Cytogenetic Studies on Willow Aphids

Abstract

Summary Cytogenetic study was carried out on willow aphids viz. Cavariella aegopodii and Tuberolachnus salignus in order to ascertain the karyotype and sex determination in these aphids from different localities of Himachal Pradesh, India. In Cavariella aegopodii, collected from Shimla, Mashobra and Shoghi localities, 2n is 10. There is 1 pair of long, 2 pairs of medium sized and 2 pairs of short chromosomes. However, karyotypic variation was observed in aphid populations collected from the Solan locality, where the variable diploid chromosome numbers such as 2nϭ8, 9 and 10 were also recorded. The male sexuals of Cavariella aegopodii are diploid having 2nϭ9 with 4 pairs of autosomes and a single X chromosome. The various stages of meiosis in the testes of the male mainly occur during the early developmental stages and can also be found in the first and second instar nymphs. The Cavariella aegopodii has XX-XO type of sex determination system.In Tuberolachnus salignus collected from the Shimla, Mashobra and Shoghi localities, 2n is 20. The idiogram of Tuberolachnus salignus reveals the gradual decrease in chromosome length. However, karyotypic variation was observed in aphids collected from the Solan locality where the diploid chromosome number (2n) ranged from 18 to 20.

Population genetics of Tuberolachnus salignus, an obligate parthenogenetic aphid

“…A recent study on T. salignus in India reported a karyotypic variation with 2 n in the range 18–20 in one out of four localities studied; the other three localities only had specimens where 2 n = 20 (Dhatwalia & Gautam, 2009). Blackman and Spence (1996) had also reported chromosomal numbers of 2 n = 20 for T. salignus from the U.K. but did not report karyotypic variation.…”

The karyotype studies of some aphid species (Aphidoidea: Hemiptera) from Niğde province in Türkiye

“…The tendency to favor the inheritance of chromosomal fragments causes repetitive substitutes in the karyotypes of some aphids like Myzus persicae. Furthermore, aphids have a repetitive expression of the gene encoding telomerase, therefore they can also start the resynthesis of telomeres at the inner cut-off points, leading to the stabilization of chromosomal fragments (Wilson et al, 2003;Dhatwalia & Gautam, 2009).…”

“…Dutta & Gautam (1994) provided information about the chromosomal compositions of 52 aphid species belonging to 34 genera and 21 of them were reported for the first time. The sex diagnosis and karyotype of Cavariella aegopodii (Scopoli, 1763) and Tuberolachnus salignus (Gmelin, 1790) were detected in different localities of India in a study by Dhatwalia & Gautam (2009). Although they determined the diploid chromosome number of C. aegopodii as 2n=8, 9 and 10, the male diploid chromosome number comprised eight autosomal and a single X chromosome.…”