Material and methods

Plant:

     The stem bark of the plant Lantana indica and Alstonia scholaris were collected from the botanical garden of DDU, Gorakhpur University, Gorakhpur, Uttar Pradesh, India. First of all, stem bark of both the plants were washed separately with water and then dried in an incubator at about 37°C. Then dried stem bark of Lantana indica and Alstonia scholaris were powdered with the help of mechanical device.

Extraction of compounds:

     300 gram powder of stem bark of Lantana indica or Alstonia scholaris were subjected to extraction through Soxhlet apparatus in methanol solvent for about 50 hours and a concentrated solution was obtained. After evaporation of solvent, the extracted compound in dried form was obtained. This extracted compound was stored in air-tight desicator and further used for experiments.

Animal:

     The fresh water harmful snail Lymnaea acuminata (3.65± 1.00 cm total shell height and 1.40 ± 0.50 cm total shell width), were collected from the fresh water bodies of Gorakhpur. Prior to experiment snails were allowed to acclimatize for 72h.

Toxicity experiment:

     The experiment was conducted in freshwater ponds, 29.28 m³ in area and 9.19 m³ in water volume. Each pond was stocked with 100 snails with a size difference not greater than 1.5 times (APHA, 1992). The experimental animals were exposed continuously 24h up to for 96h to four different concentrations. Control groups were kept under similar conditions without any treatment. Mortality was recorded after every 24h during the observation period of 96h. Contraction of the snail body within the shell and no response to a needle probe were taken as evidence of death of snails. Dead animals were removed to prevent the decomposition of body in pond.
     Lethal concentration (LC₅₀) values for different exposure periods, lower confidence limits (LCL) and upper confidence limits (UCL), slope value,‘t’ ratio and heterogeneity were calculated by using probit log analysis of POLO Plus computer programme of Robertson et al., 2007.