Ips subelongatus (Motschulsky) - Larch bark beetle

Coleoptera: Scolytidae

IDENTIFICATION

Adult beetles are completely brown and 4.5 to 6.0 mm long. Adults have four spines on each side of the elytral declivity.²⁴ The 3^rd spine is the largest and is strongly capitate.²⁴ The surface of the elytral declivity is completely covered with long hairs.²⁴

HOST TREES

Larix (main host), Abies, Picea and Pinus.^{24, 26, 42}

LOCATION OF INFESTATION WITHIN THE TREE

Larvae feed in the inner bark along the length of the bole.²⁴ Immature beetles maturation feed in the inner bark of the bole and will feed in the root collar or branches if sites on the bole are unavailable.²⁴

HOST CONDITION

Healthy, dying, stressed, or cut trees. Mature trees are preferred.²⁴

DISTRIBUTION

Asian Russia, northern China and Mongolia.^{24, 42}

SIGNS AND SYMPTOMS

Maturation feeding usually occurs along the trunk but may also occur on the root collar, the upper bole, or on branches.²⁴ These maturation galleries are filled with large quantities of frass.^{24, 42}

Males initiate the attack and are joined by 2 to 5 females.⁴² The shape and depth of egg galleries vary depending on host health, but all galleries originate from a central nuptial chamber.^{24, 42} In healthy trees, egg galleries radiate downwards and upwards from the nuptial chamber, but in stressed hosts egg galleries radiate vertically and horizontally.^{24, 42} Egg galleries are usually 3.0 to 3.5 mm wide and 16 to 18 cm long, but can reach lengths up to 27 cm.²⁴ Larval galleries are usually perpendicular to the egg galleries.²⁴ Pitch tubes and reddish frass occur on the bark surface.⁴² Adults emerge from small round exit holes.^{24, 42}

If the initial attack density is not too high, I. subelongatus usually re-attacks the same host tree over several consecutive years which can lead to the death of healthy trees.^{24, 26} Additional symptoms of attack include sparse crowns, partly dead tops, wilting of needles, and fading of foliage from green to yellow and finally to red. ⁴² Resin also flows from entrance holes.²⁴

A - Adult I. subelongatus declivity. Note the large and capitate 3rd spine.

B - Adult I. subelongatus (4.5-6.0 mm long).

C - Drawing of I. subelongatus egg (16-18 cm long) and larval galleries on a healthy tree.

D - Maturation feeding galleries. In the region of larval development (A). On roots (B). Top of the trunk or on branches (C & D).

E - I. subelongatus egg and larval galleries.

F - I. subelongatus egg galleries on a stressed tree.

Photo credits

• A Yulin An, Jiangsu Entry & Exit Quarantine and Inspection Bureau of the People's Republic of China
• B Yulin An, Jiangsu Entry & Exit Quarantine and Inspection Bureau of the People's Republic of China
• C Drawing from Shamaev, A. V. 1994, Guide on identification of pests of forest trees trunks, on which the importers of Russian wood have phytosanitary requirement, Syktyvkar
• D Drawing from Issaev, A. S. 1966, Borer pests of Larix dahurica. Moscow, Nauka
• E Jun-Bao Wen, Beijing Forest University
• F Drawing from Issaev, A. S. 1966, Borer pests of Larix dahurica. Moscow, Nauka