Endomitosis in the mealy bug,Planococcus citri (Homoptera: Coccoidea)

Endomitosis in the Malpighian tubules of the mealy bug Planococcus citri (Risso) is described. The stages are identified on the basis of the length of the chromosomes and the distance between the sister chromatids or chromosomes. The appearance of the chromosomes in the various stages of endomitosis is compared to that in other hemipteran insects. During anaphase and telophase of endomitosis the ends of the sister chromatids and chromosomes tend to stay together longer than the other parts. It is suggested that in holokinetic chromosomes special regions for holding the chromatids together are concentrated near the ends of the chromosomes.Supported by grant GB1585 from the National Science Foundation, Washington, D.C.     

New observations on lecanoid spermatogenesis in the mealy bug,Planococcus citri

Summary A reexamination of the second spermatogenic division of the mealy bug, Planococcus citri (Risso), a lecanoid coccid, has revealed hitherto unknown spindle activity of the euchromatic set of chromosomes during anaphase II. An initial large half spindle elaborated by the heterochromatic chromosomes in early metaphase, gives way to a less pronounced, but clearly visible bipolar spindle involving both sets of chromosomes at early anaphase. There is no lengthening of the spindle or cell, but the separation of the chromosomes occurs around the periphery of the cell with the aid of interzonal activity. The active participation of the euchromatic chromosome during the separation is furthermore inferred by the formation of bridges resulting from euchromatic-heterochromatic translocations.     

Cytogenetic studies following high dosage paternal irradiation in the mealy bug,Planococcus citri

Summary In the mealy bug, Planococcus citri, following high dosage paternal irradiation (60,000–120,000 rep), the survivors are mostly female (about 30–40% of the unirradiated control value) whereas very few males survive (about 5% of control value). After lower doses of paternal irradiation (P. I.), however, few or no females survive while the normal number of males (never less than the control value) survive.The females developing after high dosage P. I. are gynogenetic and are triploid or diploid or 3N/2N or 2N/N mosaics (Chandra 1963).The cytology of X₁ embryos following 90,000 rep is described in this report, in comparison with data from embryos following lower doses (8,000 r) of P. I. and unirradiated controls, to illustrate the chromosomal mechanisms leading to the production of gynogenetic females and the probable reasons for lethality of X₁ males after heavy P. I.It has been shown that triploid females stem from a fusion nucleus of the first and second polar bodies. This triploid polar nucleus, which normally participates in the formation of a polyploid sector in the young embryo, undertakes a successful embryogeny in many embryos when the zygote nucleus is unable to do so because of the heavily damaged paternal complement of chromosomes. Since the chromosomes are characterized by holokinetic activity, the irradiated paternal set manages to divide with the maternal complement but did not always segregate as successfully. Restitution divisions of the zygotic nuclei result in haploid, hyperhaploid, diploid and polyploid nuclei. Most of the diploid gynogenetic females probably originate from diploid nuclei of zygotic origin although it is possible that a few diploid females and the 2N/N mosaic females develop from polar bodies.From a dissertation submitted to the University of California, in partial satisfaction of the requirements for the degree of Doctor of Philosophy.Supported in part by a National Science Foundation Grant (No. G-9772) to Professor Spencer W. Brown.N. I. H. Predoctoral Trainee in Genetics 1961–1962.     

Cytogenetics of the mealybug Planococcus citri (Risso) (Homoptera: Coccoidea): genetic markers,lethals, and chromosome rearrangements

Conventional types of cytogenetic studies with the mealybug, Planococcus citri (Risso), are possible with the use of genetic markers and meiotic analysis in the female. The loci of an eye-color mutant, salmon, and a wing-shape mutant, banjo, are linked with about 22 per cent recombination. These markers have been used in the identification and maintenance of lethals and rearrangements. All the cytologically identifiable rearrangements have proved to be reciprocal translocations, some symmetric, others, grossly asymmetric or otherwise complicated. No simple breakage products have been recovered. On the basis of their effects on crossing over, some of the lethals are believed to be associated with small rearrangements. The bivalents normally have one chiasma; only 1.2 per cent have two. Interference is decidedly decreased in chiasma formation in translocation heterozygotes, and in genetic recombination with suspected small rearrangements associated with lethals; it is also decreased, but less markedly, in genetic recombination with lethals in translocations. These various results are discussed in relationship to the holokinetic nature of the coccid chromosome, and natural increases in coccid chromosome number, as well as in regard to the effect of rearrangements on interference.Supported by grants from the National Science Foundation, currently GB 8196, and by a professorship (1968–69) for the senior author in the Miller Institute for Basic Research in Science.Dedicated to Dr. Sally Hughes-Schrader on the occasion of her seventy-fifth birthday.     

Destruction of specific heterochromatic chromosomes during spermatogenesis in the Comstockiella chromosome system (Coccoidea: Homoptera)

In male coccids with the Comstockiella chromosome system, the set of chromosomes of paternal orgin becomes heterochromatic (H) during early cleavage. Just prior to prophase I of spermatogenesis, some of the H chromosomes are destroyed; the rest are eliminated following meiosis. In this report a Comstockiella sequence is described from Dactylopius opuntiae (2n=10) in which one chromosome pair is about three times longer than the others. During prophase I the number of small H chromosomes present varied from cyst to cyst, but the long H chromosome was present in every cyst. These observations provide the best evidence to date that in the Comstockiella system a particular chromosome may always escape destruction. An analysis of Kitchin's (1975) data about the frequency of prophase I cysts with 1–4 H chromosomes in three species of Parlatoria with 2n = 8 suggested that in these species chromosomes of similar size may have very different probabilities of being destroyed. Evidence that in other species with the Comstockiella system a particular H chromosome is always retained is reviewed, and the possibility that in Ancepaspis tridentata the variation in the length of the H chromosome retained is due to the partial destruction of the longest chromosome is discussed.     

Etude de la chambre filtrante de Planococcus citri (Insecta,Homoptera)

Résumé Le tube digestif des cochenilles se caractérise par la présence d'un dispositif intestinal appelé chambre filtrante. Celle-ci, formée par l'accolement des deux extrêmités de l'intestin moyen, est supposée intervenir dans le transit alimentaire en éliminant par «voie raccourcie» l'eau ingérée en excès, mais ce rôle est resté jusque là hypothétique.Chez Planococcus citri, l'étude cytologique et histochimique révèle des caractères propres aux parties de l'intestin moyen participant à la réalisation de ce dispositif. Ces caractères suggèrent une fonction particulière qui peut être liée à un mouvement de l'eau. Les cellules sont de taille très réduite. Par endroits, des différences ultrastructurales s'observent entre les deux anses accolées (présence de vacuoles et d'espaces extracellulaires développés). Les cellules non modifiées de l'anse de départ présentent un caractère morphologique particulier, le système d'espaces intercellulaires et un caractère histochimique dominant, l'importante quantité de glycogène. Les cellules non modifiées de l'anse de retour présentent une structure inhabituelle, les «expansions tubulaires» associées aux microvillosités. En absence du «plasmalemma mitochondrial complex» le passage de l'eau se ferait par osmose dans deux directions: d'une part à travers les épithéliums amincis, d'autre part par le réseau d'espaces intercellulaires.

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Studies on the filter-chamber of Planococcus citri risso (Insecta, Homoptera)Histochemistry and ultrastructure

Summary The digestive tract of the coccids is characterized by the presence of a filter chamber formed by the apposition of the two extremities of the midgut. It is supposed that the filter chamber plays a role in the elimination of excess water by a short circuit but this assumption is still hypothetical.In Planococcus citri, cytological and histochemical studies have revealed structural peculiarities in those parts of the midgut which participate in the organization of the filter chamber, which suggest a particular function. The cells are highly reduced in size. In certain regions ultrastructural differences exist between the two apposed extremities of the midgut such as the presence of a vacuole and of highly developed extra-cellular spaces. These features may be related to water transport. The conventional cells of the proximal end of the midgut show the presence of a system of intercellular spaces and are very rich in glycogen. The conventional cells of the distal end of the midgut possess extracellular microtubules associated with the microvilli. In absence of a plasmalemma mitochondrial complex the transport of water could occur by osmosis across the thinned epithelium and the network of intercellular spaces.

Cet article recouvre en partie le travail d'une thèse de Docteur-Ingénieur soutenue à l'Université Paris VI en 1972.     

Identification of Planococcus citri (Homoptera: Pseudococcidae) and the description of a new species

Planococcus pacificus sp.n. is described from the South Pacific, Australia and South East Asia. P.citricus is synonymized with P.citri. A key and illustrations are given to separate the species discussed from each other and from the similar P.ficus group.     

Translocations between Eu- and heterochromatic chromosomes,and spermatocytes lacking a heterochromatic set in male mealy bugs

In male mealy bugs the chromosomes of paternal origin become heterochromatic (H) early in embryogeny while those of maternal origin remain euchromatic (E). First instarPseudococcus obscurus Essig males which were irradiated with 3000 r of X-rays carried translocations between E and H chromosomes [T(E;H)'s] in their spermatocytes. In the T(E;H)'s the border between the E and H segments was usually quite sharp, but occasionally short E segments may have become either partially or completely heterochromatic. During the second meiotic division the E and H sets normally segregate to opposite poles. The T(E;H)'s often formed bridges in AII and TII, but in most of the cells they did succeed in reaching one of the poles. The segregation of the T(E;H)'s depended on the relative size of their E and H segments. When the E and H segments were of the same size, the T(E;H)'s segregated more often with the E chromosomes, even though the latter have been observed to be attached to their pole with fewer spindle fibers. Thirty-five of the 173 males analyzed had sectors in their testes which lacked an H set. The number of cysts per sector suggested that each sector was derived from a single irradiated cell. The karyotypes observed in some of the sectors indicated that the lack of an H set was the result of reversal of heterochromatization and not due to the loss of the H set and the endoduplication of the E set. Most of the cells lacking an H set divided normally during the first meiotic division. The second division, however, was abortive and resulted in the production of diploid sperm. Two possibilities for the origin of spermatocytes lacking an H set are considered: (i) that these spermatocytes resulted from X-ray induced reversal of heterochromatization in spermatogonia, and (ii) that these spermatocytes originated from presumptive cyst wall cells whose H set had undergone reversal prior to the irradiation.Supported by grant GB 6745 from the National Science Foundation, Washington, D. C.     

Origin of mono- and binucleate cells with heterochromatic chromosomes in the malpighian tubules of the european elm scale,Gossyparia spuria (Coccoidea: Homoptera)

Males of the European elm scale, Gossyparia spuria (Erioccoccidae) have two Malphigian tubules, each made up of mononucleate and binucleate cells. Both types of cells may contain heterochromatic (H) chromosomes which form an H body. The cells with H bodies (H cells) usually appeared singly anywhere along the tubule. However, when two or more H cells were present they tended to be closer to each other than would be expected by chance. The possible origin of this tendency is discussed. Following squashing, the nuclei of the binucleate cells were much larger than those of most other somatic cells, suggesting that they were highly endopolyploid. However, the H bodies of the cells of the tubules were of about the same size as those of the other cells. These observations suggested that the H chromosomes of the binucleate cells did not replicate while the euchromatic chromosomes of these cells replicated several times. The great majority of the nuclei of the H cells contained a single H body per nucleus. An analysis of the number of H bodies in binucleate cells indicated that when two H bodies were present in the same nucleus they usually did not fuse. Thus, they were believed also not to fuse in the mononucleate cells. Since almost all the mononucleate H cells had only a single H body (rather than 2) it was concluded that they did not originate from binucleate cells by nuclear fusion.     

Differential DNA synthesis in heterochromatic and euchromatic chromosome sets of Planococcus citri

In males of the mealy bug Planococcus citri, Nur (1966) counted five heterochromatic (H) and about 5, 10, 20, 40, or 80 euchromatic (E) chromosomes in testis sheath nuclei which were undergoing endomitosis. He suggested that the H chromosomes were not replicating and that the nuclei were becoming polyploid as a result of successive cycles of replication of only the E chromosomes. This hypothesis was tested using autoradiography with H³-thymidine to detect DNA synthesis and microspectrophotometric measurements of the Feulgen reaction in nuclei to detect quantitative changes in DNA. — The integrated absorbance of the whole nucleus and of the isolated clump of heterochromatic chromosomes (H body) in polyploid testis sheath nuclei were measured using the mechanical scanner of the CYDAC system. The absorbance of the H body was similar in all testis sheath nuclei examined and was not significantly different from the absorbance of a haploid set of H chromosomes measured after meiosis. The absorbance of the euchromatic component varied in different sheath nuclei, the values closely corresponding to the terms of the series 2c, 4c, 8c. This series is expected if the DNA in the E chromosomes is exactly doubled at each cycle of replication. — Autoradiographs showed that most labeled sheath nuclei had silver grains localized exclusively over euchromatin. With one exception, the remainder of the labeled nuclei had silver grains over both euchromatin and the H body. The observation that euchromatin was much more heavily labeled than the H body and that labeled H bodies occurred at a low frequency and only in the presence of labeled euchromatin suggests that the H body did not incorporate the label and that the silver grains over the H body were the result of -particles which originated in proximal euchromatin.     

A radiation analysis of a comstockiella chromosome system: destruction of heterochromatic chromosomes during spermatogenesis in Parlatoria oleae (Coccoidea: Diaspididae)

In the males of the olive scale insect, Parlatoria oleae (2n=8), the paternal set of chromosomes becomes heterochromatic during late cleavage or early blastula and remains so until spermatogenesis. Immediately before the onset of meiosis in the males one or more heterochromatic chromosomes disappear from each primary spermatocyte. At prophase four euchromatic and from one to three heterochromatic chromosomes are present in each cell. The disappearance of the heterochromatic chromosomes before meiosis could be due either to the dehetero-chromatization of the heterochromatic chromosomes and their subsequent pairing with their euchromatic homologues, or to the destruction of the heterochromatic chromosomes. — The alternative interpretations of spermatogenesis in P. oleae were tested by using chromosome aberrations, which had been induced in the heterochromatic set by paternal X-irradiation, as genetic markers in breeding tests of about 400 X₁ males. Meiosis was examined in X₁ males which showed conspicuous chromosomal rearrangements in their somatic cells. The absence of either heteromorphic chromosome pairs or multivalents at spermatogenesis and the failure of the X₁ males to transmit any form of chromosome aberration induced by paternal irradiation is strong evidence that the heterochromatic chromosomes are destroyed in P. oleae. — The evolutionary relationships of the chromosome systems in the coccids are considered. Models are outlined for the derivation of a Comstockiella system involving chromosome destruction either from a lecanoid sequence or from a hypothetical Comstockiella sequence involving chromosome pairing. Problems concerning the control of chromosome destruction are discussed.From a dissertation submitted in partial fulfillment of the requirements of Doctor of Philosophy in Genetics.This work was supported by grant GB 8196 from the National Science Foundation to Dr. Spencer W. Brown, and by a National Institutes of Health Fellowship 1 F02 CA 44173-01 to the author from the National Cancer Institute.Dedicated to Dr. Sally Hughes-Schrader on the occasion of her seventy-fifth birthday.     

美盾蚧属一新种记述（同翅目：蚧总科，盾蚧科）

本记述采自安徽黄山寄生于竹类上的美盾蚧属一新种。模式标本保存于安徽省黄山市林业局。     

Chromosome systems in the eriococcidae (Coccoidea Homoptera)

Spermatogenesis is described in two eriococcid species and the observations are compared to those previously reported. In Gossyparia spuria the diploid chromosome number is 28 in both males and females. In the female all the chromosomes are euchromatic. In most male tissues 14 of the chromosomes are euchromatic (E) and 14 are heterochromatic (H). Prior to the first meiotic division in males the number of H chromosomes was reduced. During prophase I all the cells showed 14 E chromosomes and from 1 to over 9 H chromosomes. The range of chromosome numbers in metaphase I was similar to that in prophase I. All the chromosomes divided in anaphase I, and, following differential uncoiling at interkinesis, the E and H groups of chromosomes segregated from each other at anaphase II. Only the E groups formed sperm. The presence of a variable number of H chromosomes and a haploid number of E chromosomes in spermatogenesis suggested the presence of the multiple-D variant of the Comstockiella chromosome system. In this system some of the H chromosomes become euchromatic prior to prophase I of spermatogenesis and pair with their E homologues. All the remaining H chromosomes are thus univalents, while among the E elements, some are univalents and the rest are bivalents. The observed reduction in the number of H chromosomes in the first meiotic division which was previously attributed to pairing among the H chromosomes, is now interpreted to be the result of the return of some of the H chromosomes to a euchromatic state and to their subsequent pairing with their E homologues. Spermatogenesis in Eriococcus araucariae was similar to that of G. spuria except that the reduction in the number of H chromosomes was not as extensive. The chromosome systems of the two species are compared to those of other eriococcids and the differences are briefly discussed.Supported by grant GB1585 from the National Science Foundation, Washington, D. C.     

Harmful B-chromosomes in a mealy bug: additional evidence

The B-chromosomes (B's; supernumeraries) of the mealy bug, Pseudococcus obscurus Essig, segregate preferentially into the two functional products of male meiosis. This segregation thus serves as an accumulation mechanism. A cytological study of a population from Oakland, California, confirmed the results obtained earlier that the B's are harmful and are maintained only because of their accumulation mechanism. The wild females were studied directly. The number of B's in the males was determined by analyzing ten or more daughters of females without B's (0B females) after these were inseminated by wild males. The 0B females were exposed to the wild males in screen cages. The analysis of 4732 daughters of 231 caged females indicated that among the males which inseminated these females, there were 19.9% 0B males and the mean number of B's was 1.46 ± 0.07. Among 224 wild females which were collected at about the same time there were 12.5% 0B females, and the mean number of B's was 1.88 ± 0.09. Since the frequencies of the B's in the population changed only slightly from generation to generation, the expected zygotes of this generation were assumed to be similar to those from which both the males and the females developed. The expected zygotes were calculated from the observed frequencies of the B's among the sperm and the known rates of transmission in females. The zygotes were very similar to the females but quite different from the males. It was concluded, therefore, that the B's had little or no effect on the females carrying them, but reduced the fitness of the males. The fitness of the 0B, 1B, 2B, 3B and 4B males was calculated to be 1.00, 0.64, 0.56, 0.38 and 0.20 respectively. The rate of transmission of the B's decreased with the increase in the number of B's, from 0.84 in 1B males to 0.51 in 4B males. This decrease, and the decrease in male fitness with the increase in the number of B's are expected to help stabilize the number of B's in the population.This paper is dedicated to Professor Sally Hughes-Schrader on the occasion of her seventy-fifth birthday.Supported by grants GB 1585 and GB 6745 from the National Science Foundation, Washington, D. C.     

The amount of heterochromatic proteins in the egg is correlated with sex determination in <Emphasis Type="Italic">Planococcus citri</Emphasis> (Homoptera,Coccoidea)

In the mealybug Planococcus citri, there are no identifiable sex chromosomes. Early in the development of embryos destined to become males, the genome contributed by the sperm undergoes heterochromatization and, following an inverted type of meiosis, will be eliminated. Only two vital sperms are therefore produced, both carrying the same maternally derived genome. A differential distribution observed on the two spermatids during male germline cyst formation of chromatin remodeling factors such as HP1 and methylated K9 histone H3 prompted us to propose an imprinting/sex determination model in which the imprinted sperm is the one to undergo heterochromatization at syngamy. The sex ratio is normally 1:1, but aged females are known to produce almost exclusively male progeny, suggesting that the imprinting pattern of the male gamete in P. citri, though necessary, is apparently not sufficient for sex determination. We report here that egg cells of aged females show larger amounts of HP1 and Su(Var)3–9 than egg cells of young females. These data suggest that a determinant of sex may be the amount of maternally derived heterochromatic proteins.     

Meiotic parthenogenesis and heterochromatization in a soft scale,pulvinaria hydrangeae (Coccoidea: Homoptera)

Summary Meiotic parthenogenesis of a type not previously described was found in Pulvinaria hydrangeae Steinweden. During diakinesis 8 bivalents were formed. At prometaphase the spindle was tripolar but anaphase I was bipolar and normal. After completion of division of the primary oocyte, the following sequence occurred: 1. polar body I divided, usually into 3 products; 2. the secondary oocyte divided to yield the egg pronucleus and polar body II; 3. the egg pronucleus divided into its two haploid products; and 4. the second polar body divided. The products of the egg pronucleus fused while dividing to restore the diploid chromosome number; this division may be equated to the first cleavage division. The products of the polar bodies did not take part in the formation of the embryo proper or the mycetocytes.Among the embryos produced by females of two out of the three populations studied some of the embryos showed a heterochromatic chromosome set, characteristic of males in this and related families. The reproductive system of the females as well as the eggs did not contain any sperm; thus the male embryos were apparently produced parthenogenetically.The euchromatic and heterochromatic chromosome sets were genetically identical, since they both originated from the egg pronucleus by mitosis. The heterochromatization of one set but not the other might be due in part to a previous difference in their position in the cytoplasm.The females were completely homozygous yet they produced male and female embryos. Thus it appears that sex determination in the group does not depend on the segregation of genetic factors in either males or females.In addition to male and female embryos, three types of degenerating embryos were observed. It is believed that these embryos were formed by polyploid somatic cells which invaded abnormal eggs and embryos and took over development.     

The DNAs of the A and B chromosomes of the mealy bug,Pseudococcus obscurus

When the DNA of mealy bugs carrying B chromosomes (+ B:DNA) was compared to the DNA of individuals not possessing Bs (-B:DNA), no significant differences were found using isopycnic centrifugations in CsCl or thermal denaturation analyses. Both DNAs had buoyant densities of 1.693 g/cm³ in neutral CsCl gradients and 1.748 g/cm³ in alkaline CsCl gradients. Satellite DNAs were not detected. The average T_m of +B:DNA was 67.9° C in 0.1 SSC while -B:DNA had an average T_m of 67.4° C in the same solution. However, in situ molecular hybridizations with complementary RNAs (cRNAs) transcribed in vitro from each type of DNA showed considerable differences with regard to the amount of labeling of B chromosomes. Using cRNA to +B:DNA, the average number of silver grains over a B chromosome was 2.1 × the average number of silver grains over individual non-B chromosomes (A chromosomes). In contrast, the ratio (B/A) using cRNA to -B:DNA was less than 0.14. The results are interpreted as meaning that very little DNA is shared in common by both A and B chromosomes.     

The type-species of Lindingaspis MacGillivray (Homoptera: Coccoidea: Diaspididae)

Melanaspis samoana Lindinger the type-species of Lindingaspis is re-described and illustrated from syntype specimens and a lectotype is selected.