Repellent Effects of Selected Organic Leaf Extracts of Tithonia diversifolia (Hemsl.) A. Gray and Vernonia lasiopus (O. Hoffman) against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Abstract

Introduction. Sitophilus zeamais infestation is among the major setbacks to sustainable maize farming and availability. It causes an estimated annual loss of 5–10% and 20–30% of the total maize grains loss in the temperate and tropical zones, respectively. Although synthetic pesticides are quick and effective in managing crop pests, their overuse and misuse is discouraged due to their detrimental effects on human and environment. Natural pesticidal products that are extracted from plants are particularly gaining importance as an alternative to synthetic pesticides. They are available, easily biodegraded and have low toxicity to nontarget organisms. Most botanical pesticides act on insects by repelling them away from the crops in the field or in the stores. Therefore, this study aimed to determine repellency potential of organic leaf extracts of Tithonia diversifolia and Vernonia lasiopus on S. zeamais. Materials and methods. The phytochemical profile of T. diversifolia and V. lasiopus was determined using GC-MS. Laboratory-based experiments were carried out using area preference method to assess the efficacy of the extracts against weevils for a test period of 5 h. Six groups of experiments were set up with ten S. zeamais in each test: positive control (Actellic), negative control (solvent only), and four different experimental extract concentrations (25, 50, 75, and 100%). Results. The results indicated that T. diversifolia and V. lasiopus leaf extracts possess potent repellency effect on weevils. All the extracts simply discouraged S. zeamais from the treated areas recording significantly good levels of repellent activities between 26 and 96%. Furthermore, the GC-MS analysis manifested the presence of bioactive compound in the extracts which are associated with the repellency effects. Conclusion. The study scientifically confirms the traditional use of the T. diversifolia and V. lasiopus and provides important platform for further study on the extracts as bioresource of botanical repellent.

Evaluation of Toxicity of Some Tropical Flora, Clay and Permethrin against Sitophilus zeamais Motsch. on Stored Maize Grains

“…The poor performance of A. conyzoides and C. nardus powders against the weevils is associated with the volatilization of the active principle from sun-drying. The data from Table 1 to 3 are contrary to reports of an increase in insecticidal activities of plant extracts against target insects with concentration and contact time (Gitahi et al, 2021a;Gitahi et al, 2021b). Therefore, the active principle(s) may have lost efficacy due to denaturation by high heat or light intensity from exposure to sunlight.…”

“…For example, Terpeol and 3-carvene demonstrated high contact toxicity to C. maculatus and S. zeamais. At the same time, citral showed high fumigant toxicity to both insect pests (Oyedeji et al, 2020) and these active principles have acetylcholine impeding activities (Oyedeji et al, 2020;Gitahi et al, 2021b).…”

“…The study conducted by Gitahi et al (2021a) and Gitahi et al (2021b) reported that extracts of T. diversifolia and V. lasiopus have substantial insecticidal activities against S. zeamais. Furthermore, C. maculatus and S. zeamais were sensitive to extracts of Lavandula alba, Lavandula stoechas and Citrus sinensis (Oyedeji et al, 2020;Patiño-Bayona et al, 2021).…”

“…The efficacy of botanical pesticides is influenced by the type and concentration of the active ingredient(s), exposure to thermo or UV radiation and duration of exposure to the target pests (Ofuya and Dawodu, 2002;Ononuju et al, 2016). The insecticidal constituents of most flora are terpenes and EOs (Oyedeji et al, 2020;Gitahi et al, 2021b). For example, Terpeol and 3-carvene demonstrated high contact toxicity to C. maculatus and S. zeamais.…”

“…In Africa, formulations of Hyptis suaveolus and Mangifera indica inhibited oviposition, while the progeny emergence of Prostephanus truncatum and S. zeamais can protect treated maize grains (90%) for 5 months (Ngamo et al, 2007;Gariba et al, 2021). In Kenya, organic extracts of Tithonia diversifolia, Vernonia lasiopus and Jatropha curcas demonstrated significant toxicities against S. zeamais (Oyedeji et al, 2020;Gitahi et al, 2021a;Gitahi et al, 2021b). Furthermore, de Araújo et al (2019) reported strong insecticidal activities of C. citratus essential oils (Eos) against S. zeamais in Brazil.…”