Vitamin A deficiency: effect on retinal structure of the moth Manduca sexta

Sphingid moths (Manduca sexta) were reared for several generations on an artificial diet deficient in vitamin A and its precursors. Retinal tissue from depleted moths was removed for histological examination. There was extensive histolysis in the retinal epithelium and underlying nervous and connective tissues. This pathology correlated with severe visual impairment, even though normal growth, metamorphosis, and reproduction occurred. In the adult this pathology could be reversed when the larvae were reared only on tobacco (its usual host) or on the artificial diet supplemented with beta-carotene or vitamin A palmitate.     

Nervous control of the heart during thoracic temperature regulation in a sphinx moth

Heating the thorax of the sphinx moth, Manduca sexta, evoked pulsations of the heart in the abdomen. These pulsations were of relatively high rate and amplitude, and traveled from the abdomen into the thorax. While heat was continuously applied exclusively to the thorax, thoracic temperature often stabilized and abdominal temperature increased sharply. Thoracic heating of moths with transected nerve cord, however, did not evoke these responses. It is inferred that the heart in the abdomen responds to overheating of the thorax through neural influence.     

Identification of an allatotropin from adult manduca sexta

A peptide that strongly stimulates the secretion of juvenile hormone from corpora allata in vitro (allatotropin) has been purified from extracts of heads of pharate adult Manduca sexta. The primary structure of this 13-residue peptide has been determined: H-Gly-Phe-Lys-Asn-Val-Glu-Met-Met-Thr-Ala-Arg-Gly-Phe-NH(2). This neurohormone has no sequence similarity with any known neuropeptide from other organisms. Synthetic allatotropin, as well as truncation fragments, including one with the five amino terminal residues deleted, showed in vitro activity indistinguishable from that of native allatotropin.     

Cellular Response to Ecdysterone in vitro

Organ cultures of hindgut from diapausing tobacco hornworm pupae, Manduca sexta (Johannson), produce an abundance of migrant cells around the original explant. With time-lapse cinematography, these cells were seen to move slowly and tended to aggregate. The addition of ecdysterone (beta-ecdysone) to these cultures stimulated a large increase in individual cell movements and the eventual disruption of cell sheets.     

2-Tridecanone: A Naturally Occurring Insecticide from the Wild Tomato Lycopersicon hirsutum f.glabratum

A nonalkaloid insecticide was isolated from the wild tomato Lycopersicon hirsutum f. glabratum and identified as 2-tridecanone, a compound 72 times more abundant in the wild tomato than in the cultivated tomato L. esculentum. Lepidopterous larvae (Manduca sexta and Heliothis zea) and aphids (Aphis gossypii) died when confined on 2-tridecanone-treated filter paper.     

Intracellular stimulation of an identified neuron evokes cardioacceleratory peptide release

The central nervous system of the tobacco hawkmoth, Manduca sexta, is known to contain two cardioacceleratory peptides (CAP's), both of which function in vivo as cardioregulatory neurohormones. Intracellular electrical stimulation of a single abdominal ganglion neuron evokes the release of CAP-like bioactivity. This stimulation-evoked bioactivity is destroyed by prior treatment with protease. The possibility that intracellular stimulation of a CAP-containing neuron synaptically activated additional spiking neurons is eliminated.     

昆虫一氧化氮合酶基因研究进展及其同源分析

概述了果蝇、家蚕、长红猎蝽、按蚊和烟草角蛾一氧化氮合酶的生理作用、生化特性、研究方法、基因克隆等方面的研究进展,并采用生物信息学方法比较了5种昆虫NOS的同源性,构建了进化树.     

Steroid-dependent survival of identifiable neurons in cultured ganglia of the moth Manduca sexta

Adult emergence at the end of metamorphosis in the moth Manduca sexta is followed by the death of abdominal interneurons and motoneurons. Abdominal ganglia removed from insects before this period of naturally occurring cell death and maintained in vitro showed neuronal death confined to the same cells that normally die in vivo. Addition of physiological levels of the steroid 20-hydroxyecdysone to the culture system prevented the selective death of these motoneurons.     

Engineering modified Bt toxins to counter insect resistance

The evolution of insect resistance threatens the effectiveness of Bacillus thuringiensis (Bt) toxins that are widely used in sprays and transgenic crops. Resistance to Bt toxins in some insects is linked with mutations that disrupt a toxin-binding cadherin protein. We show that susceptibility to the Bt toxin Cry1Ab was reduced by cadherin gene silencing with RNA interference in Manduca sexta, confirming cadherin's role in Bt toxicity. Native Cry1A toxins required cadherin to form oligomers, but modified Cry1A toxins lacking one alpha-helix did not. The modified toxins killed cadherin-silenced M. sexta and Bt-resistant Pectinophora gossypiella that had cadherin deletion mutations. Our findings suggest that cadherin promotes Bt toxicity by facilitating toxin oligomerization and demonstrate that the modified Bt toxins may be useful against pests resistant to standard Bt toxins.     

JH Zero: New Naturally Occurring Insect Juvenile Hormone from Developing Embryos of the Tobacco Hornworm

A new insect juvenile hormone was isolated from developing embryos of the tobacco hornworm moth, Manduca sexta. The new hormone was found with juvenile hormone I and is a 1-carbon homolog of this substance. The assigned structure is methyl (2E,6E,10-cis)-10,11-epoxy-3,7-diethyl-11-methyl-2,6-tridecadienoate, which constitutes a trishomosesquiterpenoid skeleton. This is the first chemical idetification of any juvenile hormone from insect eggs.     

Conversion of beta sitosterol to cholesterol blocked in an insect by hypocholesterolemic agents

Two vertebrate hypocholesterolemic agents (triparanol and 22,25-diazacholesterol) block the conversion of beta-sitosterol to cholesterol in the larva of the tobacco hornworm, Manduca sexta (Johannson). A primary site of inhibitory action is the terminal step in this conversion-the reduction of desmosterol (24-dehydrocholesterol) to cholesterol. This is also the site at which these compounds inhibit de novo cholesterol biosynthesis in higher animals. Both agents severely inhibit growth and maturation of the tobacco hornworm.     

N-beta-Alanyldopamine: Major Role in Insect Cuticle Tanning

N-beta-Alanyldopamine is the major tyrosine metabolite in the hemolymph and cuticle during pupal tanning in the tobacco hornworm, Manduca sexta L. Its concentration in hemolymph increases over 800-fold above larval levels by the start of tanning and decreases as the pupal cuticle darkens and hardens. It is a major catechol in species representing several insect orders and is the preferred substrate for pupal cuticular o-diphenol oxidase. In insects, N-beta-alanyldopamine appears to be the main precursor for tanning chemicals at certain developmental stages.     

Evolution of a polyphenism by genetic accommodation

Polyphenisms are adaptations in which a genome is associated with discrete alternative phenotypes in different environments. Little is known about the mechanism by which polyphenisms originate. We show that a mutation in the juvenile hormone-regulatory pathway in Manduca sexta enables heat stress to reveal a hidden reaction norm of larval coloration. Selection for increased color change in response to heat stress resulted in the evolution of a larval color polyphenism and a corresponding change in hormonal titers through genetic accommodation. Evidently, mechanisms that regulate developmental hormones can mask genetic variation and act as evolutionary capacitors, facilitating the origin of novel adaptive phenotypes.     

Juvenile hormone is required to couple imaginal disc formation with nutrition in insects

In starved larvae of the tobacco hornworm moth Manduca sexta, larval and imaginal tissues stop growing, the former because they lack nutrient-dependent signals but the latter because of suppression by juvenile hormone. Without juvenile hormone, imaginal discs form and grow despite severe starvation. This hormone inhibits the intrinsic signaling needed for disc morphogenesis and does so independently of ecdysteroid action. Starvation and juvenile hormone treatments allowed the separation of intrinsic and nutrient-dependent aspects of disc growth and showed that both aspects must occur during the early phases of disc morphogenesis to ensure normal growth leading to typical-sized adults.     

Thoracic Temperature Stabilization byn Blood Circulation in a Free-Flying Moth

The sphinx moth, Manduca sexta, maintains its thoracic temperature within a degree of 42 degrees C while in free flight over a range of air temperatures from about 17 degrees to 32 degrees C. Tying off the dorsal vessel abolishes temperature control. Moths with tied off vessels overheat and then stop flying at air temperatures of about 23 degrees C. However, flight at this temperature is possible when the thoracic scales are removed. The mechanism of temperature control involves transfer of the heat produced in the thorax to the blood pumped from the dorsal vessel, and the subsequent dissipation of this heat when the blood returns to the relatively cool abdomen.     

Insect prothoracicotropic hormone: evidence for two molecular forms

In an insect, the tobacco hornworm Manduca sexta, the cerebral neuropeptide prothoracicotropic hormone (PTTH), the primary effector of postembryonic development, exists as two molecular forms. These two PTTH's elicit characteristic in vitro dose responses of activation of prothoracic glands from different developmental stages, an indication that during development the glands change in their sensitivity to the neurohormones. Both PTTH's are active in a specific in situ bioassay. Since they may be released in situ at stage-specific times to evoke distinctly different developmental responses, the PTTH neuroendocrine axis appears to be an effective system for determining the functions of molecular forms of a neurohormone in the regulation of growth and development.     

RH 5849, a Nonsteroidal Ecdysone Agonist: Effects on Larval Lepidoptera

The ecdysone agonist RH 5849 (1,2-dibenzoyl-1-tert-butylhydrazine) causes the premature initiation of molting at all stages of larval development of the tobacco hornworm, Manduca sexta. This phenomenon occurs without an increase in the endogenous ecdysone (20-hydroxyecdysone) titers. RH 5849 likewise provokes the initiation of molting in larval abdomens in the absence of a source of endogenous hormone. Although substantially less active than 20-hydroxyecdysone in vitro, RH 5849 was 30 to >670 times as active as the authentic molting hormone in bioassays with isolated larval abdomens or intact hornworms. This reversal in potency can be attributed to the superior transport properties and metabolic stability of RH 5849 relative to 20-hydroxyecdysone. Thus RH 5849 and its analogs are relatively persistent ecdysone agonists that halt feeding in larval lepidoptera by forcing an ultimately lethal, developmentally premature molt.     

Aromatic cross-links in insect cuticle: detection by solid-state 13C and 15N NMR

Cross-polarization magic-angle-spinning nuclear magnetic resonance spectroscopy has been used to determine insect cuticle composition and cross-link structure during sclerotization or tanning. Unsclerotized cuticle from newly ecdysed pupae of the tobacco hornworm, Manduca sexta L., had a high protein content with lesser amounts of lipid and chitin. Concentrations of chitin, protein, and catechol increased substantially as dehydration and sclerotization progressed. Analysis of intact cuticle specifically labeled with carbon-13 and nitrogen-15 revealed direct covalent linkages between ring nitrogens of protein histidyl residues and ring carbons derived from the catecholamine dopamine. This carbon-nitrogen adduct was present in chitin isolated from cuticle by alkaline extraction and is probably bound covalently to chitin. These data support the hypothesis that the stiffening of insect cuticle during sclerotization results primarily from the deposition of protein and chitin polymers and their crosslinking by quinonoid derivatives of catecholamines.     

The cellular and physiological mechanism of wing-body scaling in Manduca sexta

In animals, appendages develop in proportion to overall body size; when individual size varies, appendages covary proportionally. In insects with complete metamorphosis, adult appendages develop from precursor tissues called imaginal disks that grow after somatic growth has ceased. It is unclear, however, how the growth of these appendages is matched to the already established body size. We studied the pattern of cell division in the tobacco hornworm Manduca sexta and found that both the rate of cell division and the duration of growth of the wing imaginal disks depend on the size of the body in which they develop. Moreover, we found that both of these processes are controlled by the level and duration of secretion of the steroid hormone ecdysone. Thus, proportional growth is under hormonal control and indirectly regulated by the central nervous system.