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).