THE SIX-SPOTTED LEAFHOPPER, MACROSTELES FASCIFRONS (STÅL.) AND ASTER YELLOWS IN MANITOBA

Abstract

The six-spotted leafhopper overwintered in the egg stage only. Adults migrated into Manitoba in substantial numbers on strong south winds in mid-May. The migrant population reached a peak of about 80 leafhoppers per 100 sweeps in mid-June on cereals. There was a high mortality of migrants in late June and early July. The non-migrant population originated partly from overwintered eggs but mostly from eggs laid by migrants. New generation adults appeared in late June. Distinct broods were not apparent in the field because generations overlapped. The peak of population, about 400 leafhoppers per 100 sweeps, was reached about mid-August. Four generations were reared in a year. In general field collections the percentage of leafhoppers transmitting the aster yellow virus did not exceed 1 per cent. The percentage transmission was highest in the migrant population but dropped in July and August with the increase in local population. The rate of virus transmission was low in June and July but reached a peak in August in conjunction with the peak in population. Some weeds are a source of aster yellows virus. In Manitoba, early maturing crops generally escape severe aster yellows infection but it is often a problem on late crops.