Introduction
From midsummer onwards, the catches of cereal aphids in the suction traps usually dominate the Scottish aphid bulletin and affect significantly the index that is used to estimate the vector pressure for aphid-transmitted potato viruses. Two species, the Rose-Grain aphid (Metopolophium dirhodum) and the Bird Cherry-Oat aphid (Rhopalosiphum padi), are known to be vectors of non-persistently transmitted potato viruses (e.g. PVY) and because they can occur in high numbers in the suction traps, each individual species can make a relatively high contribution to the overall aphid vector pressure index. SASA is currently conducting field trials on virus transmission to determine whether these contributions are appropriate when attributed to data from suction trap catches.
As would be expected, cereal aphids are also important pests of cereal crops, causing direct damage by feeding on crops and through the transmission of viruses such as barley yellow dwarf virus (BYDV).
Cereal aphids in 2010
Although three of the four species of cereal aphids which are particularly abundant in the aphid traps are well below their usual population levels for this time of year, the population of the one species that has been most strongly associated with the transmission of Potato Virus Y (PVY) in Scotland is very high when compared to the previous 25 years.
This species, the Rose-Grain aphid (Metopolophium dirhodum) is flying in sufficiently high numbers to indicate that there could be significant risk of transmission of PVY. In particular, we are concerned that the high levels of PVY present in the 2009 crop will be carried over to 2010 to provide a high level of inoculum for further transmission.
Therefore, seed potato crops of varieties susceptible to PVY may be at significant risk of virus transmission and growers should consider taking appropriate action to prevent transmission of PVY by a non-colonising aphid.
Potato varieties that have been revealed by virus testing of leaf samples collected during classification inspections as particularly prone to the acquisition of PVY include King Edward, Harmony, Shepody, Maris Peer, Nicola.
Although the majority of this species have been caught in the Dundee trap, numbers caught in the Elgin and Edinburgh traps have been extremely when compared to the same traps in the previous twenty-five years. This means that although the risk of PVY transmission by this species has been lower in these areas, it has still been exceptionally high in comparison to previous years. Therefore, we continue to recommend that growers in all areas take appropriate action to prevent transmission of PVY by non-colonising aphid in any crops that have yet to be burned down.
