title: Weakening density dependence from climate change and agricultural intensification triggers pest outbreaks: a 37-year observation of cotton bollworms.
abstract: 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 the 37-year population dynamics of an important agricultural insect pest, the cotton bollworm (Helicoverpa armigera), in North China from 1975 to 2011. Quantitative time-series analysis provided strong evidence explaining long-term population dynamics of the cotton bollworm and its driving factors. Rising temperature and declining rainfall exacerbated the effect of agricultural intensification on continuously weakening the negative density dependence in regulating the population dynamics of cotton bollworms. Consequently, ongoing climate change and agricultural intensification unleashed the tightly regulated pest population and triggered the regional outbreak of H. armigera in 1992. Although the negative density dependence can effectively regulate the population change rate to fluctuate around zero at stable equilibrium levels before and after outbreak in the 1992, the population equilibrium jumped to a higher density level with apparently larger amplitudes after the outbreak. The results highlight the possibility for exogenous factors to induce pest outbreaks and alter the population regulating mechanism of negative density dependence and, thus, the stable equilibrium of the pest population, often to a higher level, posing 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 target the strengthening and revival of weakening density dependence caused by climate change and human activities.
authors.affiliation: State Key Laboratory of Integrated Management of Pest and Rodents, Institute of Zoology, Chinese Academy of Sciences Beijing, 100101, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Ouyang
authors.affiliation: Department of Botany and Zoology, Centre for Invasion Biology, Stellenbosch University Matieland, 7602, South Africa.
authors.forename: Cang
authors.initials: C
authors.lastname: Hui
authors.affiliation: Fisher College of Business, Ohio State University Columbus, Ohio, 43210.
authors.forename: Saiying
authors.initials: S
authors.lastname: Ge
authors.affiliation: Institute of Plant Protection, Shandong Academy of Agricultural Sciences Jinan, 250100, China.
authors.forename: Xin-Yuan
authors.initials: XY
authors.lastname: Men
authors.affiliation: Department of Entomology, China Agricultural University Beijing, 100193, China.
authors.forename: Zi-Hua
authors.initials: ZH
authors.lastname: Zhao
authors.affiliation: Institute of Bamboo, Nanjing Forestry University Nanjing, 210037, China.
authors.forename: Pei-Jian
authors.initials: PJ
authors.lastname: Shi
authors.affiliation: State Key Laboratory of Integrated Management of Pest and Rodents, Institute of Zoology, Chinese Academy of Sciences Beijing, 100101, China ; College of Plant Protection, Hunan Agricultural University Changsha, 410128, China.
authors.forename: Yong-Sheng
authors.initials: YS
authors.lastname: Zhang
authors.affiliation: Department of Botany and Plant Sciences, Ecological Complexity and Modeling Laboratory, University of California Riverside, California, 92521-0124.
authors.forename: Bai-Lian
authors.initials: BL
authors.lastname: Li
keywords: Climate change; density dependence; human activity; population dynamic; time series; variation partitioning