Abstract: The fungi of Mycosphaerella larici-leptolepis,Botryosphaeria laricina,Triphragmiopses laricimum and insects of Coleophora dahurica,Adelges laricis,Cinara laricis are common pests on larch (Larix olgensis). Each species possesses different ecological niche on larch crown. The effects of different insects (or developmental phases) and diseases on larch crown showed the phenomena of alternate emergence over time,inter evasion and selecting different ecological environments.The life table of 6 pests showed that the insect pests were major pests of the larch crown from late May to early July.After late July when fungi diseases invaded the needles and shoots,the larch was injured seriously.When3 insect pests attached larch only,the Kx value in life table was 0.016～0.0197. While the diseases affected,Kx was up to 0.124,reaching0.26 on September 7. The fungal diseases seriously defoliated larch trees in August,which could affect continuously the growth of larch for 3 years,and most seriously in second year. C.dahurica defoliated trees in May.

Key words: Larch, Disease and insect pests, Ecological effect, NDVI maximum, Tibetan Plateau, precipitation change, precipitation concentration index, precipitation centroid