Phytolacca dodecandra berries as a means of controlling bilharzia-transmitting snails
As part of the search for effective control over bilharzia transmitting snails, a project was launched in Ethiopia to further the development of the use of P. dodecandra berries. Its aim was to select and test P. dodecandra types for their suitability for cropping and their molluscicidal potency. Results showed that fairly small quantities of berries and a simple method of application could be used to control snails.
Dimorphic P. dodecandra produce long and short staminate flowers on racemes. The latter produce the berries, which possess their strongest molluscicidal activity when harvested at a fully developed though unripe stage.
Short staminate types of P. dodecandra found in Ethiopia at altitudes higher than 1500 m with acceptable molluscicidal potency and favourable agronomic qualities were selected. A propagation method with non-woody branches was successfully developed. After 5-6 weeks, cuttings were planted out and produced berries on some scale a few months later. Mature shrubs gave an average yield of 264 g of dried berries per bush.
The active molluscicidal compounds in the berries of P. dodecandra are triterpenoids to which branched trisaccharides are linked at C3. They are readily soluble in water. 70% Ethanol berry extracts are non-molluscicidal. Comparing aqueous and ethanol berry extracts on TLC results in a different resolution of corresponding spots. Suggesting that ethanol inactivates an enzyme complex which, during aqueous extraction, allows the saponines to be converted into their molluscicidal active form. Thus, berry powder applied directly, without over night waiting for the active principles to emerge, can only be marginally active in comparison with berry powder soaked during the night before treatment of a fresh-water body.
During the dry season of 1980 and 1981 in January and February, three tests were carried out in rivers densely populated with bilharzia infected Biomphalaria pfeifferi snails. Control was effectuated by siphoning berry suspensions into the rivers over a period of 5-6 hours. With only 2.5 – 3.5 kg of berries, soaked during the night, snail populations could be reduced to almost nil. Except for fish, the water fauna was not affected. However, 4 weeks after treatment fish was present again.
Although the history of bilharzia control suggests that a molluscicide alone, including the one derived from P. dodecandra berries, probably cannot solve the bilharzia problem since the other host, man, has to be cured at the same time, P. dodecandra could nevertheless become an important weapon in the fight against this disease. Results of this project indicate that dense populations of the intermediate snail host can be controlled with only a few kilos of berries. – ChB Lugt, M van Kregten
Ned Tijds Fytoth 2017 (30) nr 1: pag 6-8