One of the major threats to the health of seed potato crops is the transmission of viruses by aphids

The viruses may be persistent (e.g. Potato Leaf Roll Virus; PLRV) or non-persistent (e.g. potyviruses such as PVY, PVA). This distinction is important in determining how long it takes an aphid to acquire the virus from an infected host plant and transmit it on to another plant. This in turn has an impact on which aphids can transmit the virus and how to manage them using insecticides or other means.

The main virus species in GB potato crops is currently Potato Virus Y (PVY)

There are two main methods of post-harvest testing for the presence of virus in potato tubers.  The standard growing on ELISA test and molecular methods using real-time polymerase chain reaction (PCR)

Standard Growing On test (GO)

Potato tubers are prepared and treated with gibberellic acid which promotes the break of dormancy and induces sprouting.  These samples are planted out and leaf samples are taken 5 – 6 weeks after planting.  The leaf tissues are tested using the ELISA method which uses antibodies which are specific to certain groups of viruses. 

Direct Tuber Testing (DTT)

DTT uses molecular methods which detect the presence of virus nucleic acid within the tuber sample.

Other differences between the two tests are mainly cost and turnaround time. The standard growing on test requires more handling and plant growth time (usually between 4 – 6 weeks) but is slightly more cost effective.  The molecular method is more expensive but the advantage here is a faster turnaround time usually within days.

Aphid monitoring

There are two main methods for monitoring aphid flights: the national suction trap network and in-field traps.

Suction traps give a regional indication of aphid flights. Field traps, like the yellow water traps, tell you what is moving on a local scale.

Winged aphids tend not to be active below~10^oC.

Aphid forecasting

Long-term (56 years in 2020) aphid data (from the suction-trap network) and weather data (Met Office and others) is used to forecast the date of the first aphid flights, as well as aphid abundance in spring and early summer. Visit the Rothamsted Insect Survey website for the most recent forecast.

Does the timing of aphid flights matter (early vs late season)?

Mathematical modelling work from the US suggests that an early-season peak in the numbers of non-colonizing aphids resulted in the highest number of PVY-infected plants at the end of the season, while mid- and late-season peaks caused relatively little virus spread. We don’t know if this work is directly transferable to GB. Modelling using Scottish aphid and seed certification data indicates that the inclusion of aphid data up to the end of July is important in understanding virus spread in Scotland.

Where is the virus coming from?

Aphids are not believed to carry PVY over long distances and therefore the most likely sources of virus are the input seed and/or neighbouring potato crops and groundkeepers that are already infected with virus. 

Left uncontrolled, even small outgrade piles can be a source of virus inoculum.

Can aphids be tested to see if they are carrying PVY?

Currently, this can't be done reliably due to the non-persistent nature of virus transmission and the short period of contact with the aphid’s mouthparts. Virus particles are believed to dissociate from the mouthparts once aphids are held in collecting fluids, e.g., as used suction and yellow water traps.

Can aphids be tested to see if they are resistant to insecticides?

There have been research projects to monitor for evidence that resistance might be evolving. This requires live aphids. It is also possible to monitor the occurrence of already known resistance mechanisms, such as resistance to pyrethroids in the Peach-potato aphid. This can be done using dead aphids, for example, samples from the suction trap network. The results are reported via the Insecticide Resistance Action Group (IRAG).