Insecticidal and Antifungal Activities of Chemically-Characterized Essential Oils from the Leaves of Withania frutescens L.

The current study was conducted to investigate antifungal and insecticidal activities of essential oil extracted from the Moroccan Withania frutescens L. (EOW), and their chemical composition was profiled. To achieve this goal, EOW was extracted by the hydro-distillation method and their phytochemical constituents were characterized by gas chromatography-mass spectrometry analyses (GC-MS). Insecticidal activity was evaluated by use of four tests: contact toxicity, inhalation toxicity, and repellent tests. Antifungal activity was evaluated on Fusarium oxysporum f. sp. Ciceris (F. oxysporum) using different concentrations of EOW. GC/MS analysis revealed that EOW was rich in carvacrol (31.87%), thymol (30.08%), and camphor (9.13%). At a 1-µL/L dose, EOW exhibited mortality rates of 23.13 ± 1.07% and 24.41 ± 1.21% against Callosobruchus maculatus (C.maculatus) by inhalation and contact, respectively. Notably, EOW dose of 20 μL/L caused significant mortality rates of 95.1 ± 3.5% and 76.69 ± 1.71% by inhalation and contact, respectively. EOW exhibited an inhibitory effect on mycelial growth against the tested fungi F. oxysporum of 100% and 93.5 ± 1.1% for the 9 and 4.5 mg/mL doses, respectively. The reduced mycelial growth rate for F. oxysporum was recorded to be 0.3 ± 0.1 and 0.6 ± 0.1 mm/h for the EOW doses of 2.25 and 4.5 mg/mL, respectively. The outcome of the present work showed that EOW has a promising antifungal and insecticidal activity, and it can therefore be employed as a natural alternative insecticidal and mycocidal agent to replace the chemically-synthesized ones.

Effect of Cowpea Seed Beetle (Callosobruchus maculatus) Infestation on Selected Landraces of Bambara Groundnut During Storage

The study was carried out to assess the effect of Callosobruchus maculatus infestation on selected Bambara groundnut (Vigna subterranean) landraces in Gombe during storage to determine the Landrace (s) that are less susceptible to infestation caused by C. maculatus during storage. The trial was done in the Botany laboratory of Gombe State University, Gombe. Seeds were collected from five different Landraces, 40 grams each of healthy and C. maculatus infestation free seeds were infested with two males and three females. Completely Randomized Design (CRD) with three replicates was used to assess the effects of C. maculatus infestation on the selected landraces of Bambara groundnut during storage. The results of the analysis of variance displayed significant differences (p≤ 0.05) among the parameters studied. It indicated that the Mottled and Cream landraces are relatively less susceptible and witness lower damage from the bruchids attack 14.6 (36%) and 17 (46%), whereas Red and Black landraces are more susceptible 24 (61 %) and 22 (57 %) (recorded higher damage from the C. maculatus in terms of percentage weight loss recorded). These results showed the existence of variation among the different Bambara groundnut landraces used due to the infestation of C. maculatus. It can be observed from this study that the use of infestation free landraces at storage time may perhaps be a worthwhile and auspicious factor for integrated pest management especially on bruchids in Bambara groundnuts. additionally, Mottle and Cream landraces might be employed as sources of resistance genes for the subsequent plant improvement program.

Susceptibility of different life stages of Callosobruchus maculatus and Callosobruchus chinensis to ECO2FUME gas and its impact on cowpea seeds quality

ECO2FUME gas is an alternative to toxic phosphine fumigant and as a quarantine treatment for the control of a particularly recalcitrant pest, Callosobruchus maculatus and Callosobruchus chinensis. This gas was used to fumigate stored cowpea piles under gas-proof sheets to assess its performance against different developmental stages of Callosobruchus maculatus and Callosobruchus chinensis. The mortality was determined on four developmental stages of C. maculatus and C. chinensis, employing ECO2FUME at different concentrations 25, 30, 40, and 50 g/m3 for 3-days. All stages of both insect species in packed cowpea stacks were completely controlled at 3-days when applied with an ECO2FUME application rate of 50 g/m3. Cases of pupae of C. maculatus and C. chinensis exhibit the highest resistance than other stages, with 78.2 and 73.93% mortality respectively, at 40 g/m3 after 3-days post-exposure to ECO2FUME. Suppression of F1 generation was obtained after fumigation with the same concentration (50 g/m3). Quality (in terms of cowpea germination) and all chemical constituents of cowpea seeds were non significantly (P≤0.05) affected by the fumigation concentration of 50 g/m3.

Biological activities and chemical composition of Mentha piperita and Syzygium aromaticum essential oil fractions against cowpea weevil, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae)

Callosobruchus maculatus (Fabricius) is one of the major, common, pests of stored grains as it causes quantitative and qualitative losses in legume crops. This research sought to find the most active fraction in Mentha piperita and Syzygium aromaticum essential oils, to evaluate bioactivity of those crude essential oils and active fractions against C. maculatus, and to identify the compounds contained in the active fraction. The essential oils were fractionated using three solvents, namely n-hexane, ethyl acetate, and methanol. The n-hexane fraction was identified as the active fraction, causing mortality, oviposition deterrence, and ovicidal effects. In fumigation chambers, LD95 values of M. piperita (Mnf) and S. aromaticum n-hexane fractions (Snf) were 0.045 ml/l and 0.057 ml/l respectively. ED50 values for oviposition deterrence were 0.016 ml/l for Mnf and 0.022 ml/l for Snf. ED50 value of ovicidal effects for Mnf- and Snf-treated eggs were 0.014 ml/l for both fractions. GC-MS analysis showed 8 dominant compounds in Mnf and 5 dominant compounds in Snf. Overall it is concluded that Mnf and Snf oils have effective biological activities against stored pest C. maculatus and have potential to be considered as alternatives to synthetic insecticides.