Temporal and spatial population dynamics of Psammotettix alienus, a vector of wheat dwarf virus

The influence of weather and cropping practices on the population dynamics of the leafhopper Psammotettix alienus, a vector of wheat dwarf virus, is examined. The occurrence of the two annual generations was monitored by water traps in winter wheat fields in Central Sweden from autumn 1997 to autumn 2000. Surveys were also carried out in unploughed fallows, leys and permanent pastures. The results indicate that cold weather in early summer affected nymphal development negatively, and that the negative effect on population size may persist into the following year. On the other hand, warm weather in the autumn may result in a large overwintering population. Very few P. alienus were caught during weeks with average maximum temperatures <10°C, and in warmer weather catches increased with temperature. Consequently, late sowing of winter wheat decreases oviposition opportunities and the risk of virus spread because leafhopper activity ceases as temperatures decrease in the autumn. Adults of the spring generation were most abundant in fallows. However, phenological data indicated that the progeny were unlikely to reach the adult stage because fallows were usually terminated before nymphal development was complete.