In order to update knowledge on the spatio-temporal evolution of Helicoverpa armigera, the geographical areas and the seasons of predilection of adult and larval populations have been studied in the last six years from 2012 to 2017. Monitoring of natural adult populations in different locations has established that populations are more abundant in South cotton production areas compared to the north. The most important outbreaks occurred in two phases (August and Mid-October to Mid-November. The monitoring of larval populations carried out on farm scale showed that infestations started on cotton early August and increased in September and October, reflecting a strong relationship between the evolutions of adult populations, larval infestations and cotton phenology. Late sowings D5 and D6 exhibited higher levels of infestation (0.213 to 0.762 larvae/30 plants) as compared to early sowing (0.21-0.31 larvae/30 plants). Annual variations of pest infestation levels increased from years to years, fluctuating from 0.008 to 0.024 larvae/30 plants over the study period. Mapping of the geographic distribution of infestation showed more severe pest pressure in the North East and South East cotton areas particulary in mostly in surrounding areas of Niakara, Ouangolo, Niellé and Bouaké (1.02 ; 0.86 ; 0.83 and 0.74 larvae/30 plants). With regard to the emerging status of H. armigera over recent years, the current pyrethroid resistance management strategy deserves to be improved on the basis of the pest geographic and seasonal profiles.

In Côte d'Ivoire, the loss of cotton yield is mainly due to attacks caused by pest insects such as, the pink worm, Pectinophora gossypiella Saunders. For decades, the repeated use of chemical insecticides to control these pests has threatened the viability of the production system. Faced with the negative consequences linked to the use of synthetic chemicals, the search for alternative methods is essential. The objective of this study is therefore to evaluate the chemical properties and the insecticidal activity of essential oils extracted from Cymbopogon citratus, Cymbopogon nardus and Citrus sp on P. gossypiella. In the laboratory, nine concentrations (0.25; 0.50; 1; 2; 4; 8; 16; 32 and 64 %) for each of the three essential oils, with three replications, were tested by topical application method on adults of the pest using a micro-applicator. Results showed that the pest developed variable levels of sensitivity to those plant oils. The one extracted from C. citratus was the most toxic to P. gossypiella. The lethal concentrations (LC50 and LC90) measured were 1.67 and 4.07 % respectively. Furthermore, the results of the gas chromatography coupled mass spectrometry (GS/SM) analysis indicated that the essential oils of the three aromatic plants evaluated were strongly composed of monoterpenes (91.57-100 %). C. citratus extract was the richest in oxygenated monoterpenes (73.71 %) followed by C. nardus extract (46.59 %). The essential oil of C. citratus can be used rationally as an alternative option to chemical in the current cotton pest control program in Côte d’Ivoire.