STUDIES ON THE LIFE HISTORIES OF DIPLOSTOMUM NIEDASHUI AND DIPLOSTOMUM HUPEHENSIS Ⅰ. THE EXPERIMENTAL BIONOMICS OF THE EARLY LARVAE

Water temperature shows a marked influence upon the incubation period of the eggs of the two species. Within the range of 20—35℃, the higher the temperature, the shorter is the incubation period. The curves of egg incubation rate of both species related to temperature are logistic. They can be expressed respectively by the following formulas:N1+=1+e4.9347-0.1872t/0.1095 and Nh=1+e5.2077-0.2117t/0.1104 Where, Nn, Nh—rate of D. niedashui and D. hupehensis respectively; t—temperature.When the water temperature increases, the instantaneous hatching rate of both species increases according to the following equations: Yn=0.0205t—0.3119 and Yh=0.030t—0.5171.Where, Yn, Yh—instantaneous rate of each species; t—temperature.The miracidia of these allied species show a strong positive phototaxis and prefer swimming near the surface of water. The two cercariae shed from the gastropods 18—25 days after infection. They appear to be phototatic and suspending near the surface of water. The cercariae emerge from the snails discontinuously and in spurts at intervals. The emergence peak of the cercariae of both species appears from 8 to 10 am every day. Their emergence begin to reduce by 2 pm and completely cease, after 6 pm.The populations of the two cercarie may also increase in logistic curves. They can be expressed respectively by the integral form of the logistic equations:Nn=209 362.8315/1+e4.3368-0.1308t and Nh=448 376.6514/1+e5.8165-0.1495t* Where, Nn, Nh—population of each species; t—day.