Browsing by Author "Zhao, Zi-Hua"

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    Effects of agricultural intensification on ability of natural enemies to control aphids
    (Springer Nature, 2015-01-26) Zhao, Zi-Hua; Hui, Cang; He, Da-Han; Li, Bai-Lian
    Agricultural intensification through increasing fertilization input and cropland expansion has caused rapid loss of semi-natural habitats and the subsequent loss of natural enemies of agricultural pests. It is however extremely difficult to disentangle the effects of agricultural intensification on arthropod communities at multiple spatial scales. Based on a two-year study of seventeen 1500 m-radius sites, we analyzed the relative importance of nitrogen input and cropland expansion on cereal aphids and their natural enemies. Both the input of nitrogen fertilizer and cropland expansion benefited cereal aphids more than primary parasitoids and leaf-dwelling predators, while suppressing ground-dwelling predators, leading to an disturbance of the interspecific relationship. The responses of natural enemies to cropland expansion were asymmetric and species-specific, with an increase of primary parasitism but a decline of predator/pest ratio with the increasing nitrogen input. As such, agricultural intensification (increasing nitrogen fertilizer and cropland expansion) can destabilize the interspecific relationship and lead to biodiversity loss. To this end, sustainable pest management needs to balance the benefit and cost of agricultural intensification and restore biocontrol service through proliferating the role of natural enemies at multiple scales.
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    An optimization approach to the two-circle method of estimating ground-dwelling arthropod densities
    (Florida Entomological Society, 2014-06) Shi, Pei-Jian; Zhao, Zi-Hua; Sandhu, Hardev S.; Hui, Cang; Men, Xing-Yuan; Ge, Feng; Li, Bai-Lian
    Information on ground-dwelling arthropod densities is important for efficient management in agro-ecosystems. A method of using paired pitfall traps with different inter-trap distances, called the two-circle method (TCM), was proposed recently for accurate and efficient estimation of arthropod densities. Using the numbers of individuals caught in paired traps and the inter-trap distances between the paired traps as input, the TCM can simultaneously estimate the effective trapping radius and the population density by fitting a nonlinear model. However, the previous fitting procedure (using the nonlinear least squares approach) provides the estimates and standard errors of only these two variables, and often suffers from its hypersensitivity to the initial values assigned in the nonlinear regression. To estimate the confidence intervals of these estimates and to assess the effects of the number of replications per distance class and the number of distance classes on the accuracy of density estimates, we provide a new procedure for fitting the model by using the optimization function. Evaluation based on simulated and field data suggests that the TCM could provide a reliable estimate of density by using at least 15 paired traps per distance class and at least 4 distance classes.
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    Weakening density dependence from climate change and agricultural intensification triggers pest outbreaks : a 37-year observation of cotton bollworms
    (John Wiley & Sons Ltd., 2014-08-12) Ouyang, Fang; Hui, Cang; Men, Xin-Yuan; Zhao, Zi-Hua; Shi, Pei-Jian; Zhang, Yong-Sheng; Li, Bai-Lian
    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 agroecosystem 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.