Scientific description of Aphids (2020)Based on J. Kroschel. et al. (2020) Insect Pests Affecting Potatoes in Tropical, Subtropical, and Temperate Regions. In: Campos H., Ortiz O. (eds) The Potato Crop. Springer, Cham
The authors of this content are Jürgen Kroschel, Norma Mujica, Joshua Okonya, Andrei Alyokhin
Macrosiphum euphorbiae (Thomas, 1878) (Hemiptera: Aphididae)
The green peach aphid, Myzus persicae, is thought to have its origins in China, just as its overwintering host plant, the peach (Prunus persica (L.) Batsch) (image below). However, the green peach aphid is highly adaptable and is currently cosmopolitan in distribution.
The potato aphid (M. euphorbiae) originated in North America but has spread to the temperate parts of Europe and Asia and is found in all potato growing areas globally (CABI 2017c, d).
Winged green peach aphid start infestations on potato (a), wingless green peach aphids start colonies under the leaf (b), aphid colonies on potato tuber sprouts in stores (c), where they transmit viruses to seed potatoes. (Courtesy: CIP)
Both species are extremely polyphagous, being capable of feeding on several hundred-plant species (Blackman and Eastop 2000).
Symptoms of infestation
Aphids can damage potato plants directly by feeding on sap, and indirectly by transmitting various viral diseases. Direct damage. Continuous sucking of sap by large numbers of aphids considerably weakens and slows plant development.
Removing sap and injecting toxic saliva causes leaf deformation. The weakened plant produces low quality tubers.
During feeding, aphids excrete honey dew which promotes growth of a sooty black mold on plant leaves or stems, hence reducing the photosynthetic area for the plant. Indirect damage. The most important damage caused by aphids in potato is virus transmission.
Symptoms of virus infestation vary depending on the virus transmitted. For instance, potato leaf roll virus (PLRV) causes leaf-rolling and tuber stem necrosis in potato. Other PLRV symptoms include thickening, curling, chlorotic spotting and yellowing of the leaves (CABI 2017c, d; Larrain et al. 2003; Salazar 1995).
Impacts on production losses
Direct damage: Large build-up in aphid population may result in death of heavily infested plants. Since aphid distribution within potato fields is usually clumped, this results in patches of dead plants, sometimes referred to as 'aphid holes.' However, this phenomenon is relatively uncommon.
In most cases, direct damage by aphids does not affect potato yields.
Indirect damage: Most aphid-related damage to potato crops is caused by virus transmission. Potato leafroll virus (PLRV) and potato virus Y (PVY) are the two most important potato-infecting viruses.
Both severely diminish potato yield and quality in most potato-growing areas. PLRV is a persistent virus transmitted exclusively by potato colonizing aphid species.
PVY is nonpersistently transmitted by at least 50 different aphid species, most of which probe potato plants with their proboscis, but do not settle nor reproduce on them. M. persicae is the most effective vector of both persistent and nonpersistent viruses.
It is also a highly polyphagous species that often moves into potato fields from surrounding crops and noncrop vegetation (CABI 2017c, d; CIP 1996; Larrain et al. 2003; Salazar 1995).
Methods of prevention and control
- Biological control.
Various natural enemies of aphids act as efficient biological control agents; among those are different predatory insects (e.g., lady beetles and larvae of green lacewings) and parasitic wasps (Aphidius spp.).
Other generalist predators include Orius spp., Geocoris spp., and Nabis spp. Guard rows of flowering vegetation planted within potato fields can provide a habitant for aphid natural enemies (Powell and Pell 2017).
Entomopathogenic fungi commonly infect aphids under field conditions and may cause epizootics that significantly reduce aphid densities (Pell et al. 2001).
Numerous biological control products that use seven species of entompathogenic fungi (mostly Beauveria bassiana and Lecanicillium spp.) are commercially available for aphid control. Proper timing is very important when using these products because fungal spores are strongly influenced by environmental conditions, such as temperature and relative humidity (Kim et al. 2013).
- Biological insecticides.
Extracts from garlic (Allium sativa L.), neem (Azadirachta indica A. Juss.), red chili (Capsicum annum L.), pyrethrum flowers (Chrysanthemum sp.), either singly or in mixtures provide some aphid control, especially at an early stage of infestation.
- Cultural practices.
Weeding and removal of alternative and overwintering hosts such as wild mustards (Brassica spp.), use of wheat straw or white plastic as mulch, and intercropping with onion, garlic or coriander (Coriandrum sativum L.) have shown to reduce aphid populations.
Planting only high-quality disease-free potato tubers and rogueing out virus-infected plants is recommended for preventing virus damage even in the presence of substantial aphid populations (CIP 1996; Larrain et al. 2003; Sanchez and Vergara 2002).
- Chemical control.
Insecticides specific to the homopterans such as spirotetramat, flonicamid and pymetrozine have low effect on natural enemies and are therefore good candidates for IPM. To the contrary, use of broad-spectrum insecticides may flair up populations of green peach aphids that recover quicker than populations of their natural enemies.
On a small scale, application of potassium-based liquid soap sprays may reduce numbers of potato-colonizing aphids. When practicing chemical control, it is important to remember that green peach aphid has a high propensity for developing insecticide resistance that rivals that of the Colorado potato beetle.
Failures have been reported for at least 69 different active ingredients, including all commonly used chemical classes (Alyokhin et al. 2013).