Abstract
Parallel trends of chromosomal evolution in Aphidococca are discussed, based on the catalogue of chromosomal numbers and genetic systems of scale insects by Gavrilov (2007) and the new catalogue for aphids provided in the present paper. To date chromosome numbers have been reported for 482 species of scale insects and for 1039 species of aphids, thus respectively comprising about 6% and 24% of the total number of species. Such characters as low modal numbers of chromosomes, heterochromatinization of part of chromosomes, production of only two sperm instead of four from each primary spermatocyte, physiological sex determination, "larval" meiosis, wide distribution of parthenogenesis and chromosomal races are considered as a result of homologous parallel changes of the initial genotype of Aphidococca ancestors. From a cytogenetic point of view, these characters separate Aphidococca from all other groups of Paraneoptera insects and in this sense can be considered as additional taxonomic characters. In contrast to available paleontological data the authors doubt that Coccinea with their very diverse (and partly primitive) genetic systems may have originated later then Aphidinea with their very specialised and unified genetic system.
Highlights
The name Aphidococca was recently introduced by Kluge (2010) for the taxon combining two closely related groups of Homoptera insects, aphids and scale insects
In general we suggest that the genetic system of aphids could be termed the Aphidoid system for the uniformity with the names of the genetic systems of scale insects
We consider that at least some of these tendencies may be regarded as additional taxonomic characters, which support the erection of Aphidococca as a higher category differing radically from other Homoptera and more widely from all Paraneoptera groups
Summary
The name Aphidococca was recently introduced by Kluge (2010) for the taxon combining two closely related groups of Homoptera insects, aphids and scale insects. The smallest chromosome number is the same for aphids and for scale insects, 2n=4, and known in species of the tribe Iceryini (Coccinea: Margarodidae), in the genus Apiomorpha Rübsaamen, 1894 (Coccinea: Eriococcidae) Some of the chromosomes in the diploid set demonstrate heterochromatinization and even aggregation of heterochromatic elements in somatic cells until late prophase (Blackman 1980), resembling the Lecanoid-Comstockioid genetic system in scale insects. There are probably a few obligatory thelytokous species of scale insects, such as Protopulvinaria pyriformis (Cockerell, 1894) and Eupulvinaria peregrina Borchsenius, 1953 (Gavrilov and Trapeznikova 2008), which never produce males in any population or geographical region.
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