Imaginal Buds Research Articles

Study of histoarchitectural changes in Anopheles stephensi larvae following exposure to Eucalyptus globulus and Aloe vera oils

Chemical-based insecticides/larvicides pose a great threat to humans. The present study describes the histopathological changes in Anopheles stephensi Liston (Diptera: Culicidae) larvae after exposure to two essential oils, i.e. Eucalyptus globulus and Aloe vera. The exposure of 4th instar larvae of An. stephensi to 90 ppm of E. globulus and 550 ppm of A. vera oils resulted in various histological alterations in organs of the head regions like disintegration of the brain and other structures, disorganization in the imaginal buds of the antennae, complete disappearance of the optic lobes, and total disruption of the inner and outer retractor muscles of the brush as compared to the control larvae. Oil-exposed larvae also exhibited diversifications in gastric ceca, disintegration of the midgut epithelium layer, rifts in microvilli, and disappearance or reduction of fat bodies as well as the epithelium layer of the hindgut. Such pathological changes restrict the larvae's ability to perform various functions, leading to their death.

Antennal Bud Development in Bracon hebetor (Hymenoptera: Braconidae) Examined by Light and Electron Microscopy during the Third and Fourth Instars

Antennal development of Bracon hebetor (Say) was examined at a cellular and ultrastructural level. Imaginal buds from parthenogenetically produced male larvae of known age were examined by dissection, light microscopy, and transmission and scanning electron microscopy. The adult male antenna consists of 18-20 cylindrical flagellar segments with proximal scape and pedicel. In the 56- to 60-h-old larva, the antennal bud is an undifferentiated, ovoid cellular mass. By 92-96 h, the bud has developed into an elongated, tubular, fully segmented appendage. Cell death, uniformly distributed in the bud, occurs at a low level throughout the 40 h but does not appear to have a major morphogenetic role. Cell size remains constant throughout the 40 h. A high level of mitotic activity is responsible for growth of the bud. A peak in mitosis is detected between 72 and 76 h, just before segmentation. Segments appear to be formed synchronously. Segmentation does not appear to involve localized zones of proliferation, or cell death, or statistically significant changes in cell size. Alterations in cellular interactions with resultant shifts in cell shape or position may be involved.

Studies on the Nuclear Polyhedrosis of Heliothis armigera (Hbn.)

Histopathological studies were made in fourth instar larvae of Heliothis armigera (Hbn.) Inoculated with a dose of 10 polyhedra per larva, Histopathological changes were discernible 48 hours after virus treatment. The most susceptible tissues were fat body, hypodermis, tracheal matrix and blood cells. Muscles, nerve tissue toregut, oesophageal valve, connective tissue surrounding the midgut, silk glands and testicular epithelium were also found to be affected by the virus to a lesser extent, Polyhedra could not be observed in the imaginal buds, malpighian tubules and hind gut.

Pathology of a nuclear polyhedrosis virus of the alfalfa looper in alternate hosts

The symptomatology and histopathology of a nuclear polyhedrosis virus isolated from a larva of the alfalfa looper, Autographa californica, was studied by examining 13 tissues in the original and following alternate hosts: cabbage looper, Trichoplusia ni; beet armyworm, Spodoptera exigua; saltmarsh caterpillar, Estigmene acrea; corn carworm, Heliothis zea; cotton leafperforator, Bucculatrix thurberiella; and diamondback moth, Plutella xylostella. In all hosts, the hypodermal, tracheal matrix, and fat body cells were infected. Other tissues infected in some hosts included the Malpighian tubules, muscle, hemocytes, ganglia, midgut, hindgut, juvenile tissue (imaginal buds), and testes. No major changes in tissue tropisms were observed. The external symptoms were typical of nuclear polyhedrosis in all species except the corn earworm; in this host, development of the disease and death were delayed.

Connective tissue membranes and their apparent role in transporting neurosecretory and other secretory products in insects

Circumstantial evidence is presented, in the fly, for the direct transport of secretory products from secretory cells to cells of target organs, by way of continuous connective-tissue membranes. Secretory material passes to the periphery of the secreting cell and accumulates in channels within the basement membrane. The channels converge and pass along connective tissue strands, or may pass directly, into channels within the sheath of the target organ; there they diverge, in some cases opening into a system of interconnecting channels. Organs for which such a system is described include the ring gland complex, the larval lateral and dorsal nerves, the recurrent nerve to the larval gut, stretch receptor-type organs, pericardial cells, ventral nephrocytes, and oenocytes. Secretion-filled channels have further been found within the basement membrane overlying the imaginal buds in the prepupal stage; channels within the basement membrane of the leg rudiments and external genitalia have been traced to connective tissue strands originating from “stretch receptor-type organs”. These ultimately connect with the lateral segmental nerves and contain suspected secretory cells; such groups of cells could well be the source of origin of an intercellular agent regulating development, and the cells could thus function as regional “differentiation centers”. Electron microscope observations by other workers have suggested a close spatial relationship between the basement membranes and the various cellular membranes. Whereas the endoplasmic reticulum is possibly involved in intracellular electron transport, the basement membranes would here appear to be concerned in intercellular transport of cellular secretory products. It is suggested that the transport by way of basement membranes may also exist in groups other than insects.

Functions of the Lymph Gland Cells during the Larval Period in Drosophila

ABSTRACT In the latter half of the second instar the lymph glands of Drosophila larvae hypertrophy and release cells into the body-cavity, many of which move to the imaginal buds (Shatoury, 1955a). These cells have been referred to as oikocytes. The optic region of the cephalic disk becomes colonized by the large cells known as hexagons. During the first half of the third instar these increase considerably in number. At about the 85-hour stage, and simultaneously with similar changes in the cells still in the lymph glands, the oikocytes in the optic disk exhibit nuclear pycnosis and the deposition of melanin. Later the cells may become vacuolarized and disintegrate. The precursors of the ommatidia can be seen in the optic disk before the oikocytes become melanized. During the latter part of the first instar oikocytes are also released from the lymph glands, and hexagons accumulate around the end of the oesophagus where it enters the proventriculus. In the immediate neighbourhood of these oikocytes the radial layer of the proventriculus shows some cellular differentiation, forming an ‘upper ring’ of highly basophilic cells. It has usually been considered that this upper ring constitutes the primordia of the imaginal fore-gut, but it has been found that the lower radial cells will also contribute to this structure. The oikocytes of the proventriculus suffer melanization and degeneration at the same time as those of the optic disk and the lymph gland. In larvae aged between 85 and 96 hours two groups of degenerating cells can be found near the cephalic end of the testis and one group in the caudal end. These three groups of cells seem to be oikocytes, and can be traced back to the first instar, when they seem to enter the testis at the same time that the proventriculus is being colonized. Their appearance in the testis is followed by the first sign of the differentiation of spermatocytes. The appearances suggest that the oikocytes, when they arrive at the testis, the proventriculus and the optic disk, play some part in stimulating those processes of differentiation which bring these organs into the condition from which they can undergo metamorphosis. The simultaneous degeneration of these cells at the end of the third instar would seem to indicate that this stimulus is no longer needed after that time. Shatoury (1956) has suggested that the mechanism which brings about this degeneration involves the formation of auto-antibodies.

The Development of Gastric Tumours in Drosophila Larvae

ABSTRACT A sex-linked factor in Drosophila, lethal-no-imaginal-buds (1-nib) produces two main effects: reduction, or even complete absence of the imaginal buds; and excessive proliferation of the epithelium of the stomach, leading to occlusion of the gut and death from starvation. The intensity with which these two effects are expressed varies independently in different stocks. This paper is primarily concerned with the formation of the gastric tumour. The first pair of lymph glands, after their breakdown in the later part of the first instar, usually regenerate only incompletely. With increasing abnormality of the glands, there was an increasing tendency for excessive proliferation, or for cellular degeneration, in the testes, hind-gut primordia, and stomach, in that order. In severely affected larvae, the lymph glands degenerate at the end of the second instar. This is followed by, and is thought to be the cause of, a strong hypertrophy of the gastric epithelium, which leads to the filling up of the gut lumen with cells and anuclear cytoplasmic masses. It is probable that a preliminary stage in the development of this hypertrophy is the proliferation of the cells of the mid-gut imaginal primordia. Similar proliferation and/or hypertrophy occurs in the hind-gut and salivary gland primordia. The cells of all these proliferations eventually undergo degenerative processes involving the deposition of melanin, when they become converted into melanotic ‘tumours’. These are usually anchored to their places of origin, in contrast to the free tumours found in some other Drosophila stocks. Preliminary experiments indicate that the development of the proliferations can be suppressed by the injection of normal lymph glands into early third instar larvae. In individuals from which the cephalic buds are missing, there is no development of the optic glomeruli in the brain. In the stock lethal-malignant (Shatoury, 1955) the lymph glands undergo pathological changes of a different type; they become excessively hypertrophied in the late third instar, and develop into a metastasizing tumour which eventually undergoes various degenerative changes. In this stock also the gastric epithelium begins to exhibit excessive hypertrophy at the same time as the lymph glands become abnormal. A full gastric tumour may develop; in this case the basement cells are involved in addition to the main epithelium. It is suggested that the complex interrelations between the lymph glands, the migratory cells given off from them (oikocytes), and the apparently hormonally controlled proliferative tendencies of tissues such as the gastric epithelium, constitute a novel type of epigenetic system, which may be special to the larvae of holometabolous insects or even of Drosophila alone.

Behaviour op lethal-no-imaginal-bud larvae towards imaginal bud and lymph gland transplants.

1. Lethal-no-imaginal-bud larvae become phenotypically normal if early third instar lymph glands or imaginal buds are transplanted into them before they develop the lethal phenotype. Both tissues were thrown down as melanised black bodies at the end of the third instar. 2. It was argued that the lymph gland transplant has inhibited the development of cell hypertrophy through its secretion, while the imaginal bud transplant seems to have stimulated the production of corresponding antibodies. The imaginal buds are thought to behave as isoantigens in the bud-free haemolymph ofl-nib larvae. 3. Early third instar wild type buds, or even saline solution, caused the melanisation of the cells of the lymph glands if injected into early third instar wild type larvae.

Developmental Interactions in the Development of the Imaginal Muscles of Drosophila

ABSTRACT The thorax of Drosophila contains two main sets of muscles, the dorsal flight-muscles and a lateral set. Among the latter are the trochanteral depressors of the legs, of which those associated with the second legs are the largest. The development of all these muscles during the pupal period is described and an account is given of the effects of the contraction of the tendons of the longitudinal muscles in producing the curvature of the mesothorax and the formation of the post-notum. The dorsal flight-muscles develop from an interaction between (a) three pairs of larval muscles; (b) mesoderm cells derived from the mesothoracic imaginal buds; (c) cells which migrate from the developing trochanteral depressors of the second leg. It is the latter cells which are responsible for splitting the three larval muscles of each side into six. The fibrillar muscles of the lateral set have a similar origin. The trochanteral depressors are tubular, not fibrillar, in structure. They are formed from mesoderm cells of the leg imaginal buds. If the imaginal bud of a first or third leg is removed from the late larva, not only the leg but also the corresponding trochanteral depressor is missing from the adult. If a second leg bud is removed, the dorsal flight-muscles and the lateral fibrillar muscles on that side also fail to develop. In extreme bithorax phenotypes, in which the metathoracic bud has formed a structure externally resembling a mesothorax, this region does not contain a second set of flight-muscles, although there are sometimes small badly differentiated representations of them. The secondary scutellum is not provided with a post-notum. If the normal mesothoracic bud of one side is extirpated from a larva which is developing the bithorax phenotype, the transformed metathoracic bud may shift forward and fuse with the mesothoracic bud of the opposite side. In some such cases the metathoracic mesoderm, in association with cells from the second trochanteral depressor, has developed into flight-muscles. It is concluded that the migrating cells of the second trochanteral depressor provide a stimulus which is essential for the differentiation of the flight-muscles.

Lethal no-differentiation and the development of the imaginal discs during the larval stage inDrosophilia.

1. Lethal no-differentiation, symboll-nd, is characterised by the failure of some or all of the imaginal buds to continue differentiation during the larval third instar. This is due to abnormal proliferation of the imaginal disc mesoderm. 2. There is a well-defined sequence in the sensitivity of the different organs to the lethal effect, the legs being the most commonly affected, and the genital disc the least commonly. 3. The abnormal proliferation of the mesoderm is preceded by degenerative changes in the lymph glands. 4. The mechanism of differentiation of the imaginal buds is discussed and it is argued that the organisation of the imaginal organs is determined primarily by the mesoderm. 5. It is suggested that the proliferation of the imaginal bud mesoderm is normally inhibited by a "bud-differentiation hormone" secreted by the lymph glands. The requirements of the different imaginal discs from this postulated hormone were represented by a histogram, in fig. 14.

The Development of the Midgut in the Larva of Aedes Dorsalis Meigen

It is common knowledge that insect larvae are usually adapted for efficient food acquisition. Adults are specialized for reproduction. Nutritive materials accumulated by the larvae are utilized during metamorphosis for energy of transformation from larva to imago. Attempts to explain the manner in which the larval stored foods are utilized have not always been strictly accurate. One of the best explanations stresses the importance of digestion of larval tissues and subsequent replacement by imaginal tissue developed from regenerative buds or nuclei. Trager (1937), working with Aedes aegypti , says that trichogenous cells, anal gills, foregut, midgut, colon, salivary glands, large oenocytes, main tracheal trunks and longitudinal abdominal muscles of the larva are destroyed during the pupal stage or shortly after. Larval hypodermis, fat body, thoracic ganglia, Malpighian tubules, heart and pericardial cells persist essentially unchanged into the adult. Woolley (1943) and Christensen (1941) find no evidence of histolysis in the nervous system and the internal reproductive system respectively of Aedes dorsalis . Richins (1938) finds in the midgut of this same species, however, a striking example of larval tissue degeneration with replacement by imaginal buds.

Some Developmental Effects of X-Rays in Drosophila

ABSTRACT If Drosophila larvae homozygous for the third chromosome recessive straw-3 are treated with X-rays, back-mutations of the straw-3, gene to its normal allelomorphs take place in somatic cells, and the cells of the wings give rise to hairs which can be recognized as wild type (Waddington, 1940b). In one attempt to follow out this matter in more detail high doses (7000 r. units) were applied. The resulting mortality was, it might be said, 100 %. That is, no flies emerged; but on dissecting the pupa cases, it was found that a considerable proportion had developed up to the hatching stage, but had not been able to free themselves from the pupal integuments. These flies were found to exhibit some rather remarkable deformities, and the experiment has therefore been repeated a number of times. It is the purpose of the present paper to describe in some detail the developmental abnormalities produced by such heavy doses of X-rays. Friesen (1936) originally described some abnormalities (which he termed ‘Roentgenmorphoses’) produced by slightly smaller doses, and some further notes on such cases have been published by Enzmann & Haskins (1938a, b) and Haskins & Enzmann (1937). All the abnormalities found by these authors can probably be considered as due to inhibitory actions of X-rays on various developmental processes; but, as will be clear later, the striking feature of the animals to be discussed in the present communication is that in some of them the growth of certain rudiments has been actually stimulated by the radiation. A preliminary communication of the experiments recorded in this paper has been published (Waddington, 1942).

THE RENEWAL AND REPLACEMENT OF THE STYLETS OF SUCKING INSECTS DURING EACH STADIUM, AND THE METHOD OF PENETRATION

In a study of the mouth parts of the scale and aphis, certain conclusions corresponding to those of Hermann Weber were independently drawn. While several phases of the subject need clarifying, it is definitely established that the retort-shaped organs at the bases of the stylets are masses of hypodermal cells constituting deep invaginations of the integument. Within these invaginations, which lengthen out in a circular manner during each stadium, new stylets are built up for each successive instar. In those members of the Hemiptera in which the head is deflected, the four stylets are separately coiled in the cephalic region and at a definite stage during each ecdysis the new stylets pass down to take the place of the old which are discarded at the moult.The manner of this renewal and replacement of the stylets appears to be, in many respects, unique. But, inasmuch as the stylets are simple hollow chitinous structures, they may be said histologically to bear a closer resemblance to other cuticular processes than they do to the more complex organs arising from imaginal buds during metamorphosis. An analogy to the renewal of the stylets is presented in the development of the spines and hairs of the body. The methods whereby the coiled stylets are expelled from the head are discussed.The action of the protractor muscles in the aphis and scale is altogether inadequate to explain the means of penetration into the compact tissues of woody growths. More especially is this the case where the stylets are much longer than the labium, and are, moreover, looped within the body and thus neutralize the effect of muscular action at the base. New facts are advanced to supplement those already known, and it is submitted that the stylets are propelled forward by successive short holds contrived by the joint action of the labrum and labium. In the aphis the main function of the stylet muscles is directional control of the tips, enabling a short stylet to explore a large area. The absence of this control in the scale is compensated for by the provision of longer stylets. Directional control permits of selective feeding, giving rise to a sense of taste. This is manifest in specific types of injury to the host plant and also by a modification in the insect of accessory structures of the mouth.

On the development of imaginal buds in normal and mutant Drosophila melanogaster

AbstractDefinite information concerning the time of development and location of the different imaginal discs of Drosophila melanogaster was needed in order to interpret especially the gynandromorphs, mosaics, and intersexes that have been extensively reported in cultures of this fly. This information was also desirable for many of the mutant types. It was not known, for example, when an organ was reduced or absent, whether its imaginal disc showed a corresponding reduction, or whether it was full size in the larvae and pupae, and failed to carry through to the later stages.Three mutant types with eyes smaller than those of the wild type, namely, lozenge, bar, and eyeless, were examined. It was found that there is a corresponding difference in size as far back as the imaginal disc could be detected. Similarly for the two mutants, vestigial and no‐wing. Conversely for the mutant, bithorax, in which the metathorax is larger than the normal and has assumed many of the characters of the normal mesothorax, the imaginal disc was correspondingly enlarged.It follows that the effects of the mutant genes for these characters can be observed in the very earliest condition of the imaginal disc.

HISTOGENESIS IN INSECT DEVELOPMENT, AND CELL SPECIFICITY

In the development (ontogeny) of insects with complete meta morphosis the imaginal antennae, mouth-parts, legs and wings are produced from small buds, or histoblasts, in the larval derm. These histoblasts or imaginal buds arise by the shallow or deep invagination (one for each histoblast) of small @regions of the larval cellular skin layer including originally, in each case, only @comparatively few derm cells. The position of these invagina tions, and -therefore the participation of derm cells in the future leg or wing development, seems to be determined wholly with reference to the future imaginal organ, and not at all with refer ence to any difference in degree of differentiation among the cells of the larval derm. The wing-buds arise from the latero-dorsal regions of the mesoand meta-thoracic segments, the leg-buds from the latero-ventral regions of each of the three thoracic segments. The larval derm is certainly not to be looked on as composed of wholly undifferentiated embryonic cells. These derm cells make up a definite organ, or part, of the larval body, with defini tive position and particular functions. All these cells, and no others in the body, secrete' chitin; some of them secrete noxious fluids, ill-smelling, acrid, poisonous. Many of them, perhaps all, secrete moulting fluid at the times of the regular larval moults; many are specially sensitive, many bear sense-hairs or papilke. The invagination and beginning development of small parts of this derm, in a wingless and legless larva of a fly or honeybee or of some other specialized insect, may occur in a very early lar val stage (in some cases, indeed, indications of the future histo blasts are apparent in just-hatched Iarv@e), but in most cases the invagination does not appear until a certain part of the free lar val life has been lived. That is, the larval derm has for awhile