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Plantwise Technical Factsheet

foxglove aphid (Aulacorthum solani)

Host plants / species affected
Achillea millefolium (yarrow)
Allium sativum (garlic)
Beta vulgaris var. saccharifera (sugarbeet)
Betula pubescens (Downy birch)
Capsella bursa-pastoris (shepherd's purse)
Capsicum annuum (bell pepper)
Cichorium intybus (chicory)
Citrus
Citrus deliciosa (mediterranean mandarin)
Citrus reticulata (mandarin)
Citrus sinensis (navel orange)
Convolvulus (morning glory)
Cucumis sativus (cucumber)
Digitalis purpurea (foxglove)
Fragaria ananassa (strawberry)
Freesia
Glycine max (soyabean)
Helianthus annuus (sunflower)
Hordeum vulgare (barley)
Lactuca sativa (lettuce)
Lupinus (lupins)
Nicotiana tabacum (tobacco)
Phaseolus vulgaris (common bean)
Pimpinella saxifraga
Plantago (Plantain)
Polyphagous (polyphagous)
Rumex (Dock)
Silene latifolia subsp. alba (white campion)
Solanum lycopersicum (tomato)
Solanum melongena (aubergine)
Solanum tuberosum (potato)
Stellaria media (common chickweed)
Tragopogon (goat's-beard)
Tulipa (tulip)
Vicia faba (faba bean)
Viola wittrockiana (wild pansy)
List of symptoms/signs
Growing point  -  distortion
Growing point  -  honeydew or sooty mould
Leaves  -  honeydew or sooty mould
Leaves  -  leaves rolled or folded
Leaves  -  necrotic areas
Stems  -  honeydew or sooty mould
Whole plant  -  dwarfing
Symptoms

Light infestations of A. solani can severely injure potato foliage. Its feeding causes discoloured spots on tobacco, and heavily infested plants can show large necrotic areas, sometimes resulting in the senescence of the entire leaf. Feeding also causes irregular curling of young potato leaflets and it is speculated that growth of the leaflet is hindered as a result of the feeding puncture. In potato stores, A. solani can attack potato sprouts.

Indirect damage is caused by honeydew production and virus transmission. Honeydew, a sticky liquid excreted by the aphid, covers the foliage and is often colonized by black saprophytic fungi, hampering respiration and photosynthesis.

Prevention and control

Cultural Control

Selection of growing area

Because virus spread is related to aphid populations, seed production areas should be selected on the basis of aphid population studies. Aphid populations are generally low in areas with low temperature, abundant rainfall and high wind velocity. Within a potato growing area, to reduce dissemination of viruses through viruliferous aphids, seed potato fields should be located upwind from commercial potato fields and alternative host crops. Seed production areas ideally should be completely separated from commercial potato production.

Planting time

The timing of aphid migration may be more important than the total number of aphids trapped, as aphid flights often reach definite peaks at certain times of the year. Virus spread early in the season is more serious than later on, as young plants are generally more susceptible. Furthermore, plants that are infected early become more efficient sources for further virus spread than plants infected later in the season.

Infection sources

Primary hosts of the virus should be eliminated. Within a seed field, eliminate infected potato plants as early as possible. Yellow, flowering weeds and any other host plants within and around the field should also be removed.

Harvesting time

After a viruliferous aphid has fed on potato foliage, the virus requires time to infect the tubers. In order to avoid this, highest-grade seed potatoes should be harvested no later than 8 to 10 days after population studies reveal a critical aphid build-up or increase.

Tuber storage

Aphids readily colonize tuber sprouts and so potato tubers must be protected during storage by preventing access of aphids and by using aphicides. Seed potatoes are very susceptible to infection at this stage, and so potato stores should be fumigated when migration has finished, ensuring even distribution of smoke.

Host Plant-Resistance

Glandular pubescence, a non-specific arthropod resistance mechamism in the wild potato, Solanum berthaultii, has been used in potato breeding as a defence against a variety of insect pests, including potato aphids, the potato leaf hopper (Empoasca fabae) and the potato flea beetle (Epitrix cucumeris). Mizukoshi and Kakizaki (1995) reported the trapping of early instars of A. solani in the trichomes of Phaseolus vulgaris, resulting in differential mortality between cultivars. Obrycki et al. (1983) reported that glandular pubescent potato cultivars and naturally occurring predators and parasitoids are compatible and complementary methods for managing aphids on potatoes. Gibson (1971) reported A. solani resistance in three Solanum species.

Soybean cv. Adams is tolerant to infection by Soybean dwarf virus (SbDV) in the field and exhibits antibiosis to A. solani, which transmits SbDV (Takahashi et al., 2002; Ohnishi et al., 2012).

Snowdrop lectin (Galanthus nivalis agglutinin, GNA) has been shown to have insecticidal effects against A. solani when incorporated in artificial diet and/or expressed in transgenic potato (cv. Desireé) (Down et al., 1996).

Chemical Control

In non-persistent transmission of viruses, aphids transmit viruses faster than common aphicides can react to kill the vector. Within a field, aphicides may slightly reduce non-persistent virus transmission, but they cannot prevent it; neither can they control infections brought from outside the field by migrating aphids.

In the persistent transmission of viruses, the incubation period is long enough to allow aphicides to control vectors. Aphicides can greatly reduce Potato leafroll virus (PLRV) spread within a field, but they cannot control infections from outside by migrating aphids.

Mineral oil sprays are effective in reducing non-persistently transmitted viruses, but fail to prevent PLRV spread.

Rasocha (1997) describes carbamates and pyrethroids used for aphid control. The systemic insecticide imidacloprid was used to control aphid vectors of Soybean dwarf virus in Japan (Honda et al., 1991). Fenthion and etofenprox were used by Okubo (1993b) during early stages of soyabean growth. 

Extracts of the weed Artemisia vulgaris have shown toxicity to potato aphids (Metspalu and Hiiesar, 1994). Natural essential oils have also shown effectiveness against A. solani in the laboratory (Tomova et al., 2005; Górski and Piatek, 2009; Górski and Kania, 2010).

Dried tobacco leaf smoke showed some effectiveness against aphid pests, including A. solani, on organic cucumber in a greenhouse in Korea, depending on the amount of tobacco used and smoking time (Park et al., 2014).

Biological Control

Examples of biological control agents used against A. solani in greenhouses include the cecidomyiid predator Aphidoletes aphidimyza and the parasitoids Aphelinus abdominalis and Aphidius spp. (Belousov, 1998; Gillespie et al., 2001; Çota and Isufi, 2009). However, use of natural enemies against A. solani in greenhouses has had varying levels of success and few insecticides used for aphid control are also compatible with biological control programmes against other pests (Bünger et al., 1999; Dewhirst et al., 2012; Buitenhuis et al., 2013).

In a field study in Belgium, rates of parasitism of A. solani on potato were 63.5% in 2000 and 89.2% in 2001, and this aphid species was the preferred host of several species of Aphidiidae (Jansen, 2005).

In greenhouse experiments, Aphidius gifuensis has shown promise as a biological control agent of A. solani and Myzus persicae on sweet pepper (Capsicum annuum), especially when these aphids occur together (Messelink et al., 2011). Aphidius erviAphidius matricariaeEphedrus cerasicola and Praon volucre showed rates of parasitism of A. solani ranging from 24 to 51% in cage experiments on strawberry in Belgian greenhouses (Hance and Salin, 2014). Jandricic et al. (2014b) documented the efficacy of Beauveria and Metarhizium against A. solani for the first time and discuss the potential of entomopathogenic fungi as control agents of greenhouse pest aphids. Cladosporium aphidis and Lecanicillium spp. have also shown virulence to A. solani (Gui et al., 2005; Kim et al., 2007).

Attempts have been made to use flightless coccinellids to improve the biological control of insect pests such as aphids, as the adult beetles are unable to fly away from the host plants. In microcosm experiments inundative augmentation of natural flightless morphs of Adalia bipunctata revealed no differences in consumption behaviour of A. solani between flightless and winged beetles. Although flightless beetles had a longer residence time on the plants than winged beetles, they only resulted in significantly better biological control of M. persicae. Control of A. solani was thought to be less effective because the aphid tends to drop from the plant as an escape response upon disturbance. It is concluded that the natural flightless strain of A. bipunctata may improve the biological control of aphids but that the effect will vary with the species of aphid used (Lommen et al., 2008a,b). In a preliminary release experiment in greenhouses, a flightless strain of Harmonia axyridis was more effective in suppressing A. gossypii than the wild-type strain, and releases of larvae of the flightless strain were more effective in suppressing A. solani than the release of adults. These results suggest that it may be more effective to release larvae of flightless H. axyridis than wild-type larvae or flightless adults in biological control programmes (Seko et al., 2014).

Pheromonal Control

Although it does not appear to have been used commercially, A. solani reacted to alarm pheromones from Aphis craccivora in the laboratory (Mizukoshi, 1991).

IPM

Direct control of virus spread is not feasible. Indirect control, however, helps to reduce virus transmission. This includes consideration of the growing area, agricultural practices and chemical control (Raman, 1985). Bermudez (1982) recommends setting up of field units for data collecting on aphid population in principal potato areas used for seed potato production. From these units, information on periodic build up of aphids and diffused to farmers to time final vine killing and/or timely application of systemic insecticides.

Benuzzi (1996) describes strategies of biological and integrated control against arthropod pests, including A. solani, of Capsicum annuum in Italy. Trottin-Caudal and Millot (1993) have developed an integrated pest control programme for tomatoes as a protected crop (glass and plastic houses). Kibata (1982) describes an integrated control approach which has been successful in Kenya. It utilizes virus-resistant cultivars, certified seed, the removal of diseased plants and the use of systemic insecticides at planting, followed by foliar-sprayed systemic insecticides.

Impact

A. solani is becoming an increasingly economic important pest of several agricultural crops worldwide and has recently undergone a status change from an occasional pest to a serious pest of vegetables and ornamental plants in greenhouses of North America and the UK (Jandricic et al., 2010, 2014a). A. solani was first recorded on citrus in the north of Iran in 2003-2004 (Alavi and Rezvani, 2007).

In most potato growing areas, A. solani is one of the most economically important pests, causing injury either directly by their feeding punctures or indirectly by spreading virus diseases. With the use of organic insecticides, direct feeding damage has become less serious. However, more stringent permitted levels of virus infection in seed potato certification programmes has increased the importance of aphids as virus vectors, since a very small percentage of infection can lead to rejection of an entire seed lot.

A. solani is an important vector of Potato virus Y, Potato virus A, Potato virus X and Potato leafroll virus (Culjak et al., 2013). The aphid also transmits other viruses, including Cucumber mosaic virus (Contangelo et al., 1994), Soybean dwarf virus (Honda et al., 1996; Ohnishi et al., 2012), Bean yellow mosaic virus (Yahia et al., 1997), Turnip yellows virus (Schliephake et al., 2000), Zucchini yellow mosaic virus (Katis et al., 2006) and Johnsongrass mosaic virus (Mariño et al., 2010).

The economic injury level (EIL) for A. solani on greenhouse pepper (Capsicum annuum) was estimated at 57 cumulative A. solani-days and the economic threshold was established at 20 cumulative A. solani-days to prevent aphid density from reaching the EIL between sampling periods (Sanchez et al., 2007). In another study on greenhouse pepper, the EIL obtained was so low that treatment was required as soon as aphids were detected to prevent economic losses (Hermoso de Mendoza et al., 2006).

Related treatment support
 
External factsheets
NCAT ATTRA Pest Management Publications, The National Center for Appropriate Technology (NCAT), 2000, English language
University of California IPM Pest Management Guidelines, University of California, 2012, English language
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