Snejana Grozeva

Cytogenetics of the true bug infraorder Cimicomorpha (Hemiptera, Heteroptera): a review

Abstract The Cimicomorpha is one of the largest and highly diversified infraorders of the Heteroptera. This group is also highly diversified cytogenetically and demonstrates a number of unusual cytogenetic characters such as holokinetic chromosomes; m-chromosomes; multiple sex chromosome systems; post-reduction of sex chromosomes in meiosis; variation in the presence/absence of chiasmata in spermatogenesis; different types of achiasmate meiosis. We present here a review of essential cytogenetic characters of the Cimicomorpha and outline the chief objectives and goals of future investigations in the field.

Cytogenetic characterization of the Trinidad endemic, Arachnocoris trinitatus Bergroth: the first data for the tribe Arachnocorini [Heteroptera: Cimicomorpha: Nabidae]

As an extension of the ongoing cytogenetic studies of the bug family Nabidae (Heteroptera: Cimicomorpha), the first evidence for the tribe Arachnocorini (the subfamily Nabinae), with reference to the Trinidad endemic, Arachnocoris trinitatus Bergroth, is provided. This is an attempt to gain a better insight into the evolution, systematics and within-family relationships of the family Nabidae. The studies were conducted using a number of cytogenetic techniques. The male karyotype (chromosome number and size; sex chromosome system; NOR location; C-heterochromatin amount, distribution and characterization in terms of the presence of AT-rich and GC-rich DNA), and male meiosis with particular emphasis on the behavior of the sex chromosomes in metaphase II are described. Also investigated are the male and female internal reproductive organs with special reference to the number of follicles in a testis and the number of ovarioles in an ovary. A. trinitatus was found to display a number of characters differentiating it from all hitherto studied nabid species placed in the tribe Nabini of the subfamily Nabinae, and in the tribe Prostemmatini of the subfamily Prostemmatinae. Among these characters are chromosome number 2n = 12 (10 + XY), the lowest within the family, nucleolus organizer regions (NORs) situated on the autosomes rather than on the sex chromosomes as is the case in other nabid species, and testes composed of 3 follicles but not of 7 as in other nabids. All the data obtained suggest many transformations during the evolution ofA. trinitatus.As an extension of the ongoing cytogenetic studies of the bug family Nabidae (Heteroptera: Cimicomorpha), the first evidence for the tribe Arachnocorini (the subfamily Nabinae), with reference to the Trinidad endemic, Arachnocoris trinitatus Bergroth, is provided. This is an attempt to gain a better insight into the evolution, systematics and within-family relationships of the family Nabidae. The studies were conducted using a number of cytogenetic techniques. The male karyotype (chromosome number and size; sex chromosome system; NOR location; C-heterochromatin amount, distribution and characterization in terms of the presence of AT-rich and GC-rich DNA), and male meiosis with particular emphasis on the behavior of the sex chromosomes in metaphase II are described. Also investigated are the male and female internal reproductive organs with special reference to the number of follicles in a testis and the number of ovarioles in an ovary. A. trinitatus was found to display a number of characters differentiating it from all hitherto studied nabid species placed in the tribe Nabini of the subfamily Nabinae, and in the tribe Prostemmatini of the subfamily Prostemmatinae. Among these characters are chromosome number 2n = 12 (10 + XY), the lowest within the family, nucleolus organizer regions (NORs) situated on the autosomes rather than on the sex chromosomes as is the case in other nabid species, and testes composed of 3 follicles but not of 7 as in other nabids. All the data obtained suggest many transformations during the evolution of A. trinitatus.

The origin of the achiasmatic XY sex chromosome system in Cacopsylla peregrina (Frst.) (Psylloidea, Homoptera)

The status of an extra univalent, if it is a B chromosome or an achiasmatic Y chromosome, associating with the X chromosome in male meiosis of Cacopsylla peregrina (Frst.) (Homoptera, Psylloidea) was analysed. One extra univalent was present in all males collected from three geographically well separated populations, it was mitotically stable, and showed precise segregation from the X chromosome. These findings led us to propose that the univalent represents in fact a Y chromosome. The behaviour of the X and Y chromosomes during meiotic prophase suggested that their regular segregation was based on an achiasmatic segregation mechanism characterised by a ‘touch and go’ pairing of segregating chromosomes at metaphase I. To explain the formation of the achiasmatic Y within an insect group with X0 sex chromosome system, it was suggested that the Y chromosome has evolved from a mitotically stable B chromosome that was first integrated into an achiasmatic segregation system with the X chromosome, and has later become fixed in the karyotype as a Y chromosome.

Achiasmatic male meiosis in Cimex sp. (Heteroptera, Cimicidae)

Abstract Chromosomes and their behaviour in spermatogenesis in Cimex species (Heteroptera, Cimicidae) from a bat species Myotis emarginatus were studied by using both a conventional staining method and sequence-specific fluorochromes CMA3 and DAPI. Spermatogonial metaphase revealed 28 autosomes, one large Y chromosome and four small X chromosomes. The Y was almost fully C-band positive as well as most telomeres of autosomes. The same regions appeared to be CMA3 and DAPI positive, indicating that in heterochromatin GC-rich clusters are dispersed within AT-rich repeats. In meiosis homologous chromosomes in bivalents are physically associated with one or seldom two sites or collochores, i.e. meiosis is achiasmatic. In MI cells chromosomes in bivalents were aligned in parallel, but at early AI bivalents open out and chromosomes move to the poles one telomere foremost. Meiosis is post-reductional for the sex chromosomes.

Achiasmatic male meiosis in Myrmedobia coleoptrata (Fn.) (Heteroptera, Microphysidae)

Abstract Mitosis and male meiosis were studied in Myrmedobia coleoptrata (Fn.), (Heteroptera,Microphysidae). Spermatogonial metaphase revealed 14 chromosomes (2n=12 + XY).The nucleolar organizing region was found on the X chromosome. No m-chromosomes were present in the complement. Male meiotic prophase was characterized by a prominent condensation stage. At this stage, the sex chromosomes were positively heteropycnotic and appeared as separate univalents, while in autosomal bivalents homologous chromosomes werealigned side by side along their entire length, i.e. meiosis is achiasmatic. Meiosis was prereductional for the autosomes and post-reductional for the X and Y chromosomes. Meiosis was further characterized by non-radial arrangement of chromosomes in metaphase I plate and radial arrangement in metaphase II. Cytological characteristics of achiasmatic meioses and their distribution within Heteroptera are discussed

Sex chromosome pre-reduction in male meiosis of Lethocerus patruelis (Stål, 1854) (Heteroptera, Belostomatidae) with some notes on the distribution of the species

Abstract The karyotype and meiosis in males of giant water bug Lethocerus patruelis (Heteroptera: Belostomatidae: Lethocerinae) were studied using standard and fluorochrome (CMA3 and DAPI) staining of chromosomes. The species was shown to have 2n = 22A + 2m + XY where 2m are a pair of microchromosomes. NORs are located in X and Y chromosomes. Within Belostomatidae, Lethocerus patruelis is unique in showing sex chromosome pre-reduction in male meiosis, with the sex chromosomes undergoing reductional division at anaphase I and equational division at anaphase II. Cytogenetic data on the family Belostomatidae are summarized and compared. In addition, the structure of the male internal reproductive organs of Lethocerus patruelis is presented, the contemporary distribution of Lethocerus patruelis in Bulgaria and in the northern Aegean Islands is discussed, and the first information about the breeding and nymphal development of this species in Bulgaria is provided.

Karyotypes, male reproductive system, and abdominal trichobothria of the Berytidae (Heteroptera) with phylogenetic considerations

The karyotype of fourteen species of Berytidae has been investigated (ten of them in this paper). All studied Metacanthinae, except possibly Metatropis, have 2n(♂)= 14 + XY. In three examined genera of Berytinae the karyotypes are dissimilar: in Neides and Apoplymus (Berytinae) the chromosome number is 2n(♂)=14 + XY, as for Metacanthinae. In Berytinus spp. the chromosome number is very high (B.distinguendus: 2n(♂)=30 + XY; B.clavipes: 2n(♂)=32 + XY: B.minor: 2n(♂)=40 + XY).

Comparative cytogenetic study of three Macrolophus species (Heteroptera, Miridae).

Abstract Macrolophus pygmaeus (Rambur, 1839) (Insecta, Heteroptera, Miridae) is a predator of key vegetable crop pests applied as a biocontrol agent in the Mediterranean region. Macrolophus pygmaeus and Macrolophus melanotoma (A. Costa, 1853) are cryptic species with great morphological similarity which results in their misidentification and negative consequences for the conservation of their populations on greenhouse and outdoor crops. In order to find out specific markers for their separation we studied the karyotype, male meiosis and heterochromatin composition of these species and additionally of a third species (as a reference one), Macrolophus costalis Fieber, 1858. We demonstrate here that all the three species share achiasmate male meiosis and sex chromosome pre-reduction. On the other hand, the species differ in karyotype, with 2n=28 (26+XY) in Macrolophus pygmaeus, 2n=27 (24+X1X2Y) in Macrolophus costalis, and 2n=34 (32+XY) in Macrolophus melanotoma, and heterochromatin distribution and composition. In addition, the species differ in sperm morphology: sperm cells of Macrolophus costalis are significantly longer with longer head and tail than those of Macrolophus melanotoma and Macrolophus pygmaeus, whereas sperm cells of Macrolophus melanotoma have a longer tail than those of Macrolophus pygmaeus. All these characters can be used as markers to identify the species, in particular the cryptic species Macrolophus melanotoma and Macrolophus pygmaeus.

Sixth European Hemiptera Congress

Since 1998, when the First European Hemiptera Congress (EHC) took place in the small seaside resort Amaliapolis, Greece, the Hemiptera congresses are regularly held every two-three years: EHC 2 in Fiesa, Slovenia (2001), EHC 3 in St. Petersburg, Russia (2004), EHC 4 in Ivrea, Italy (2007) and EHC 5 in Velence, Hungary (2009).

Achiasmate male meiosis in two Cymatia species (Hemiptera, Heteroptera, Corixidae).

Abstract The karyotype and male meiosis, with a particular focus on the presence or absence of chiasmata between the homologs, were studied in the water boatman species Cymatia rogenhoferi (Fieber) and Cymatia coleoptrata (Fabricius) (Corixidae, Cymatiainae). It is shown that the species have 2n = 33 (28A+2m+X1X2Y) and 2n = 24 (20A+2m+XY) respectively, post-reduction of sex chromosomes, and achiasmate meiosis of an alignment type in males. Cytogenetic and some morphological diagnostic characters separating Cymatia Flor from the rest of Corixidae are discussed.