The effects of annona formulations on mosquitoes and non-target invertebrates in the laboratory and semi-field conditions

Larvicidal efficacy of plant leaf ethanolic extracts, fractions and formulations of Annona squamosa, A. senegalensis and A. montana were evaluated against anopheline and culicine mosquitoes larvae in the laboratory and semi-field conditions in search an alternative to synthetic insecticides. The impacts of water parameters on the efficacy of the formulations and the impact of formulations on non-target invertebrates were assessed. Leaf extracts from Annona were fractionated by solvent-solvent extraction to get petroleum ether, dichloromethane, ethyl acetate, butanol and water fractions. Fine clay soil and rice husks were used in preparation of formulations at various ratios of crude extracts and leaf powders or rice husks using DMSO and ethanol as molding solvents. Extracts, fractions and formulations were evaluated against the mosquitoes larvae. The crude extracts of A. montana had the highest efficacy with LC50 values of 33.1 and 19.7 µg/ml against An. gambiae s.s and C. quinquefasciatus, respectively in 24 h. The dichloromethane fractions exhibited significantly higher efficacies than their crude extracts against both mosquito species. Ethanol based formulations showed a higher efficacy than those of DMSO. The fine clay soil formulation containing 70% of the plant powders performed better than the other ratios at100 µg/ml. In the semi-field environment, formulations containing A. montana leaf powder showed the highest efficacy against anopheline larvae but lowest against culicine. The formulations had minimal impact on non-target invertebrates. In conclusion, there formulations, with other studies might be used as an alternative to synthetic insecticides.