Three treatments of the Completely Randomized Design Essay

The experiment followed the Completely Randomized Design (CRD) consisting of three treatments (application of etofenprox at the estimated LC50 and LC10, and the control). Each treatment was replicated four times, and the experiment was carried out for three consecutive generations of BPH. The susceptible rice variety used in this study was Cisadane. The rice seedlings (three seedlings pot-1) were transferred into plastic pots (diameter of 16 cm and height of 16 cm) when they were 17 d-old. Thirty six plots were prepared and they were divided into three groups of 12 plots. Each group was used for each generation of BPH. At 25 d after transplanting (DAP), the first group of plants were treated according to the tested concentrations of etofenprox with the spray volume of 400 litre ha-1 and they were covered with a cylindrical plastic tube with diameter of 18 cm and height of 100 cm. Before use, ventilation windows were made at the two opposite sides of the cover by cutting the plastic (5x5 cm) and replaced it with white cloth. In addition, the plastic was covered with white cloth at the top. Two d after spraying, 20 third instars of BPH reared from the laboratory (the first generation) were released through the window into each potted plant. Mortality of BPH was assessed on the third d after release and the adults produced from the surviving nymphs were sexed on the seventh d after release. The surviving adults remained on the rice plants until they all died. The number of nymphs emerged from each treatment were collected and recorded every other d. Observation of nymphs was terminated when no nymphs emerged during the last four consecutive d. The collected nymphs (the second generation) were reared in a plastic jar containing rice seedling. BPH collected from different treatments were reared separately.
When the rice plant reached 50 d-old, the second group of 12 pots was treated using similar procedure as for the first generation, excepts the spray volume was increased to 500 litre ha-1 and the nymphs released to the plants were the second generation. Observation procedures were similar to the one described for the first generation. The last application was conducted to 75 d-old plants with the spray volume of 600 litre ha-1 and the nymphs used were the third generation produced by the surviving adults of the second generation. Thus, the first to the third application were only different in the spray volume and the generation of BPH used. In other words, the nymphs used for the last application were resulted from the adults surviving from the two consecutive generations applied with sublethal concentration of etofenprox.
While the first application (25 DAP) was on-going, a few web spiders was found surrounding rice pots. Therefore, we repeated the first application as described above, except the plants were 20 d-old. The second and third applications described above were not repeated because there were no disturbances and nymphs of the second generation were sufficient to continue the experiments.