Long-term relationships between the abundance of pest molluscs and weather in agricultural fields in South Australia

Invasive snails, Cernuella virgata, Theba pisana and Cochlicella acuta, infest grain crops prior to harvest in early summer in southern Australia. They breed in autumn–early winter and peak in abundance in spring following the recruitment of young snails. Long-term studies (20 years) were established on three farms in South Australia (two practicing pasture–cereal rotations and one continuous cropping) to better understand the role of prevailing weather in driving the population dynamics of the three snail species and to develop predictive models that might assist farmers and off-farm grain handlers to anticipate future peaks in snail abundance and tailor their management practices accordingly. The three species are asynchronous in their population dynamics; they peak in numbers in different years. The abundance of C. virgata in late spring (preharvest) was most closely associated with, and could be broadly predicted by, the previous autumn to spring rainfall, but no significant associations were found between the rainfall and the abundance of C. acuta and T. pisana. Local air temperatures had little apparent association with the abundance of all three species. Broader scale weather, exemplified by the El Niño Southern Oscillation Index, was only occasionally, and weakly, related to the spring abundance of C. virgata.