Biodegradation of Applied Plant Extracts of C. cinerariifolium, E. camaldulensis and N. tabaccum in the Habitats of Third Instar Larvae of the Malaria Vector Anopheles gambiae s.s. Giles (Diptera: Culicidae) Larvae is a Function of Time

Experiments for determination of extracts persistence were carried out in accordance with the methods used by Attia et al. (2015). One highest extract of each plant was placed in 300 ml disposable bowls separately in their relevant concentrations: DCM C. cinerariifolium (164.86 ppm), DCM E. camaldulensis (168.65 ppm) and ethanol extract of N. tabaccum (189.58 ppm). Distilled water was added into each bowl to make 300 ml of water and concentration in the form of pools. By use of a mouth aspirator 25 3rd instar larvae were collected and dipped into the bowl of extract and distilled water solutions. Observation for larval mortality was not a requirement for extract persistence but larvae were included as it could be done under the normal mosquito control programme in the field. Then samples of the solution were taken daily, hourly and in minutes to observe how the extracts were reducing in time to the point of zero. Sample analysis was done using Gas Chromatography- Mass Spectrometry (GC-MS) technique. 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 35 days and in light it took 12 days to decompose. The dark-light degradation periods for N. tabaccum struck a balance in the two regimes taking 18 days of light and 28 days of darkness. Decomposition of all the plant extracts were generally impressive as the periods were very short in comparison with the decomposition periods of chemical insecticides.