Bioactivity and Synergism of Tagpo (Ardisia tomentosa) Molluscicidal Extracts

Population control of golden apple snails (GAS, Pomacea canaliculata) is beneficial in rice farming; however, the associated control measures can be expensive and time-consuming. Currently, farmers use synthetic molluscicides such as niclosamide to control GAS infestation, but this has some drawbacks. For example, niclosamide has broad toxicity to non-target organisms and negatively affects the growth of rice seedlings. Plant extracts with potent bioactivity and low toxicity to non-target organisms are attractive alternatives to synthetic molluscicides. In this study, the bioactivity of the crude fruit extract of tagpo (Ardisia tomentosa) was assessed against GAS and tilapia (Oreochromis niloticus) fries. The potential molluscicidal synergism between tagpo extract and niclosamide was also assessed by dose-response modeling. To generate data, snails and fish fries were exposed to six or eight concentrations of test substances in one or three trials for 24 h (48 h for fish assay) followed by a 24-h recovery. Snail and fish mortality was assessed by motility criterion to model doseresponse curves and estimate lethal concentrations. Lethal ratio tests were performed in R and interpreted at 95% confidence level. The results showed that tagpo extract exhibited high molluscicidal activity against GAS (LC50 = 27.83 ± 0.53 ppm, value ± standard error, simulated field conditions); however, it showed toxicity to tilapia fries (LC50 = 5.36 ± 0.21 ppm). Both tagpo extract and niclosamide also exhibited synergistic bioactivity on snails, thus supporting tagpo extract as a novel source of potent molluscicides worthy of further development.