Action of brassinosteroids in the cotton leafworm Spodoptera littoralis.

The two native plant hormones 24-epibrassinolide and 24-epicastasterone showed 50% competition for binding at IC(50) of 1-3.6 microM with [(3)H]ponasterone A using cultured imaginal wing discs from last-instar larvae of the cotton leafworm, Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae). However, culture of imaginal wing discs in different concentrations of brassinosteroids, even up to 100 microM, demonstrated no induction of evagination. In contrast, 20E and the non-steroidal agonist RH-5992 competed respectively about 23- and 42-fold more effectively with labeled ponasterone A, and their ability (EC(50)) to induce disc evagination in vitro was 158 and 87 nM, respectively. Injection of 10 microg of brassinosteroids in newly-moulted last-instar larvae did not cause mortality above controls; higher mortalities were scored when brassinosteroids were injected late in the last instar.     

Imaginal disc development in a non-pupariating lethal mutant inDrosophila melanogaster

Summary Imaginal disc development in the non-pupariating lethall(1)npr-1, a mutant that maps to an ecdysone early puff site, is studied in situ, in vitro and in transplanted discs. Disc development is slightly abnormal from the middle of the third instar with severe abnormalities appearing after the rise in 20-hydroxyecdysone that triggers metamorphosis. The mutant discs only partly evaginate and do not undergo any of the detailed morphological changes characteristic of metamorphosis. Treatment of the mutant dises in vitro with colcemid and trypsin facilitates evagination but the appendages remain morphologically abnormal. A number of differentiative processes occur in mutant discs in situ and in discs transplanted into wild type hosts in spite of the absence of normal morphogenesis. Implications of the observations for normal disc development are discussed. Possible modes of action of thel(1)npr-1 gene are also discussed in light of the observation that the mutant gene maps to a locus which is thought to have a regulatory function in development.     

Isolation and characterization of X-linked lethal mutants affecting differentiation of the imaginal discs in Drosophila melanogaster

Summary Twenty-seven late larval or early pupal lethal mutations were isolated for the X-chromosome, some of which showed structural and/or functional deficiencies of the imaginal discs. The mutants were grouped according to the size and morphology of their discs as follows: 1. discs normal: 18 mutants. 2. discs small: 2 mutants. 3. discs degenerate: 4 mutants. 4. discless: 1 mutant. 5. discs heterogeneous: 2 mutants. Preliminary characterization of the mutants included a study of disc morphology, puparium formation and pupal molt, in vivo and in vitro evagination of the imaginal discs, autonomy of the mutation in the disc tissue (differentiation after transplantation and gynander mosaicism test). Possible relations between disc morphology and the former characteristics are discussed.     

Fine structural features of developing leg discs of the blowfly,Sarcophaga bullata (Parker)

The mesothoracic leg discs of the blowfly, Sarcophaga bullata (Parker) were studied by electron microscopy during the third larval instar. As the peripodial membrane and separation form, the cells of the disc become elongated and perpendicularly oriented toward the separation. The cellular organelles do not undergo significant changes until the late third instar. At this time, there is a significant increase in the amount of granular endoplasmic reticulum and in the number of inclusions, particularly in those cells located more deeply in the disc. Nucleolar enlargement and an increase in the number of mitochondria are also observed at this time. The cells at the border of the disc form a columnar epithelium whose surface develops microvilli-like projections. These projections. These projections reach their maximum development towards the end of third instar. It is suggested that some of the observed changes may represent a phenotypic expression of secretion of cuticular material.     

Neural development in an imaginal disc mutant of Drosophila melanogaster

The neural phenotype of an imaginal disc degenerate mutant l(1)d deg-3 was studied in histological sections. The mutant larvae showed severe abnormalities in the imaginal neural development. Gynandromorphs, which are composed of genetically mutant and nonmutant cells, were generated and analyzed as late larvae. The results of mosaic analysis were consistent with l(1)d deg-3 gene acting autonomously in the imaginal disc and imaginal neural cells. The optic lobe development patterns observed in the larval mosaics provided evidence for an eye disc-optic lobe interaction during the late third instar larval stage.     

The mechanism of evagination of imaginal discs of Drosophila melanogaster,: III. Evidence for cell rearrangement

The shape and arrangement of cells in leg discs of Drosophila melanogaster at different stages of evagination were examined by scanning electron microscopy. The observations indicate that the change in shape of the disc during evagination is largely a result of cell rearrangement. This process involves small movements of many cells within the disc epithelium while close associations between neighboring cells are maintained.     

The effect of ecdysterone and juvenile hormones on protein synthesis and development of imaginal wing discs ofDrosophila melanogaster

The effect of ecdysterone and juvenile hormone on protein synthesis and development of imaginal wing discs ofDrosophila melanogaster has been studied. It is found that juvenile hormone apparently does not inhibit the synthesis of the ecdysterone-inducible proteins, although wing disc development is inhibited to various extent by different juvenile hormones. It is suggested that the ecdysterone-inducible proteins are not involved directly in the initiation of wing disc evagination, it is possible that some of these proteins are involved in the maintenance of chromatin activities or they are involved in gene activation.     

Biological control of the black vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae) with entomopathogenic nematodes (Nematoda: Rhabditida)

Trials conducted under glasshouse conditions showed that control of Otiorhynchus sulcatus larvae in strawberry plants can be effective using Steinernema carpocapsae and Heterorhabditis megidis, given that temperature and moisture extremes are avoided. In field experiments, the double line T-Tape® drip irrigation system performed better than the single line T-Tape® system, effectively distributing the nematodes along and across strawberry raised beds, and placing them close to the root zone where O. sulcatus larvae feed. As soil temperatures are satisfactory for nematode infectivity from late spring to early autumn, nematode applications were aimed at late instar larvae during spring, and early instar larvae during summer. Late summer field treatment with S. carpocapsae induced 49.5% reduction of the early instar larvae, and field application of the same nematode species in late spring resulted in 65% control of late instar larvae. In the same trial, spring application of H. megidis caused 26% mortality of late instar larvae of O. sulcatus.     

The mechanism of evagination of imaginal discs of Drosophila melanogaster. V. Evagination of disc fragments.

Experiments designed to test the hypothesis that imaginal disc evagination may be accomplished by a continuous circumferential constriction of the basally located microfilaments in disc cells [Fristrom, D., and Fristrom, J. W. (1975). Develop. Biol.43, 1–23] are presented. Discs were cut in various planes so as to interrupt the hypothesized lines of constriction and the resulting fragments tested for the ability to evaginate in vitro. Fragments from each type of cut were able to undergo evagination without resealing of the would surfaces. Furthermore, sections of evaginated cut fragments showed no evidence for a general contraction of the basal cell surface. We conclude that the ability to evaginate is an intrinsic property of each fragment independent of its attachment to the rest of the disc.     

The Mechanism of Evagination of Imaginal Discs of Drosophila melanogaster

The evagination of imaginal leg discs to produce legs is a usefulmodel for studying morphogenesis. Evagination of imaginal legdiscs occurs in vitro in defined culture media in the presenceof the molting hormone ß-ecdysone. Evagination involveslimited, organized movement of imaginal disc cells. The movementappears to be a result of contractile activity, coordinatedwith the presence of appropriate structural and surface propertiesof disc cells. However, ecdysone does not produce its effectsdirectly, but acts through the genome to cause evagination.Evagination is a result then of increased synthesis of differentproteins, one of which is myosin. If the results on discs aregeneralizable they indicate that similar morphogenetic processesare the direct result of the readout of the specific geneticprograms.     

Analysis of morphogenetic movements in the development of the notum anlage of Drosophila melanogaster

Summary A comparison of the morphogenetic maps of the notum anlage of Drosophila melanogaster derived from the gynandromorph data and mosaics induced by somatic crossing-over during the first instar larval stage revealed that practically no major morphogenetic movements occur in the development of the anlage between the blastoderm and first instar larval stages and the adult stage. By comparing the morphogenetic map derived from gynandromorphs and the fate map derived from data on the transplantation of fragments of the mature wing imaginal disc, it was observed that no major morphogenetic movements occur in the notum anlage between the stages of the allocation of the disc and the mature disc. The results are consistent with the observations of other authors concerning the larval development of eye-antenna, wing and leg discs.     

Desensitization of fifth instar Spodoptera litura to azadirachtin and neem

The deterrence of azadirachtin, in its pure form and as a constituent of neem seed extract, to fifth instar Spodoptera litura (Fab.) larvae, was measured using cabbage, Brassica oleraceae (L.) var. capitata, leaf disc assays. Paired-choice assays, in which larvae could choose between feeding on a treated (1.3 ng azadirachtin per square cm leaf area) or an untreated leaf disc for 2 h, were conducted at 24 h intervals throughout the fifth instar. In addition, no-choice assays, in which larvae could feed on only one leaf disc (10 ng azadirachtin per square cm leaf area) for 1.5 h, were conducted consecutively over a six hour period at the beginning of the fifth instar. The effects of hunger and habituation on desensitization in our no-choice tests were partitioned. After repeated exposures, larvae became desensitized to pure azadirachtinal in both choice and no-choice tests, but did not desensitize to neem containing the same absolute amount of azadirachtin in choice tests. Hunger was responsible for approximately one third of the desensitization response in the no-choice tests. Sensitivity to azadirachtin was independent of age within the fifth instar.     

Effect of cytochalasin B on the evagination in vitro of leg imaginal discs

Cytochalasin B (1 μg/ml) completely inhibited the evagination of isolated leg imaginal discs cultured in vitro in a synthetic medium (ME) containing α-ecdysone (3 μg/ml). In discs precultured for 6 hr in medium ME without the drug, then transferred to cytochalasin B-containing medium, continuation of evagination was stopped immediately. The inhibition of evagination was completely reversible, provided pretreatment with cytochalasin B did not exceed 8 hr. Results are discussed in view of what is known on the effect of cytochalasin B on other developmental systems. Findings are compatible with the primary action of the drug being an alteration of cell surface properties, thus bringing to light the importance of these properties in the course of normal imaginal disc evagination.     

The development of the sensory organs of the legs in the blowfly,Phormia regina

Summary The development of the sensory neurons of the legs of the blowfly,Phormia regina has been described from the third instar larva to the late pupa using immunohistochemical staining. The leg discs of the third instar larva contain 8 neurons of which 5 come to lie in the fifth tarsomere of the developing leg. Whereas 2 neurons persist at least to the late pupa, the other cells degenerate. The first neurons of gustatory sensilla arise in the fifth tarsomere at about 1.5 h after formation of the puparium. Most of these sensilla, however, appear within a short time period beginning at about 18 h. The femoral chordotonal sensory neurons first appear at the time of formation of the puparium, as a mass of cells situated in the distal femur. During later pupal development 2 groups of these cells come to lie at the femur-trochanter border, where they become the proximal femoral chordotonal organ of the adult; the remaining cells become the distal femoral chordotonal organ. Other scolopidial neurons appear later in development. The nerve pathways of the late pupal leg are established either by the axons of the cells that are present in the larval leg disc or by new outgrowing processes of sensory neurons. In the tibia, the initial direction of new outgrowth differs in different regions of the segment: proximal tibial neurons grow distally, while distal tibial neurons grow initially proximally.     

A high-resolution morphogenetic map of the second-leg basitarsus inDrosophila melanogaster

Summary The lineages of cells on the second-leg basitarsus ofDrosophila melanogaster were analyzed by examining gynandromorphs andMinute mosaics. Bracts lie proximal to bristles on the adult basitarsus, yet bract precursor cells were found to originate lateral to bristle precursor cells. In 6 of the 8 longitudinal rows of bristles on this segment, the bract cells arise ventral to the bristle cells; in the others they arise dorsally. The lateral cell origins are interpreted as reflecting a pattern of lateral cell movements associated with evagination of the leg disc. An unusual discrepancy was observed in the relative frequencies of male vs. female bracts and bristles in gynandromorphs. The discrepancy suggests that there is a cell-autonomous sexual difference in either the time at which cells begin moving during evagination or the speed with which they move.On the basis of the results, it is reasoned that the bristle pattern of the basitarsus does not originate in its final form. Prior to evagination, the bristle cells of each row are apparently closer together than in the final pattern, and the rows are farther apart. Evidence is presented which suggests that the bristle cells of each row may originally be arranged in a jagged line which is later straightened by cell movements.The two locations where the anterior/posterior compartment boundary of the second leg passes through the basitarsus were found to vary relative to the bristle pattern. If this boundary is assumed to be a fixed line of positional values, then the extent of the observed variability — which is estimated to be ± 1 or 2 cell diameters — provides a measure of the precision of patterning around the circumference.     

Genesis of the reproductive system of mosquitoes II. Male of Aedes stimulans (walker)

The imaginal male of mosquitoes bears a combination of organs and appendages that make it morphologically distinctive. Its reproductive organs produce sperm cells, convey and extrude them, provide accessory fluids, and insure copulation and insemination. In Aedes stimulans (Walker) these organs are derived from one of the two sets of primordia provided by the embryo. The second set of primordia is capable of producing the feminine reproductive system under unusual circumstances. Testes are derived from two compact ovoid masses of cells suspended in the hemocoel of abdominal segment 6. Each enlarges slowly throughout larval instars 1–3 and elongates very rapidly late in instar 4. Specialization of the cellular mass into sperm cells proceeds forward from the caudal end early in pupal life. From the beginning, a sheath of nutritive cells or fatbody encases each gonad, and no tracheation of the mass is evident although one small trachea sends branches to the encasing fatbody late in larval life. The efferent canal from each testis is derived from a tenuous filament extending caudally from each gonad to the venter of segment 9 and a small cluster of cells in the wall of the hemocoel on the ental surface of imaginal disc 9. Early in pupal life the filaments become the tubular vasa efferentia. The caudal clusters are primordial terminal parts of the lateral tract that become vasa deferentia, seminal vesicles and associated accessory glands. The ejaculatory canal comes from a short pouch derived from the median genital plate of disc 9. All external parts except the paraprocts are products of disc 9. The bilateral buds begin to proliferate in larval instar 4 and become the basistyles, dististyles and claspettes of the gonapophyses during pupal life. The phallosome is derived from the median genital plate. Primordia of a possible feminine reproductive system and cerci remain undifferentiated and disappear early in pupal life in the normal course of events. Primordia that were recognizable include those of ovaries, parts of lateral oviducts, median genital tract and cerci.     

Analysis of differential proteins in two different wing‐types of female Nilaparvata lugens

Nilaparvata lugens (stal) is a rice pest and contains long‐winged and short‐winged varieties, called the wing differentiation. This study compared the protein profiles of the two wing‐types in females and two wing‐disc types 5th‐instar females by two‐dimensional electrophoresis analysis. We detected 172 and 174 protein spots in adults and 5th‐instar nymphs, respectively. The number of proteins with higher content in the long‐winged (disc) individuals is much more than that in the short‐winged (disc) individuals. A total of 32 differential protein spots were found, of which 20 were successfully identified. Their main function is about catabolic process, fiber and nucleoside binding, and they constitute 52 protein–protein interactions, which is around the glycolysis as the core. These results enrich the research on the protein Level in wing development, and provide more references for future studies.     

Microhabitat use by larvae and females of a rare barrens butterfly,frosted elfin (<Emphasis Type="Italic">Callophrys irus</Emphasis>)

The frosted elfin (Callophrys irus) is a localized and declining butterfly found in xeric open habitats maintained by disturbance. We described the effects of woody plant canopy cover, topography and host plant size and density on the quality of microhabitat of wild indigo (Baptisia tinctoria) host plants containing late instar frosted elfin larvae at four study sites in southeastern Massachusetts, United States. We also assessed whether females preferentially depositing eggs on host plants within specific microhabitats, therefore conferring greater survivorship to the larvae through the late-instar stage. We found that moderate amounts of canopy cover and large plant size characterized larvae-occupied host plants. In the absence of tree canopy cover, late instar larvae density remained low even when host plant density was high. However, females oviposited on wild indigo plants without regard to any of the vegetative or environmental variables we measured. These results indicate that canopy cover was an important characteristic of microhabitats containing late instar larvae, and late instar larvae occupancy was determined by suitable microhabitat conditions, and not female oviposition selection. Managing for canopy cover and microhabitat heterogeneity within relatively open habitats is recommended for the maintenance of frosted elfin populations.     

kurtz, a novel nonvisual arrestin, is an essential neural gene in Drosophila

The kurtz gene encodes a novel nonvisual arrestin. krz is located at the most-distal end of the chromosome 3R, the third gene in from the telomere. krz is expressed throughout development. During early embryogenesis, krz is expressed ubiquitously and later is localized to the central nervous system, maxillary cirri, and antennal sensory organs. In late third instar larvae, krz message is detected in the fat bodies, the ventral portion of the thoracic-abdominal ganglia, the deuterocerebrum, the eye-antennal imaginal disc, and the wing imaginal disc. The krz(1) mutation contains a P-element insertion within the only intron of this gene and results in a severe reduction of function. Mutations in krz have a broad lethal phase extending from late embryogenesis to the third larval instar. The fat bodies of krz(1) larva precociously dissociate during the midthird instar. krz(1) is a type 1 melanotic tumor gene; the fat body is the primary site of melanotic tumor formation during the third instar. We have functionally rescued these phenotypes with both genomic and cDNA transgenes. Importantly, the expression of a full-length krz cDNA within the CNS rescues the krz(1) lethality. These experiments establish the krz nonvisual arrestin as an essential neural gene in Drosophila.     

Cell rearrangement and cell division during the tissue level morphogenesis of evaginating Drosophila imaginal discs

The evagination of Drosophila imaginal discs is a classic system for studying tissue level morphogenesis. Evagination involves a dramatic change in morphology and published data argue that this is mediated by cell shape changes. We have reexamined the evagination of both the leg and wing discs and find that the process involves cell rearrangement and that cell divisions take place during the process. The number of cells across the width of the ptc domain in the wing and the omb domain in the leg decreased as the tissue extended during evagination and we observed cell rearrangement to be common during this period. In addition, almost half of the cells in the region of the leg examined divided between 4 and 8 h after white prepupae formation. Interestingly, these divisions were not typically oriented parallel to the axis of elongation. Our observations show that disc evagination involves multiple cellular behaviors, as is the case for many other morphogenetic processes.