Insecticidal and Repellent Effects of Azadirachta indica and Calotropis procera Extracts on Bactrocera dorsalis in Senegal

Abstract

The introduction of new regulations in the field of food safety has resulted in the withdrawal of numerous synthetic active substances from the market, due to their unacceptable adverse effects on human and animal health. The aim of this work is to study the insecticidal or insect repellent effect of two plants on the fruit fly Bactrocera dorsalis, with a view to using them as alternatives to synthetic pesticides. Therefore, Azadirachta indica (A. indica) and Calotropis procera (C. procera), two species that are very abundant in almost all regions of Senegal, were chosen. Extractions of leaf and bark powders from the two plants were carried out using methanol and acetone as solvents. This study showed that extraction yields were higher for leaves than for barks, regardless of the species studied. Phytochemical characterisation of the extracts from plant organs for these two species revealed the presence of several secondary metabolites (alkaloids, flavonoids, tannins and terpenoids), in different proportions. These different metabolites showed no insecticidal effect against this fly. On the other hand, the greater or lesser presence of these secondary metabolites in the different species studied resulted in insect repellent effects. For Azadirachta indica, acetone is more appropriate for extracting leaves, whereas methanol seems to be the most appropriate for bark. However, for Calotropis procera, the opposite effect was obtained. In Azadirachta indica, the terpenoid content is higher in the crystalline and non-crystalline leaf fractions (++) than in the non-crystalline bark fractions (+). In both cases, it was found that P-value = 0.039 < 0.05, indicating that both tests were significant. Indeed, in the case of Azadirachta indica, a repellent action was observed against flies, while in the case of Calotropis procera, an attractive action was noted. These insect repellent effects were obtained using methanolic and acetone extracts of A. indica and C. procera leaves at doses of 5, 10 and 20 mg/mL, respectively. Thus, these two plants studied can be used as alternatives to insecticides in the control of the Bactocera dorsalis fly, which devastates mangoes.