The Research On Growing Character Of O.h. Robertsoni Yunnan Strain

Objective:According to the strategy for Schistosomiasis control and prevention in mountain areas China, the research team used O.h. r. yunnan strain (intermediate host of Yunnan Schistosomiasis) as study object, the natural adaptation reproduction of Oncomelania in different density and different altitude were studied through regular observing the reproduction of Oncomelania, the aims of the research were to understand the interaction of snail mouth change, to explore the critical value of snail mouth change and the threshold of control snail, and to provide a basis for establishing the strategy for killing snail and implementing the work of killing snail.Methods: 1.Snails with five spin size and unmating in experimental fields from Dali city were captured. These snails were randomly grouped after mating. The density was 2,4,6,8,10,20,40,80,100,150,200,400,800, and 1000 snails per cage respectively. A density was arranged 2 groups. Snails were screened after breeding of one year and the reproduction of snails were observed.2. Five experimental fields from different altitude (1980 meters,2246 meters,2635 meters,2864 meters, and 3001 meters) located in Canshan mountain were selected. One hundred living snails were randomly regarded as a group. Six groups placed in the same place were breed. Of them,2 groups were selected randomly and the reproductions of snails were observed.3. Automatic temperature and humidity machine placed in experimental fields was used to record the temperature and the humidity.Results:1. In different density of snails, the highest production rate was 6 snails per cage. The number of young snail increased 13.17 times. The number of dead young snail was only 2 snails. The second production rate was 4 snails per cage. The number of young snail increased 4.25 times. The number of young snail increased 3.13 times in 8 snails per cage. The production rate of cage with low density was higher than that of cage with high density. The effective production rate of snails decreased with the increase of density of snails, and the production rate of snails was stable in a lower level when reaching certain density of snails.2. The reproduction rate and living rate in 5 experimental fields were 83% and 113%,65% and 103%,2% and 67%,0 and 0.38%,0 and 0.03%, respectively. The reproduction rate of snails decreased with the increase of altitude. The reproduction rate in 2635 meters was low. Snails cannot reproduce in 3000 meters. There was statistical significance.Conclusion:1. The reproduction rate of snails is correlated with the density of snails. The reproduction rate of snails in low density is higher than that of in high density and a certain threshold exists.2. The effective reproduction rate and living rate of snails decreased with the increase of altitude and statistical significance exists.3. The distribution range of snails will increase with the warmer of weather and the increase of available accumulated temperature yearly.