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The peach potato aphis Myzus persicaeThe peach potato aphid Myzus persicae is a globally distributed aphid species, located in all but the coldest terrestrial habitats, where it has been found on a wide range of host plants. At present its presence has been recorded from species of nearly 130 plant families.
The economic importance of M. persicae is related not only to the direct damages that this species may cause on plants (such as legumes, cucurbits, crucifers and solanaceous crops), but also to the virus transmission (more than 180 plant viruses have been identified as transmitted by the peach potato aphid).
The green peach aphid M. persicae is resistant to more insecticides than any other insects. M. persicae indeed has a documented resistance to 71 synthetic chemical insecticides.
M. persicae is a notable example of a heteroecious parthenogenetic aphid species. Its reproduction is based on parthenogenesis only from spring to autumn, then as the day length drops below a critical level (about 8 hours), apterous holocyclic viviparae produce gynoparae and males on secondary (herbaceous) hosts which migrate to the primary host, peach, Prunus persica L. (Rosaceae). The gynoparae then give birth to oviparae that lay the overwintering eggs after mating with males. Three other life cycle categories, excluding holocyclic ones, have been described in relation to the photoperiodic response, i.e. anholocyclic, androcyclic and intermediate. Anholocyclic populations are unable to produce the sexual morphs and overwinter as parthenogenetic females on weeds or winter crops. Androcyclic population, under short day conditions, produce parthenogenetic morphs and males, which are able to mate with oviparae of holocyclic or intermediate clones. Intermediate genotypes produce many apterous and alate virginoparae, some males and alate females which give birth both to virginoparae and oviparae. The different overwintering strategies of aphids offer a biological advantage, in terms of spread and survival, since they are able to adapt to various climatic conditions.
The standard female karyotype of this species is 2n = 12, but specimens with a chromosome complement of either 2n = 13 or 14 have also been reported. Variations in the chromosome structure have been also observed and they are mainly due to chromosomal translocations and, occasionally, to fragmentations that result in an increased chromosome number. Several populations of M. persicae were heterozygous for a translocation between autosomes 1 and 3 and this particular rearrangement has been shown to be involved in resistance to organophosphate and carbamate insecticides.
Chromosomal rearrangements in M. persicae have been hypothesized to affect some complex phenotypic traits, such as the host plant choice. A peculiar example of host adaptation concerns M. persicae strains feeding on tobacco. Morphometric analyses of specific taxonomic markers revealed that they are distinguishable from those living on other host plant so that the tobacco-feeding form was elevated to the status of a separate species. Further molecular evidences failed to confirm the genetic isolation of the population living on tobacco, although other data as well as behavioural/pheromonal evidence suggests that the two forms undergone some significant degree of ecological-evolutionary divergence.