In the Aershan area of Inner Mongolia, after the third outbreak of the moth Dendrolimus superans Butler in 2002, there was a rapid invasion of several secondary insect borers such as the beetles Monochamus urussovi Fischer von Waldheim, Monochamus sutor Linnaeus, Acanthocinus carinulatus Gebler and Ips subelongatus Motschulsky. This led to great losses of trees in Larix gmelinii Rupr. plantations. No previous research has investigated the ecological niches of these larch borers. We studied their niches in the Aershan area, using ecological niche theory including the concepts of niche breadth, niche overlap, proportion of niche similarity and the interspecific competition coefficient. The results showed that none of these secondary borers damaged healthy L. gmelinii trees. I. subelongatus was the most abundant of the four beetles, with up to 252 individuals found within a 1-2 m length of trunk. The spatial niche breadth of I. subelongatus was greatest in weak standing larch; When in middle-aged larch, it reached 0.5782, and in old larch it reached 0.5498. The spatial niche breadth of A. carinulatus was 0.5143 in middle-aged larch and 0.6294 in old, dead, standing larch, which was greater than in the weak larch. The spatial niche breadth of M. urussovi was smallest in both weak and dead larch. Although the spatial niche breadth of M. sutor was not large, the abundance of this insect was nearly the same as that of A. carinulatus, the dominant longhorned beetle. Niche breadth reflects the degree to which a species occupies a specific niche, and can show proportions of populations distributed among different resource types; it does not reflect abundance. The spatial niche overlap of I. subelongatus with the other three longhorned beetles was large in standing larch. This was because I. subelongatus was distributed throughout each resource type, and had the greatest niche breadth. The spatial niche proportion of I. subelongatus was high in comparison with that of the other three beetles, indicating that demand for space of the four species showed little difference. The spatial interspecific competition coefficient of the four species was high, because of their different areas of damage, which suggests that these four pests can coexist. I. subelongatus and A. carinulatus damage only the phloem. Young larvae of M. urussovi and M. sutor also damage the phloem, while mature larvae bore into the xylem. Thus, the four borers are able to share the same ecological niche, leading to more serious larch damage. Strong competition causes high mortality of I. subelongatus and A. carinulatus larvae, and these can also be preyed on or parasitized by natural enemies. The damage caused by I. subelongatus is the most serious of the four insect borers. Control measures may be needed. Insecticide spraying may be appropriate for I. subelongatus as this borer damages the tops of trunks and it is possible to specifically target this area. However, a greater dosage may be needed on the lower trunks where these four pests are most abundant.