Ips subelongatus
(larch bark beetle)

Ips subelongatus is not explicitly regulated by the European Union (EU, 2000). There is, however, ambiguity about its phytosanitary status, since it is considered by some authors to form part of I. cembrae, which is regulated. Besides, I. subelongatus is virtually (except for a small area in northeastern European Russia) a member of the category "non-European Scolytidae", which is also regulated. In practice, it would be logical to consider that the same risk applies as for I. cembrae., or possibly even more, since the central European larch forests, where I. cembrae occurs, face an additional risk from I. subelongatus. In general, I. subelongatus is reported to be rather more damaging to the local Larix species in Asia than I. cembrae is in Europe.

I. subelongatus also presents a risk to other continents where Larix plantations are exploited, particularly North America.

Phytosanitary Measures

Appropriate measures would be to require treatment (debarking or kiln-drying) or "pest-free area" for wood, and treatment or "pest-free area" for bark. For plants for planting, which present little risk, only very large plants (above 3 m) might considered ("pest-free place of production"). It may be appropriate to extend the requirement to other, less important hosts (Picea, Pinus).

Fumigation schedules for sulfuryl fluoride and phosphine have been worked out in Japan (Soma et al., 1998). Methyl isothiocyanate has also been tested (Naito et al., 1999).

Larix spp. are the main hosts. The beetle may also occasionally breed in species of the genera Pinus, Picea, Abies and other coniferous trees.

I. subelongatus is common in stands of different density and species composition but only if they include larch species. It is not found in pine forests and dark coniferous forests. However, it can invade every coniferous species in stands which include larch species. Sometimes during outbreaks, beetles go up to bare mountainous areas. They can reach 2000 m above sea level. I. subelongatus is the most numerous in larch stands which are characterized by a large volume of impaired and dying trees (in areas of mass reproduction of primary pests, in burnt-out forests etc.), as well as on cutting areas and timber yards (in the presence of freshly felled larch trees). Quite often during outbreak I. subelongatus invades fully sound trees of every age.

When attcking impaired but viable trees, I. subelongatus invades the middle and apical parts of the stem first. For larch trees that are dying it prefers to invade the lower stem, which retains the sappy bast for the longest time.

Beetles start to leave winter asylums in the middle of May. Their mass emergence takes place either at the end of this month or in the first 10 days of June. Mass emergence does not exceed three to five days, although some specimens fly to the end of June. The first copulation cells appear at the end of May, the first gallery systems with finished female galleries appear at the beginning of June.

The gallery system of I. subelongatus resembles that of I. sexdentalis, but is smaller in size. Usually, three maternal galleries extend away from the copulation cell in the longitudinal direction. Two of them go in the same direction (up or down).

It is sometimes possible to find gallery systems with two or four maternal galleries. The length of the maternal galleries is usually 13-17 cm, but they sometimes exceed 25 cm.

Females gnaw egg notches on each side of the gallery. They can make over 50 notches in one gallery. Females do not lay eggs in every notch, and a number of the eggs perish; this is why the number of egg notches does not always agree with the number of larval galleries. Nevertheless the number of larval galleries can be very large, so they get entangled or run into a common weaving cavity at a short distance from the female gallery. Isolated larval galleries do not normally exceed 5 cm. Their width close to the egg notch is around 0.7-1.2 mm. Their width at the end part is around 2.5-6 mm.

The first larvae appear in galleries at the end of May. The first pupae appear in the last 10 days of June; the first young beetles appear in pupa cradles at the beginning of July. The second oviposition of hibernated beetles takes place in the first half of July. Then some females of a new second generation start to lay eggs. Pupae of the summer oviposition are found until the beginning of September. I. subelongatus apparently hibernates in the Baikal region and Kazakhstan in the imago stage (Kostin, 1964). In some northern areas of the Amur Region some of the larvae hibernate (Isaev, 1963; Utkin, 1963). In Central Yakutia young beetles which emerged at the end of July or at the beginning of August start to make maternal galleries and lay single eggs. However, emerged larvae perish in the winter (Petrenko, 1965).

Additional feeding by young beetles occurs in places of their development or in isolated single or group galleries. They are found on tops and branches of dead or dying trees, as well as on stems of young growth. These feeding galleries created by the young adult beetles are 3-7 cm long. They extend away from the common entry like a fan, are crowded and almost always penetrate the alburnum.

Some of the adults hibernate in pupa cradles or in the adult feeding galleries. In most cases hibernation takes place in forest litter under the moss cover 4-5 cm thick and in soil (Florov, 1949). Hibernating beetles are found in the soil at the end of August, although at the same time pupae can still be found in the tree.

I. subelongatus is very similar to I. cembrae, but the range of the two species does not overlap.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control measures include forest management and sanitation: improving the resistance of forests, cutting and elimination of infested trees. Insecticides such as phoxim can be applied to felled "trap trees" on which the beetles have aggregated.