends on the starch content in the wood

Most obvious sign of infestation = presence of small piles of fine flour-like wood sawdust (or frass) on or under the wood

 

Sirex wasps (wood wasps, horntails)

Description

Large wasps (1 to 5 cm) with a thick waist (adults lack the thin waist found in many wasp species)

Females have a prominent ovipositor (egg-laying apparatus, 'sting') projecting from below the abdomen

Adults are metallic blue-black with some yellow/orange markings

Larvae are creamy white, cylindrical body with a typically dark spine at the rear end

Species: Sirex noctilio, Sirex juvencus, Urocerus gigas

Life cycle

Adults emerge in spring and typically infest fresh killed trees and logs (sometimes living trees), they don’t eat 

The female lay eggs in solid wood (through the bark), injecting spores of tree disease-causing fungus Amylostereum areolatum along with a phytotoxic (plant-poisioning) mucus

Larva tunnel in the wood (tunnel is about 5 mm diameter), they live entirely within the host wood or tree

Life cycle is 1-3 years 

Degradations

Sirex sp. and Urocerus gigas attack only softwoods, Tremex sp. attack hardwoods (poplar, willow)

Attack both sapwood and heartwood, producing U-shaped tunnels (up to 20 cm length) tightly packed with course frass

Exit holes and tunnels are circular in cross-section and 3 to 6 mm in diameter.

Occasionally adults emerge through paneling, siding (…) in new houses but do not reinfest processed wood

In Europe, they are not a serious pest of trees or structures

Sirex noctilio – an invasive Wood Wasp species

Females are are 15–35mm long, dark, metallic-blue with amber-coloured legs and wings

Males are 13–32mm long, have a blue-black head and front section and an orange abdomen with a dark tip and no 'sting'

Larvae are creamy white and have an obvious head, 3 pairs of very short legs and a segmented, cylindrical body with a typically dark spine at the rear end.

As larvae, woodwasps only eat Amylostereum areolatum, a fungus that the mother deposits into the pine trees with her eggs

Native to Eurasia and Morocco, sirex wood wasps were accidentally introduced to the southern hemisphere, including Australia (since 1961), New Zealand (1900), South Africa (1994), South America (Uruguay 1980) and more recently North America (found in NY in 2004).

Sirex noctilio is the most damaging invasive pine plantation pest in the southern hemisphere, killing millions of pine trees. Trees die as the fungus spreads, disrupting the tree's vascular system.

Sirex noctilio certainly has the potential to devastate pine plantations across the U.S. In South American plantations growing North American pines, tree mortality sometimes exceeded 80%.

Quarantine pest in the US, can be transported through wood packaging materials

Control

Prevent its arrival in a country: inspection of all goods that are likely to harbor the pest at ports of entry. Until 2004, this was successful at preventing S. noctilio from becoming established in the U.S.

Control the spread of the insect within the country:

Proper forest management (removing damaged and diseased trees)

Remove dead trees infested with Sirex woodwasps and chip or burn as soon as possible

Biological control agents:

Nematode Deladenus siricidicola

Parasitoid wasps Rhyssa persuasoria