Novel molluscicide against Pomacea canaliculata based on quinoa ( Chenopodium quinoa) saponins

Abstract

A novel molluscicide against Pomacea canaliculata snails (Golden apple snail, GAS) based on quinoa saponins ( Chenopodium quinoa) is presented. Quinoa is a pseudocereal extensively cultivated and consumed in Bolivia and Peru. The external husk of the grains is removed prior to human consumption due to the bitter taste imparted by their high saponin content (predominantly bidesmosidic saponins), and constitutes a by-product with no commercial value. When tested against GAS, quinoa husks showed no activity up to 121 ppm product (approximately 35 ppm saponins). To increase their molluscicidal properties, the husks were treated with alkali to convert bidesmosidic saponins to more active monodesmosides. This product killed 100% GAS under laboratory conditions at 24 h at approximately 33 ppm product. Surprisingly no toxicity to fish, such as goldfish or tilapia, was observed up to the highest concentration tested (e.g., 54 ppm product). This is a main advantage in relation to available commercial molluscicides that kill fish at product doses lower than those that kill GAS (e.g., niclosamide). The product was also tested preliminary under field conditions in Northern Argentina with similar GAS mortality results. A preliminary LC/ESI–MS/MS study revealed that the husks contained a mixture of known and novel bidesmosidic and monodesmosidic saponins. However, the alkali treated husks did not contain monodesmosidic saponins as expected, but large molecular weight saponin derivatives, probably formed between the saponins and other compounds present in the quinoa hulls under alkaline conditions. Due to the complex nature of these compounds, no direct relationship could be established between product efficacy and a higher content of monodesmosidic saponins. The results suggested that the molluscicidal properties are probably related to the formation of more hydrophobic compounds after alkaline treatment that have higher affinity with the cholesterol present in GAS gills.