A Comparative Study Of The Effects Of Melia Volkensii (Gurke) Extracts And Azadirachtin On Growth And Oviposit I On Of Pedes Pegypti L. (Diptera: Culicidae

Abstract

.Three fractions and one compound from melia volkensii (Gurke) were tested for toxicity and growth inhibition effects against the second instar larvae of j:}edes aegypti L. in the laboratory. Their effects were compared with that of a natural growth inhibitor, azadirachtin A. The-dosage-mortality test data revealed that all the test substances from M volkensii had a higher acute toxicity on the larvae than azadirachtin A after 48 hours, though azadirachtin A gave higher percentage total mortality rates on the earlier developmental stages in the long run. Both azadirachtin A and M.volkensii test substances showed good growth inhibition effects. The increasing order of LC50 (ppm) in 48 hours was as follows: fraction 4:6&1:1 = 9.4; fraction B = 18.2; fraction A = 44.5; compound 55.3; and azadirachtin A = > 200 (282.9) In the limited field trial studies, fraction B from m volkensii at concentrations of 50 and 100ppm regulated the pre-imaginal stages of ae. aegypti. When the above substances were tested for any effec t on hatchability of ae. aegypti eggs and any influence on the oviposition behaviour of the adult females of the same mosquito, the two less toxic test substances (fraction A and compound from m volkensii and azadirachtin A increased the rate of hatching of the eggs but the two toxic fractions (4:6&1:1 and B) from N. v o l k erre i i slightly increased hatchability and then caused drastic inhibition on hatching after reaching their critical levels. At the highest concentration tested (200ppm) , N. volkensii test substances deterred oviposition of the adult Pie. aegypti females and had an ovicidal effect on the eggs. The effect of pellets formulated from the acetone extract fraction of N. volkensii on third- and fourth instar larvae of PIe. aegypti was also investigated. The results showed that the pellets caused a total percentage mortality of 95% on the larvae when applied on water as larval food. Since the active products from N. vollkensii fruit extracts have higher acute toxic action to Pie. aegypti larvae than azadirachtin A and may also be potent as insect growth inhibitors, they can possibly be used in the control of mosquitoes.