One of the critical design parameters used in evaluating soil structure is the friction angle, derived from Mohr's Circle failure criterion. The soil friction angle is an engineering parameter estimated in the laboratory to quantify the soil shear strength in geotechnical applications. This paper indicates an experimental study investigating the impact of particle size on different sandy soils shear strength behavior. The direct shear test equipment is useful for simulating various stress regimes to determine the soil strength by employing a slow moving lateral force to a consolidated sample along a shear plane. A series of direct shear tests were conducted to investigate the interface behavior of soil. Soil samples were selected from different locations in New Mexico, United States. The influence of soil particle size on the soil's shear strength behavior is discussed by performing a series of symmetric direct shear tests according to ASTM D3080 and analyzing the results. To minimize errors, electronic transducers were used to measure vertical and horizontal displacements. DS7 is geotechnical testing software controlling the test by utilizing a data logger. The investigation indicates that the maximum vertical deformation for all different kinds of sandy soils accrued simultaneously. It was concluded that a soil's friction angle is affected by coarse-grained material. Accordingly, sandy soils with bigger particle size record a higher friction angle than soils containing small particles. Furthermore, a non-linear regression analysis was performed to determine the direct relationship between soil's friction angle and soil particle characteristics.

BACKGROUND: The Guatemalan potato tuber moth, Tecia solanivora, has been the most important pest species in Hispanico‐American potato fields since its first record on potatoes in 1956 in Guatemala. This insect pest has been spreading to other parts of the world, including the Canary Islands in Europe. Tuber moth control relies heavily on the use of insecticides, including pyrethroids. Here, we assessed the likelihood of control failures and performed concentration–response bioassays in five Colombian strains of T. solanivora to evaluate their susceptibilities to the pyrethroid permethrin.RESULTS: Evidence of control failures was observed in four strains tested, which exhibited moderate resistance levels (i.e. ranging from 5.4‐ to 24.4‐fold). However, no spatial dependence was observed between the permethrin LC₅₀ values and the geographic distances among the tuber moth strains. In order to evaluate whether permethrin resistance was mediated by potential mutations in the para‐type sodium channels of T. solanivora, the IIS4–IIS6 region of the para gene was PCR amplified and sequenced from the five strains tested. As demonstrated across a range of different arthropod species that exhibited knockdown resistance (kdr), we observed a single point substitution (L1014F) at high frequencies in the para gene of all four resistant strains.CONCLUSION: This is the first identification of a target‐site‐alteration‐based resistance in the Guatemalan potato tuber moth T. solanivora, which is widespread and exhibits high frequencies among geographically distant strains, indicating that pyrethroids are probably becoming ineffective for the control of this pest species. © 2016 Society of Chemical Industry

The high insecticidal efficacy of a garlic essential oil-based nano-emulsion makes this formulation a viable alternative to conventional pesticides for aphid control.

The phenomenon of insecticide resistance is defined as the ability of insect populations to develop the capacity to survive doses of insecticides that would otherwise be lethal. This phenomenon can be attributed to the natural selection of individuals with genetic mutations that confer resistance. A comprehensive understanding of insecticide resistance mechanisms is crucial for developing novel control strategies within existing integrated pest management plans. In this context, this review examines the research conducted to characterize the resistance of agricultural pests (insects/mites) to insecticides/acaricides in Colombia. A search of relevant scientific literature was conducted using keywords in the databases. A literature review revealed that, according to reports from Colombia, there have been 27 documented instances of insecticide/acaricide resistance across 12 species. Conversely, the Arthropod Pesticide Resistance Database (APRD) indicates the existence of 98 reports of resistance to insecticides/acaricides distributed across 10 species. A single instance of acaricide resistance was identified in the respiratory target; all other cases demonstrated resistance to the nervous and muscular targets. In this review, we present the main results, which are focused on determining toxicity curves and calculating lethal concentrations. We highlight the research carried out in the last decade, which makes use of new molecular techniques and allows a more detailed view of the resistance mechanisms. Furthermore, we suggest novel methodologies that could be employed to improve current integrated pest management plans.