Impacts of Tomicus minor on distribution and reproduction of Tomicus piniperda (Col., Scolytidae) on the trunk of the living Pinus yunnanensis trees

This study investigated the impacts of Tomicus minor on Tomicus piniperda w hen the two Tomicus species coexist in the trunks of living Yunnan pine (Pi nus yunnanensis L.) trees growing in the Kunming region, in south-western C hina. Tomicus piniperda mostly locates in the mid- and upper trunks of Yunn an pine tree; whereas T. minor mainly attacks the mid- and lower trunks. In the mid-trunk area from 1.0 to 5.0 m above ground, there are overlapping a ttack zones for the two Tomicus species, which accounts for an average of 8 0% of the entire zone occupied by T. piniperda and an average of 70% of the zone occupied by T. minor. In correspondence with their attack distributio ns, the average attack densities of the two species varied with height alon g the trunk, with 165.3 egg galleries per m(2) at a height of 6 m for T. pi niperda, and 138.2 egg galleries per m(2) at the 1 m height for T. minor. I t is suggested that. minor adjusts its attack pattern with respect to T. pi niperda, and thereby minimizes interspecific competition. No remarkable dif ference of average T. piniperda egg gallery length was found between the zo ne in which only T. piniperda occurred and the zone in which T. piniperda a nd T. minor coexisted; this is suggested to be due to low host quality in t he upper trunk region where only T. piniperda was present. The number of T. piniperda larval galleries was highest when only T. piniperda was present, and decreased as T. piniperda and T. minor coexisted, particularly in the case when the density of T. piniperda was less than that of T. minor. Avera ge larval density was 1649 larval galleries per m(2) where only T. piniperd a occurred. However, when T. piniperda coexisted with T minor, T. piniperda larval density averaged 1010 per m(2) when T. piniperda density was higher than T. minor, and averaged 442 per m(2) when T. piniperda density was les s than T, minor, which led to the conclusion that T. minor makes a negative impact on T. piniperda reproduction when the two Tomicus species jointly c olonize the same trunk of Yunnan pine tree.