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Quasi-static tensile tests are commonly used to determine the mechanical properties of fiber bundles. These tests are generally carried out at a low standard speed of 1 mm.min−1, which is recommended for elementary fibers, although other moderate and high speeds are rarely used. In this study, tensile tests were carried out on coir and sisal fiber bundles from the coastal region of Cameroon using four different speeds: 1, 2, 5, and 10 mm.min−1 to assess mechanical properties. Samples were prepared by attaching the two ends of each randomly selected fiber bundle to a paper frame to obtain a length of 30 mm. The results showed a significant effect of extension speed, indicating a decrease in tensile strength and Young's modulus, and an increase in strain at break with increasing speed. These trends were correlated with the power functions. A strong dependence between fiber bundle diameter and tensile strength was also observed. Furthermore, statistical analysis based on the Weibull distribution highlighted the dispersion of mechanical properties, demonstrating a reduction in dispersion with increasing extension speed for coir fibers. These data can be used to develop specific standards for these natural fibers and contribute to the advancement of composites based on plant fibers. [ABSTRACT FROM AUTHOR]

The flea beetle Nisotra uniformis Jacoby is a widespread pest of malvaceous crops for which synthetic chemical insecticides remain the principal control tool, particularly in sub-Saharan Africa. With the ultimate aim of developing a microbial alternative for N. uniformis control, we conducted laboratory experiments (25 ± 1°C; 70 - 80% RH) to evaluate the biological attributes of three Cameroonian isolates of the entomopathogenic fungi Beauveria bassiana (Balsamo-Crivelli) Vuillemin and Metarhizium anisopliae sensu lato (Metchnikoff) Sorokin. Spore germination rates of the isolates varied from 0.5% after 4 hrs to 100% after 24 hrs on PDA medium, with MIITAC11.3.4 spores germinating fastest. Pathogenicity tests consisted of dipping adult beetles in conidial suspensions. All isolates were pathogenic to N. uniformis, with corrected mortalities varying between 23.3 - 86.7%. BIITAC-O-2 had the lowest LC50 at 5.17 × 106 conidia/ml, while MIITAC11.3.4 and BIITAC6.2.2 had LC50 at 4.11 × 107 conidia/ml, and 2.00 × 108 conidia/ml, respectively. BIITAC6.2.2 produced the shortest time to the highest mortality rate (1.17 days) and the shortest LT50 of 1.64 days but only at the highest concentration, followed by the two highest concentrations of MIITAC11.3.4 (LT50 at 3.43 and 5.70 days). The c parameter in the Weibull model showed that BIITAC-O-2 caused the highest rate of increase in mortality (2.42) at the highest concentration, followed by MIITAC11.3.4 (1.09) and BIITAC6.2.2 (0.50). The results of our study provide the basis for including N. uniformis in the ongoing development of BIITAC6.2.2 and MIITAC11.3.4 into biopesticide while continuing with further laboratory studies on BIITAC-O-2. [ABSTRACT FROM AUTHOR]