[Objectives]  Pinus yunnanensis Franch is an important tree species in plantation forests in southwestern China. Recently, outbreaks of wood boring pests such as Monochamus alternatus Hope, Tomicus spp., Dioryctria rubella Hampson and brown-spot needle blight have been found in P. yunnanensis plantations, threatening local forest health. This study used the dieback rate of the tree canopy as an indicator of tree condition and identified the main factors that cause canopy dieback. A mathematical relationship between the degree of canopy damage and the species and abundance of pest insects was developed to improve the precision of pest monitoring methods and provide accurate early warning of pest infestation in P. yunnanensis plantations. [Methods]  In the sample areas, 35 P. yunnanensis with partly withered canopies and 29 completely withered trees were investigated. Species and amounts of different pests in the canopies and trunks of these trees were identified and counted. The correlation between dieback rate and damage factors was analyzed using Pearson correlation coefficients. A multiple linear stepwise regression was used to identify the main factors causing canopy dieback and model the major pest populations based on canopy dieback. [Results]  A highly positive relationship between dieback rate and Tomicus spp. abundance was found, whereas a weak, or no, relationship was found between dieback rate and diameter at breast height, shoot disease rate and other factors. A chi-square test showed that shoot disease didn’t influence shoot dieback significantly. We developed a regression model to estimate the population abundance of Tomicus spp. from dieback rate: Y=12.0984+0.9835 X, Adj-R²=0.8081. This indicated that tree vigor declined as Tomicus spp. abundance increased during the shoot feeding phase. Tomicus spp. and M. alternatus mainly damaged trunks of dying and withered trees during the trunk colonization phase. [Conclusion]  The shoot feeding behavior of Tomicus spp. causes partial withering of the canopy and a decline in the vigor of P. yunnanensis, whereas complete withering of the canopy and death follows colonization of the trunk by M. alternatus and Tomicus spp. The dieback model developed in this study can help estimate the mixed population of Tomicus spp. in canopies during the shoot feeding phase and provide a reliable theoretical foundation for pest space remote sensing or unmanned aerial vehicle monitoring.