Induction of perfect superlarvae by the application of juvenile hormone analogue to starved larvae of the silkworm, Bombyx mori

doi:10.1016/0022-1910(86)90126-5

Journal of Insect Physiology

Volume 32, Issue 12, 1986, Pages 1065-1073

https://doi.org/10.1016/0022-1910(86)90126-5 Get rights and content

Abstract

Topical application of juvenile hormone analogue, methoprene, induced a supernumerary larval moult in the silkworm, Bombyx mori. The incidence changed greatly depending on developmental stages and physiological states of the methoprene-treated larvae. When methoprene was applied to feeding larvae, only those treatments from the middle of the 2nd instar until the middle of the 4th instar were effective. An 18-h starvation period from the beginning of the 4th instar and a dose of 1 μg of methoprene per larva were required for 100% incidence of the perfect superlarvae. Allatectomy had no effects on the induction of superlarvae by methoprene. The treated 4th-instar larvae ecdysed to the 5th instar without any delay compared to the controls, and underwent an additional larval ecdysis 4.5 days later. The induced 6th-instar larvae took 8.5 days until the onset of cocoon spinning. The induced superlarvae showed reduced growth rates but an increase of final mass due to prolonged feeding period. A sharp but reduced peak in ecdysteroid titre in the haemolymph appeared one and a half days prior to each larval ecdysis in the treated larvae, suggesting that methoprene provokes the extra larval moult through an additional release of ecdysteroids.

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Cited by (26)

MicroRNA let-7 is required for hormonal regulation of metamorphosis in the silkworm, Bombyx mori
2022, Insect Biochemistry and Molecular Biology
Citation Excerpt :
When the JHs titer declines to a trace level in the final instar, larval-pupal and pupal-adult metamorphoses are induced by 20E (Belles, 2020; Nijhout, 1994). Topical application of JHs or JH analogs during larval development of numerous insects inhibits normal metamorphosis, leading to supernumerary larval molts or prepupal arrest (Kadono-okuda et al., 1986; Kamimura and Kiuchi, 2002). Conversely, the deprivation of JH by the surgical removal of the corpora allata (CA) from the penultimate larvae induces precocious metamorphosis (Dominick and Truman, 1985).
The heterochronic microRNA let-7, which was first identified in Caenorhabditis elegans, controls the timing of developmental programs, and let-7 triggers the onset of the juvenile-adult transition in bilaterians. The expression of let-7 is strongly induced during the last larval stage of C. elegans and is highly expressed in the late last instar larvae/nymphs of the fly Drosophila melanogaster and the cockroach Blattella germanica. In the silkworm Bombyx mori, the expression of let-7 remarkably increases in the corpus cardiacum-corpus allatum complex (CC-CA) at the beginning of the last larval instar and is maintained at high levels during this instar. To determine the biological function of let-7 in B. mori, we generated a let-7 knockout line and a transgenic UAS-let-7 line. The let-7 knockout larvae were developmentally arrested in the prepupal stage and became pupal-adult intermediates after apolysis. When let-7 was ubiquitously overexpressed under the transcriptional control of an Actin3-GAL4 driver, developmental timing and growth of larvae were severely impaired in the penultimate (L4) instar, and these larvae underwent precocious metamorphosis from L4. Furthermore, our results showed that reception and signaling of ecdysteroids and juvenile hormones (JHs) normally occurred in the absence of let-7, whereas the biosynthesis of ecdysone and JHs were affected by disruption and overexpression of let-7. Together, the present study demonstrates that let-7 is required for the coordination of the biosynthesis of ecdysone and JH to ensure the developmental transition during the metamorphosis of B. mori.
Improved strength of silk fibers in Bombyx mori trimolters induced by an anti-juvenile hormone compound
2018, Biochimica et Biophysica Acta - General Subjects
Citation Excerpt :
The growth and molting of silkworms are closely regulated by the hormones ecdysone, which causes molting, and juvenile hormone (JH), which prevents metamorphosis [31–33]. Considerable research has been undertaken to develop improved varieties of silkworm through disruption of the natural hormonal balance [34–36]. Currently, a number of treatments have been identified to induce precocious metamorphosis, for example, the juvenile hormone inhibitors KK-42, SD-III, SM-1, and YA20 and juvenile hormone analogues such as Kang-20 and methoprene [37–41].
Bombyx mori silk fibers with thin diameters have advantages of lightness and crease-resistance. Many studies have used anti-juvenile hormones to induce trimolters in order to generate thin silk; however, there has been comparatively little analysis of the morphology, structure and mechanical properties of trimolter silk.
This study induced two kinds of trimolters by appling topically anti-juvenile hormones and obtained thin diameter silk. Scanning electron microscope (SEM), FTIR analysis, tensile mechanical testing, chitin staining were used to reveal that the morphology, conformation and mechanical property of the trimolter silk.
Cocoon of trimolters were highly densely packed by thinner fibers and thus had small apertures. We found that the conformation of trimolter silk fibroin changed and formed more β-sheet structures. In addition, analysis of mechanical parameters yielded a higher Young's modulus and strength in trimolter silk than in the control. By chitin staining of silk gland, we postulated that the mechanical properties of trimolters' silk was enhanced greatly during to the structural changes of silk gland.
We induced trimolters by anti-juvenile hormones and the resulting cocoons were more closely packed and had smaller silk fiber diameters. We found that the conformation of trimolters silk fibroin had a higher content of β-sheet structures and better mechanical properties.
Our study revealed the structures and mechanical properties of trimolter silk, and provided a valuable reference to improve silk quality by influencing molting in silkworms.
Applying fenoxycarb at the penultimate instar triggers an additional ecdysteroid surge and induces perfect extra larval molting in the silkworm
2002, General and Comparative Endocrinology
When the juvenile hormone analog fenoxycarb was topically applied to the silkworm Bombyx mori at the beginning of the 3rd or 4th (penultimate) instar, an extra larval molt was induced. The 5th instar period was shortened to about 5 days and the extra 6th instar ranged from 8 to more than 20 days, depending on the dose applied. Starvation before fenoxycarb treatment strongly enhanced the incidence of extra molting up to 100%. When 1 ng was applied in the 4th instar after a 2-day starvation, most larvae underwent an extra molt, metamorphosed to pupae, then to fertile adults. Combining starvation and fenoxycarb application thus induces a perfect extra molt efficiently. In perfect extra molting larvae, profiles of total ecdysteroid titer during the 4th and 5th instars were similar to that during the 4th instar in the control, and the ecdysteroid profile during the extra 6th instar was similar to that during the control 5th (last) instar. At ecdysteroid peaks, 20-hydroxyecdysone (20E) and ecdysone (E), generally regarded as the active molting hormone and its precursor, had similar titers in the 6th instar, whereas E was much less than 20E in the 4th and 5th instars in the extra molting larvae. E was also abundant only in the last larval instar in the control. These results suggest that both 20E and E contents are important for regulation of larval molt and metamorphosis in silkworms and that fenoxycarb triggers the extra molt by inducing an additional larval molt type of ecdysteroid surge before the last larval instar.
Occurrence of non-stationary larval moults during diapause in the corn- stalk borer, Sesamia nonagrioides (Lepidoptera: Noctuidae)
1997, Journal of Insect Physiology
Last-instar larvae of the corn stalk borer, Sesamia nonagrioides (Lep.: Noctuidae), enter a facultative diapause under short photoperiods. In this noctuid, diapause development is characterized by the ability of larvae to perform several larval moults (up to seven) before pupation. Surprisingly, these supernumerary moults were not stationary and larval growth did occur as shown by growth in head-capsule width and weight of diapausing larvae. These heavy diapause larvae produced heavier pupae than non-diapausing strains. The number of supernumerary moults varied for insects, although they were reared under the same conditions. Pupal weight of diapause larvae was independent of the number of supernumerary moults performed. Using a radiochemical assay, we show that corpora allata from Sesamia nonagrioides larvae produced juvenile hormone (JH) -III, JH-II and their respective diols and acids. Although corpora allata of day-4 diapause-destined larvae exhibited the same biosynthetic pattern, no labelled products could be detected in the incubation medium containing corpora allata from non-diapausing larvae of the same age. Biosynthetic activity of the corpora allata was detected throughout diapause.
Regulation of juvenile hormone biosynthesis by ecdysteroid levels during the early stages of the last two larval instars of Bombyx mori
1996, Journal of Insect Physiology
Juvenile hormone (JH), produced by the corpora allata (CA), is critical for the regulation of insect postembryonic development. In the present study, a radiochemical assay was used to examine developmental changes in the JH biosynthetic rate in vitro in Bombyx mori; its regulation by the ecdysteroid levels in the haemolymph during the early stages of the last two larval instars was clarified. During the early stages of the penultimate larval instar, the ecdysteroid titres were maintained at levels ranging from 42 to 57 $ng ml$ , the JH biosynthetic rate fluctuated but was maintained at detectable levels. During the early stages of the last larval instar, the ecdysteroid titres decreased to very low levels (3–12 $ng ml$ ), CA ceased to produce JH midway through the instar. The ecdysteroid levels during the early stages of these two larval instars were artificially changed by various experimental manipulations, then, changes in the JH biosynthetic rate were assessed and the subsequent development of larvae was carefully examined. We concluded that whether CA continued to produce JH or became inactive during subsequent development is controlled by the ecdysteroid levels present in the haemolymph. Low ecdysteroid levels are a prerequisite for CA to become inactive and thus an important developmental signal preceding larval-pupal transformation. Incubation of isolated CA from newly-ecdysed last instar larvae with 20-hydroxyecdysone revealed that 20-hydroxyecdysone directly stimulates CA activity.
Variations in larval growth and metabolism of an estuarine shrimp Palaemonetes pugio during toxicosis by an insect growth regulator
1993, Comparative Biochemistry and Physiology. Part C, Comparative
1. Exposure of the estuarine shrimp, Palaemonetes pugio, to a juvenile hormone analogue (⩾8 μg methoprene 1⁻¹) throughout larval development inhibited successful completion of metamorphosis.
2. Methoprene exposure retarded growth in early larval stages and postlarvae, but enhanced growth in premetamorphic larvae.
3. Respiration rates of early larvae were elevated by methoprene exposure, but not so older larvae or post larvae.
4. Lower net growth efficiency (K₂ values) in methoprene-exposed early larvae suggests that increased metabolic demands reduced assimilated energy available for growth.
5. Modifications in O:N ratios of premetamorphic larvae and postlarvae suggest that methoprene altered substrate utilization patterns during metamorphosis.

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Journal of Insect Physiology

Abstract

References (32)

Progress of developmental programme during the last larval instar of Bombyx mori: Relationships with food intake, ecdysteroids and juvenile hormone

J. Insect Physiol.

Ecdysone changes in the haemolymph of two silkworms (Bombyx mori and Philosamia cynthia) during larval and pupal development

FEBS Lett.

Juvenile hormone titres and metabolism during starvation-induced supernumerary larval moulting of the tobacco hornworm, Manduca sexta L.

J. Insect Physiol.

Metabolic shift from lipogenesis to glycogenesis in the last instar larval fat body of the silkworm, Bombyx mori

Insect Biochem.

Growth parameters associated with endocrine events in larval Trichoplusia ni (Hübner) and timing of these events with developmental markers

J. Insect Physiol.

Ecdysteroid levels and developmental events during larval moulting in the silkworm, Bombyx mori

J. Insect Physiol.

Relationship between starvation and supernumerary ecdysis and recognition of the penultimate-larval instar in the common cutworm, Spodoptera litura

J. Insect Physiol.

Supernumerary instars produced by chilled wax moth larvae: Endocrine mechanisms

J. Insect Physiol.

Juvenile hormone and insect embryonic development: Its potential role as an ovicide

Temporal organization of endocrine events underlying larval-larval ecdysis in the silkworm, Bombyx mori

J. Insect Physiol.

Temporal organization of endocrine events underlying larval-pupal metamorphosis in the silkworm, Bombyx mori

J. Insect Physiol.

Growth in insects

The influence of juvenile hormone on the growth and metamorphosis of Bombyx larvae

Bull. Seric. exp. Stn

Regulation of corpus allatum activity in last instar Manduca sexta larvae

Chilled Galleria mellonella larvae: Mechanism of supernumerary moulting

Physiol. Ent.

Moulting, growth and survival of Galleria mellonella L. (Lep. Pyralidae) treated with juvenoids

Z. ang. Ent.

Cited by (26)

MicroRNA let-7 is required for hormonal regulation of metamorphosis in the silkworm, Bombyx mori

Improved strength of silk fibers in Bombyx mori trimolters induced by an anti-juvenile hormone compound

Applying fenoxycarb at the penultimate instar triggers an additional ecdysteroid surge and induces perfect extra larval molting in the silkworm

Occurrence of non-stationary larval moults during diapause in the corn- stalk borer, Sesamia nonagrioides (Lepidoptera: Noctuidae)

Regulation of juvenile hormone biosynthesis by ecdysteroid levels during the early stages of the last two larval instars of Bombyx mori

Variations in larval growth and metabolism of an estuarine shrimp Palaemonetes pugio during toxicosis by an insect growth regulator