From midsummer onwards, the catches of cereal aphids in the suction traps usually dominate the Scottish aphid bulletin and significantly affect the index that is used to estimate the vector pressure for aphid-transmitted potato viruses. Three species, the Rose-Grain aphid (Metopolophium dirhodum), the Grain aphid (Sitobion avenae) 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 has recently conducted field trials that support the role of cereal aphids, particularly the Rose-Grain aphid and the Grain aphid, in virus transmission.
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 and PVY transmission in 2018
During 2018, all four dominant species of cereal aphids were caught in high numbers in the aphid traps when compared with an 'average' year. For the period when most virus transmission is believed to occur (before 31 July), the catches of the Rose-Grain aphid ranked 8th over the last 32 years, the Bird Cherry-Oat aphid ranked 6th and the Grain aphid ranked 9th. These are the three species most strongly associated with the transmission of the most prevalent potato virus (PVY) in Scotland. Therefore, it is anticipated that the incidence of plants showing mosaic symptoms in 2019 will be higher than the levels observed in the 2018 potato crop. Virus management options will need to be considered should high populations of aphid vectors develop over the season.
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.
Cereal aphids in 2019
The first cereal aphids of 2019 were caught in the Scottish traps on the week ending 14th April, coming in early when compared to previous seasons. Although May's rainfall appears to be holding numbers at bay, periods of prolonged warm temperatures may lead to an increase in numbers early in the season.
As the Inverness trap has only recently started operation, we will be reporting on Edinburgh and Dundee catches only.
Please note that most of the graphs below represent actual numbers of aphids caught in these two east coast suction traps using a log scale. Viewing population data on a log scale makes it easier to spot subtle changes in numbers when comparing 2018 data to the large number of aphids caught in previous seasons.
Rose-Grain aphid in 2019
25 Rose-Grain aphids (Metopolophium dirhodum) have now been caught in the Scottish (Dundee and Edinburgh) suction traps up to 9 June, ranking 7th over the last 32 years of trapping. Between 3 and 9 June, none were caught in the Dundee trap, while six were caught at Edinburgh. The first individual of this season was caught in Edinburgh on 8 April, which is the earliest record for this species for Edinburgh in the last 32 years.
Grain aphid in 2019
27 Grain aphids (Sitobion avenae) have been caught in the Scottish (Edinburgh and Dundee) suction traps to 9 June, ranking 11th from the last 32 years of monitoring. The first individual was caught at Edinburgh on the 7th May; the first at Dundee was caught on the 23rd May.
Bird Cherry-Oat aphid in 2019
33 Bird Cherry-Oat aphids (Rhopalosiphum padi) have been caught in the Scottish (Dundee and Edinburgh) suction traps up to 9 June. The 2019 total catch for this species now ranks 15th over the last 32 years. The first Scottish individual was caught on the 25th April in Dundee; the first in Edinburgh was caught on the 12th May.
Apple-Grass aphid in 2019
83 Apple-Grass aphids (Rhopalosiphum oxyacanthae) have been caught up to 9 June. This 2019 season total currently ranks 12th over the last 32 years. 21 of these were caught at Dundee, the rest at Edinburgh.