Phytochemical profiling, antioxidant activities, enzymatic activities and insecticidal potential of aqueous extracts of four plants on the larvae of Helicoverpa armigera (Lepidoptera: Noctuidae), the main pest of cotton plant in Ivory Coast.

In the context of climate change, the Ivorian cotton industry is facing with the loss of sensitivity of pests (Helicoverpa armigera) and the appearance of new so-called emerging insects. Faced with this situation, cotton producers tend to use insecticide products in high doses, in excess of the norm. However, the misuse of chemical products poses many health risks. Therefore, to limit the use of chemicals, aqueous extracts of local plants with insecticidal properties were examined in the laboratory and in the field. Four local plant species were selected [Anacardium occidentale (Anarcardier); Azadirachta indica (Neem); Hyptis suaveolens (Hyptis) and Tephrosia vogelii (Tephrosia)]. After determining the chemical profiles of the four extracts by high performance liquid chromatography (HPLC)-mass spectrometry, their inhibitory activities were assessed in cholinesterase and tyrosinase. The sensitivity of Helicoverpa armigera larvae was evaluated by ingesting the aqueous extracts at several concentrations ranging from 2% to 64% in an artificial nutrient substrate. Then, the mortality rates of the larvae during 72 h were evaluated and the lethal concentrations were determined. The results of chemical analyses (HPLC) showed that the richest aqueous extract in phytochemicals with 54 elements detected was that of cashew (A. occidentale). T. vogelii, A. indica and H. suaveolens presented 44, 45, and 39 chemical compounds, respectively. In addition, the total phenolic content was higher in A. occidentale (110.67 mg gallic acid equivalents/g) followed by A. indica (42.43 mg gallic acid equivalents/g). The highest antioxidant ability was observed with the aqueous extract of cashew (A. occidentale). Anti-enzymatic activities such as acetylcholinesterase, butyrylcholinesterase and tyrosinase inhibition were most pronounced in A. occidentale (2.35 ± 0.02 mg galanthamine equivalent/g, 3.77 ± 0.01 mg galanthamine equivalent/g and 71.28 ± 0.07 mg kojic acid equivalent/g, respectively). The most toxic aqueous extract for H. armigera larvae was that of cashew with a lethal concentration LC50 = 11.68%. Moreover, the principal component analysis performed showed that the insecticidal activity is strongly correlated with the antioxidant and enzymatic activities of the aqueous extracts. Then, the hierarchical ascending classification showed cashew as the best plant. For the sustainability of cotton production, it would be necessary to limit the use of chemical-synthetic insecticides through the use of plant extracts, especially from cashew leaves.

In Vitro and Molecular Docking Evaluation of Larvicidal Effects of Essential Oils of Five Aromatic Plants on the Fall Armyworm Spodoptera frugiperda JE. Smith (Lepidoptera: Noctuidae) from Ivory Coast.

Faced with the serious consequences resulting from the abusive and repeated use of synthetic chemicals, today rethinking crop protection is more than necessary. It is in this context that the essential oils of the Lamiaceae Ocimum gratissimum and Ocimum canum, the Poaceae Cymbopogon citratus and nardus and a Rutaceae Citrus sp. of known chemical compositions were experimented. The evaluation of the larvicidal potential of the essential oils was done by the method of topical application of the test solutions, on the L1-L2 stage larvae from the first generation of S. frugiperda obtained after rearing in an air-conditioned room. Lethal concentrations (LC10 , LC50 and LC90 ) were determined after 48 h. After assessing the larvicidal potential of essential oils, molecular docking was carried out to study protein-ligand interactions and their propensity to bind to insect enzyme sites (AChE). The essential oil of O. gratissimum was the most effective with the lowest lethal concentrations (LC10 =0.91 %, LC50 =1.91 % and LC90 =3.92 %). The least toxic oil to larvae was Citrus sp. (LC10 =5.44 %, LC50 =20.50 % and LC90 =77.41 %). Molecular docking revealed that p-cymene and thymol from O. gratissimum essential oil are structurally similar and bind to the AChE active site via predominantly hydrophobic interactions and a H-bond with Tyr374 in the case of thymol. The essential oil of O. gratissimum constitutes a potential candidate for the development of biological insecticides for the fight against insect pests and for the protection of the environment.

Chemical Composition, Antioxidant Activity, Cholinesterase Inhibitor and in Vitro Insecticidal Potentiality of Essential Oils of Lippia multiflora Moldenke and Eucalyptus globulus Labill. on the Main Carpophagous Pests of Cotton Plant in Ivory Coast.

The abusive and repeated use of synthetic chemical insecticides has proven to be harmful to human health and the viability of the cotton production system in Ivory Coast, so it is imperative to find alternatives. . Thus, the objective of this study was to study the chemical composition and biological activity of essential oils of Lippia multiflora (Verbenaceae) and Eucalyptus globulus (Myrtaceae) and to evaluate their insecticidal potential in the laboratory on three main pests of cotton. After essential oils extraction, their chemical composition was determined. Also, antioxidant activity and cholinesterase inhibitor of essential oils were evaluated. After that, different concentrations of the two essential oils were prepared and applied by contact on groups of insects constituted by ten. The essential oil of L. multiflora was the most toxic for the three pests tested. Indeed, the lethal concentrations (LC50 ) were 1.74 %, 1.39 and 7.20 %, respectively, on Pectinophora gossypiella, Thaumatotibia leucotreta and Helicoverpa armigera. In contrast, the values obtained with E. globulus essential oil were nine to two times greater (16.05 %, 10.23 % and 16.32 %, respectively on these pests). With respect to the chemical composition of the essential oils, E. globulus essential oil was the richest in oxygenated monoterpenes (65 %) with 1,8-cineole or eucalyptol as the majority compound (61.6 %). The essential oil of L. multiflora was distinguished by a lower proportion of oxygenated monoterpenes (44.3 %), but it contained more terpene elements (24 vs. 15 for the essential oil of E. globulus). The essential oils of L. multiflora and E. globulus also showed significant inhibition of acetyl (2.13 and 2.16 mg galantamine equivalent (GALAE)/g, respectively) and butyryl cholinesterase (4.03 and 3.61 mg GALAE, respectively). L. multiflora was differentiated by its good inactivation of tyrosinases (163.46 versus 58.95 mg kojic acid equivalent (KAE)/g in E. globulus). Better antioxidant activity was observed with L. multiflora essential oil relative to DPPH (7.05±0.34 mg trolox equivalent (TE)/g). Biopesticides based on L. multiflora essential oil could be developed for the phytosanitary protection of cotton plant.

Application of Essential Oils of Ocimum gratissimum and Cymbopogon citratus as Bioinsecticides for the Management of Two Major Biting-Sucking Insects (Bemisia tabaci Gennadius and Jacobiella fascialis Jacobi) and the Improvement of Seed and Fiber Quality of Cotton Plants in Ivory Coast.

In recent years, in all cotton production areas in Ivory Coast, whitefly (Bemisia tabaci) and jassid (Jacobiella facialis), two biting sucker insects were causing depreciation of quality of the cottonseed and fiber obtained at harvest. However, the excessive use of synthetic chemical insecticides against these pests presents a danger for the sustainability of the production system. This study aims to evaluate the insecticidal efficacy of essential oils of Ocimum gratissimum and Cymbopogon citratus on B. tabaci and J. fascialis and on the technological parameters of the cottonseed and fiber. A field experiment was conducted in which essential oils of O. gratissimum and C. citratus were applied to cotton plants every two weeks from day 45 to 115 after emergence using a backpack sprayer. The effects of these extracts were compared to those of a synthetic chemical insecticide composed of acetamiprid and alphacypermethrin known under the trade name IBIS A 52 EC (positive control). After 160 days of cultivation where entomological data were collected, the seed cotton samples were harvested, ginned and submitted for analysis. O. gratissimum essential oil at concentrations of 1 and 5 % gave to the cotton plants better protection against whiteflies and jassids. In addition to the synthetic chemical, these cotton plants received a better proportion of healthy cottonseed, fat and a fiber with very good reflectivity. The essential oil of O. gratissimum could therefore be integrated into the phytosanitary protection programs of the cotton plant.

Chemical Composition and Spectrum of Insecticidal Activity of the Essential Oils of Ocimum gratissimum L. and Cymbopogon citratus Stapf on the Main Insects of the Cotton Entomofauna in Côte d'Ivoire.

Among the alternatives to environmentally toxic and socio-economically unacceptable chemical pesticides, essential oils from Ocimum gratissimum and Cymbopogon citratus were tested on the main pests and beneficial insects of the cotton plant in Côte d'Ivoire. After extraction and chemical analysis of the essential oils, field trials were carried out using a Fisher block system with three treatment repetitions where their effects compared with those of a registered synthetic insecticide (IBIS A 52 EC). Foliar applications of the products were carried out in accordance with the cotton plant protection extension programme in Côte d'Ivoire from the 45th to the 115th day after plant emergence, with one application every fortnight. Twenty-three and forty compounds representing about 96 and 99 % of the oil composition of O. gratissimum and C. citratus respectively were elucidated. The most abundant compounds were p-cymene and thymol (O. gratissimum) and myrcene, neral and geranial (C. citratus). The essential oil of O. gratissimum at concentrations of 2 and 5 % showed insecticidal activity on all pests (biting-sucking and carpophagous), except the phyllophagous Syllepte derogata. C. citratus, at a low concentration (1 %), was particularly toxic to whiteflies (Bemisia tabaci), however, it favoured the action of beneficial insects, specifically black ants and ladybirds in the cotton plots, unlike the chemical product. EO of O. gratissimum (1.60 and 4.62 mg GALAE/g, respectively) and C. citratus (2.26 and 2.78 mg GALAE, respectively) exhibited also significant acetyl and butyryl cholinesterase inhibitors. Insecticide formulations based on the essential oils of O. gratissimum and C. citratus offer favourable prospects for their use in cotton cultivation as an alternative to chemical pesticides.

Annual and geographical variations in the specific composition of jassids and their damage on cotton in Ivory Coast.

In recent years, jassids have become a real problem for cotton growing in Ivory Coast. It is important to investigate the causes of this problem. The aim of this study was to highlight the diversity of jassid species and their impact on cotton growing in Ivory Coast. The collections carried out in 2021 identified three species. Jacobiasca lybica (Bergevin & Zanon, 1922) is the most abundant, with proportions ranging from 73.3 to 93.3% depending on the site. The other two species are Empoasca papayae (Oman, 1937) (8.3%) and Empoasca facialis (Jacobi, 1912) (5%). In 2022, collections revealed the invasion of a new species, Amrasca biguttula (Shiraki, 1913), which became dominant with proportions of 90 to 100% depending on the site. Two other species, Jacobiasca lybica (Bergevin & Zanon, 1922) (2.7%) and Empoasca facialis (Jacobi, 1912) (1.3%), cohabit with Amrasca biguttula (Shiraki, 1913). Thus, while the damage noted in 2021 was attributable to Jacobiasca lybica (Bergevin & Zanon, 1922), that observed in 2022 is essentially due to Amrasca biguttula (Shiraki, 1913), with incidences exceeding the economic impact threshold. The North-East of the cotton basin was the area most affected by attacks by these two species. The results of the study reveal significant changes in jassid species composition and climatic conditions in the cotton-growing areas of Ivory Coast, from 1 year to the next. This situation also explains the variations in damage levels.