Abstract: Cephalcia kunyushanica is a typical monophagous defoliating insect species. To determine the factors affecting C. kunyushanica population distribution in different Japanese red pine (Pinus densiflora) stands, an analysis was made on the relationships of C. kunyushanica larval density with the composition type and diversity of tree species and the site and stand factors. The annual fluctuation of C. kunyushanica population in pure Japanese red pine stand and in the mixed forests of Japanese red pine with the tree species from the same genus (Pinus) or the same order (Pinales, except for Pinus) or with broadleaf trees species in Kunyu Mountain from 2009 to 2011 was also compared. No significant correlations were observed between C. kunyushanica larval density and site and stand factors. There existed differences in the larval density and Shannon index among different stand types, and the variation trends of the two indices were totally different. Forest type was the most important predictor variable in random forests regression used for predicting the larval density of C. kunyushanica. C. kunyushanica larval density was the highest in pure Japanese red pine stand and not significantly different from that in the Japanese red pine stand mixed with Pinus sp., but was significantly higher than that in the Japanese red pine stand mixed with broadleaf and Pinales sp. species in each of the three years. Furthermore, tree species composition was more important than tree species richness in mixed stands. From 2009 to 2010 and from 2010 to 2011, the coefficient of annual variation of C. kunyushanica population was lower in the Japanese red pine stand mixed with broadleaf trees and Pinales sp. than in the Japanese red pine stand mixed with Pinus sp. or in pure Japanese red pine stand, suggesting that C. kunyushanica population was more stable in the Japanese red pine stand mixed with broadleaf tree species than in Japanese red pine stand mixed with Pinus sp. or in pure Japanese red pine stand. Our results suggested that the association of Japanese red pine mixed with Pinus sp. could actually receive more damage by defoliating insect species than the association of Japanese red pine mixed with Pinales sp. and broadleaf trees. The taxonomic kinship of a focal tree and its neighbor trees played an important role in the likelihood of associational resistance or associational susceptibility, and the stands of mixed tree species of close genetic relationship to focal tree species had higher larval density and lower stability of C. kunyushanica than the stands composed of genetically distant trees species.

Key words: water retentive agent, winter wheat, growth, yield, water use efficiency, root morphology.