An optimization approach to the twe-circle method of estimating groun-dwelling arthropod densities

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

Weakening density dependence from climate change and agricultural intensification triggers pest outbreaks : a 37-year observation of cotton bollworms

CITATION: Ouyang, F. et al. 2014. Weakening density dependence from climate change and agricultural intensification triggers pest outbreaks : a 37-year observation of cotton bollworms. Ecology and Evolution, 4(17):3362–3374, doi:10.1002/ece3.1190.The original publication is available at http://onlinelibrary.wiley.comUnderstanding 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.http://onlinelibrary.wiley.com/doi/10.1002/ece3.1190/abstractPublisher's versio

Chemical RNA Modifications: The Plant Epitranscriptome

International audienceRNA post-transcriptional modifications create an additional layer to control mRNA transcription, fate, and expression. Considering that they are non-genetically encoded, can be of reversible nature, and involved in fine-tuning gene expression, the landscape of RNA modifications has been coined the "RNA epig-enome" or "epitranscriptome." Our knowledge of the plant epitranscriptome is so far limited to 3′-uridylation and internal m 6 A and m 5 C modifications in Arabidopsis. m 6 A is the most abundant and well-studied modification on mRNAs, and involves the activities of evolutionarily conserved "writer" (methyltransfer-ase), "reader" (RNA binding proteins), and "eraser" (demethylases) proteins. In Arabidopsis, m 6 A is crucial for embryogenesis, post-embryonic growth, development , phase transition, and defense responses. Conversely to animals, our understanding of the roles of m 6 A is limited to the finding that it is an mRNA stabilizing mark. Yet likely to exist, its roles in controlling plant mRNA maturation, trafficking , storage, and translation remain unexplored. The m 5 C mark is much less abundant on the transcriptome and our knowledge in plants is more limited. Nonetheless, it is also an important epitranscriptomic mark involved in plant development and adaptive response. Here, we explore the current information on m 6 A and m 5 C marks and report knowledge on their distribution, features, and molecular, cellular , and physiological roles, therefore, uncovering the fundamental importance in plant development and acclimation of RNA epigenetics. Likely to be widespread in the green lineage and given their crucial roles in eukaryotes, the fostering of data and knowledge of epitranscriptome from cultivated plant species is of the utmost importance