Ips sexdentatus (Boerner) - Six-spined engraver beetle

Coleoptera: Scolytidae

IDENTIFICATION

Ips sexdentatus is the largest species in the genus Ips, measuring 5.5 to 8.2 mm in length.^{4, 131} Adult beetles are dark brown and cylindrical.⁴ The head is covered by a thoracic shield and the head is not visible when viewed dorsally.⁴ Both sexes have six spines on each side of the declivity, of which the 4^th is the largest and capitate.²⁴

HOST TREES

Pinus (main host), Abies, Larix, Picea and Pseudotsuga.^{4, 17}

LOCATION OF INFESTATION WITHIN THE TREE

Larvae feed on the inner bark of the lower bole.¹³² This species prefers to attack larger trees with thick bark.^{4, 66}

HOST CONDITION

This insect rarely attacks healthy vigorous hosts, preferring recently cut, weakened, dying or windthrown trees.^{4, 77, 78, 131}

DISTRIBUTION

Europe, Asian Russia, Mongolia, China and Thailand.^{4, 17, 24}

SIGNS AND SYMPTOMS

Males initiate the attack and create a large nuptial chamber beneath the bark.^{4, 131} Males are joined by 2 to 5 females that create individual egg galleries, radiating longitudinally in opposite directions from the nuptial chamber.^{4, 131, 132} Egg galleries are usually 15 to 35 cm long and 4 to 5 mm wide.^{4, 131, 132} Eggs are deposited in individual niches along each side of the egg gallery.⁴ Larval galleries run approximately perpendicular to the egg gallery and are 8 to 10 cm long.^{4, 24, 132} Larval galleries increase in size as the larvae grow.⁴ Both egg and larval galleries are mainly found in the inner bark and barely etch the sapwood.¹³¹ Large round pupal chambers are located at the end of the larval galleries.^{4, 131} Round exit holes on the bole, approximately 4 mm in diameter, will be apparent once adults emerge.⁴

Breeding attacks are characterized by the presence of reddish-brown frass on the bark surface of trees, freshly cut logs, or windthrow.⁴ If relatively vigorous trees are attacked, pitch tubes can be found on the bole.^{4, 127} The needles of attacked trees turn from green to yellow and then reddish-brown.⁴ Ips sexdentatus acts as a vector for a bluestain fungus, Ophiostoma brunneo-ciliatum, which also damages the tree and stains the wood.^{4, 24, 79}

A - Star shaped I. sexdentatus gallery system with six egg galleries radiating from the nuptial chamber.

B - Egg galleries (15-35 cm long) of I. sexdentatus.

C - Reddish-brown crown of I. sexdentatus attacked tree.

D - Immature I. sexdentatus beetle (5.5-8.2 mm long).

E - Pitch tube around entrance hole of I. sexdentatus.

F - Reddish-brown frass around the base of I. sexdentatus attacked tree.

G - Chlorotic foliage and woodpecker damage on I. sexdentatus attacked trees.

Photo credits

• A Louis-Michel Nageleisen, Département de la Santé des Forêts, France, Image 1190017, www.invasive.org, Feb. 5, 2004
• B Louis-Michel Nageleisen, Département de la Santé des Forêts, France, Image 1190019, www.invasive.org, Feb. 5, 2004
• C Louis-Michel Nageleisen, Département de la Santé des Forêts, France, Image 1190018, www.invasive.org, Feb. 5, 2004
• D Gyorgy Csoka, Hungary Forest Research Institute, Image 1231218, www.invasive.org, Feb. 5, 2004
• E Fabio Stergulc, University of Udin, Image 1433026, www.invasive.org, Feb. 5, 2004
• F Fabio Stergulc, University of Udin, Image 1433028, www.invasive.org, Feb. 5, 2004
• G Fabio Stergulc, University of Udin, Image 1433027, www.invasive.org, Feb. 5, 2004