Genome Size and Sex Chromosome Variability of Bed Bugs Feeding on Animal Hosts Compared to Cimex lectularius Parasitizing Human (Heteroptera: Cimicidae).

Genome size and chromosome number of five Cimicidae species were compared with the similar data recently received from Cimex lectularius parasitizing human. The average nuclear DNA content (males) was 2C = 1.47 pg in C. hemipterus, 2C = 1.61 pg in C. hirundinis, 2C = 1.80 pg in C. lectularius from bats, 2C = 1.68 pg in C. pipistrelli, and 2C = 1.22 pg in Paracimex cf. chaeturus. In the genomes of all cimicid species analyzed, the average GC content ranged from 32.74% in C. pipistrelli to 35.87% in P. cf. chaeturus. Chromosome variability with two male cytotypes, 2n = 28 + X1 X2 Y and 28 + X1 X2 X3 Y, was confirmed in C. pipistrelli. In addition, intraspecific variability in chromosome number was revealed in C. lectularius from bats with 2n = 26 + X1 X2 Y and 26 + X1 X2 X3 Y. We suggest that the origin of intraspecific variability in chromosome number of C. lectularius from bats and C. pipistrelli is not only the result of simple fragmentation, but additive rearrangements like duplications are probably also involved. © 2019 International Society for Advancement of Cytometry.

Nuclear Genome Size in Contrast to Sex Chromosome Number Variability in the Human Bed Bug, Cimex lectularius (Heteroptera: Cimicidae).

The human bed bug Cimex lectularius is one of the most prevalent human ectoparasites in temperate climate zones. The cytogenetic features of this resilient pest include holokinetic chromosomes, special chromosome behavior in meiosis, and numerical variation of chromosomes, where the diploid number ranges from 26 + X1 X2 Y to 26 + X1-20 Y. It is desirable to assess the nuclear DNA content of various cytotypes for a further detailed study of the C. lectularius genome. Detailed knowledge of the DNA content of this parasite could also clarify the origin of additional chromosomes. The average nuclear genome size C. lectularius with 2n = 26 + X1 X2 Y is 2C = 1.94 pg for males and 1.95 pg for females. There is a significant correlation between genome size and the number of chromosomes, but in some specimens with additional chromosomes, nuclear genome size decreases or remains average. Several species used as the internal reference standard were tested for further investigations of genome size in C. lectularius, and the plant Solanum pseudocaspicum turned out to be the most suitable. © 2019 International Society for Advancement of Cytometry.

Host association drives genetic divergence in the bed bug, Cimex lectularius.

Genetic differentiation may exist among sympatric populations of a species due to long-term associations with alternative hosts (i.e. host-associated differentiation). While host-associated differentiation has been documented in several phytophagus insects, there are far fewer cases known in animal parasites. The bed bug, Cimex lectularius, a wingless insect, represents a potential model organism for elucidating the processes involved in host-associated differentiation in animal parasites with relatively limited mobility. In conjunction with the expansion of modern humans from Africa into Eurasia, it has been speculated that bed bugs extended their host range from bats to humans in their shared cave domiciles throughout Eurasia. C. lectularius that associate with humans have a cosmopolitan distribution, whereas those associated with bats occur across Europe, often in human-built structures. We assessed genetic structure and gene flow within and among populations collected in association with each host using mtDNA, microsatellite loci and knock-down resistance gene variants. Both nuclear and mitochondrial data support a lack of significant contemporary gene flow between host-specific populations. Within locations human-associated bed bug populations exhibit limited genetic diversity and elevated levels of inbreeding, likely due to human-mediated movement, infrequent additional introduction events per infestation, and pest control. In contrast, populations within bat roosts exhibit higher genetic diversity and lower levels of relatedness, suggesting populations are stable with temporal fluctuations due to host dispersal and bug mortality. In concert with previously published evidence of morphological and behavioural differentiation, the genetic data presented here suggest C. lectularius is currently undergoing lineage divergence through host association.

Description of a new genus, Chileana (Hymenoptera: Chalcidoidea: Torymidae), with four new species.

Chileana Jansta & Krízková gen. nov. and four new species, C. cyanea Jansta & Krízková sp. nov., C. maculata Jansta & Krízková sp. nov., C. tricarinata Jansta & Krízková sp. nov. and C. penai Jansta & Krízková sp. nov., all from Chile, are described. The placement of this new genus within the tribe Monodontomerini is discussed and several characters suggest a close relationship to Zaglyptonotus. 

Mitochondrial DNA and morphology show independent evolutionary histories of bedbug Cimex lectularius (Heteroptera: Cimicidae) on bats and humans.

The bedbug, Cimex lectularius, is a well-known human ectoparasite that is reemerging after a long absence of several decades in developed countries of North America and Western Europe. Bedbugs' original hosts were likely bats, and the bedbugs are still common in their roosts. Using morphometry and sequences of mitochondrial cytochrome oxidase subunit I and 16S genes, we showed that the populations on bats and humans are largely isolated and differ in morphology. The character of the morphological difference suggests it to be due to adaptation to different hosts, namely adaptations to different sensory, feeding, and dispersal needs. Using the molecular data, we estimated the time of splitting into bat- and human-parasitizing groups using the isolation-with-migration model. The estimate is surprisingly long ago and seems to predate the expansion of modern human from Africa. The gene flow between bat- and human-parasitizing bedbugs is limited and asymmetric with prevailing direction from human-parasitizing populations to bat-parasitizing populations. The differentiation of the populations fits the concept of host races and supports the idea of sympatric speciation. Furthermore, our findings contradict recently formulated hypotheses suggesting bat roosts as a source of bedbug's resurgence as a human pest. Also, we extend the known host range of the bedbug by two bat species.

Fine structure of the midgut epithelium of Nicoletia phytophila Gervais, 1844 (Zygentoma: Nicoletiidae: Nicoletiinae) with special emphasis on its degeneration.

The midgut epithelium of Nicoletia phytophila is composed of columnar digestive cells and regenerative cells that form regenerative nests. The cytoplasm of midgut epithelial cells shows typical regionalization in organelle distribution. Two types of regenerative cells have been distinguished: cells which are able to divide intensively and cells which differentiate. Spot desmosomes have been observed between neighboring regenerative cells. The occurrence of intercellular junctions is discussed. The midgut epithelium degenerates both in an apoptotic and necrotic way. Necrosis proceeds during each molting period (cyclic manner), while apoptosis occurs between each molting, when the midgut epithelium is responsible for e.g. digestion. These processes of epithelium degeneration are described at the ultrastructural level. Our studies not only add new information about fine structure of the midgut epithelium of N. phytophila, but contribute to resolving the relationships within the Zygentoma. There are no doubts about the very close sister position of Nicoletiidae and Ateluridae. The midgut epithelium characters confirm their close relationship. However we do not recommend classifying the atelurid genera only within Nicoletiidae: Nicoletiinae.

Nymphal development of Rhopalus maculatus and Chorosoma schillingii (Hemiptera: Heteroptera: Rhopalidae: Rhopalinae) and development of trichobothrial pattern in Rhopalidae.

The nymphal morphology of the family Rhopalidae is well known for several species, most of which are pests. Ontogenetic changes in morphology are described in detail for two members from two tribes of the subfamily Rhopalinae, Rhopalini: Rhopalus (Aeschyntelus) maculatus (Fieber) and Chorosomini: Chorosoma schillingii (Schilling). Keys to the nymphal instars of both species are provided. The special types of nymphal setae and lateral abdominal processes are described in R. maculatus. The ontogenetic development of abdominal trichobothria is described, and the known trichobothrial patterns within the Rhopalidae are discussed.

Ultrastructure of the midgut in Heteroptera (Hemiptera) with different feeding habits.

Heteroptera have diverse feeding habits with phytophagous, zoophagous, and haematophagous species. This dietary diversity associated with the monophyly of Heteroptera makes these insects a good object for comparative studies of the digestive tract. This work compares the ultrastructure of the middle midgut region in the phytophagous Coptosoma scutellatum (Plataspidae), Graphosoma lineatum (Pentatomidae), Kleidocerys resedae (Lygaeidae), and zoophagous Rhynocoris iracundus (Reduviidae), Nabis rugosus (Nabidae), and Himacerus apterus (Nabidae), to verify if diet affects midgut cells in phylogenetically related insects. The middle region of the midgut was used for comparison because it is the main site for digestion and absorption of the midgut. The digestive cell ultrastructure was similar in the six species, with features of secretory, absorptive, transport, storage, and excretory cells, suggesting a stronger correlation of middle digestive cell ultrastructure with the phylogeny of these species than with the different heteropteran feeding habits.

Comparison of different cytogenetic methods and tissue suitability for the study of chromosomes in Cimex lectularius (Heteroptera, Cimicidae).

In the article we summarize the most common recent cytogenetic methods used in analysis of karyotypes in Heteroptera. We seek to show the pros and cons of the spreading method compared with the traditional squashing method. We discuss the suitability of gonad, midgut and embryo tissue in Cimex lectularius Linnaeus, 1758 chromosome research and production of figures of whole mitosis and meiosis, using the spreading method. The hotplate spreading technique has many advantages in comparison with the squashing technique. Chromosomal slides prepared from the testes tissue gave the best results, tissues of eggs and midgut epithelium are not suitable. Metaphase II is the only division phase in which sex chromosomes can be clearly distinguished. Chromosome number determination is easy during metaphase I and metaphase II. Spreading of gonad tissue is a suitable method for the cytogenetic analysis of holokinetic chromosomes of Cimex lectularius.

Extensive fragmentation of the X chromosome in the bed bug Cimex lectularius Linnaeus, 1758 (Heteroptera, Cimicidae): a survey across Europe.

Variation in the number of chromosomes was revealed in 61 samples of Cimex lectularius Linnaeus, 1758 from the Czech Republic and other European countries, hosted on Myotis Kaup, 1829 (4) and Homo sapiens Linnaeus, 1758 (57). The karyotype of all the specimens of Cimex lectularius analysed contained 26 autosomes and a varying number of the sex chromosomes. The number of sex chromosomes showed extensive variation, and up to 20 fragments were recorded. Altogether, 12 distinct karyotypes were distinguished. The male karyotypes consisted of 29, 30, 31, 32, 33, 34, 35, 36, 37, 40, 42 and 47 chromosomes. The females usually exhibited the number of chromosomes which was complementary to the number established in the males from the same sample. However, 11 polymorphic samples were revealed in which the karyotypes of females and males were not complementary each other. The complement with 2n = 26+X1X2Y was found in 44% of the specimens and 57,4% samples of bed bugs studied. The karyotypes with higher chromosome numbers as well as individuals with chromosomal mosaics were usually found within the samples exhibiting particularly extensive variation between individuals, and such complements were not found within samples contaning a few or single specimen. The occurrence of chromosomal mosaics with the karyotype constitution varying between cells of single individual was observed in five specimens (4.3%) from five samples. We assume that polymorphism caused by fragmentation of the X chromosome may result in meiotic problems and non-disjunction can produce unbalanced gametes and result in lowered fitness of individuals carrying higher numbers of the X chromosome fragments. This effect should be apparently enhanced with the increasing number of the fragments and this may be the reason for the observed distribution pattern of individual karyotypes in the studied samples and the rarity of individuals with extremely high chromosome numbers. The assumed lowering of the fitness of individuals carrying higher numbers of the X chromosome fragments could affect population dynamics of variable populations.

Fine structure of the midgut epithelium in two Archaeognatha, Lepismachilis notata and Machilis hrabei (Insecta), in relation to its degeneration and regeneration.

In two archaeognathans, Lepismachilis notata and Machilis hrabei, the midgut epithelium and processes of its regeneration and degeneration have been described at the ultrastructural level. In both analysed species, the midgut epithelium is composed of epithelial and regenerative cells (regenerative nests). The epithelial cells show distinct regionalization in organelles distribution with the basal, perinuclear, and apical regions being distinguished. Degeneration of epithelial cells proceeds in a necrotic way (continuous degeneration) during the entire life of adult specimens, but just before each moult degeneration intensifies. Apoptosis has been observed. Regenerative cells fulfil the role of midgut stem cells. Some of them proliferate, while the others differentiate into epithelial cells. We compared the organisation of the midgut epithelium of M. hrabei and L. notata with zygentoman species, which have just been described.