Understanding drivers of population fluctuation,especially for agricultural pests,is central to the provision of agro-ecosystem services.Here,we examine the role of endogenous density dependence and exogenous factors of climate and human activity in regulating a population of an important agricultural insect pest,the cotton bollworm(Helicoverpa armigera),in North China over a 37-year period,from 1975 to 2011.Quantitative time-series analysis provided strong evidence explaining the long-term population dynamics of the cotton bollworm and its driving factors.Rising temperature and declining rainfall exacerbated the effects of agricultural intensification by continuously weakening the density dependence that regulates the population dynamics of cotton bollworms.Consequently,ongoing climate change and agricultural intensification unleashed the tightly regulated pest population and has triggered the regional outbreak of H.armigera in 1992.Although density dependence effectively regulated the population with small oscillations around stable equilibrium prior to the 1992 outbreak,after the outbreak,the population carrying capacity increased and a stable equilibrium that has greater oscillations.The results highlight the possibility for exogenous factors to induce pest outbreaks and alter the population density dependence regulating mechanisms,thus the stable equilibrium of the pest population.Increasing carrying capacity can bring considerable risks to the provision of agro-ecosystem services and regional food security.Efficient and timely measures of pest management in the era of Anthropocene should consider changes in density dependence mechanisms caused by climate change and human activities.