Effects of Botanical Pesticides And Climate on the Lifecycle of Spodoptera Frugiperda (Lepidoptera: Noctuidae) on Maize in Côte D’ivoire

Abstract

Spodoptera frugiperda (Lepidoptera: Noctuidae), a new invasive insect pest of maize, has successfully established itself in Africa, particularly in Côte d'Ivoire. The management of this pest is mainly based on synthetic insecticides. Hence the need to develop an alternative, affordable and sustainable control method. This thesis aims to reduce the use of synthetic insecticides against S. frugiperda and to model its potential distribution in Côte d'Ivoire. The study conducted in two climatic zones (Sub-Sudanian and Guinean) allowed the collection of biodemographic parameters and population dynamics in these zones following the rearing of S. frugiperda in semi-natural conditions both in dry and rainy seasons. Then, the efficacy of aqueous extracts from 4 local plants (Ricinus communis, Azadirachta indica, Tephosia vogelii and Lippia multiflora) was tested against S. frugiperda. Finally, the current and future distribution of the pest in Côte d'Ivoire was modeled by MaxEnt according to the MIROC and BCC-CSM models for low (RCP 4.5) and high (RCP 8.5) emissions. Results showed that S. frugiperda is a holometabolous pest with a developmental cycle of six larval stages with high survival rates. Biological and demographic parameters were more important in the rainy season. Seasonal variations of S. frugiperda population in a maize field showed that the percentage of damage varied with phenological stages and seasons. The highest number of moths in Sub-Sudanian zone (131.25± 35.76) and Guinean zone (47.75± 27.87) were obtained during the rainy season at the whorl stage and the lowest in Sub-Sudanian zone (30.33 ± 13.05) and Guinean zone (4.67±1.45) at the maturation stage. The results of the bioactivity of local plants showed that they had toxic and anti-appetent effects on S. frugiperda. The highest mortality rate was caused by R. communis (65%) while the lowest rate (40%) was recorded with L. multiflora. In addition, A. indica produced the highest anti-appetent rate (90.05%). Regarding the distribution of the pest, the results showed that only the western part of Côte d'Ivoire is unsuitable for its development. Among the climatic parameters, the temperature remains the main factor of the distribution of S. frugiperda. The pest will not be able to proliferate in 2050 and 2070 in Côte d'Ivoire due to unfavorable climatic conditions for its development.