The epidemiology of Wheat dwarf virus in relation to occurrence of the leafhopper Psammotettix alienus in Middle-Germany.

Occurrence of the leafhopper Psammotettix alienus Dahlb. and its infectivity with Wheat dwarf virus (WDV) were studied in cereal crops in Saxony-Anhalt (Middle-Germany) in 2000 and 2001. The leafhoppers were collected with a sweep net and/or a cage trap and their WDV infectivity was determined by transmission to test plants. In 2000, adult leafhoppers were caught from the second week of May to the third week of December, whereas in 2001 they were trapped from the fourth week of May to the second week of December. Nymphs and adults were caught in spring in young actively growing crops and in summer in maturing crops and also in self-sown cereal stands. However, only adults were found in autumn in newly sown crops. The peak population density of adult leafhoppers was in self-sown cereal plants in September when there were 25 individuals per m(2) in 2000 and 15 in 2001. The proportion of leafhoppers that were infective with WDV when transferred to barley test plants ranged from 5 to 79% in 2000 and from 0 to 56% in 2001. Two leafhoppers collected in June 2000 in a crop of maturing winter barley each infected both barley and wheat plants with WDV. It is concluded that the same leafhoppers are able to acquire both virus strains and transmit them to cereals.