Pseudaulacaspis Pentagona (Targ.) (Coccoidea)

ON SEX DETERMINATION IN THE DIASPINE SCALE PSEUDAULACASPIS PENTAGONA (TARG.) (COCCOIDEA) SPENCER W. BROWN’ AND FREDERICK D. BENNETT Department of Botany and Commonwealth Institute of Biological Control, Imperial College of Tropical Agriculture, St. Augustine, Trinidad, B. W. I. Received January 15, 1957 F the three sections into which the coccids may be subdivided, the diaspidoid 0 or true scales represent “the largest in point of included species and morpho- logically the most highly specialized of the entire superfamily” (HUGHES-SCHRADER 1948). Although economically of very great importance, the true scales have been little investigated in regard to either cytology or genetic systems. SCHRADER(1929) reported a chromosome number of eight for females of As- pidiotus hederae, a species which exhibits an obligate type of diploid thelyotoky to be found also in other sections of coccids (HUGHES-SCHRADER1948). The same chromosome number was reported by DICKSON(1932) for Aonidiella aurawtii from SCHRADER’Scounts in embryos of undetermined sex. Resistance of A. aurantii to cyanide was found to be inherited; of special significance was DICKSON’Sdemonstra- tion that the males transmitted only the factor or factors received from their mothers. DICKSONinterpreted his data as revealing sex-linkage in an XX-XY-scheme; they would obviously conform equally well to a haplo-diploid sex differential. More recently LINDNER(1954) has reported haplo-diploidy in the diaspidoid scale, Aspidiotus perniciosus; the males have four, the females, eight chromosomes. LINDNERalso briefly described a typical meiotic sequence in the females and the substitution of a simple mitotic division for meiosis in the males. The subject of the present report, Pseudaulacaspis pentagona was chosen for study because of puzzling facts in regard to its life cycle observed by MR. E. C. G. BED- FORD and BENNETTat the laboratory of the Bermuda Department of Agriculture. These observations have been reported in part in a technical bulletin on mass rearing of scales (DUSTAN1953) and a further descriptive treatment is in preparation by BENNETT. Females of P. pentagona will lay no eggs unless mated. Following normal matings, their egg production shows a noteworthy example of combined sexual dimorphism and sexual dichronism, or production of the two sexes in two different time intervals. Development of the embryo has advanced considerably by the time the eggs are extruded. Those laid first are coral in color and, as shown by isolation tests, contain female embryos. Without interruption, a second series of eggs is produced; these are pinkish-white and contain male embryos. The two series total 150-200 eggs per female and the sex ratio, as determined in Bermuda, is approximately 1: 1. The emergent crawlers also show the same sexual color difference. The work summarized 1 Fellow of the John Simon Guggenheim Memorial Foundation, and on leave from the Depart- ment of Genetics, University of California, Berkeley, Calif. 1956-57. 2 Present address: Department of Entomology, University of California, Berkeley, California. SEX DETERMINATION IN SCALE 511 in the present report was undertaken primarily to find out the sex determining mechanism in this species. MATERIALS AND METHODS Irish potatoes infested with P. pentagona were obtained from mass cultures main- tained at the laboratory of the Commonwealth Institute of Biological Control lo- cated at the Imperial College of Tropical Agriculture, St. Augustine, Trinidad, B. W. I. Culture methods were essentially those outlined by DUSTAN(1953). Orig- inal stocks for the mass cultures were taken from Stuchyturpketa cayennensis in Trinidad. Virgin females were easily obtained by isolating in screened glass jars infested potatoes from which all male scales had been removed. Production of a secondary covering by unmated females provides a certain criterion of their virginity. Matings were controlled by placing potato pieces bearing pre-emergent males in the isolation jars with the females. Testes were removed in water and fixed, stained, and squashed in aceto-carmine. For squashes of eggs and embryos, ovarian contents were fixed for one to two hours in Carnoy’s fixative consisting of four parts chloroform, three parts absolute alcohol and one part glacial acetic acid. Material for sectioning was fixed in San Felice, embedded in paraffin, cut at 8-12 microns, and stained in crystal violet. When de- sired, the degree of flattening of the squashes could be controlled by squashing under the dissecting microscope. As a rule, only moderate pressures were used for squashing and, as shown by comparison with the sections, the squashes did not suffer troublesome distortion. Clinical facilities available for a brief period at a local hospital were used for the X-ray treatments. Dosage was controlled by varying duration of exposure and is believed to have been sufficiently accurate for the comparative purposes of the present report. Males were exposed on thin potato pieces. To prevent death of females through subsequent desiccation of the potato, they were irradiated on uncut potatoes; an approximately flat surface was chosen for exposure and outlined with crayon. Original negatives of 900X magnification were produced on contrast process orthochromatic film by use of a Leitz Makam camera and enlarged on printing to 2300X (except for fig. 24 which is 1650X). The drawings are diagrammatic sketches made directly from the binocular research microscope (10 X 90 optics) and usually combine details from several focal planes. All illustrations were made from the squash preparations. OBSERVATIONS Lije cycle of P. pentagona The pertinent facts in regard to oviposition have already been cited in the intro- duction. Further information, chiefly in regard to chronology, will be briefly noted here. The duration of each stage is that determined from the mass cultures at St. Augustine, Trinidad. 512 SPENCER W. BROWN AND FREDERICK D. BENNETT The eggs hatch about three days after they are laid and the crawlers move out from under the maternal protective covering. The female crawlers scatter themselves widely over the potato surfaces while the males group themselves in tight colonies. Both sexes are ready for mating about 20 days after hatching. The adult, winged males appear in the late afternoon and die by the following morning. Egg production begins 16-17 days after mating and continues without interruption for about six days. As previously stated, those eggs containing female embryos are laid first. Females live for only a short time after cessation of laying. If unmated, the females begin to build a secondary covering at 3-4 days past the normal mating time. Production of this additional cover will continue for about 15-20 days unless the females mate in the meantime. On mating, production of the secondary covering ceases except for completion of a small section for later sheltering of the eggs. Cytological observations Spermatogenesis. Details of spermatogenesis were obtained solely from squashes. In order to assure observation of all stages, slides were prepared daily over a period of a week from cultures in which age of males varied by only one or two days. The spermatogenic mitosis occurred at about 12 days after hatching or eight days before the males emerged as adults. A typical resting nucleus precedes the quite clear prophase which marks the onset of the spermatogenic mitosis; undoubtedly only this one mitosis replaces meiosis. The haploid complement of eight chromosomes is easily observed at late prophase (figs. 1, 13) and occasionally in the less highly condensed metaphase plates (figs. 2, 14). The spermatocytes do not divide and sperm formation begins shortly after telophase (figs. 3, 4). The spermatocytes clump together soon after the sperm tails have begun to protrude. Oogenesis. The ovarioles, each with a single egg, occur along the lateral oviducts and each terminates in three massive nurse cells. The symbionts, yeast-like in ap- pearance, form a collar between the egg and the nurse cells; when the latter undergo dissolution, the symbionts enter the egg protoplasm where they remain in a group at the distal end during the early embryonic stages. Earlier stages of meiosis were not studied in detail. At late diakinesis, several nucleoli are present and the eight bivalents are quite contracted (fig. 15). The bivalents show an obvious bipartite structure; closer inspection demonstrates that each of the two parts consists of two chromatids. Both products of the first division prepare for a second, but the changes in the first polar body are retarded and it never completes a second mitosis (fig. 16). At the time of fertilization, the egg nucleus is near the center of the cell while the two polar bodies remain a short distance apart from each other, near the surface of the cell and near the distal end. Origin of polyploid cells. The polyploid cells which appear as a sector of the very young embryo are destined, according to SCHRADER(1923) and WALCZUCH(1932) to harbor the yeast-like symbionts. The later history of the polyploid cells was not followed in P. pentagonu, but their origin differs somewhat in detail from that previously reported. HUGHES-SCHRADER(1948) has summarized the earlier observations : the two polar bodies unite to form a triploid polar nucleus; division products of the I 2 3 -3- 88-49 6 IO II 12 FIGURES14.-Diagram of spermatogenesis. FIGURE1.-Late prophase. FIGURE2.-Metaphase. FIGURE3.-Telophase. FIGURE4.-Early stage in sperm formation. FIGURES5-12.-Diagrammatic sketches. FIGURE5.-Union of cleavage nucleus (center) with first (upper) and second (lower) polar bodies; chromosomes of polar bodies show varying degrees of contraction and splitting. FIGURE6.-Late prophase in cell of polyploid sector of embryo; pentaploid, with 40 chromosomes. FIGURE7.-First division of zygotic nucleus with 16 chromosomes and three fragments; from an untreated culture. FIGURE8.-Division figure from embryo with 17-chromosomes. FIGURE9.-Division figure from embryo with 9-chromosomes. FIGURES10-12.--Fragment chromosomes in embryos after parental irradiation.

Load more