Myzus persicae
(green peach aphid)

M. persicae is probably of Asian origin, like its primary host plant (Prunus persica) but now occurs everywhere in the world except where there are extremes of temperature or humidity.

Aerial dispersal of winged forms over long distance is the main mode of dispersal of this cosmopolitan pest. However, phytosanitary measures are important to stop the spread of virus-infected planting material (for example, seed potatoes) from which native aphid vectors could spread subsequently.

Open vegetation; crops and herbaceous plants in open situations. Peach orchards.

The winter (primary) host of M. persicae is almost invariably Prunus persica (peach), including var. nectarina; sometimes P. nigra in USA, and possibly P. tenella, P. nana, P. serotina, P. americana and peach-almond hybrids. It is not clear whether the sexual part of the life-cycle is completed on species other than P. persica and P. nigra.

M. persicae is highly polyphagous on summer hosts, which are in over 40 different families, including Brassicaceae, Solanaceae, Poaceae, Leguminosae, Cyperaceae, Convolvulaceae, Chenopodiaceae, Compositae, Cucurbitaceae and Umbelliferae. Summer hosts include many economically important plants.

M. persicae is heteroecious holocyclic (host alternating, with sexual reproduction during part of life-cycle) between Prunus (usually peach) and summer host plants, but anholocyclic on secondary (summer) hosts in many parts of the world where peach is absent, and where a mild climate permits active stages to survive throughout the winter. It is usually anholocyclic in tropics and sub-tropics, with exceptions: for example, Ghosh and Verma (1990) reported apterous oviparous females of M. persicae for the first time from India, collected on Prunus persica. Blackman (1974) discussed the life-cycle variability of M. persicae on a worldwide basis.

For host-alternating populations, in spring, winged female emigrants (alate virginoparae) produced from the fundatrices migrate to summer hosts. A series of generations of wingless (apterous) and alate virginoparae are produced viviparously by thelytokous (all-female) parthenogenesis. These develop on summer hosts until reduced daylength (critical photoperiod between 12.5 and 14 hours in Europe), in conjunction with temperature below a certain threshold, induces autumn migrants (gynoparae) which migrate back to peach. Gynoparae will attempt to colonize a range of trees and shrubs, but the sexual part of the cycle is only completed on Prunus persica and close relatives. Gynoparae produce oviparae (mating females) that feed and develop on peach leaves. Males are produced after gynoparae (1 month later in a study from Italy) on the summer hosts, and migrate independently to peach, where they mate with the oviparae, which by then have become adult. Males appear to be attracted by sex pheromone released by sexual females, and are also attracted to the odour of the winter host (Tamaki et al., 1970). Oviparae lay 4-13 eggs, usually in crevices around and in axillary buds. Up to 20,000 eggs may occur per P. persica tree, although 4000 is around average, with large variation between trees (van Emden et al., 1969). The eggs overwinter in diapause, requiring a period of chilling to develop, and are extremely cold resistant (surviving temperatures as low as -46°C). Hatching coincides with swelling of flower buds, which provide food for first fundatrices. High fundatrix mortality may occur (van Emden et al., 1969). Fundatrigeniae feed on opened buds, flowers and soft shoots of the peach tree. Winged female emigrants are produced in the second generation after the fundatrix, but production of wingless females may continue for several generations, with increasing numbers of emigrants being produced as the nutritional suitability of the peach tree declines.

On the summer hosts, populations tend to be dispersed. M. persicae tends to feed on older senescing leaves, often along the leaf veins. van Emden et al. (1969) described how a range of host-plant variables affected aphid development and fecundity. Plant nutrition is a factor in the induction of winged forms, along with temperature, but there is also a strong genetic component. In laboratory experiments, low temperature promoted, while high temperature tended to suppress, the development of winged forms. Kuo (1991) described development and reproduction on radishes and potatoes at six constant temperatures (5-30°C) in the laboratory. M. persicae is relatively cold resistant. Howling et al. (1994) described mortality of aphids at various cold temperatures and their results suggested that an acclimatized overwintering population of M. persicae would persist without significant mortality after a period of 7-10 days with -5°C frosts each night.

Between six and eight generations developed on sugar-beet plants during the growing season in the Czech Republic, wheras 10-25 generations a year were possible on potatoes in southwestern USA. Wingless parthenogenetic females produce 30-80 progeny each. Higher growth rates have been observed on virus-infested plants. Winged females alight fairly indiscriminately on summer hosts, as expected for a polyphagous species, although they have a landing preference on yellow and yellow-green surfaces. Decreased departure rates account for accumulation on favoured hosts.

M. persicae has 2n=12 chromosomes normally, but a form heterozygous for a chromosomal translocation is worldwide and common (Blackman et al., 1978). M. persicae is a highly variable species; strains, races and biotypes have been distinguished by morphology, colour, biology, host-plant preference, ability to transmit viruses and insecticide resistance (van Emden et al., 1969). A distinct form of M. persicae (=nicotianae Blackman) occurs throughout most of the world on tobacco (Blackman, 1986; Takada and Tamura, 1987). Hybridisation in a region where the two forms both have a sexual phase on peach may account for the fact that both now have the same genes for insecticide resistance (Field et al., 1994). Remaudiere et al. (1991) reported a winged viviparous albino of M. persicae from South America.

The literature on M. persicae is probably larger than for any other aphid species. Major reviews of this aphid include those by van Emden et al. (1969) and Mackauer and Way (1976).

Aphid natural enemies tend to be habitat-specific rather than host-specific, so the important natural enemies attacking particular aphid pests on crops tend to vary according to the crop, the circumstances under which it is grown and the climate. This is particularly true of aphid pests attacking a range of different crops over large geographical areas. Besides, many parasitoids are members of species complexes, morphologically very similar but with different host preferences and geographical distributions. Those in the list of natural enermies are only a selection of species that have been considered as important by investigators and should not be taken as definitive.

M. persicae is attacked by over 30 species of primary parasitoid. Most also attack a range of other aphid species, although some, for example, Trioxys similis, appear host-specific. T. angelicae is a parasitoid on Prunus only. M. persicae is the preferred host for Aphidius matricariae and Aphelinus semiflavus in the USA. Aphidius colemani is also an important natural enemy in North and South America. The second and third aphid nymphal instars are usually preferred by ovipositing parasites (Hågvar and Hofsvang, 1991) with older nymphs usually avoided as they result in small parasite adults emerging which leave few offspring; though Aphidius gifuensis prefers third and fourth instars (van Emden et al., 1969). Parasites often use aphid honeydew as a host-finding cue (Hågvar and Hofsvang, 1991).

Coccinellids, adults and larvae, are important predators worldwide, particularly Adonia spp., Coccinella spp., Hippodamia spp. and Scymnus spp. Coccinella septempunctata and Chilomese sexmaculata were the most abundant predators in potatoes, and other crops, in India (for example, Raj, 1989; Gupta and Yadava, 1989). Important syrphid larvae predators worldwide include Episyrphus balteatus, Ischiodon scutellaris, Metasyrphus corollae and Scaeva pyrastri. Kumar et al. (1987) provided a key for syrphid larvae that prey on M. persicae in India.

Van Emden et al. (1969) provided an extensive list of known natural enemies of M. persicae, which has been updated from the literature to 1996. Halima et al. (1993) described parasites and predators attacking M. persicae in Tunisia, and Nakata (1995) described fluctuations of aphids and their natural enemies on potato in Japan. In India, the common myna bird (Acridotheres tristis) was recorded preying on M. persicae in cumin (Gupta and Yadava, 1989).

Kish et al. (1994) described infestation of M. persicae by Verticillium lecanii on peach leaves, and Beauveria bassiana and Conidiobolus sp. on potatoes; while aphids collected from weeds growing in and near a peach orchard were infected with Entomophaga chromaphidis, Conidiobolus obscurus and V. lecanii. Aphids on potatoes and non-solanaceous hosts in Idaho, USA, were infected with Pandora neoaphidis, Chromaphidis and Conidiobolus spp. (Kish et al., 1994). Li et al. (1992) described Entomophthorales in China. Pathogenicity of these fungi is greatest when humidity is high.

Methods have been developed for diagnosing economically important characteristics of field-collected aphids. Enzyme-linked immunosorbent assay (ELISA) is widely used to detect plant viruses carried by M. persicae (for example, Carlebach et al., 1982; Reinhardt et al., 1988). Levels of insecticide resistance in individual aphids can be estimated from their esterase content measured by immunoassay, and DNA diagnostic methods for resistant M. persicae have also been developed (Field et al., 1997).

On Prunus persica, inspect for curled leaves, in which colonies develop in early spring.

Monitoring is important in field crops, but M. persicae transmits viruses of crops such as sugar beet and potato at low densities, and is therefore difficult to detect on the crop before the damage is done. Suction and yellow traps are the most efficient way to detect first migration of winged aphids into the crop. Networks of suction traps have been developed to monitor migrating aphids, for example, the Rothamsted Insect Survey in the UK and AGRAPHID in France (Hulle et al., 1987), as part of the 'Euraphid' forecasting system in European Union countries. Much effort has been expended on developing forecasting methods, for example for sugarbeet (Harrington et al., 1989). Appropriate applications of insecticides are often based on monitoring data. Insecticide application in sugar beet against M. persicae is only necessary when aphids are carrying yellows viruses. Vertical nets placed downwind of fields of infected potato plants can be used to quantify the proportion of M. persicae carrying virus (diagnosed by use of ELISA; see Diagnosis).

M. persicae is a member of a group of closely related and very similar-looking species in the subgenus Nectarosiphon. Some of these are specific to particular host plants and confined to Europe; see Blackman and Paterson (1986) for a key to these. Others are more widely distributed: Myzus certus is a red species that restricts its feeding to Caryophyllaceae and Violaceae, and occurs in Europe and North America. This species does not host-alternate to peach; a sexual generation, with wingless males, can occur on Caryophyllaceae. Myzus dianthicola is a deep yellow-green colour and is only known from carnations (Dianthus) causing chlorotic patches on the leaves. It is recorded from USA, Europe and New Zealand, and has no sexual phase.

Myzus antirrhinii is mid-green to dark grey green and rather polyphagous. It forms dense colonies on certain host plants, for example, Buddleja, Antirrhinum and Pittosporum, but it sometimes also occurs on field crops. Production of winged morphs is rather sporadic, and it has no sexual phase. M. antirrhinii is known from western USA and Canada, Europe and Australia.

Myzus nicotianae occurs in most parts of the world where tobacco is grown. It has slight but consistent morphological differences from M. persicae and Blackman (1986) gives linear discriminant functions for winged and wingless females, but the two taxa can only be reliably separated using multivariate morphometrics.

M. nicotianae is anholocyclic (permanently parthenogenetic) almost everywhere, but has a sexual phase on peach in some parts of the world (for example, northern Greece) and some hybridization with M. persicae may occur, which would account for the fact that it has the same genes for insecticide resistance as M. persicae (Field et al., 1994), and the same resistance-linked chromosomal translocation. Because the extent of gene flow between the two taxa is still uncertain, and because the two are confused in the literature, data for M. nicotianae is here included in the treatment of M. persicae.

Electrophoretic techniques can distinguish between M. persicae and M. antirrhinii, based on patterns of esterases (Ffrench-Constant et al., 1988; Blackman and Spence, 1992).

Two other widely distributed and polyphagous pest species are less closely related but liable to confusion with M. persicae: the shallot aphid, Myzus ascalonicus, which is straw-coloured with contrastingly black tips to antennae and legs, and Myzus cymbalariae, which is yellowish brown to dark reddish brown. Both these species have siphunculi much shorter than those of M. persicae. The preferred hosts of both species are in Alliaceae and Caryophyllaceae.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Chemical Control

As M. persicae is mainly important as a virus vector, a high level of control as provided by insecticides is often required. However, insecticides are relatively ineffective for non-persistent viruses, because transmission by the aphid occurs in just a few seconds. Moreover, there are varied restrictions on active ingredients in different parts of the world, and further restrictions on formulation, method of application, crop and time of year. Additionally, resistance to most groups of insecticides that defeats their use has appeared in many places (Foster et al., 2007; Bass et al., 2014). The aphid has several mechanisms conferring resistance primarily to different groups of insecticides; amplification of carboxylesterase for organophosphate insecticides, insensitive target site (MACE) against dimethyl carbamates, knock-down resistance (kdr and super-kdr) against pyrethroids and most recently a mechanism known as Nic-R++ against neonicotinoids (Bass et al., 2011). Other insecticides such as pymetrozine and flonicamid may therefore be required to obtain adequate control of the aphid, and diamide insecticides should become available in the future. 

IPM Programmes

Insecticidal soaps have been found useful in greenhouses, where they have low toxicity to many beneficial organisms. The fungal pathogen Lecanicillium lecanii is compatible with insecticides and is effective against M. persicae in a wide range of greenhouse crops, but only where high humidities can be maintained. In field crops, however, the main form of IPM is the modification of choice of insecticide and time of application to minimise damage to indigenous natural enemies

Biological Control

Releasing natural enemies produced by commercial breeding companies has become a routine component in the control of M. persicae on greenhouse crops (Powell and Pell, 2007). Here lacewing larvae have given good control on aubergines, and the midge Aphidoletes aphidimyza has proved an effective predator of the aphid on peppers. However. Most releases are of parasitoids of M. persicae, the main species being Aphidius colemani, Aphidius matricariae and Aphidoletes abdominalis. 

Host-Plant Resistance

Host-plant resistance to insects is commonly based on secondary plant chemistry. As M. persicae can attack plants in many unrelated botanical families, such resistance is hard to obtain, and the focus has been more on morphological plant characters. Glandular trichomes on potatoes are an important resistance factor. Gibson and Pickett (1983) described the release of the repellent aphid alarm pheromone chemical, (E)-ß-farnesene, from these glandular hairs of wild potato. Trichomes also release a sticky exudate, which immobilizes aphids, and contains toxic sucrose ester compounds, shown to inhibit settling and probing. Glandular hairs have been bred into resistant potato cultivars (Vallejo et al., 1994). Gatehouse et al. (1996) reported enhanced resistance to M. persicae in transgenic potato plants expressing lectins, but such plants present a potential toxicity hazard to humans and have not been commercialised.

Increased waxiness in brassicas decreased aphid colonization, mainly due to a non-preference resistance mechanism (Stoner, 1992).

Cultural Control

Most cultural measures are aimed at reduction of the virus problem, and are particularly important when rapidly transmitted non-persistent viruses are involved. Among cultural control methods recommended  are early sowing (e.g. of potatoes), weed management and the use of certified seeds, known to be virus-free (for example, seed potatoes). In peach orchards normal pruning procedures on peach to reduce the number of overwintering eggs are effective control against overwintering eggs. This in turn is also beneficial to crops to which aphids migrate in summer. In potatoes, sprout inhibitor is sprayed to reduce emergence of infested volunteer plants which could serve as reservoirs of infection for the following year's crop. In sugarbeet, where beet itself is the most important reservoir of infection, elimination of overwintering plants is important.

Some success in reducing M. persicae numbers and virus has been achieved in high value field crops by the expensive technique of laying aluminium foil between the plant rows to reflect the sky and disorientate arriving aphids. This approach has been modified and costs reduced by spraying the crop with highly reflective kaolin-based particles (Glenn and Puterka, 2005). Lightweight row covers ('horticultural fleece') of spun-bonded polyester or polyethylene can protect seedlings from viruliferous M. persicae (Harrewijn et al., 1991); the plants grow through the fleece as they get older.