The abusive use of synthetic pesticides in the phytosanitary protection of cotton in Côte d'Ivoire threatens the viability of the production system. The search for alternative control methods is therefore necessary. Phytosanitary strategies involving plant-based biopesticides have been explored. The insecticidal activity of essential oils of plant species of the genus Ocimum has been the subject of numerous investigations. The objective of this study is to compare the insecticidal potential of two species of the same genus Ocimum gratissimum and O. canum on a major cotton pest, the pink worm Pectinophora gossypiella. Adults of the insect were exposed in the laboratory to the toxic effect of different concentrations of these oils by topical application using a micro applicator. The lethal concentrations causing respectively 50 % (LC50) and 90% (LC90) death in the populations tested were determined for each of the essential oils. The oil extracted from O. gratissimum was the most toxic with LC50 and LC90 respective values of 1.01 % and 5.05 % as compared to O. canum (LC50 = 11.33 % and LC90= 30.04 %). The high toxicity of O. gratissimum may be explained by the presence of 24.57 % thymol and 37.79 % p-cimene in its chemical composition. The extract of O. gratissimum has shown in laboratory the highest potentiel insecticidal activity, it‘s field use can therefore be suggested for the control of this cotton pest.

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.

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.

23 Diversité floristique en culture d'ananas (Ananas comosus (L.) Merr.) en basse Côte d'Ivoire INVENTAIRE DE LA FLORE ADVENTICE EN CULTURE D'ANANAS (Ananas comosus (L.) MERR.) DANS LA LOCALITE DE BONOUA EN BASSE CÔTE D'IVOIRE