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The brown planthopper (BPH), Nilaparvata lugens, is a serious threat to rice production in Vietnam and insecticides are widely used for its control. Migration of the BPH have one of its roots in tropical Vietnam in the Mekong River Delta and the insecticide resistance status of BPH populations from Vietnam is thus important for East Asia. In the present investigation, we evaluate the susceptibility of BPH populations from nine provinces from the Red River Delta, the Central Coastal region and the Mekong River Delta of eight insecticides during 2015-17. BPH field populations of Vietnam have developed a low to moderate level of resistance to the neonicotinoids dinotefuran, nitenpyram and imidacloprid, the pyrethroid etofenprox, the anticholinesterase fenobucarb, as well as fipronil and pymetrozine, and the growth regulator buprofezin. There was a correlation of in toxicology of fipronil, dinotefuran, etofenprox, buprofezin, which represents four different modes of action. The neonicotinoid nitenpyram, pymetrozine and fenobucarb did not show correlation in toxicology to any of the investigated insecticides. For most insecticides, a gradient of susceptibility was established from the Red River Delta in the north, through the Central Coastal region and to the Mekong River Delta in the south of Vietnam. The most susceptible populations were from the north. Insecticide resistance of the BPH populations in Vietnam is not at an alarming level and they are not the direct origin of high insecticide resistance found in East Asia. The cross-resistance pattern of BPH populations in Vietnam, where insecticides with different modes of action correlated, indicate that insecticides should be used with caution. There could be a buildup of a general metabolic resistance, which alone or in combination with the emergence of target-site resistance mutations will cause control problems. The results will be beneficial for development of resistance management strategies to prevent and delay development of insecticide resistance in BPH not only for Vietnam, but also for more northern Asian regions due the migration of BPH from tropical Vietnam.

The paper presents a dynamic analysis of train-track systems supported by viscoelastic foundations by combining Timoshenko’s beam theory and moving element method (MEM). In the proposed method, a three-node beam element is utilized to get a high order approximation for the deflection of Timoshenko beam. The reduced integral method is applied in order to avoid the shear-locking phenomenon when computing the shear strain energy of the rail beam. In addition, the behavior of train-track system with respect to time is deduced by using Newmark’s constant acceleration method. Numerical results show that the proposed method is free of shear locking and gives a good agreement with Koh et al.’s method using Euler-Bernoulli beam theory.

Recently, a cell-based smoothed discrete shear gap method (CS-FEM-DSG3) based on the firstorder shear deformation theory (FSDT) was proposed for static and free vibration analyses of Mindlin plates. The CS-FEM-DSG3 uses three-node triangular elements that can be easily generated automatically for arbitrary complicated geometric domains. This paper further extends the CS-FEMDSG3 for static, free vibration, and dynamic response of the stiffened plate resting on viscoelastic foundation subjected to a moving vehicle. The viscoelastic foundation is modeled by discrete springs and dampers whereas the stiffened plate can be considered as the combination between the Mindlin plate and the Timoshenko beam elements. The moving vehicle is transformed into one concentrated load at its central point. Some numerical examples are investigated and numerical results show that the CS-FEMDSG3 overcomes shear-locking phenomena and has a fast convergence. The results also illustrate the good agreement of the CS-FEM-DSG3 for static and free vibration analyses of un-stiffened plate compared with the previous published methods. In addition, the numerical results for dynamic analysis of stiffened plates by the CS-FEM-DSG3 also show the expected property in which the deflection of the stiffened plate is much smaller than those of the un-stiffened plate.

A linearly conforming point interpolation method (LC-PIM) was recently proposed for the solid mechanics problems. In this paper, the LC-PIM is further extended to perfect visco-elastoplastic analyses of 2D solids. A dual formulation for the LC-PIM with displacements and stresses as the main variables is performed. The von-Mises yield function and the Prandtl-Reuss flow rule are used. In the numerical procedure, however, the stress variables are eliminated and the problem becomes only displacementdependent. The numerical results show that the LC-PIM is much more accurate than the FEM and possesses the upper bound property which is very meaningful for the viscoelastoplastic analyses which almost have not got the analytical solutions. This suggests that we can use two models, LC-PIM and FEM, to bound the solution, and can even estimate the global relative error of numerical solutions.