Toxicological Efficacy of Flower Extracts From Chrysanthemum cinerariifolium and Leaf Extracts From Eucalyptus camaldulensis and Nicotiana tabaccum on Anopheles gambiae s.s. Giles Mosquito Larvae.

Abstract

In this study crude flower extract of Chryasathemum cinerariifolium , and crude leaf extracts of Eucalyptus camaldulensis and Nicotiana tabaccum were tested for their larvicidal activity against the third instar larvae of Anopheles gambiae s.s. Giles (Diptera: Curicidae), a member of Anopheles gambiae complex. Six different solvents were used to extract the oils namely ethanol, methanol, DCM, hexane, ethylacetate and aqueous. Larvae had 24 hour exposure and observed separately in control at 50,100,150,200,250 and 300 ppm concentrations of the extracts. The six different solvent extracts of the plants showed good larvicidal activity. The highest potency was recorded by DCM extract of C.cinerariifolium (LC50= 164.68 ppm, LC90 = 255.17 ppm) achieving 100% mortality of the larvae. Similarly, ethanol of C. cinerariifolium, DCM and methanol of E. camaldulensis, and ethanol of N. tabaccum exhibited 100% larval mortality at LC50 and LC90 for which the concentrations were respectively 187.78 ppm, 268.26 ppm; 168.65 ppm, 315.85 ppm; 197.46 ppm, 329.68 ppm; and 189.58.58 ppm, 320.75 ppm. Second to these was methanol of C. cinerariifolium 98% mortality (LC50222.45 ppm) and ethanol of E. camaldulensis 96% mortality at 210.15 ppm. The rest of the extracts also indicated appreciable results ranging from 80% (ethyl acetate of E.camaldulensis at LC50 of 260 ppm) as lowest to hexane C. cinerariifolium and DCM N. tabaccum both at 88% larval mortality and LC50s of 230.66 ppm and 229.72 ppm respectively. There was no mortality observed in controls. A general observation made was that the larvae were susceptible to all treatments. The larvicidal activity of the treatments were dose and time independent i.e. larval mortality increased as the dose and time increased and all of the volatile oils showed significant larvicidal activity against the larvae on 24 hours exposure. The LC50 and LC90 with their 95 percent confidence limits of the oils were determined using log probit analysis test and was found statistically significant ( p = < 0.05) . From these results it was observed that the five extracts namely DCM of C. cinerariifolium, DCM of E. camaldulensis, ethanol of C. cinerariifolium, methanol of E. camaldulensis, and ethanol of N.tabaccum contained toxic compounds to mosquito larvae. However, the DCM flower of C. cinerariifolium and DCM leaf extract of E.camaldulensis showed the highest activity on the larvae than all extracts. In the determination of synergism and antagonism, seventeen activities were synergistic at the combination ratio of 1:1(100 ppm: 100 ppm). Amongst them were C. cinerariifolium methanol + N. tabaccum aqueous; C. cinerariifolium methanol + Nt aqueous; and C. cinerariifolium DCM + E.camaldulensis hexane. In that order they demonstrated to be the best synergist combinations at their combination levels. The weakest synergist combinations were C. cinerariifolium methanol + E.camaldulensis ethyl acetate; and E.camaldulensis DCM + Nt hexane. There were ten antagonistic activities. Of these the combination between methanol of C. cinerariifolium and hexane of N. tabaccum indicated best antagonist followed by methanol of C. cinerariifolium in combination with ethyl acetate of E. camaldulensis in the ratio 1:1.(100 ppm : 100 ppm). The former showed the best antagonism in their LC50 each at 224.45 ppm and 224.35 ppm giving a combination antagonistic activity of 232.66 ppm. This is the only combination that gave a small range between the combination activities and the single crude leaf toxic concentrations i.e. a difference of 7.20 ppm for methanol and 4.20 ppm for hexane. In this case methanol of C. cinerariifolium was a synergist to N. tabaccum hexane. All extracts were tested on the susceptible and field strain larvae against Resistance Ratio (RR). It was revealed that the laboratory susceptible strain showed complete larval mortality at high concentrations (DCM C. cinerariifolium, 0.996; E. camaldulensis methanol; 0.998, E. camaldulensis DCM; 0.993 and Ethanol N. tabaccum, 0.999) while the field strain was susceptible to low concentrations of all extracts (RR varying from 1.003 to 1.891). Results indicated presence of cross-resistance among the field strain in 24 h post-recovery period, especially during the long rain periods. For persistence the results of the three plants indicated that under light regime C. cinerariifolium took 5 hours and 30 minutes to completely decompose under light regime and 28 days to decompose under darkness. E. camaldulensis decomposition under dark regime was 12 days and that of light regime was 35 days. The dark-light degradation periods for N. tabaccum slightly stretched higher than those of other plants and disappeared within 18 days of light and 28 days of darkness. All the extracts showed potential in the control of the malaria vector mosquito and therefore can be developed for use.