Monitoring aphids and virus to improve forecasts of Barley Yellow Dwarf Virus

Abstract

1. Sets of data were collected from four locations in England over three seasons (1989/90 to 1991/92) with the objective of providing the basic data necessary for developing a reliable forecasting scheme for barley yellow dwarf viruses (BYDV) in autumn-sown cereals applicable to all the major cereal growing regions of Britain.

2. The sets of data have two major components. Firstly, the numbers of vector aphids flying in autumn were monitored with suction traps, and their virus content and ability to colonise crops was determined by additional tests. Secondly, crop validation experiments examined vector aphid colonisation and virus spread within plots of winter barley sown on different dates.

3. Suction trap data indicate that the bird cherry aphid was the most abundant species each autumn. Numbers were largest in 1991 and smallest in 1990.

4. The infectivity index, defined as the product of the number of migrant vector aphids and the proportion that are viruliferous, was greatest for the earliest sown crops indicating a greater risk of primary infection with BYDV in these plots. Infectivity indices were greatest in 1989 and smallest in 1990.

5. Aphid infestations in crops were always greatest on the earliest- sown barley. The largest infestations occurred in 1989/90. Numbers of the bird cherry aphid were generally greater than those of the grain aphid.

6. Early-sown winter barley had greater BYDV infection than that sown later. MAV-like isolates, transmitted by the grain aphid, were dominant in the north (Leeds) whereas PAV-like isolates, transmitted most efficiently by the bird cherry aphid, were dominant in the east (Rothamsted and Wye). In the south west (Starcross) both serotypes were common. RPV-like isolates were rare. PAV infection tended to be less in later-sown crops, while MAV infection was less influenced by sowing date.

7. The increase in infection detected in mid-September sown barley did not correspond well with the increase in aphid infestation. The PAV-like isolates tended to be spread earlier than MAV.

8. The proportion of crop-colonising forms of the bird cherry aphid differed from one autumn to another.

9. Colonising and non-colonising forms of the bird cherry aphid in autumn could not be identified morphometrically, nor by the use of aphid acquire BYDV at a similar rate in autumn, but the colonising form transmits the virus more efficiently to new plants.

11. The non-colonising forms of the bird cherry aphid tend to fly higher and longer than the colonising forms. Virus sources may therefore be several kilometres from infected fields.