Effects of Weismann ring gland on RNA synthesis in imaginal wing disks of Calliphora erythrocephala

Imaginal wing disks of Calliphora erythrocephala have been studied in normal animals and in permanent larvae surgically deprived of the ring gland. By the end of larval life, uridine incorporation in the nuclear RNA and the ribosomal RNA increases for a brief period. This phenomenon does not occur in permanent larvae. A quantitative study suggests that renewal of a part of the ribosomal RNA might precede wing evagination.     

Ecdysteroid synthesis by the ring gland of Drosophila melanogaster during late-larval,prepupal and pupal development

Radioimmunoassay has been used to determine the characteristics of ecdysteroid synthesis by ring glands and brain-ring gland preparations from late 3rd-instar larvae of Drosophila melanogaster cultured in vitro. The rate of synthesis and secretion is linear for at least 4 hr in culture. Using a 4-hr culture period, variation in the rate of ecdysteroid synthesis by brain-ring gland preparations during larval, prepupal and pupal development has been examined. The rate of synthesis and secretion is highest in late 3rd-instar larvae and decreases after puparium formation. During pupal development, at a time when the endogenous ecdysteroid titre is again increasing, the rate of ecdysteroid synthesis by brain-ring gland preparations remains low and is only 10% of that prior to puparium formation. It is, therefore, likely that the ring gland is not a major source of ecdysteroids during this period.     

Control of growth and differentiation of the wing imaginal disk of Precis coenia (Lepidoptera: Nymphalidae)

During the last larval instar, the wing imaginal disks of Precis coenia grow continuously. The rate of disk growth is not disk-autonomous but closely matches the rate of somatic growth of the larva, so that the size of the disks is a function of the size of the body, irrespective of the growth rate of the larva. When larvae are starved, their wing disks cease growth within 4 h, which indicates the existence of an efficient coupling mechanism between the growth of the soma and growth of the imaginal disks. Disk growth is inhibited by juvenile hormone in a dose-dependent manner. In the presence of the hormone the wing disks stop growing even while the larva continues to grow normally. During the last larval instar the wing imaginal disks also undergo a complex differentiation, consisting of the development of the lacunae and tracheation that define the future adult wing venation system. In normally growing larvae, differentiation of the wing disk is tightly correlated with wing size. Differentiation and size can be dissociated by starvation. If larvae are starved at any time after differentiation has begun, differentiation continues at a normal rate, even though the wing disk does not grow. Differentiation does not begin spontaneously in larvae that are starved before differentiation has begun. These findings indicate that the initiation of differentiation and its continuation are controlled independently. Juvenile hormone inhibits differentiation in a dose-dependent manner. Upon treatment with juvenile hormone, the stage of differentiation becomes fixed. These findings indicate that continued differentiation of the wing disk can only occur in the absence of juvenile hormone. Although the circulating level of juvenile hormone may be elevated during starvation, it is unlikely that this elevation is responsible for the observed effect of starvation on growth and differentiation of the disk.     

Crowding and nutrition in the induction of macropterous alatae in Drepanosiphum dixoni

Macropterous alatae in Drepanosiphum dixoni develop when the larvae are reared in crowded conditions. The larvae are sensitive to crowding during the first two instars. Although no macropterous alatae develop unless the larvae experience crowding during the first 6 to 8 days of their life, nevertheless the length of the wings of the brachypterous alatae is influenced by shorter periods of crowding. The longer the period of crowding the longer the wings, until after 6 to 8 days of crowding full-sized wings develop. The wing muscles only develop when the aphid has full-sized wings. Poor nutrition and whether the parents are macropterous or brachypterous influence the susceptibility of the larvae to crowding.     

The calcified puparium of the face fly, Musca autumnalis (Diptera: Muscidae)

The general composition of the calcified puparium of Musca autumnalis was determined. Ash-weight analyses show that 62% of the puparium is inorganic material. The major components of the puparium are calcium, magnesium, phosphate and carbonate. Calcium and magnesium phosphate are the predominant salts in the puparium, with a lesser contribution by their respective carbonates. Scanning electron microscopy revealed that the exocuticle was the site of calcification in the puparium. Inorganic analyses of the insoluble salt isolated from face fly larvae showed it to be compositionally identical with the puparial salt. Major organic components of the puparium are lipid, chitin and protein. The presence of carbonic anhydrase and alkaline phosphatase activity in post-feeding larvae was confirmed.     

Reversal of pupal diapause in Sarcophaga argyrostoma by temperature shifts after puparium formation

Puparia from Sarcophaga argyrostoma larvae reared under short days were collected daily within 24 hr of their formation and divided into two groups: one which remained at the larval rearing temperature, and one which was transferred to a different temperature. Such temperature shifts after puparium formation can modify the subsequent incidence of pupal diapause. Temperature step-ups decrease the percentage of diapause; temperature step-downs increase it. The degree of this effect increases with the size of the temperature step. The effectiveness of a temperature step-up declines with increasing time after puparium formation.The percentage of diapause finally achieved in any group is a function of both the number of inductive (short-day) photoperiods experienced during larval life and the magnitude and direction of the subsequent temperature step. Temperature step-ups can permit the expression of photoperiodic information which would otherwise be masked. A model is presented to account for these findings.     

Oögenesis defects in the ecd-1 mutant of Drosophila melanogaster, deficient in ecdysteroid at high temperature

Oögenesis defects observed in ecd-1 females depend on the stage at which the shift from the permissive temperature (20°C) to the non-permissive temperature (28.5°C) is performed. Pupae shifting earlier than 48 hours after puparium formation have underdeveloped ovaries and die at emergence. In ecd-1 females shifted 2 days or more after puparium formation, egg chambers develop normally up to the early vitellogenic stage, and then degenerate—no mature oöcytes are formed. When the shift is performed after maturation of the females at 20°C, their egg-laying rate decreases slowly after the shift; the eggs display abnormal chorions and fail to develop into larvae. By shifting the ecd-1 females back to 20°C, a complete reversal of abnormalities of eggshell formation and egg development may be observed. The temperature-sensitive periods related to these different defects were determined. For egg development, the period extends from 2 days to 1 day before laying. For eggshell formation, the beginning and end of the temperature-sensitive period were not separated—both were located around 24 hours before laying. For the block of vitellogenesis, we concluded that this is probably due to an inhibition of yolk uptake. This inhibition would be effective only in follicles younger than the previtellogenic stage 7 when submitted to the non-permissive temperature.     

Spatial and temporal relationships between cell death and tissue overgrowth in imaginal wing disks of the Drosophila mutant l(3)c43hs1

The temperature-sensitive mutant l(3)c43hs1 is lethal at the restrictive temperature late in the last larval instar and has wing disks that show excessive growth when larvae are reared at 25 degrees C. Such mutant disks give rise to defective wings showing duplications and deficiencies. Abnormal folding patterns are localized to the region between the wing pouch and the area where adepithelial cells are found; the disks retain an epithelial morphology. Apoptotic cell death is distributed throughout the wing disks without any obvious concentration of dead cells in a specific area. Cell death is seen as early as 12 hr after a shift to the restrictive temperature. Temperature shift experiments also show that cell death precedes the onset of overgrowth, but since the spatial distribution of death is not localized to the regions of abnormal folds, it is unlikely that cell death and overgrowth are causally related.     

Relationships between the parasitoid Hyposoter exiguae and Trichoplusia ni: Prevention of host pupation at the endocrine level

RNA synthesis in normal Trichoplusia ni fifth instars and hosts parasitized at ca. 12 hr post-ecdysis was followed by measuring ³H-uridine incorporation with an autoradiographic technique.Uptake of ³H-uridine was high in control prothoracic glands at 6 and 30 hr and their cytology indicated an active secretory phase which was most pronounced at 30 hr. At the same time, glands of parasitized larvae decreased incorporation and appeared less active than controls. At > 75 hr, control fat body cells incorporated almost no label but were filled with RNA-protein granules apparently sequestered from the haemolymph preparatory to pupation. With respect to incorporation and cytology, fat body of parasitized larvae was unchanged from earlier in the instar, which indicates that the changeover to pupal preparations had not taken place. Imaginal wing disks incorporated label and grew appreciably in control larvae but abruptly decreased uptake and showed no size increase in parasitized larvae. Incorporation of Malpighian tubule, midgut epithelium, and certain muscles at > 75 hr showed little change in parasitized larvae, but in controls activity was reduced and histolysis occasionally was evident in muscles.The parasitoid, Hyposoter exiguae, apparently prevented host larvae from pupating by preventing activation of host prothoracic glands in the fifth instar. Other tissues which are normally activated for metamorphosis by the prothoracic glands continued normal larval activities until the end of the association.     

The control of growth and differentiation of the wing imaginal disks of Manduca sexta

During the larval feeding period, the growth of the wing imaginal disks of Lepidoptera is dependent on continuous feeding. Feeding and nutrition exert their effect via the secretion of bombyxin, the lepidopteran insulin-like hormone. When larvae stop feeding and enter the wandering stage in preparation for metamorphosis, the control of imaginal disk growth becomes feeding and nutrition-independent. Growth of the wing imaginal disks of non-feeding wandering stage Manduca sexta can be stopped by removal of the brain, indicating that a brain-derived factor is required for continued disk growth. Isolated wing disk growth in vitro requires both 20-hydroxyecdysone (20E) and either brain extract or bombyxin to achieve normal growth. In vitro, brain extracts and synthetic bombyxin have little or no effect in stimulating disk growth, but they greatly enhance the effect of 20E, indicating that 20E and bombyxin act synergistically to modulate growth of the imaginal disk. Brain extract and bombyxin induce a suite of insulin-response events in cultured wing disks, which indicate that bombyxin and 20E act through separate and synergistic pathways. The dose-response to 20E reaches a plateau at about 0.1 microg/ml. Tracheal differentiation of the wing disks can be induced to initiate in vitro by a low concentration of 20E, whereas higher concentrations of 20E only stimulate growth.     

Spatial and temporal relationships between cell death and tissue overgrowth in imaginal wing disks of the Drosophila mutant I(3)C43hs1

The temperature-sensitive mutant l(3)c43^hs1 is lethal at the restrictive temperature late in the last larval instar and has wing disks that show excessive growth when larvae are reared at 25°C. Such mutant disks give rise to defective wings showing duplications and deficiencies. Abnormal folding patterns are localized to the region between the wing pouch and the area where adepithelial cells are found; the disks retain an epithelial morphology. Apoptotic cell death is distributed throughout the wing disks without any obvious concentration of dead cells in a specific area. Cell death is seen as early as 12 hr after a shift to the restrictive temperature. Temperature shift experiments also show that cell death precedes the onset of overgrowth, but since the spatial distribution of death is not localized to the regions of abnormal folds, it is unlikely that cell death and overgrowth are causally related.     

Relation between cell number and pupal development of wing disks in Bombyx mori

The effects of JH and ecdysone on pupal differentiation of the wing disk of Bombyx mori were studied in vivo and in vitro. JH prevents pupal differentiation during larval life by stopping a particular stage of the cell cycle. Immediately after allatectomy, a cell cycle sets in without ecdysone, but afterwards wing disks obtain the competence to differentiate to the pupal type in response to ecdysterone. Disks older than 2 days after allatectomy can develop to the pupal type with an abrupt increase of mitosis in a certain concentration of ecdysterone in vitro. Once the disks have gained such competence and begun pupal development, JH no longer exhibits the effect that prevents DNA synthesis, which is enhanced by ecdysterone. It is therefore suggested that there are two phases in DNA synthesis: one which is important for achieving competence and is inhibited by JH and relatively independent of ecdysone; and another which is important for morphogenetic development and depends on ecdysone but is not inhibited by JH.     

The development of wing imaginal disks of Drosophila virilis after culture in vitro

Drosophila virilis wing disks cultured in vitro in Schneider medium and then transplanted into mature larvae for metamorphosis revealed a shift from successful development of the thoracic area accompanied by poor development of the wing area, to the opposite condition when the period in vitro was increased to 7 days. Cultures in adult hosts for the same length of time maintained the former condition. Labelling experiments with H³-thymidine revealed a substantial decrease in uptake during the first 24 hr in vitro followed by a slight increase after 4 days.     

Parameters influencing the acquisition of competence for metamorphosis in imaginal disks of Drosophila

When imaginal disks from first and early second instar larvae of Drosophila are transplanted into larval hosts that are ready to pupate, they are unable to differentiate adult structures. The disks gradually become competent to respond with imaginal differentiation towards the end of the second larval instar (Fig. 1). The first sign of imaginal differentiation is a light-orange pigment that appears in the presumptive eye region when eye-antennal disks from early second instar larvae were subjected to immediate metamorphosis. This pigment was identified as being composed of ommochromes and drosopterins.Incompetent eye-antennal disks from early second instar donors were cultured in adult females for 2 to 5 days, and then retransplanted into late third instar larval hosts. If the adult host flies were kept on standard food the disks grew by cell multiplication (Fig. 2c) and became competent to undergo imaginal differentiation (Fig. 3). If, on the other hand, the adult hosts were starved on a protein-free sugar diet, cell divisions were effectively blocked in the disks. These did not noticeably grow (Fig. 2b) and remained incompetent (Fig. 3). The block caused by starvation proved to be reversible. Based on these results the hypothesis is advanced that the acquisition of competence requires a minimum number of cell divisions to take place in the disk primordium.     

鲈鲤仔鱼的异速生长模式

采用实验生态学方法研究了鲈鲤(Percocypris pingi pingi)仔鱼(0～57日龄)的异速生长模式.结果显示:鲈鲤仔鱼全长由慢速生长到快速生长的转折点为25日龄;其多数外部器官均具有异速生长特点,头部和尾部的生长快于躯干部,均在22 ～ 27日龄出现生长拐点;眼径在14 ～ 15日龄较早出现生长拐点,促使眼睛充分发育,以提高早期仔鱼开口期摄食外源食物的能力;吻长在33～34日龄出现生长拐点,促进了口的充分发育,以适应不同的饵料环境;胸鳍、背鳍、尾鳍、臀鳍和腹鳍分别在13～14日龄、31～32日龄、32 ～33日龄、38 ～39日龄、43 ～ 44日龄出现生长拐点,除胸鳍和尾鳍外,其余各鳍的鳍条均在拐点处分化完全,即鲈鲤仔鱼的游泳能力已得到大幅提高.研究表明,鲈鲤仔鱼的异速生长模式,保证了各重要功能器官的充分发育,以适应多变的环境,有效地保障了其早期的生存,可为育苗生产和野生早期资源的保护提供技术支撑.     

Developmental constraints on the evolution of wing-body allometry in Manduca sexta

Artificial selection on body size in Manduca sexta produced genetic strains with large and small body sizes. The wing-body allometries of these strains differed significantly from the wild type. Selection on small body size led to a change in the scaling of wing and body size without changing the allometry: the wings were smaller relative to the body, but to the same degree at all body sizes. Selection for large body size led to a change in allometry with a decrease in the allometric coefficient, wing size becoming progressively smaller relative to body as body size increased. When larvae were deprived of food so as to produce adults of a range of small body sizes, all strains retained the same allometric coefficient but showed an increase in the scaling factor. Thus individuals starved as larvae had a smaller adult body size but had proportionally larger wings than fed individuals. We analyzed the developmental processes that could give rise to this pattern of allometries. Differences in the relative growth of body and wing disks can account for the differences in the allometric coefficients among the three body size strains. The change in wing-body allometry at large body sizes was primarily due to an insufficient time period for growth. The available time period for growth of the wing imaginal disks poses a significant constraint on the proportional growth of wings, and thus on the evolution of large body size.     

Wing development and parthenogenesis induced in progenies of kinoprene-treated gynoparae of Aphis fabae and Myzus persicae

Presumptive gynoparae of Aphis fabae and Myzus persicae were exposed to various levels of kinoprene (Zoecon's ZR 777) by being placed as 4th-instar alatiform larvae on bean or radish seedlings that had been sprayed with different concentrations of kinoprene in an acetone-tween-water emulsion. Larvae exposed to the highest (0.1%) concentration tested developed into adults 1 to 2 days sooner than those on control plants. The adults on the treated plants had variously deformed wings, reduced sclerotization (and pigmentation in the case of M. persicae) and other apteriform features. On reaching adulthood the affected aphids settled to feed and started to larviposit some days earlier than the control aphids. After two weeks as adults, treated gynoparae of M. persicae produced more larvae than the 7 to 9 typically deposited by control gynoparae under the short-day and cool temperature conditions employed in these tests.Whereas most or all of the larvae produced by the control gynoparae developed into oviparae (apterous, egg-laying, sexual females), gynoparae exposed to 0.1% kinoprene-treated plants predominantly produced alatiform viviparous offspring. If the latter were allowed to develop on untreated plants they deposited a few oviparous larvae. Alatiform virginoparae of M. persicae (from the same holocyclic strain that produced the gynoparae) also responded to kinoprene by developing wing deformities and by producing alatiform offspring. In contrast, alatiform virginoparae from an androcyclic strain of M. persicae, although developing wing deformities, produced only apterous progeny.The stimulation by kinoprene of wing development and parthenogenesis in the progeny of treated gynoparae is discussed in the light of our present knowledge of these aspects of aphid polymorphism.     

Ultrastructure of salivary glands of Drosophila lebanonensis during normal development and after in vivo ecdysterone administration

Changes in the morphology of the salivary glands of Drosophila lebanonensis have been followed at both the light and electronmicroscopic level during a period of 30 hr before puparium formation and during puparium formation itself. Three striking differences were observed in comparison to other Drosophila species studied: (1) the secretion product of Drosophila lebanonensis has a different stainability to PAS reagent and uranyl acetate and no internal structures or “caps” can be observed; (2) the release of this secretion product is not restricted to a time period shortly before puparium formation but is a continuous process starting about 24 hr before puparium formation; and (3) the histolysis of these glands starts immediately after puparium formation, whereas in other Drosophila species this event starts 5 hr later.Puparium formation of Drosophila lebanonensis is controlled by the circadian oscillation. Injection of ecdysterone before the “gate” period results in changes in the cuticle as observed during normal development, but is not followed by the histolysis of the glands. Injection of ecdysterone after the “gate” is not followed by changes in the cuticle but histolysis is induced.     

Manifestations of resistance to Haemonchus contortus in sheep: Worm populations and abomasal changes in sheep superinfected with 1,000,000 larvae of H. contortus

The super-infecting dose produced a marked rise in gastric pH in all sheep from the 3rd day after administration of larvae. Expulsion of the existing population of adult worms may have begun on the 4th day but was still only completed in 3/6 sheep on the 5th day. The larvae caused extensive damage in the individual glands which they parasitised. Very few of the 10⁶ larvae survived for 27 days and only in 1/8 sheep had they developed beyond early 4th stage at 27 days. Extensive histological changes were seen in the fundic mucosa beginning as early as 2 days after the superinfection. While the pH change preceded expulsion of the adults and was consistent in its timing, the timing of the expulsion was irregular. This throws doubt on the hypothesis that the change in physico-chemical conditions produced by the superinfecting larvae is the only cause of the expulsion of the adult worms.