Population dynamics of cereal aphids in different seasons and the importance for the transmission of barley yellow dwarf virus (BYDV) in winter barley and winter wheat in the production region of Bonn in 1989/90

Experiments were conducted on the appearance of cereal aphids on winter barley und winter wheat from October 1989 to July 1990. Additionally the barley yellow dwarf transmission rate was determined by estimating infected plants symptomatologically. In the different periods "autumn/winter" (H), "spring" (F) and "summer" (S) an aphid infestation was allowed while outside of this periods infestation was prevented by insecticides. Two controls were established, the first with insecticides (KM) during the whole investigation time and the second without any insecticides (KO). In winter barley aphids occurred in October. From January the aphid population increased and in February more than 80 % of all plants were infested. In the H-plots the aphid population collapsed after the beginning of the insecticide applications in the middle of February. In the F-plots aphids were noticed from end March till early May and in the S-plots from middle of May till early July. At the end of April nearly all plants in the KO-plots revealed symptoms of a virus infestation. The average yield in this plots was about 29.5 % less than that of the KM-plots. In the other variants the plants showed only few or no virus infestation, thus no significant differences in yield were found comparing to the KM-plots. In winter wheat a few number of aphids were observed in November and from then no aphids could be found until March. However, aphid population in KO-plots increased in May. In the F-plots aphid infestation were noticed from middle of March till the beginning of May and in the S-plots from middle of May till middle of July. In winter wheat plants expressing symptoms of virus infestation were less than in barley. The most serious infestation of plants by BYDV was found in the KO-plots, where about 20 % of all plants showed virus symptoms