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Simple Summary: The class Insecta constitutes the largest group of terrestrial animals, with more than a million described species. As in all other animals, insect genomes contain clusters of specific genes, which are essential for producing and assembling ribosomes. These clusters harbor two types of repetitive DNA, i.e., 45S and 5S ribosomal DNA (rDNA). Currently, 45S and 5S rDNA clusters have been studied in about 1000 and 100 insect species, respectively. Although the number of species with known 45S rDNA clusters constitutes less than 0.1 percent of the described members of this enormous group, certain conclusions can already be drawn. Since haploid karyotypes with single 45S and 5S rDNA clusters predominate in both basal and derived insect groups, this character state is apparently ancestral for the class Insecta in general. Nevertheless, the number, chromosomal location, and other characteristics of both 45S and 5S rDNA sites substantially vary across different species, and sometimes even within the same species. There are several main factors and mechanisms that either maintain these parameters or alter them on the short-term and/or long-term scale. Currently, clusters of 45S and 5S ribosomal DNA (rDNA) have been studied in about 1000 and 100 species of the class Insecta, respectively. Although the number of insect species with known 45S rDNA clusters (also referred to as nucleolus-organizing regions, or NORs) constitutes less than 0.1 percent of the described members of this enormous group, certain conclusions can already be drawn. Since haploid karyotypes with single 45S and 5S rDNA clusters predominate in both basal and derived insect groups, this character state is apparently ancestral for the class Insecta in general. Nevertheless, the number, chromosomal location, and other characteristics of both 45S and 5S rDNA sites substantially vary across different species, and sometimes even within the same species. There are several main factors and molecular mechanisms that either maintain these parameters or alter them on the short-term and/or long-term scale. Chromosome structure (i.e., monocentric vs. holokinetic chromosomes), excessive numbers of rRNA gene copies per cluster, interactions with transposable elements, pseudogenization, and meiotic recombination are perhaps the most important among them. [ABSTRACT FROM AUTHOR]

Simple Summary: The order Hemiptera is incredibly diverse in terms of modes of parthenogenetic reproduction. In this article, we review all currently known data on reproduction by true parthenogenesis, specifically thelytoky, in two major hemipteran suborders, Fulgoromorpha (planthoppers) and Cicadomorpha (leafhoppers). We discuss distribution patterns, ecology, mating behavior, acoustic communication, and the cytogenetic and genetic diversity of parthenoforms. We also highlight examples in which natural populations show a shift in sex ratio toward females and discuss possible causes of this phenomenon, primarily the influence of endosymbiotic bacteria capable of altering the reproductive strategies of the hosts. Insects are renowned for their remarkable diversity of reproductive modes. Among these, the largest non-holometabolous order, Hemiptera, stands out with one of the most diversified arrays of parthenogenesis modes observed among insects. Although there are extensive reviews on reproduction without fertilization in some hemipteran higher taxa, no such analysis has been conducted for the large suborders Fulgoromorpha (planthoppers) and Cicadomorpha (leafhoppers). In both groups, there are species that reproduce by true parthenogenesis, specifically thelytoky, and in Fulgoromorpha, there are species that reproduce by pseudogamy or, more specifically, sperm-dependent parthenogenesis. In this review paper, we give and discuss the only currently known examples of true parthenogenesis in Fulgoromorpha and Cicadomorpha, mainly from the planthopper family Delphacidae and the leafhopper family Cicadellidae. We analyze patterns of distribution, ecology, mating behavior, acoustic communication, and cytogenetic and genetic diversity of parthenoforms and discuss hypotheses about the origin of parthenogenesis in each case. We also highlight examples in which natural populations show a shift in sex ratio toward females and discuss possible causes of this phenomenon, primarily the influence of endosymbiotic bacteria capable of altering the reproductive strategies of the hosts. Our review is mainly based on studies in which the authors have participated. [ABSTRACT FROM AUTHOR]

Simple Summary: The jumping plant louse Cacopsylla ledi (Flor, 1861) (Hempitera: Psylloidea) is a triploid apomictic parthenogenetic species. Occasionally, so-called rare males and diploid females that can interbreed with each other are found in the populations. If these bisexuals were able to move to a new area and establish a new population, this could eventually lead to the formation of a new bisexual species through a founder event. By using cytological and molecular approaches, we were able to find a bisexual lineage occurring together with triploid females in northern Fennoscandia and originating from rare males and diploid females, as evidenced by a shared haplotype with triploid parthenogenetic females. An independent bisexual population of parthenogenetic origin was found in the Kola Peninsula. By contrast, another bisexual lineage in southern Fennoscandia carried a different haplotype than the triploids in the same population. This lineage appeared to represent the ancestral bisexual C. ledi, which had moved postglacially northwards along with the triploid parthenogenetic females. As these lineages are well separated from each other, the population in the Kola Peninsula has the potential to develop into a new bisexual species refuting the view that parthenogenesis is an evolutionary dead end. A widely accepted hypothesis is that parthenogenesis is an evolutionary dead end since it is selectively advantageous in the short term only but results in lowered diversification rates. Triploid apomictic parthenogenesis might represent an exception, as in favorable environments, triploid females are able to produce rare males and diploid females. The aim of the present study was to analyze the modes of reproduction and their evolutionary implications in the parthenogenetic psyllid Cacopsylla ledi (Flor, 1861) from Fennoscandia. The cytogenetic assessment of ploidy levels and the analysis of the COI haplotype revealed two geographically separated bisexual lineages implying genuine bisexual populations. The southern lineage occurring south of latitude 65° N in Finland showed a COI haplotype different from that of parthenogenetic triploids in the same population but identical to the haplotype of specimens in a genuine bisexual population in the Czech Republic. This allows us to suggest that bisexuals in southern Fennoscandia represent the original bisexual C. ledi. By contrast, in the northern bisexual lineage north of latitude 65° N, rare males and diploid females carried the same haplotype as triploids in the same population, having been produced by the triploids. In the Kola Peninsula, a genuine bisexual population of presumably rare male/diploid female origin was discovered. As this population is geographically isolated from populations of the ancestral bisexual C. ledi, it can develop into a new bisexual species through peripatric speciation during evolution. Our findings demonstrate that apomictic triploid parthenogenesis is not necessarily an evolutionary dead end but is able to lead to the emergence of a new bisexual species of parthenogenetic origin. [ABSTRACT FROM AUTHOR]

Simple Summary: Tingidae, or lace bugs, is a family of herbivorous true bugs, with approximately 2600 identified species in 318 genera classified in two or sometimes three subfamilies, among which the largest subfamily Tinginae comprises about 2500 species. Here, an account is given of the karyotypes of 16 lace bug species studied using conventional chromosomal techniques and FISH with two repetitive DNA probes, 18S rDNA and (TTAGG)n. We also summarize and analyze all information accumulated to date on karyotypes of lace bugs. In general, such information is available for 60 species and 22 genera of Tinginae. We show that lace bugs are characterized by: (1) very conservative karyotypes, with six pairs of autosomes in a haploid set; (2) either an XY or X(0) sex chromosome system; (3) a conventional sequence of sex chromosome divisions in male meiosis; (4) absence of the (TTAGG)n mechanism for maintaining telomere integrity; (5) four discrete patterns of 18S rDNA chromosomal localization. We conclude that the search for chromosomal landmarks is of paramount importance for the characterization of the lace bug cytogenetics in more detail. The lace bug family Tingidae comprises more than 2600 described species in 318 genera that are classified into the subfamilies Tinginae (about 2500 species and 300 genera), Cantacaderinae, and Vianadinae. We provide data on karyotypes of 16 species belonging to 10 genera of the tribes Tingini and Acalyptaini (Tinginae) studied using conventional chromosome staining and FISH. The species of Tingini possess 2n = 12A + XY, whereas those of Acalyptaini have 2n = 12A + X(0). FISH for 18S rDNA revealed hybridization signals on one of the medium-sized bivalents in species of both tribes. FISH with a telomeric probe TTAGG produced no signals in any species. In addition, we provide a list of all data obtained to date on Tingidae karyotypes, which includes 60 species from 22 genera of Tinginae. The subfamily is highly conservative in relation to the number and size of autosomes, whereas it shows diversity in the number and chromosomal distribution of the rDNA arrays, which may be located either on a pair of autosomes (the predominant and supposedly ancestral pattern), on one or both sex chromosomes, or on an autosome pair and the X. The absence of the "insect" telomeric sequence TTAGG in all species implies that Tinginae have some other, yet unknown, telomere organization. [ABSTRACT FROM AUTHOR]

Simple Summary: Wolbachia has many varied impacts on the biology and evolution of insects and some other groups of invertebrates. The number of studies that have particularly addressed the impact of Wolbachia infection on reproduction and processes of speciation and diversification of host species has grown rapidly over the past decade. Despite that, our current knowledge on Wolbachia is limited, and comprehensive large-scale biogeographical studies devoted to the incidence of Wolbachia within a certain taxon or groups of taxa, although they are of great importance, are still scarce. In the present study, we focused on several Palaearctic Cacopsylla (Hemiptera, Psylloidea) species with different (parthenogenetic and bisexual) reproductive strategies. We conducted PCR screening of 526 specimens collected in different geographical regions of Europe and Russia in order to estimate a broad pattern of Wolbachia incidence and prevalence of five Cacopsylla species, Cacopsylla. borealis, Cacopsylla. lapponica, Cacopsylla. myrtilli, Cacopsylla. ledi, and Cacopsylla. fraudatrix. We revealed significant differences in infection frequencies between the species and even distinct populations of the same species, which, however, did not correlate with reproduction strategy or gender. These findings provide a starting point for understanding the role of Wolbachia infection in Cacopsylla evolution and diversity. Wolbachia is one of the most common intracellular bacteria; it infects a wide variety of insects, other arthropods, and some nematodes. Wolbachia is ordinarily transmitted vertically from mother to offspring and can manipulate physiology and reproduction of their hosts in different ways, e.g., induce feminization, male killing, and parthenogenesis. Despite the great interest in Wolbachia, many aspects of its biology remain unclear and its incidence across many insect orders, including Hemiptera, is still poorly understood. In this report, we present data on Wolbachia infection in five jumping plant-lice species (Hemiptera, Psylloidea) of the genus Cacopsylla Ossiannilsson, 1970 with different reproductive strategies and test the hypothesis that Wolbachia mediates parthenogenetic and bisexual patterns observed in some Cacopsylla species. We show that the five species studied are infected with a single Wolbachia strain, belonging to the supergroup B. This strain has also been found in different insect orders (Lepidoptera, Hemiptera, Plecoptera, Orthoptera, Hymenoptera, Diptera) and even in acariform mites (Trombidiformes), suggesting extensive horizontal transmission of Wolbachia between representatives of these taxa. Our survey did not reveal significant differences in infection frequency between parthenogenetic and bisexual populations or between males and females within bisexual populations. However, infection rate varied notably in different Cacopsylla species or within distinct populations of the same species. Overall, we demonstrate that Wolbachia infects a high proportion of Cacopsylla individuals and populations, suggesting the essential role of this bacterium in their biology. [ABSTRACT FROM AUTHOR]