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Effect of inert dust on the mortality of Sitophilus zeamais (Coleoptera: Curculionidae)

Efeito de pós inertes na mortalidade de Sitophilus zeamais (Coleoptera: Curculionidae)

Abstract

The maize weevil, Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae), generally reaches pest status in stored grain. Chemical control is the most used method for population suppression, which can cause adverse impacts, thus creating a need for alternatives such as using inert powders. The present work aims to verify the effect of different concentrations of different types of inert powders on the mortality of S. zeamais in the laboratory. To this end, the experiments were carried out in a completely randomized design, with 13 treatments and four replications, ten adults per replication, where the effect of different inert powders (basalt powder, gypsum powder, and diatomaceous earth) was tested at concentrations of 0.025 g, 0.05 g, 0.1 g and 0.2 g/20 g of corn grains. Variance, normality, and homoscedasticity tests were applied in addition to controlling efficiency (CE%), median lethal time (TL50), and survival curves. All treatments caused mortality in S. zeamais, and all concentrations with diatomaceous earth were more efficient, with 100% mortality at 20 days, followed by the treatment of 0.2 g of gypsum powder/20 g of corn grains, with superior efficiency, to 95% in 20 days and 100% in 30 days. The results indicated that treatments with diatomaceous earth had the highest mortality rate and the best average survival time.

Keywords:
beetle; corn; alternative control; gypsum

Resumo

O gorgulho-do-milho, Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae), geralmente atinge o status de praga em grãos armazenados. O controle químico é o método mais utilizado para sua supressão populacional, podendo causar impactos adversos, surge assim a necessidade de alternativas como o uso de pós inertes. O presente trabalho tem como objetivo verificar o efeito de diferentes concentrações de diferentes tipos de pós inertes na mortalidade de S. zeamais no laboratório. Para tanto, os experimentos foram realizados em delineamento inteiramente casualizado, com 13 tratamentos e quatro repetições, 10 adultos por repetição. Onde testou-se o efeito de diferentes pós inertes (pó de basalto, pó de gesso e terra diatomácea), nas concentrações de 0,025 g, 0,05 g, 0,1 g e 0,2 g/20 g de grãos de milho. Sendo aplicados testes de variância, normalidade e homocedasticidade, além de eficiência de controle (CE%), tempo letal mediano (TL50) e curvas de sobrevivência. Todos os tratamentos causaram mortalidade em S. zeamais, e todas as concentrações com terra diatomácea foram mais eficientes com 100% de mortalidade aos 20 dias, seguido do tratamento de 0,2 g de pó de gesso/20 g de grãos de milho, com eficiência superior a 95% aos 20 dias e 100% em 30 dias. Os resultados indicaram que os tratamentos com terra diatomácea apresentaram a maior taxa de mortalidade e a melhor média em termos de tempo de sobrevivência.

Palavras-chave:
besouro; milho; controle alternativo; gesso

1. Introduction

The production of corn grains in Brazil is forecast at 116.1 million tons in 2024 (IBGE, 2024INSTITUTO BRASILEIRO DE GEOGRAFIA E ESTATÍSTICA – IBGE, 2024 [viewed 1 May 2024]. IBGE: safra de 2024 deve ser de 298,3 milhões de toneladas [online]. Available from: https://agenciagov.ebc.com.br/noticias/202404/estimativa-cai-0-8-e-preve-safra-de-298-3-milhoes-de-toneladas-em-2024
https://agenciagov.ebc.com.br/noticias/2...
). The good results of the agricultural output of stored grains are directly linked to the adoption of best storage, production, and protection practices, which are essential to guarantee the viability of production. This prevents losses after harvest and the product's devaluation (Lorini et al., 2015LORINI, I., KRZYZANOWSKI, F.C., FRANÇA-NETO, J.B., HENNING, A.A. and HENNING, F.A., 2015. Integrated pest management of stored grains and seeds. Brasília: Embrapa, 84 p.; Mussalama et al., 2023MUSSALAMA, A.Z., TEIXEIRA, C.M., NUNES, A.M., PEREIRA, C.M.P. and GARCIA, F.R.M., 2023. The action of clove (Syzygium aromaticum) and thyme (Thymus vulgaris) essential oils in the control of Acanthhoscelides obtectus (Coleoptera: Chrysomelidae) in a laboratory. Anais da Academia Brasileira de Ciências, vol. 95, no. 2, e20201915. http://doi.org/10.1590/0001-3765202320201915. PMid:37341267.
http://doi.org/10.1590/0001-376520232020...
).

Among the pests of stored grains is Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae), considered the main pest of stored corn grains (Trematerra et al., 2013TREMATERRA, P., IANIRO, R., ATHANASSIOU, C.G. and KAVALLIERATOS, N.G., 2013. Behavioral responses of Sitophilus zeamais Motschulsky adults to conditioned grain kernels. Journal of Stored Products Research, vol. 53, pp. 77-81. http://doi.org/10.1016/j.jspr.2013.02.005.
http://doi.org/10.1016/j.jspr.2013.02.00...
). This insect damages grains due to its ability to penetrate deeply into its mass to feed. After ovipositing, its larvae develop inside the grain (Nwosu, 2018NWOSU, L.C., 2018. Impact of age on the biological activities of Sitophilus zeamais (Coleoptera: Curculionidae) adults on stored maize: implications for food security and pest management. Journal of Economic Entomology, vol. 111, no. 5, pp. 2454-2460. http://doi.org/10.1093/jee/toy187. PMid:29982773.
http://doi.org/10.1093/jee/toy187...
), causing losses in final production and having high biotic potential (Lorini et al., 2015LORINI, I., KRZYZANOWSKI, F.C., FRANÇA-NETO, J.B., HENNING, A.A. and HENNING, F.A., 2015. Integrated pest management of stored grains and seeds. Brasília: Embrapa, 84 p.). In addition to favoring the production of mycotoxins from pre-existing fungi in corn grains (Ferreira-Castro et al., 2012FERREIRA-CASTRO, F.L., POTENZA, M.R., ROCHA, L.O. and CORREA, B., 2012. Interaction between toxigenic fungi and weevils in corn grain samples. Food Control, vol. 26, no. 2, pp. 594-600. http://doi.org/10.1016/j.foodcont.2012.02.016.
http://doi.org/10.1016/j.foodcont.2012.0...
) and contributing to the emergence of secondary pests, increasing the rate of damage to the final product (Alencar et al., 2011ALENCAR, E.R., FARONI, L.R.D., FERREIRA, L.G., COSTA, A.R. and PIMENTEL, M.A.G., 2011. Quality of corn stored and infested by Sitophilus zeamais and Tribolium castaneum. Engenharia Agrícola, vol. 19, no. 1, pp. 9-18.). This can result in post-harvest losses of around 15% in the field, 13 to 20% during grain processing, and between 15 and 25% in storage (Manandhar et al., 2018MANANDHAR, A., MILINDI, P. and SHAH, A., 2018. An overview of the post-harvest grain storage practices of smallholder farmers in developing countries. Engenharia Agrícola, vol. 8, no. 4, pp. 57.).

Chemical control with synthetic insecticides has been the most used method to control pests such as corn weevils (Kim et al., 2019KIM, B.S., SONG, J.E., PARK, J.S., PARK, Y.J., SHIN, E.M. and YANG, J.O., 2019. Insecticidal effects of fumigants (EF, MB, and PH3) towards phosphine- susceptible and -resistant Sitophilus oryzae (Coleoptera: Curculionidae). Insects, vol. 10, no. 10, pp. 327. http://doi.org/10.3390/insects10100327. PMid:31575082.
http://doi.org/10.3390/insects10100327...
). Fumigant insecticides are the most applied in Brazil (Jagadeesan et al., 2018JAGADEESAN, R., SINGARAYAN, V.T., CHANDRA, K., EBERT, P.R. and NAYAK, M.K., 2018. The potential of co-fumigation with phosphine (PH3) and Sulfuryl fluoride (SO2F2) for the management of strongly phosphine-resistant insect pests of stored grain. Journal of Economic Entomology, vol. 111, no. 6, pp. 2956-2965. http://doi.org/10.1093/jee/toy269. PMid:30239852.
http://doi.org/10.1093/jee/toy269...
; Ayres et al., 2021AYRES, V.F.S., OLIVEIRA, M.R., BALDIN, E.L.L., CORRÊA, G.M., GUIMARÃES, A.C. and TAKEARA, R., 2021. Chemical composition and insecticidal activity of the essential oils of Piper marginatum, Piper callosum, and Vitex agnus-castus. Anais da Academia Brasileira de Ciências, vol. 93, no. 3, e20200616. http://doi.org/10.1590/0001-3765202120200616. PMid:34287460.
http://doi.org/10.1590/0001-376520212020...
; Ortega et al., 2021ORTEGA, D.S., BACCA, T., SILVA, A.P.N., CANAL, N.A. and HADDI, K., 2021. Control failure and insecticide resistance in populations of Rhyzopertha dominica (Coleoptera: Bostrichidae) from Colombia. Journal of Stored Products Research, vol. 92, pp. 101-802. http://doi.org/10.1016/j.jspr.2021.101802.
http://doi.org/10.1016/j.jspr.2021.10180...
). However, several factors negatively impact its use, such as favoring the emergence of insect resistance to chemicals. Currently, weevils of the genus Sitophilus have been reported to exhibit moderate and robust resistance to pyrethroid-based insecticides (Singh et al., 2021SINGH, S.K., JAGADEESAN, R., THANGARAJ, S.R., SELVAPANDIAN, U., NAYAK, M.K. and SUBBARAYALU, M., 2021. Phenotypic and molecular analyses in rice weevil, Sitophilus oryzae (Linnaeus) (Coleoptera: Curculionidae): identification of a super kdr mutation, T929I, conferring resistance to deltamethrin. Pest Management Science, vol. 77, no. 7, pp. 3289-3299. http://doi.org/10.1002/ps.6373. PMid:33763965.
http://doi.org/10.1002/ps.6373...
).

Insect management alternatives are being studied and introduced in Brazil (Finkler, 2012FINKLER, C.L.L., 2012. Insect control: a brief review. Anais da Academia Pernambucana de Ciência Agronômica, vol. 8, no. 9, pp. 169-189.). Inert powders are a method that was already used in family farming even before the emergence of synthetic insecticides (Lorini, 1998LORINI, I., 1998. Integrated control of stored grain pests. Passo Fundo: Embrapa, no. 52.). Among the types of inert powders, diatomaceous earth stands out, as studies have shown that corn grains without diatomaceous earth control, when infested by the corn weevil, can, in two months, go from a type 1 quality classification (presenting fewer grains with defects) for a low standard classification to be sold (Antunes et al., 2013ANTUNES, L.E.G., FERRARI FILHO, E.F., GOTTARDI, R., SANT’ANA, J. and DIONELLO, R.G., 2013. Effect of dose and exposure to diatomaceous earth from different insects in stored maize. Arquivos do Instituto Biológico, vol. 80, no. 2, pp. 169-176. http://doi.org/10.1590/S1808-16572013000200005.
http://doi.org/10.1590/S1808-16572013000...
). However, diatomaceous earth generates some unwanted impacts on grains related to the interference of their physical and mechanical characteristics (Korunic et al., 2020KORUNIC, Z., LISKA, A., LUCIC, P., HAMEL, D. and ROZMAN, V., 2020. Evaluation of diatomaceous earth formulations enhanced with natural products against stored product insects. Journal of Stored Products Research, vol. 86, pp. 101-565. http://doi.org/10.1016/j.jspr.2019.101565.
http://doi.org/10.1016/j.jspr.2019.10156...
). Therefore, the milling industry is reluctant to treat grains with diatomaceous earth due to its abrasive nature and possible damage to the machine (Losic and Korunic, 2018LOSIC, D. and KORUNIC, Z., 2018. Diatomaceous earth, a natural insecticide for stored grain protection: recent progress and perspectives. In: D. LOSIC, ed. Diatom nanotechnology: progress and emerging applications. Cambridge: Royal Society of Chemistry Publishing, pp. 219-247.). Therefore, studies are needed to deepen knowledge about different types of inert powders. Thus, the present work aims to verify the effect of various concentrations of different inert powders on the mortality of S. zeamais in the laboratory.

2. Material and Methods

The study was conducted at the Laboratory of Insect Ecology (LABEI) Institute of Biology of the Federal University of Pelotas, Campus Capão do Leão, RS (IB - UFPEL). Corn grains (Zea mays) were purchased through local trade. These were previously sieved and disinfested after being frozen for seven days at -4 °C. They were then kept in glass containers covered with Voil fabric for ten days until reaching their hygroscopic balance, thus avoiding infestations of any pre-existing pest.

To obtain insects of the same age, 20 unsexed adult insects were placed in new glass containers containing corn grains for 15 days. Then, the corn grains with possible oviposition were separated to wait for the emergence of new specimens.

The experiment was carried out in a completely randomized design with 13 treatments, four replications, and four concentrations (Table 1). Each sample unit was composed of a transparent plastic container (60 mL), the lid having a circular opening sealed with Voile fabric and 20 g of corn kernels.

Table 1
Treatments with basalt powder, gypsum powder, and diatomaceous earth at concentrations of 0.025 g, 0.05 g, 0.1, and 0.2 g/20 g of corn grains and a control group used in an experiment to control Sitophilus zeamais in the laboratory.

Each experimental unit comprised 20 g of corn kernels (±12% moisture content). Each concentration of treatments was stirred for two minutes, and ten adult weevils were placed in the containers (± 14 days old) (Jairoce et al., 2016JAIROCE, C.F., TEIXEIRA, C.M., NUNES, A.M., HOLDEFER, D.R., KRÜGER, A.P. and GARCIA, F.R.M., 2016. Efficiency of inert mineral dusts in the control of corn weevil. Revista Brasileira de Engenharia Agrícola e Ambiental, vol. 20, no. 2, pp. 158-162. http://doi.org/10.1590/1807-1929/agriambi.v20n2p158-162.
http://doi.org/10.1590/1807-1929/agriamb...
). The insects in the grain mass were kept in a B.O.D. (Biochemical oxygen demand) under temperature of 28 ± 3 °C, relative humidity of 30 ± 10%, and photophase of 12h, the same conditions previously provided for the creation of weevils in the laboratory. The insect mortality analysis was carried out over 30 days every 24 hours after application. Insect mortality was quantified, which was verified when the insect showed no movement for two minutes upon stimulation with a soft, fine-tipped brush (Antunes et al., 2013ANTUNES, L.E.G., FERRARI FILHO, E.F., GOTTARDI, R., SANT’ANA, J. and DIONELLO, R.G., 2013. Effect of dose and exposure to diatomaceous earth from different insects in stored maize. Arquivos do Instituto Biológico, vol. 80, no. 2, pp. 169-176. http://doi.org/10.1590/S1808-16572013000200005.
http://doi.org/10.1590/S1808-16572013000...
).

2.1. Statistical analysis

Initially, the mortality data were submitted to the Shapiro-Wilk normality test and Bartlett's homoscedasticity of variances. Kruskal-Wallis non-parametric analysis of variance (ANOVA) with Dunn with post hoc Bonferroni correction (P<0.05) was used for data that did not meet the assumptions of normality and homogeneity of variances, even after transformations, by “Easyanova” and “Dunn. test” packages of R 4.0.0 software (R Development Core Team, 2020R DEVELOPMENT CORE TEAM, 2020 [viewed 13 December 2021]. R: a language and environment for statistical computing [online]. Vienna: R Foundation for Statistical Computing. Available from: https://www.r-project.org/
https://www.r-project.org/...
).

The mortality data, in percentage (%), of the treatments and the control, were also used to calculate the percentage of corrected mortality (%) [or control efficiency (%)], using the mortality correction formula of Schneider-Orelli (count of dead insects; the uniform population of insects in treatments) {[MC%= (%MTrat –%MTest)/(100 – MTest)*100]; where MC is the corrected mortality (%) as a function of the control, MTrat is the mortality (%) observed in the treatment, and MTest is the mortality (%) observed in control} (Püntener, 1981PÜNTENER, W., 1981. Manual for field trials in plant protection. 2nd ed. Basileia: Agricultural Division, Ciba-Gueigy Limited.).

In addition, to evaluate the survival over time (days) of the weevils exposed to the treatments, aiming at calculating the median lethal time (LT50), Kaplan-Meier estimators (Log-Rank method) and survival curves were used. Were compared using the Holm-Sidak test (P<0.05) using the SigmaPlot 12.3 software (Systat Software, San Jose, CA, USA).

3. Results

Most treatments (basalt, diatomaceous earth, and gypsum) differed from the control group (Table 2). At ten days after application, the treatments that most differed from the control group were T9 (0.025 g of diatomaceous earth/20 g of corn), T10 (0.05 g of diatomaceous earth/20 g of corn), T11 (0.1 g of diatomaceous earth/20 g of corn) and T12 (0.2 g of diatomaceous earth/20 g of corn), with efficiencies from 81.08 to 97.30%. However, treatments T1 (0.025 g of basalt/20 g of corn), T2 (0.05 g of basalt/20 g of corn), T3 (0.1 g of basalt/20 g of corn), and T5 (0.025 g of gypsum/20 g of corn) of corn) are equal to the control group, showing low efficiency.

Table 2
Mean mortality (m) ± standard error (SE) and efficiency of control (E%) of Sitophilus zeamais exposed to different dosages of basalt dust, gypsum, and diatomaceous earth in maize grains.

At 20 days after application, treatments T8 (0.2 g of gypsum/20 g of corn), T9 (0.025 g of diatomaceous earth/20 g of corn), T10 (0.05 g of diatomaceous earth/20 g of corn), T11 (0.1 g of diatomaceous earth/20 g of corn) and T12 (0.2 g of diatomaceous earth/20 g of corn) differed more from the control group, with efficiencies ranging from 97.30 to 100%. At 30 days after application, all treatments differed from the control, with efficiencies from 63.64 to 100%.

Treatments with diatomaceous earth had the highest mortality rate and the best average survival time. Among the treatments with gypsum powder, the concentration of 0.02 g/20 g of corn kernels (T8) caused the highest mortality in the shortest exposure time after the treatments related to diatomaceous earth, differing statistically from the other treatments.

There was a statistical difference between the mortality curves; all tested treatments showed significantly higher mortality than the control (Figure 1).

Figure 1
Survival curves of Sitophilus zeamais exposed to treatments with different doses of basalt powder, gypsum, and diatomaceous earth in the laboratory. Caption: T1- 0.025 g of basalt powder in 20 g of corn kernels (250 g/t); T2- 0.05 g of basalt powder in 20 g of corn kernels (500 g/t); T3- 0.1 g of basalt powder in corn kernels (1,000 g/t); T4- 0.2 g of basalt powder in 20 g of corn kernels (2,000 g/t); T5- 0.025 g of gypsum powder in 20 g of corn kernels (250 g/t); T6- 0.05 g of gypsum powder in 20 g of corn kernels (500 g/t); T7- 0.1 g of gypsum powder in 20 g of corn (1,000 g/t); T8- 0.2 g of gypsum powder in 20 g of corn kernels (2,000 g/t); T9- 0.025 g of diatomaceous earth in 20 g of corn kernels (250 g/t); T10- 0.05 g of diatomaceous earth in 20 g of corn kernels (500 g/t); T11- 0.1 g of diatomaceous earth in 20 g of corn kernels (1,000 g/t); T12- 0.2 g of diatomaceous earth in 20 g of corn kernels (2,000 g/t) and T13- Control (without added products).

In ten days of exposure, a control efficiency above 50% was achieved for the treatment with 0.2 g of gypsum in 20 g of maize (T8) in maize grains and an efficiency superior to 80% for all treatments related to diatomaceous earth.

Around 20 days, it was possible to observe a control efficiency greater than 50% for all treatments related to basalt powder, except for T1 (0.025 g/20 g of corn) with the lowest dosage; for the gypsum powder, all reached a percentage greater than 50% and the treatment with the highest dosage (T8 - 0.2 g/20 g of corn) reached a percentage greater than 80%, and 100% of control efficiency for the treatments with diatomaceous earth, except for T10 (0.05 g/20 g of corn), with 97.3%, but without statistical discrepancy between the others. At the end of the evaluation with 30 days of exposure, it was possible to reach a percentage greater than 80% for all treatments, except for T1 of 0.025 g of basalt powder in 20 g of corn grains, which reached a percentage greater than 60%, not differing statistically from the other treatments, despite not achieving a control efficiency above 80%, it is still an interesting percentage to test its influence on natural enemies in the future, leaving open as a possible alternative for use in the field to reduction of the pest insect population.

The average survival time (TL50) of weevil adults differed significantly between treatments (GL 12; X2 541.94; P< 0.001). Accounting for about 20 days for the treatments with basalt powder, the treatment of 0.2 g/20 g of corn (T4) reached the best average (15.07 days). The average for treatments with gypsum powder was 9 to 16 days, with the treatment of 0.2 g/20 g of corn (T8) reaching the best average, covering 9.82 days. For diatomaceous earth, the average was 4 to 8 days, with the best average related to the treatment of concentration 0.2 g/20 g of corn (T12) with 4.47 days (Table 3).

Table 3
Mean mortality time (TL50, in days) of Sitophilus zeamais exposed to different concentrations of basalt dust, gypsum, and diatomaceous earth in corn kernels.

4. Discussion

All treatments tested caused mortality in S. zeamais. However, in relation to basalt dust, the present study differs from the report by Jairoce et al. (2016)JAIROCE, C.F., TEIXEIRA, C.M., NUNES, A.M., HOLDEFER, D.R., KRÜGER, A.P. and GARCIA, F.R.M., 2016. Efficiency of inert mineral dusts in the control of corn weevil. Revista Brasileira de Engenharia Agrícola e Ambiental, vol. 20, no. 2, pp. 158-162. http://doi.org/10.1590/1807-1929/agriambi.v20n2p158-162.
http://doi.org/10.1590/1807-1929/agriamb...
, where, after 21 days of exposure, all treatments already differed from the control group, reaching mortality rates above 80%. However, at a dosage of 2,000 g/t after 29 days, mortality was greater than 80%, corroborating our results for the same dosage (Jairoce et al., 2016JAIROCE, C.F., TEIXEIRA, C.M., NUNES, A.M., HOLDEFER, D.R., KRÜGER, A.P. and GARCIA, F.R.M., 2016. Efficiency of inert mineral dusts in the control of corn weevil. Revista Brasileira de Engenharia Agrícola e Ambiental, vol. 20, no. 2, pp. 158-162. http://doi.org/10.1590/1807-1929/agriambi.v20n2p158-162.
http://doi.org/10.1590/1807-1929/agriamb...
).

The main component of basalt powder is silicon dioxide (Jairoce et al., 2016JAIROCE, C.F., TEIXEIRA, C.M., NUNES, A.M., HOLDEFER, D.R., KRÜGER, A.P. and GARCIA, F.R.M., 2016. Efficiency of inert mineral dusts in the control of corn weevil. Revista Brasileira de Engenharia Agrícola e Ambiental, vol. 20, no. 2, pp. 158-162. http://doi.org/10.1590/1807-1929/agriambi.v20n2p158-162.
http://doi.org/10.1590/1807-1929/agriamb...
), which can break the waxy layer of insects' epicuticles (Subramanyam and Roesli, 2000SUBRAMANYAM, B. and ROESLI, R., 2000. Inert dusts. In: B. SUBRAMANYAM and D.W. HAGSTRUM, eds. Alternatives to pesticides in stored-product IPM. Boston: Kluwer Academic Publishers, pp. 321-380.). As a result, it is expected that the use of basalt powder will penetrate the superficial wax layer of the insect, breaking the layer of lipids that protects it and finally resulting in the insect's death due to the organism's loss of liquids (Jairoce et al., 2016JAIROCE, C.F., TEIXEIRA, C.M., NUNES, A.M., HOLDEFER, D.R., KRÜGER, A.P. and GARCIA, F.R.M., 2016. Efficiency of inert mineral dusts in the control of corn weevil. Revista Brasileira de Engenharia Agrícola e Ambiental, vol. 20, no. 2, pp. 158-162. http://doi.org/10.1590/1807-1929/agriambi.v20n2p158-162.
http://doi.org/10.1590/1807-1929/agriamb...
).

The composite gypsum from gypsum rock has interesting characteristics such as rapid hardening, mechanical strength, and adherence (Aragão, 2005ARAGÃO, M.M., 2005 [viewed 30 January 2022]. Materiais de construção II: aglomerantes: gesso: especificações e propriedades [Construction materials II: binders: gypsum: specifications and properties] [online]. Available from: http://aquarius.ime.eb.br/~moniz/matconst2/gesso
http://aquarius.ime.eb.br/~moniz/matcons...
). Gypsum treatments showed efficiencies close to diatomaceous earth treatments, as dosages of 0.1 and 0.2 g of gypsum per 20 g of corn kernels did not differ statistically from diatomaceous earth treatments. Gypsum at low concentrations is also effective in killing bean weevil, Zabrotes subfasciatus (Boheman, 1833) (Coleoptera: Chrysomelidae) (Carvalho, 2008CARVALHO, L.H.T., 2008. Insecticidal activity of vegetable powders and gypsum against bean weevil, Zabrotes subfasciatus (Boheman, 1833) (Coleoptera: Chrysomelidae). Rio Largo: Universidade Federal de Alagoas, 96 p. Dissertação de Mestrado em Agronomia.), similar to the results of our study. It was observed that larvae of the Lepidoptera species Apodemia longer fed on plants covered with gypsum powder have a 4.8 times greater tendency to die than control larvae in a study carried out to evaluate the response of these endangered larvae; it concluded that gypsum powder is capable of directly affecting populations of Lepidoptera larvae through mortality, as well as reducing development rates about low weight and prolongation of their development (Osborne and Longcore, 2021OSBORNE, K.H. and LONGCORE, T., 2021. Effect of gypsum dust on lepidopterous larvae. Ecotoxicology and Environmental Safety, vol. 228, pp. 113027. http://doi.org/10.1016/j.ecoenv.2021.113027. PMid:34861439.
http://doi.org/10.1016/j.ecoenv.2021.113...
).

In another research, the average lethal time using gypsum powder was evaluated in Diabrotica duodecimpunctata, known as cucumber beetles, and thus reported that gypsum powder was more lethal when compared to bentonite clay and less lethal when compared to kaolin (Richardson and Glover, 1932RICHARDSON, C.H. and GLOVER, L.H., 1932. Some effects of certain “inert” and toxic substances on the twelve-spotted cucumber beetle, Diabrotica duodecimpunctata (Fab.). Journal of Economic Entomology, vol. 25, no. 6, pp. 1176-1181. http://doi.org/10.1093/jee/25.6.1176.
http://doi.org/10.1093/jee/25.6.1176...
). However, when they diluted gypsum and clay powder, they found it lethal for termites (Wagner and Ebeling, 1959WAGNER, R.E. and EBELING, W., 1959. Lethality of Inert Dust materials to Kalotermes minor hagen and their role as preventives in structural pest control. Journal of Economic Entomology, vol. 52, no. 2, pp. 208-212. http://doi.org/10.1093/jee/52.2.208.
http://doi.org/10.1093/jee/52.2.208...
).

Recently, a study exposed the larval and adult stages of the beetle Callosobruchus maculatus to gypsum dust for three days, showing a mortality rate of 8.4 to 16.9% for larvae and 38.4 to 43.7% for adults on filter paper (Sulaiman and Obaid, 2019SULAIMAN, A.K. and OBAID, H.M., 2019. Studying the effect of surfaces treated with inert dust on Callosobruchus maculatus (Fab). Journal of Entomology and Zoology Studies, vol. 7, pp. 793-795.). Previously, it was reported that sprinkling Apodemia virgulate Lepidoptera adults with gypsum powder from the factory adjacent to the National Wildlife Refuge at Antioch Dunes resulted in a three-day reduction in survival after capture relative to butterflies that were not exposed to gypsum powder (Clause et al., 2015CLAUSE, A., JOHNSON, J.J. and LONGCORE, T., 2015. Effect of exposure to gypsum dust on survival of Behr’s metalmark. Los Angeles: UWG, pp. 1-4.).

Mortality of S. zeamais increases with increasing exposure time in all treatments used in this study. In addition to the increase in the applied dose, it reduces the insect's exposure time until death occurs. Corroborating studies on the control of S. zeamais when using other alternative products (Radünz et al., 2024RADÜNZ, A.L., RADÜNZ, M., BIZOLLO, A.R., TRAMONTIN, M.A., RADÜNZ, L.L., MARIOT, M.P., COTO DO TEMPLO, H.E., CALISTO, J.F.F., ZANIOL, F., ALBENY-SIMÕES, D., REZENDE, R.S. and DAL MAGRO, J., 2024. Insecticidal and repellent activity of native and exotic lemongrass on Maize weevi. Brazilian Journal of Biology = Revista Brasileira de Biologia, vol. 84, e252990. http://doi.org/10.1590/1519-6984.252990.
http://doi.org/10.1590/1519-6984.252990...
). Diatomaceous earth stood out among basalt and gypsum powders, with treatments reaching 100% mortality in the first days, as observed by Jairoce et al. (2016)JAIROCE, C.F., TEIXEIRA, C.M., NUNES, A.M., HOLDEFER, D.R., KRÜGER, A.P. and GARCIA, F.R.M., 2016. Efficiency of inert mineral dusts in the control of corn weevil. Revista Brasileira de Engenharia Agrícola e Ambiental, vol. 20, no. 2, pp. 158-162. http://doi.org/10.1590/1807-1929/agriambi.v20n2p158-162.
http://doi.org/10.1590/1807-1929/agriamb...
, where the dosage of 2,000 g/t had 100% mortality on the fifth day of exposure. Despite the high mortality at diatomaceous earth concentrations with good mean lethal time (TL50) in this study, it differed from other studies. For Ribeiro et al. (2018)RIBEIRO, L.P., LOVATTO, M. and VENDRAMIM, J.D., 2018. Evaluation of the effectiveness of two commercial formulations of diatomaceous earth in the control of the maize weevil based on toxicological parameters. Agropecuária Catarinense, vol. 31, no. 1, pp. 56-60. http://doi.org/10.22491/RAC.2018.v31n1.7.
http://doi.org/10.22491/RAC.2018.v31n1.7...
, using the same species of weevil in their research, the average lethal time it was ranged between 1.86 and 2.18 days with concentrations of 0.1 and 0.2 g of diatomaceous earth for 20 g of corn (1,000 and 2,000 g/t), while for this study the oscillation in these concentrations was between 4.47 and 5.70 days.

Dosages of 0.1 and 0.2 g of diatomaceous earth/20 g of corn were higher than 90% after ten days of exposure and 100% after 20 days, corroborating other studies involving the same dosages with humidity of 12% (Antunes et al., 2011ANTUNES, L.E.G., VIEBRANTZ, P.C., GOTTARDI, R. and DIONELLO, R.G., 2011. Physicochemical characteristics of maize grains attacked by Sitophilus zeamais during storage. Revista Brasileira de Engenharia Agrícola e Ambiental, vol. 15, no. 6, pp. 615-620. http://doi.org/10.1590/S1415-43662011000600012.
http://doi.org/10.1590/S1415-43662011000...
, 2013ANTUNES, L.E.G., FERRARI FILHO, E.F., GOTTARDI, R., SANT’ANA, J. and DIONELLO, R.G., 2013. Effect of dose and exposure to diatomaceous earth from different insects in stored maize. Arquivos do Instituto Biológico, vol. 80, no. 2, pp. 169-176. http://doi.org/10.1590/S1808-16572013000200005.
http://doi.org/10.1590/S1808-16572013000...
). The 500 g/t dosage of diatomaceous earth also drew attention, as in the study by Ceruti et al. (2008)CERUTI, F.C., LAZZARI, S.M.N., LAZZARI, F.A. and PINTO JUNIOR, A.R., 2008. Efficacy of diatomaceous earth and temperature to control the maize weevil in stored maize. Scientia Agraria, vol. 9, no. 1, pp. 73-78. http://doi.org/10.5380/rsa.v9i1.10138.
http://doi.org/10.5380/rsa.v9i1.10138...
, who observed 90% mortality of S. zeamais with this concentration. The lowest diatomaceous earth concentration (0.025 g/20 g) provided mortality more significant than 80% after ten days of evaluation, indicating that the lowest concentration used has good efficiency (Riedo et al., 2010RIEDO, I.C., NEITZKE, J. and DE OLIVEIRA, N.C., 2010. Control of Sitophilus zeamais (Coleoptera: Curculionidae) in maize (Zea mays L.) treated with diatomaceous earth. Applied Research & Agrotechnology, vol. 3, no. 1, pp. 185-188.). Currently, other studies continue to prove the efficiency of diatomaceous earth, such as, for example, research with three different types of products based on improved diatomaceous earth, carried out in Ghana in Africa, where it was reported that the product InsectoSec® caused more mortality in adults of S. zeamais, followed by Fossil Shield and Diatomenerde Probe-A (Adarkwah et al., 2022ADARKWAH, C., TUDA, M., ADJEI, R., OBENG-OFORI, D., ULRICHS, C. and SCHÖLLER, M., 2022. Evaluation of three German-enhanced diatomaceous earth formulations for the management of two major storage pests in Ghana. Journal of Stored Products Research, vol. 96, pp. 1-2. http://doi.org/10.1016/j.jspr.2022.101947.
http://doi.org/10.1016/j.jspr.2022.10194...
).

According to Garcia (2014)GARCIA, F.R.M., 2014. Zoologia agrícola: manejo ecológico de peagas. 4ª ed. Porto Alegre: Editora Rígel., it is recommended that a product has at least 80% efficiency in controlling a pest; in this sense treatments with diatomaceous earth T9 (0.025 g/20 g of corn), T10 (0.05 g/20 g of corn), T11 (0.1 g/20 g of corn) and T12 (0.2 g/20 g of corn) at ten days, adding to the previous treatments for the 20 days T8 (0.2 g of gypsum in 20 g of corn) and at thirty days, all treatments tested except T1 of 0.025 g of basalt powder in 20 g of corn (63.64%) reached this recommendation level. This can be considered a quick result, considering that, for example, female maize weevils can survive an average of 140 days, of which 104 are oviposition days. Mortality in this time frame can significantly reduce the number of new infestations, reducing the time for females to perform new oviposition (Lorini and Schneider, 1994LORINI, I. and SCHNEIDER, S., 1994. Stored grain pests: research results. Passo Fundo: Embrapa, no. 47.).

The three types of dust (basalt, gypsum, and diatomaceous earth) at certain concentrations become efficient in controlling S. zeamais. With the passage of time and increased concentration, this efficiency tends to increase. However, the treatments with diatomaceous earth were the ones that presented the best cost-benefit ratio since its toxicity is already known, followed by the treatment with 0.2 g/20 g of gypsum powder in corn, which has a very low cost to acquire. However, its content of toxicity to non-target beings is still not completely clarified. With all this, research must continue to be carried out to improve the investigation of the application logistics so that the producer can safely practice using these substances as an alternative to control insect pests of stored grains.

5. Conclusions

The results show that the mortality of Sitophilus zeamais increases according to the period in which the insect is exposed to different types of inert dust. The highest mortality rates were obtained in the period of 11, 21, and 28 days with the application of diatomaceous earth (T10 - 0.05 g/20 g of corn), gypsum powder (T8 - 0.2 g/20 g of corn) and basalt powder (T4 - 0.2 g/20 g of corn), respectively. Therefore, these three treatments can be used as an effective control for S. zeamais.

Acknowledgements

To CAPES (Finance Code 001) for granting Master's Scholarships from MGCEG and a doctoral scholarship from KJ. The publication of this article received partial support from PRPPG/UFPel and CAPES/The publication of this paper was partially supported by PRPPG/UFPel and CAPES.”

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Publication Dates

  • Publication in this collection
    05 Aug 2024
  • Date of issue
    2024

History

  • Received
    24 Nov 2023
  • Accepted
    03 May 2024
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