Evolution spatiale et temporelle des dégâts du jasside Jacobiella facialis Jacobi, 1912 (Cicadellidae) Mots clés : Jasside, pluviométrie, évolution spatio-temporelle, cotonnier, protection, Côte d'Ivoire. KONE et al. / Int. J. Biol. Chem. Sci. 11(3): 1190-1201, 2017 1191 Spatial and temporal variation of the injury levels of jassid Jacobiella facialis Jacobi, 1912 (Cicadellidae) in relation to rainfall variation for the last two decades in the cotton growing area of Côte d'Ivoire ABSTRACT Jassid Jacobiella facialis is a sucking pest of cotton in Côte d'Ivoire. For the last decades, its attacks are persistent throughout the entire crop cycle despite insecticide treatments. This study aimed at analyzing the spatial and temporal distributions of pest damage in relation to rainfall trends over the past two decades. From 1993 to 2015, pest and rainfall surveys were carried out through a network involving more than 300 fields. Data revealed an annual variation in the pest damage levels, fluctuating between 0.52 and 6.01 attacked plants for 30 explains significantly the resurgence of the pest. In fact, the distribution of high pest pressure in the Northeast corresponds, during the last decade, particularly to rainfalls lower than 320 mm. This suggests the development of a new strategy for effective management of J. facialis. P. W. E.

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.

Objective: The study of the spatio-temporal evolution of the infestations of whitefly Bemisia tabaci (Aleyrodidae) aims to acquire bioecological data exploitable in the fight against the whitefly in cotton growing of Cote d'Ivoire. Methodology and results: Average levels of infestation (NMI) were estimated from 2003 to 2015 for the entire North and South zones of cotton production. Ten (10) cotton producer plots were randomly selected by locality. The number of adult insects per plot was counted on a sample of 30 plants. These weekly surveys revealed seasonal, spatial and annual variations in B. tabaci infestations. The results showed a proliferation of B. tabaci in cotton growing in Côte d'Ivoire. B. tabaci is present from the beginning to the end of the cotton growing cycle. Strong B. tabaci outbreaks occur on average from the 96th day after seedling emergence (DAS). June cotton seedlings are heavily exposed. The insect showed a strong presence in the northeast of the cotton zone. Conclusion and application : The phytosanitary protection programs for cotton appear to have a low control of B. tabaci. A revision of the phytosanitary protection strategy for cotton is therefore necessary. Insecticidal leaf treatments carried out from the 30 th to the 45 th DAS will have to integrate aleurodicidal products in order to limit the proliferation of whiteflies at the beginning of cultivation, especially in the northeast zone. Synchronized seedlings in an area would prevent the transfer of insects to younger plants and thus greatly reduce B. tabaci infestation levels.

Variations in populations of arthropod pests, under the influence of climate change, compromise the effectiveness of the cotton phytosanitary protection strategy in Côte d'Ivoire. This study aims to establish a new classification of cotton production areas, on the basis of predominant pests. A monitoring was therefore carried out from 2016 to 2019 in 400 farmers' fields. In these fields, surveys were conducted weekly, from the 30th to the 122nd day after emergence. Data analysis, through Principal Component Analysis, identified four groups of localities. The first group includes the northeastern localities (4°W to 5°W: 8°N to 10.5°N) such as Kong, Ouangolodougou, Sordi, Tiékpè, Kaouara. This area is characterized by high infestations of most pests (jassid, white flies, exocarpic lepidoptera, endocarpic lepidoptera, phyllophagous lepidoptera and mites). The second group is intermediate between northeast and central (5.5°W to 6.2°W: 8.3°N to 10.5°N). This area is characterized by infestations of jassid, white flies and exocarpic lepidoptera (H. armigera and D. watersi). It remains less infested by endocarpic lepidoptera (T. leucotreta and P. gossypiella). The third area is located in the South (4.5°W to 8.5°W: 6°N to 8.5°N). It is essentially infested by endocarpic lepidoptera T. leucotreta and P. gossypiella. Jassid and whitefly infestations are less important in this part, compared to the northern part. The fourth and last area extends from the center to the west (6°W to 8°W: 8°N to 10.5°N). Pest infestations are lower in this area compared to other areas.