Study On The Environmental Harshness Working On Subzebrinus Erraticus

In this thesis, I researched the parasitoid predator Miltogrammoides sp. (Sarcophagidae) predating the prey Subzebrinus erraticus (Pilsbry, 1934)(SE) and measure the scars on the SE shell to know the SE suffered the predation pressure. Four experiments were performed as, 1, field observation and sampling study of predation events; 2, the quantative study of SE shells and the scars; 3. laboratory culture and observation of M. sp; 4. The shell direction in fly predation event.The results showed that: 1, the SE population has a high repair frequency up to 88.5%, Averagely, each shell has more than two scars. The frequency of scars is independent of the shape and size of shell; 2, M. sp. is a specialist parasitoid predating mature SE. Each prey snail was infected by only one M. sp; 3, the sex ratio of M. sp. is subequal to 1:1. Female flies are weighter than male flies. The body weight of M. sp from new eclosion is related to the size of SE. 4, locations of parasitoids'predation event were most frequently observed in the middle to lower portion of shrub and grass, i. e. the section within 30 ~ 45 cm yielded 43.8% successful fly predation; 5, after being predated, the shell direction is independent of the body weight and the survival time of M. sp; 6, the choice of M. sp for SE is independent of the situation of injuried degree and the number of scars on SE shell. However, the choice of a successful predation is determined by the depth of the length of scar; 7, the survival time of male M. sp is not correlated with detected SE shell features, while that of female M. sp has a positive correlation with the prey shell height and whorl number.