ABSTRACT

Mosquitoes are the number one vector involved in the transmission of human diseases responsible for human debility and mortality. Crude extracts of Carica papaya (CP) and Dacryodes edulis (DE) have been indicated as having effects on larval mortality. This work was designed to evaluate the larvicidal activities of three solvent extracts and fractions of the seeds, leaves, stems and roots of both plants against the larvae of Aedes vittatus, Anopheles gambiae and Culex quinquefasciatus by standard methods. A standard method was also adopted to determine the growth inhibitory and acetylcholinesterase inhibitory activities. Their effects on a non-target organism were determined and structural analyses of their active principle(s) by FTIR, GCMS and NMR were carried out. Preliminary studies on the crude extracts at 500ppm showed the ethanol and hexane extracts of the seeds and leaves of CP and DE had significant (p<0.05) larvicidal activites against the larvae of all three species. Extracts with mortality above 70% against at least two of the three species were assayed for their LC50 and LC90 values with concentrations of 6.25-400ppm and showed time-dependant increases in activity at 12h, 24h and 48h. The ethanol extract of the seeds of CP gave LC50 values of 100.00, 62.24 and 262.14ppm at 48h against the larvae of Aedes vittatus, Anopheles gambiae and Culex quinquefasciatus respectively. The corresponding values for the hexane extract of the seeds of CP were 61.47, 111.76 and 264.78ppm. The ethanol and hexane extracts of the leaves of CP gave LC50 values of 93.19 and 48.14ppm against Aedes vittatus while against Anopheles gambiae the values were 40.80 and 29.32ppm. The LC50 values of ethanol and hexane extract of CP against Culex quinquefasciatus were 43.96 and 74.83ppm.The ethanol extract of the seeds of DE had the lower LC50 value of 150.54, 85.99 and 110.18ppm against the larvae of Aedes vittatus,