Life history and population dynamics of Theba pisana (Mollusca: Helicidae) in a cereal-pasture rotation.
The life history, population dynamics and dispersal of the snail Theba pisana were studied in a cereal-pasture rotation in South Australia in 1984-88. The breeding season lasted from autumn to spring. Near a fence separating 2 fields in different phases of the rotation, T. pisana was predominantly annual. Further into the fields and in the roadside wasteland, it was predominantly biennial. Snails (>6 mm shell diameter) were most abundant in spring and summer in pastures. During summer, snails were aggregated within pastures, especially on weeds such as Reseda lutea and Rapistrum rugosum. Many snails were killed by burning the old pastures in autumn, prior to sowing crops. In the hottest summers, snail numbers decreased prior to burning. Production and/or survival of young snails was inhibited in crops. The edge of a crop (up to 30 m from the fence) was invaded by T. pisana from an adjacent pasture in the spring and early summer (harvest time). Marked snails released in pastures and crops moved average distances of 0.17-0.21 m/day. The directions of their movements were biased. Strategies for the control of T. pisana in cereal-pasture rotations are discussed.