Bioactivity of Some Botanical Extracts Against the Major Mosquito Disease Vectors in Sudan

Abstract

The study was conducted to evaluate the larvicidal activity of aqueous and organic solvent extracts of four indigenous plant species in Sudan , root of Balanites aegyptiaca (L) Del. (Higleeg) , shoots of Solenostemma argel Del Hyne ( Argel) , leaves of Eclipta prostrata L. (False daisy , Swamp daisy , eclipta) , and seeds of Azadirachta indica A . Juss (Neem) , against larvae of three predominant mosquito species , Anopheles arabiensis , Culex quinquefasciatus , and Aedes aegypti , vectors of many important diseases in Sudan. Larvae of each mosquito species were firstly treated with aqueous extracts of each of the four above mentioned plant species . Then the same numbers of larvae of each mosquito species were put under bioassay testing of methanolic extracts of Balanites aegyptiaca , Solenostemma argel , and Eclipta prostrata , and hexane extract of Azadirachta indica seeds.The synthetic organophosphorous larvicide , Abate® (Temephos) , was used as a standard . Statistical analysis showed significant differences between the tested concentrations of each plant , mostly with activity increases progressively with dosage rates . The root aqueous extract of Balanites aegyptiaca , gave the best larval mortality results of the three mosquito species which was comparable with that of the standard larvicide Temephos , and showed LC50 of (0.000357ml/L) for Anopheles arabiensis, followed by(0.001335 ml / L) for Culex quinquefasciatus , and lastly (0.001542 ml / L) for the Aedes aegypti. The highest concentration ( 500 ppm) of the root aqueous extract caused 100% larval mortality of the three mosquito species after 24 hours , which was comparable with that of the standard larvicide Temephos. The methanolic extract of Balanites aegyptiaca caused LC50 of 0.00 0 028 ml /L for Anopheles larvae , 0.000313 ml /L for Culex larvae and 0.001227 ml / L for Aedes larvae , respectively.Also,the highest concentration (500 ppm) of this extract caused 100% mortality of the larvae of the three mosquito species after 24 hours , which was a comparable result with that of the standard larvicide Temephos. x The Hargal shoot water extract showed also good results against the larvae of the three mosquito species compared with that of the standard larvicide , and showed an LC50 of (0.008748ml/L) for Aedes aegypti , ( 0.002706 ml / L) , and ( 0.002568 ml / L) for Anopheles arabiensis , and Culex quinquefasciatus larvae , respectively. The highest concentration of this extract (750 ppm) , caused 100% larval mortality of the three mosquito species after 24 hours ,which was comparable result with that of the standard larvicide Temephos. The methanolic extract of Hargal leaves gave comparable effects on the three mosquito species and showed LC50 of ( 0.001905 ml /L ) for Aedes aegypti,(0.001463 ml /L) for Anopheles arabiensis and ( 0.001479 ml / L) for Culex quinquefasciatus larvae , respectively Aqueous extracts of Eclipta prostrata at the highest concentration (2500 ppm) gave more than 70% larval mortality of the three mosquito species after 24 hours.The probit analysis for the aqueous extract of the plant showed LC50 of (0.003862 ml / L) for the Aedes aegypti , (0.004151 ml /L) for Anopheles arabiensis and (0.004343 ml / L) for Culex quinquefasciatus mosquito larvae. The methanolic extract of Eclipta prostrata leaves, caused more than 90% larval mortality of the Anopheles arabiensis and Culex quinquefasciatus and 78.8% of the Aedes aegypti mosquito species, respectively, after 24 hours and showed an LC50 of (0.002241 ml /L) for the Aeds aegypti , (0.001251 ml / L) for the Anopheles arabiensis and (0.001345 ml / L) for the Culex quinquefasciatus larvae . It was also observed that , solvent extract of the plant leaves was more active on the larvae of the three mosquito species than the aqueous leaves extract. xi Neem seed aqueous extract at the highest concentration gave mortality percentages, ranging between 80% -98% against the larvae of Aedes aegypti , Anopheles arabiensis and Culex quinquefasciatus , respectively , which are comparable results with that of the standard larvicide Temephos on the larvae of the three mosquito species .The LC50 of this extract was found to be (0.00 8732 ml /L) for Aedes aegypti , (0.003942 ml / L) for Anopheles arabiensis and (0.008699 ml / L) for Culex quinquefasciatus , respectively. Neem seed hexane extract gave comparable results on the larvae of the three mosquito species with regard to the increased time of exposure . It was observed that , in the case of exposing mosquito larvae to hexane extracts of Neem seed , the larval mortality percentage increased progresively with longevity of time . Moreover, solvent extracts of Neem seed in general were highly effective than aqueous extract. The highest concentration of Neem seed hexane extract , gave 87.5% , 99.8% and 98.25% larval mortality of the Aedes aegypti, Anopheles arabiensis and Culex quinquefasciatus , respectively after 24 hours . Application of the probit analysis showed an LC50 of (0.002641 ml / L) , (0.004932 ml / L) , and (0.003323 ml / L), for the Aedes aegypti , Anopheles arabiensis , and Culex quinquefasciatus mosquito species, respectively. The detected superior insecticidal activities of Higleeg root water and methanol extracsts after the bioassay on mosquito larvae are due to presence of these bioactive compounds as saponin ,triterpene , flavonoids that were normally found in the different parts of the tree. Phytochemical test of the shoot aqueous extract of Solenostemma argel revealed the presence of various chemical groups at variable levels. Polar and intermediately polar ingredients were shown in wide xii ranges . Alkaloids , saponins , flavones and amino acids were the major chemicals detected. Methanol extracts of the plant revealed more or less the same previous compounds , plus some embedded trace amounts of tannins , sterols and triterpenes . The detected groups were different according to the type of the extracts ( viz., water , methanol). Laboratory analysis of the aqueous extract of the leaves of Eclipta prostrata , revealed the presence of biologically active secondary metabolites such as saponins , phytosterols , phenols , flavonoids , tannins, terpenoids and carbohydrates. Besides , there were other phytochemicals estimated but were present only in very low concentrations. The methanolic extract yielded tannins , flavonoids coumestans,saponins and alkaloids , etc.,. In the present study , it can be concluded that , the results of the tested plant extracts against the larvae of the 3 mosquito species showed that , root extracts of Balanites aegyptiaca were found to be most toxic thus have the highest larvicidal potency on the larvae of the three mosquito species , even when tested at the lowest concentration (40 ppm) , which credited Balanites aegyptiaca root extracts to be superior upon all the other tested plant extracts , moreover , the order of larvicidal potencies among the tested plant extracts was roots of Balanites aegyptiaca > shoots of Hargal > neem seed > leaves of Tamr Al-ghanam.