- Viruses with persistent transmission (e.g. PLRV)
- Viruses with non-persistent transmission (e.g. PVY, PVS)
- There are five main species of aphid which feed on the potato crop and form colonies:
- Myzus persicae (peach potato aphid)
- Macrosiphum euphorbiae (potato aphid)
- Aphis nasturtii (buckthorn potato aphid)
- Aulacorthum solani (glasshouse potato aphid)
- Aphis fabae (black bean aphid)
- more …
- Damage can be from direct feeding or from virus transmission.
- For direct feeding damage to occur, numbers must be large. More …
- Virus transmission can occur even when numbers of aphids are low.
- In addition, many other species of aphid have the potential to transmit viruses by probing behaviour when passing through a crop in search of a more favoured food plant.
- Aphids are likely to begin flying at temperatures >14 oC, a similar time to early stages of potato development.
Aphid life cycle and behaviour
- Aphids which colonise potatoes overwinter on an alternative host and initial development in spring is on that host.
- Insecticide-resistant aphids generally have poorer winter survival than do insecticide susceptible aphids.
- Winged aphids develop when the temperature reaches approximately 14 oC and these are able to migrate to potato crops.
- Winged aphids of non-colonising species are likely to be produced at a similar temperature and have a potential to move through potato crops while searching for a more favoured host.
- Colonising aphids produce live nymphs (without an egg stage) which can result in rapid population build-up.
- Aphids are attracted to yellowing leaves, which may be senescent or already infected with virus.
- Different species of aphids may favour upper or lower leaves of potatoes, so crop monitoring should examine different layers of the canopy.
- Potato cultivars may differ in their resistance to aphids (this is distinct from resistance to viruses). More …
- Virus infection may encourage dispersion of aphids within a crop and aphid feeding may up-regulate or down-regulate potato genes to favour further feeding.
- Aphids can detect the border between dark soil and a green crop and tend to land first in the outer area of a crop; there is a potential to reduce transmission of non-persistent viruses into seed blocks by planting a barrier of another crop outside the block.
- Plants removed during roguing of a seed crop can still be a source from which viruses can be transmitted and should be removed from the field completely.
Transmission of viruses within plants
- The risk of virus transmission within a plant is highest early in the season, when foliage is immature.
- Viruses multiply in dividing cells; as plants grow, the proportion of dividing cells reduces, mature plant resistance develops and tubers are less likely to be affected.
- Transmission of viruses may occur from one stem to another via seed tubers. More …
- Plants yield poorly only if infected early.
- Early infection of seed crops also increases the risk of progeny infection which will produce plants the following year that yield poorly and form a source of inoculum for that crop.
- Control of virus transmission by aphids is therefore most important early in the season and is particularly important for seed crops or cultivars which are very susceptible to viruses.
Transmission of viruses to plants
- The most important viruses are potato leaf roll virus (PLRV) and potato virus Y (PVY) but potato virus S (PVS) may also be a problem.
- There are two types of virus.
Viruses with persistent transmission (e.g. PLRV)
- These viruses require several hours of feeding before the aphid becomes infected and then a further several hours of feeding to transmit the virus to another plant.
- These viruses are mainly transmitted by aphids which feed on potatoes.
- An aphid remains infective for a long time (often its whole life).
- These viruses may be carried into a crop by aphids.
- Chemical control can be effective.
Viruses with non-persistent transmission (e.g. PVY, PVS)
- These viruses require only a few minutes to be acquired and a few minutes to be transmitted. They are carried in the aphid stylet and are acquired and passed on during probing of leaves before feeding.
- These viruses can be transmitted by many aphids, including those which do not feed on potatoes, but the efficiency of transmission varies between species.
- Aphid remains infective for a short period (e.g. 12 hours).
- These viruses are more likely to be spread around within a crop by aphids (e.g. from plants grown from infected seed) than carried in from outside the crop.
- Feeding on uninfected plants can “strip out” the virus from aphid mouth parts.
- Chemical control is difficult due to the rapidity of transmission.
- AHDB hosts an Aphid Forecast service, based on weather forecasts and long term research of the suction trap network.
- Forecasts are based on predicted survival and flight of aphids which overwinter in active stages (as opposed to winter-hardy eggs) in the UK.
- Forecasts are available for:
- peach–potato aphid (Myzus persicae)
- potato aphid (Macrosiphum euphorbiae)
- bird cherry–oat aphid (Rhopalosiphum padi)
- rose–grain aphid (Metopolophium dirhodum)
- grain aphid (Sitobion avenae)
- mealy cabbage aphid (Brevicoryne brassicae)
- Forecasts predict:
- time of appearance of aphids in different regions
- size of aphid populations
- Forecasts provide an indication of aphid risk, which is particularly useful early in the season before mature plant resistance develops.
Assessing the risk of transmission of PVY
- Aphid vectors of PVY have been given an efficiency index based upon their ability to transmit the virus. The higher the index, the greater is the ability of the aphid to transmit PVY.
- Virus transmission efficiency is taken into account in the AHDB / FERA Aphid Monitoring scheme. Growers can participate in the scheme and have their aphids identified or use the scheme as a warning of risk in their area.
- Growers of seed crops or very virus sensitive cultivars are most likely to benefit from participation in the scheme.
- For most ware crops, warnings from the monitoring scheme may be sufficient.
- However there are greater risks for seed crops and very susceptible cultivars:
- young potato plants are at risk from even a low number of aphids with a high transmission efficiency.
- PVY can be transmitted before aphicides take effect.
- Aphid monitoring appears to provide insufficient time for action to be taken according to the results.
- Mature plant resistance is important in reducing virus transmission in the plant.
- Early growth and maturity of seed crops may be one of the most effective means of reducing the risk of PVY infection.
Method 1 (DIY)
- In seed crops a simple method of aphid monitoring can help to assess the risk of virus transmission, particularly for viruses with non-persistent transmission. This method is used in commercial seed crops.
- Select 35 plants, walking the crop in a “W”
- From each plant sample three compound leaves: one from the top of the canopy, one from the middle of the canopy and one from the bottom of the canopy.
- Count the total number of colonies found during the inspection.
- A colony comprises one leaflet with three or more aphids including at least two wingless ones.
- If five or more colonies are found during an inspection, there is a risk of virus transmission, particularly of viruses with non-persistent transmission.
- If, despite control measures, 10 or more colonies are found during inspection seven days later, there is a high risk of virus transmission and the crop should be tested for viruses.
Method 2 (aphid monitoring schemes)
- The AHDB organises an aphid monitoring scheme.
- Growers who sign up to the scheme are sent “yellow water traps”.
- The traps are placed in crops and the contents sent weekly for identification by FERA.
- Results are reported to the grower and published on the internet.
- Any grower can use the published results as a warning of aphid populations in their region.
Suction trap monitoring
- Rothamsted Research performs suction trap monitoring at a number of sites around the UK.
- The results are published on the internet and provide information on aphid migration, in particular.
- Results of in-crop monitoring are the easier to use.
- The importance of aphid predators in control of aphids is gaining increasing recognition (more …).
- Aphid predators include species from the following groups:
- Parasitoids / parasitic wasps
- Eggs are laid in aphids.
- Developing larvae consume individual aphids.
- May have limited effect of aphid control.
- Adults and larvae both eat aphids.
- Adults feed on nectar and aphids.
- Larvae feed on aphids.
- Adults feed on nectar and pollen (so may be attracted by flowering margins).
- Larvae feed on aphids.
- Parasitoids / parasitic wasps
- An integrated control programme for aphids should include care and encouragement of beneficial organisms.
Notes on aphid biology
Aphid and virus control 2021 (Sustainable control of aphids and virus transmission)
Aphids 2020 (Aphid forecasting; influence of beneficial insects)
Aphids and virus transmission 2018 (Influence of environment on virus replication; virus transmission from seed tubers; efficiency of different vectors in transmission of non-persistent viruses)
Aphids and virus transmission 2014 (Results from traps vs aphid counts; aphid life cycle and glossary; influence of environment; movement within a crop; use of barrier crops)
Aphids and virus transmission 2013 (Persistent and non-persistent transmission of viruses; method of DIY aphid monitoring; sub-lethal effects of neonicotinoids on bumblebees)
Aphid control 2011 (Time of greatest risk of virus infection)
Aphid population and control 2009 (Population and virus risk development in different seasons; use of yellow water traps)
Pest control 2001 (Includes: aphid monitoring principles; virus transmission risk principles; efficiency of vectors for non-persistent virus transmission)
Aphid control 1994 (Yield reductions due to aphids and to viruses; mature plant resistance
Identification, monitoring and forecasting of aphids
Link to external site for aphid identification
Link to external site for aphid monitoring scheme
Link to external site for aphid monitoring scheme results
Link to external site for aphid suction trap results
Link to external site for aphid forecasts