Studies Of Ecological Control The Pomacea Canaliculata (Lamarck) In Rice Paddy

The Pomacea canaliculata (Lamarck), an invasive freshwater gastropod, causing a series of problems of the production of rice, ecological environment and parasitic diseases dispersion. In recent years, with the increasing number of regions and more and more species of crops were disserved by Pomacea canaliculata (Lamarck), it has caused incalculable loss in worldwide. Currently, the methods of controlling Pomacea canaliculata (Lamarck) still focused on a single physical control, agriculture control, chemical control and so on, had not formed a set of effective integrated control of Pomacea canaliculata (Lamarck). This paper studied the bioecology characteristics and the new measure of ecological control Pomacea canaliculata (Lamarck) based on field investigation and laboratory experiment.1. The ultrastructure, especially the radula, spermary, ovary and spawn of Pomacea canaliculata (Lamarck) were observed and analyzed under scanning electron microscope. The radula of Pomacea canaliculata (Lamarck) is taenoglossate radula, dentition formula (2·1·1·1·2), the cusp of teeth is sharp. Structure of the spermary is simple, don't have seminiferous tubule, spermatogenic cells attach on the branches of the connective tissue through basement membranae, lumen of spermary is reticulation and interlinked with each other. All levels of globular spermatids distributing in the cavity of trabecular connective tissue. Female snails ovary is large, pink dendrites, closing to the digestive gland. The main structure of ovarian is follicle, and oocytes grow and mature in the follicle, the observed oocytes are well-distributed and have no significant differences between the size. Irregular soft liquid dispersed the surface of the 7d spawn, compared with the less on the 14d spawn, but there are ups and downs of the drape and fissure on the latter.2. In order to seek a feasible and efficient way to control the egg hatchling of this pest, here we systematically studied the effects of water spraying and submersion on its egg hatchling rates and durations. Our results demonstrated that water spraying and submersion could dramatically decrease the hatchling rates to maximal 5.8% and increase the hatchling duration up to 26.4 days on P. canaliculata. Not only the beginning time of water treatment, but also the frequencies of the water spraying is critical to control the hatchling rate and duration of P. canaliculata. Water submersion that began in 12 hours after the eggs laid and lasted at least 48 hours will significantly decrease the snails'hatchling rates and extend the hatchling time. In addition, compared to spraying, the water submersion could achieve more remarkable effects. The capsule of the snail's egg is able to withstand the water treatment. Based on our water spraying and submersion results, it can be concluded that 0-6 hours after egg being laid, egg capsule precipitates are beginning to form, and the capsule is completed after 12-24 hours. From this special breeding phenomenon of P. canaliculata makes the physical control by water treatment become feasible.3. We studied the controlling of Pomacea canaliculata (Lamarck) with four kinds alternative material in laboratory and plot, they are Calcium oxide, Ammonium bicarbonate, Tea seed cake and Tea saponin; and evaluated the influence of these substances to the weed, rice economic properties and rice output. The results indicated: Tea saponin, Tea seed cake and Calcium oxide achieved the better controlling result, especially the Tea saponin, when the concentration were 40mg/L and 50 mg/L, and were treated for 48 h in laboratory, the mortality of snails achieved to 100%. In the plot, both mortality of the treatment at 6.0 g/m2 with three days and 1.5 g/m2 lasted 15 days were 100%, the quick-acting and lasting effect have the distinct difference with the other substances. All of the controlling result of Tea seed cake treatment at 30 g/ m2 and 45 g/m2, Calcium oxide treatment at 45 g/m2 are above 80% after 15 days. In addition, these three kinds of substances can control the Echinochloa crusgalli (L.)Beauv effectively in the rice paddy. Ammonium bicarbonate had less effective on controlling Pomacea canaliculata (Lamarck), and can promote the occurrence Echinochloa crusgalli (L.)Beauv. At last, we confirm Tea saponin, Tea seed cake and Calcium oxide can be used as the alternative material of synthetic chemical molluscicides on controlling Pomacea canaliculata (Lamarck) in the rice paddy.4. The toxic effects of A. philoxeroides saponin at different concentrations and pH values on Pomacea canaliculata of different sizes were studied in laboratory. The results showed that the mortality of P. canaliculata increased with the concentration of A. philoxeroides saponin increasing and was averagely 79% at 72 h when the concentration was 200 mg/L. The toxic effects of the saponin at different pH values were significantly different. When the saponin concentration was 150 mg/L and its pH was 9, the mortality of P. canaliculata at 72 h was up to 89%; the toxic effect of the saponin on P. canaliculata could significantly be improved in alkaline conditions.5. We studied Procambius clarkii prey on different height of eggs on the water surface laid by Pomacea canaliculata (Lamarck) in laboratory. And we used a novel experimental design and analysis method named as UD-SVR (uniform design and support vector regression) to study the influence of environmental factors on the height of eggs laid by Pomacea canaliculata (Lamarck). The result indicated predation rate was inversely proportional to height of eggs on the water surface, and when the height was higher, the predation rate was lower. The result also showed that in the four environmental factors:size of the snails, distance between the water surface and shore, temperature at night, humidity at night. Only the distance between the water surface and shore has significant effect on the spawning height of snails, the distance between the water surface and shore was proportional to the height of eggs.