Studies On Bioecology Of The Golden Apple Snail (Pomacea Canaliculata ) And Its Status Of Distribution And Damage In Guangxi

Based on field observation and laboratory experiments, this study discusses the growth and reproduction, population structure and dynamics, endurance for extreme conditions of the golden apple snail (Pomacea canaliculata), and reveals the basic biological and ecological characteristics. It also carries a pilot investigation on the snails'status of distribution and damage in Guangxi Zhuang Autonomic Region, and makes a primary evaluation of economic loss caused by the snail. These conclusions will serve as a guidance for snail control or utilization.The apple snail remains active for 10 months in Guilin, from March to December, and they stay hibernation for only 2 moths in winter. Egg-oviposition begins in April and lasts to December. The eggs laid in December generally can not hatch because of low temperature, so the effective oviposition period is from April to November lasting for 8 months, among which the breeding peak is in May and June and a lower one in August and September. Its reproduction capacity is very high, a middle-size female snail can lay over 9000 grains of effective eggs, which can hatch out more than 8000 baby snails with the average egg hatch rate of 86.1%, Many predators prey on apple snails, but they cast away the eggs.The golden apple snail has a chaos copulation system, just like as most of other lower animals. For the size of copulation partner, female snails have no choice, but the male do have, they are apt to copulate with the bigger female snails. Furthermore, the sex ratio of the natural snail population is changing with its size, when the snails are in the initial stage of sex maturation (with the shell height of 20-30mm), the number of the male are about equal to that of the female; as the shell height between 30mm and 40mm, the sex ratio of♀:♂dramatically increase to 1.66; but on the contrary, when the shell height is over 50mm, the ratio decreases to 0.64.In experiments under condition of small containers, no mater in dry or wet conditions, the smaller snails have a lower mortality rate, the larger the higher, and the mortality rates in dry condition are generally lower than those in wet condition. In optimal temperature and humidity conditions, the snails can endure 11 days with nothing to eat, after the seventeenth day, the two sexes show a different capacity of endurance for hunger, i.e., the female can endure a longer period of hunger than the male, the male have a longest period of 42 days enduring hunger, while the female 71 days. The temperature range for the snails remaining activity is 8-38℃, the range for the snails remaining alive is 0-40℃, the snails with different size between 15-45mm show no difference in capacity of temperature endurance.The livability with that the natural swamp snail population live through the winter is 78.0%, and the snails which live successfully through the winter are mainly below 30mm in shell height. In the period from June to December, the snails turn from action to hibernation, though the reproductive rate is very high in breeding period, the natural population suffers a high pressure of predation and has a low surviving rate with its density of 478 snails/ m2 in June to 46 snails/ m2 in December, the surviving rate is only 9.6%. The experimental populations, which is with a high density effect but no predation pressure, have a higher surviving rate of 45.3% from May to November, the populations have been becoming sparse with a steady speed in growing seasons, and with a very high surviving rate of 92.6% living through the winter; because of the high density, the growth and development of individuals are severe inhibited, and all individuals have a shell height not more than 30mm and the average individual weight is not more than 0.4g after growing for around a year,.Through the killing experiment of 9 kinds of poisonous plants picked in Ginlin to the apple snails, we find that the leaves of Melia azedarach L. has the best killing effect.The apple snail has already spread widely in Guangxi with nearly all cities and counties having the snail distribution, and now and in a quite long period of future the snail may take the dominant position in all freshwater snail species in Guangxi. With more concretion, the snail's distribution in Guangxi present a tendency of reducing from the south-east to the west-north, there has severe snail damage in agriculture in most parts of the east and the middle area,; in the western part of the middle area, there has some extent of snail damage; other areas of Guangxi has distribution of the snail, but no damage for agriculture because of the unfavorable climate and physiognomy. The total farmland area suffered severe snail damage in Guangxi is 430215 ha, the pesticide expenditure farmers expend every year for apple snail control is $32,270,000(RMB), the loss of rice caused by snail is 103,000,000kg, the value of the rice loss is $144,200,000(RMB)yuan, so the direct economic loss caused by the apple snail is $176,470,000(RMB).