Larvicidal effects of mineral turpentine, low aromatic white spirits, aqueous extracts of Cassia alata, and aqueous extracts, ethanolic extracts and essential oil of betel leaf (Piper betle) on Chrysomya megacephala.

摘要

BACKGROUND: Many methods have been employed, with variable success, in the treatment of cutaneous myiasis caused by Chrysomya species. AIMS: Experiment 1: to assess the larvicidal effect of mineral turpentine (MT) and the main ingredient of MT, low aromatic white spirits (LAWS), on Chrysomya megacephala larvae in vitro. Experiment 2: to assess the larvicidal effects of aqueous extracts of winged senna (Cassia alata), and aqueous extracts, ethanolic extracts and essential oil of betel leaf (Piper betle). METHODS: In experiment 1, two samples of LAWS were obtained from two industrialists (samples 1 and 2). Adult flies of C. megacephala were bred in the insectory of the Department of Parasitology, Faculty of Medicine, University of Colombo. Petri dishes were prepared with pads of cotton wool. These cotton pads were soaked separately in MT, LAWS samples 1 and 2, and normal saline as a control. Ten larvae were placed in each Petri dish. The activity of the larvae was observed and recorded half-hourly. MT and the two samples of LAWS were analyzed by chromatography. In experiment 2, volatile essential oil of betel was prepared using a standard steam distillation process. An ethanolic extract of betel was obtained after boiling the crushed leaf with water, and mixing the stock with ethanol. Betel oil dilutions of 1-4% were prepared using 1% Tween 80 (v/v aq) as a solvent, with 0.05 g/100 mL sodium lauryl sulphate (as stabilizer) and 0.01 g/100 mL methyl paraben (as a preservative). Cotton wool swabs soaked in 1, 2, 3 and 4% essential oil of betel in 1% Tween 80 (v/v aq) prepared as above, 1, 2, 3 and 4% ethanolic extract of betel, 50 and 25% aqueous extract of C. alata, and 50 and 25% aqueous extract of betel were placed in separate Petri dishes. Ten larvae were placed in each Petri dish. 1% Tween 80 solvent with the stabilizer and the preservative, but without betel essential oil, was used as a negative control and MT was used as a positive control. Larval motility was assessed as before. RESULTS: MT and the two LAWS samples killed the larvae in vitro within 4 h. Chromatography showed more unidentified constituents in MT than in pure LAWS, indicating additional substances in MT. The 4 and 3% preparations of the essential oil of betel were effective in killing 100% of the larvae of Chrysomya within 3 h 30 min. The 2% extract of betel essential oil killed 96.7% of larvae in 4 h. Ethanolic and aqueous extracts of betel, the aqueous extract of C. alata, normal saline and the Tween 80 solvent were not larvicidal. CONCLUSIONS: MT and LAWS, the main ingredient of MT, were effective in killing Chrysomya larvae. Essential oil obtained from betel leaves also showed a dose-dependent larvicidal effect on Chrysomya larvae. This natural product may be effective in the treatment of wound myiasis.