elocation-id: e3633
Sitophilus zeamais is an insect considered a primary pest of stored corn grains whose damage compromises corn production. In the search for options for its control, nanotechnology combined with plant extracts could be a viable option. The research was conducted in 2023 at the Department of Agricultural Parasitology with the aim of evaluating the insecticidal effect of two commercial extracts: Higuer® and Etos®, alone and in combination with nano- and microparticles of silicon, copper, zinc and graphite. The residual film bioassay technique was used for the evaluation; the nanoformulations were prepared at the concentration of 3% of each of the nano- and micromaterials. LC50 of two commercial extracts alone and in combinations with nano- and microparticles was determined. It was observed that extracts combined with silicon nanoparticles have the lowest values of LC50, followed by a copper, graphite, and zinc nanoparticles. In the values of the combinations with microparticles, they were equal to or higher than those found with the extract alone. It was concluded that the combination of the two extracts with the silicon nanoparticles stands out from the rest of the materials as they have lower LC50 values.
corn weevil, nanotechnology, stored grains.
The pest of Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) is considered the primary pest of corn grain, causing losses due to direct and indirect damage amounting to about 90% of production in severe infestations (Achimon et al., 2022). Although the chemical method represents the main means of control, there have been situations such as resistance, damage to non-target insects, and environmental pollution (Andrade-Bustamante et al., 2023).
Recent research highlights the benefits of nano and microparticles and their combinations with extracts of the genus Sitophilus; for example, silicon as it provides high mortality and reduction in LC50 values (Seham and Sleem, 2020), copper and zinc with mortalities of up to 90 and 70%, respectively (Badawy et al., 2021), and graphene with mortalities of 100% (Moisidis et al., 2022).
Derived from this, the need arises to explore new technologies that allow more efficient control; in this sense, we find the use of nano- and micro-scale particles focused on agricultural applications (Sousa et al., 2023), generating the development opportunity to use extracts of plant origin and their mixtures with nano- and microparticles of different elements and materials, providing a potential alternative to the method chemical to achieve control of pest insects of stored grains (Jasrotia et al., 2022).
The objective of this research was to evaluate the insecticidal effect of two commercial plant extracts and their combination with nano and microparticles of silicon, copper, zinc, and graphite on adult insects of S. zeamais, a pest of stored corn grains, under the hypothesis that combinations with nanomaterials will present an insecticidal effect with LC50 values lower than their microparticulate counterparts and extracts alone.
This research was conducted at the Insect Toxicology Laboratory of the Department of Agricultural Parasitology of the Antonio Narro Autonomous Agrarian University (UAAAN), for its acronym in Spanish, located in Buena Vista, Saltillo, Coahuila, Mexico. The adult insects of S. zeamais were obtained from pre-existing colonies of the toxicology laboratory of the UAAAN, free of chemical applications, kept in corn grains with a photoperiod of 12:12 (L:D) and relative humidity (RH) of 35%.
The extracts used, Higuer®, made from castor oil plant (Ricinus communis L.) and Etos®, made from pepper (Piper nigrum L.), as well as the nano- and microparticles of silicon, copper, zinc, and graphite, with spheres of 40-80 nanometers and particles of 100 microns, were provided by the company Culta, SA de CV, located in Ciudad Mante, Tamaulipas, Mexico.
The experimental design used was completely randomized with six concentrations plus a control for each extract alone and its combination with each type of material. Three replications per concentration and 30 insects per experimental unit. The nano and microformulations were prepared at the concentration of 3% in 100 ml beakers using test tubes, micropipettes, and distilled water.
The bioassay was by the residual film technique (FAO, 1974), in which each Petri dish was impregnated with 1 ml of each concentration, both of extract alone and nano and microformulated, with data collection at 24, 48 and 72 h, considering those insects that did not respond to the heat stimulus when placed on a plate as death criteria. The mortality data were corrected using Abbott (1925) formula, considering a mortality value not greater than 15% of the control for each treatment; in those treatments where there was no mortality in the control, direct data were recorded and the median lethal concentration (LC50) was estimated by means of a probit analysis (Finney, 1971) using the statistical program of SAS System for Windows, version 9.0.
The estimated LC50 values for Higuer®, alone and its combinations, are shown in Table 1. The combination with nano silicon presents the lowest value of LC50 with 57.2 ppm, followed by graphite, copper, and zinc. For its part, the combination of the Higuer® extract with the micromaterials leads to an increase in LC50 compared to the extract alone (81.8 ppm). The use of R. communis extract has been reported as an effective method for controlling S. zeamais, such as Wale and Assegie (2015), who estimated an LC50 value of 2 040 ppm.
For their part, El-naby et al. (2020) evaluated nanoemulsions of R. communis and the extract alone against Sitophilus oryzae, estimating the LC50 of the nanoemulsion at 1 300 vs. 2 500 ppm of the extract alone, results that differ from the one obtained in this work (Higuer® 81.8 and Higuer® + nano silicon 57.2 ppm), which is much lower than those reported by these authors.
Although it was observed that the fiducial limits overlap and are statistically equal, the treatment that presents the lowest LC50 value is sought among the extracts alone and their combinations with nano- and microparticulate materials.
The estimated LC50 values for the Etos® extract alone and its combinations are shown in Table 2. In the combination of the extract with nanoparticles, the values of LC50 decrease compared to the extract alone, with silicon standing out with 67.77 ppm, followed by copper, graphite, and zinc. P. nigrum extract is a good tool for the control of the genus Sitophilus in accordance with mortalities reported by Abdel-Mogib et al. (2017), 100% on adults of S. oryzae; however, the estimated LC50 value corresponds to 2 400 ppm.
Likewise, Choden et al. (2021) evaluated P. nigrum extract on adults of S. zeamais and obtained an LC50 of 500 ppm, higher than in this research (102.2 ppm). Regarding nanoformulations with P. nigrum, Rajkumar et al. (2020) evaluated chitosan nanoparticles loaded with the essential oil against S. oryzae and reported an LC50 of 25.03 vs 48.97 ppm of the extract alone, although the LC50 value decreased, it differs from the present work (Etos® 102.2 vs Etos® + nano silicon 67.7 ppm).
For copper nanoparticles, LC50 values in ppm of 71.8 and 79.2 ppm, Higuer® and Etos®, respectively, were obtained; in contrast, Dikbaş et al. (2021), when evaluating copper nanoparticles on S. zeamais, achieved mortalities of 100% with an LC50 of 6 ppm, thanks to the addition of chitinase of bacterial origin to the nanoformulation. On the other hand, Wazid et al. (2020) reported that silicon nanoparticles were the most effective on S. oryzae, followed by copper and zinc. As for nanographene, Moisidis et al. (2022) evaluated two types of nanographene and reported that they achieved 100% mortality against S. oryzae at 500 ppm.
In the case of micromaterials, the lowest values were found with silicon microparticles and only with this, there is a slight decrease in the value of LC50 compared to extracts alone. Ciniviz and Mutlu (2020) evaluated microparticulate silicon (8-12 μ) on S. zeamais, achieving mortalities from 91 to 100% with 1 500 to 2 000 ppm. For their part, Das et al. (2019) evaluated nano- and microparticles of aluminum, titanium, and zinc on S. oryzae and achieved mortalities of 100% with aluminum nanoparticles, followed by titanium and zinc, and they conclude that nanomaterials were better than microparticles, coinciding with this study.
The fact that nanoparticles combined with extracts have lower values of LC50 compared to microparticles is attributed to the fact that they exhibit properties such as carriers of active compounds, large specific surfaces, and better capacity of adhesion and penetration into insect structures (Menossi et al., 2021).
The combinations of the Higuer® and Etos® extracts with the silicon nanoparticles represented a viable option in the control of S. zeamais since all the treatments presented the lowest LC50 values, respectively, followed by options with copper, graphite and zinc. In relation to microparticles, they presented values equal to or higher than those reported in the extracts alone. Therefore, it is recommended to carry out research on this type of particles.
Achimón, F. F.; Peschiutta, M. L.; Brito, V. D.; Beato, M. M.; Pizzolitto, R. P.; Zygadlo, J. A. and Zunino, M. P. 2022. Exploring contact toxicity of essential oils against Sitophilus zeamais through a meta-analysis approach. Plants. 11(22):3070. Doi: https://doi.org/10.3390/plants11223070.
Rajkumar, V. V.; Gunasekaran, C. C.; Dharmaraj, J. J.; Chinnaraj, P. C.; Paul, C. A. and Kanithachristy, I. I. 2020. Structural characterization of chitosan nanoparticle loaded with Piper nigrum essential oil for biological efficacy against the stored grain pest control. Pesticide Biochemistry and Physiology. 166(1):1-9.
Sousa, P. A.; Neto, J. J.; Barbosa, J. V.; Peres, J. J.; Magro, A. A.; Barros, G. G. and Bastos, M. M. 2023. Novel approach for a controlled delivery of essential oils during long-term maize storage: clove bud and pennyroyal oils efficacy to control Sitophilus zeamais, reducing grain damage. Insects.14(4):366-383.