Melanization In Larvae Research Articles

Low toxicity contributes to Sporothrix globosa invade the skin of patients in low-epidemic areas of China.

This study aims to assess the clinical characteristics of sporotrichosis in low-endemic areas of China, including the prevalence geography, genotypic traits of patients, clinical manifestations, and strain virulence and drug sensitivities. The objective is to improve the currently used clinical management strategies for sporotrichosis. Retrospective data were collected from patients diagnosed with sporotrichosis through fungal culture identification. The isolates from purified cultures underwent identification using CAL (Calmodulin) gene sequencing. Virulence of each strain was assessed using a Galleria mellonella (G. mellonella) larvae infection model. Invitro susceptibility testing against commonly used clinical antifungal agents for sporotrichosis was conducted following CLSI criteria. In our low-endemic region for sporotrichosis, the majority of cases (23) were observed in middle-aged and elderly women with a history of trauma, with a higher incidence during winter and spring. All clinical isolates were identified as Sporothrix globosa (S. globosa). The G. mellonella larvae infection model indicated independent and dose-dependent virulence among strains, with varying toxicity levels demonstrated by the degree of melanization of the G. mellonella. Surprisingly, lymphocutaneous types caused by S. globosa exhibited lower invitro virulence but were more common in affected skin. In addition, all S.globosa strains displayed high resistances to fluconazole, while remaining highly susceptible to terbinafine, itraconazole and amphotericin B. Given the predominance of elderly women engaged in agricultural labour in our region, which is a low-epidemic areas, they should be considered as crucial targets for sporotrichosis monitoring. S. globosa appears to be the sole causative agent locally. However, varying degrees of melanization in larvae were observed among these isolates, indicating a divergence in their virulence. Itraconazole, terbinafine and amphotericin B remain viable first-line antifungal options for treating S.globosa infection.

A pheromonotropic peptide of Helicoverpa zea, with melanizing activity, interaction with PBAN, and distribution of immunoreactivity.

The sequence of an 18-amino acid residue peptide was deduced from the gene encoding PBAN and other peptides with common C-termini in Helicoverpa zea. The peptide caused melanization in larvae and pheromone production in females of H. zea, and was designated pheromonotropic melanizing peptide (Hez-PMP). The peptide has a 83% sequence homology with a pheromonotropic peptide isolated from Pseudaletia separata. PMP caused melanization and mortality when injected into larvae just before molting. Whereas intense melanization was caused with a dose of 1,000 pmol, peak mortality occurred at 100 pmol, with 50% of larvae dying within 48 h after injection. Pheromonotropic activity of PMP was dose dependent. Co-injection of Hez-PMP and Hez-PBAN into a female resulted in suppression of the pheromonotropic effect of PBAN. Whole-mount immunocytochemical studies revealed PMP-like immunoreactivity in frontal ganglion, subesophageal, thoracic, and abdominal ganglia as well as the esophageal nerve.

A serpin mutant links Toll activation to melanization in the host defence of Drosophila.

A prominent response during the Drosophila host defence is the induction of proteolytic cascades, some of which lead to localized melanization of pathogen surfaces, while others activate one of the major players in the systemic antimicrobial response, the Toll pathway. Despite the fact that gain-of-function mutations in the Toll receptor gene result in melanization, a clear link between Toll activation and the melanization reaction has not been firmly established. Here, we present evidence for the coordination of hemolymph-borne melanization with activation of the Toll pathway in the Drosophila host defence. The melanization reaction requires Toll pathway activation and depends on the removal of the Drosophila serine protease inhibitor Serpin27A. Flies deficient for this serpin exhibit spontaneous melanization in larvae and adults. Microbial challenge induces its removal from the hemolymph through Toll-dependent transcription of an acute phase immune reaction component.

Effect of Gamama Radiation on Phenoloxidase Activity in Mediterranean Fruit Fly (Diptera: Tephritidae) Larvae

The effect of gamma radiation on the phenoloxidase activity in larvae of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), was examined. Phenoloxidase activity was determined by spectrophotometrically measuring the increase in optical density at 490 nm because of the conversion of L-Dopa to Dopachrome, or by observing the degree of melanization in larvae killed by freezing. Both methods produced comparable results. In unir-radiated larvae, phenoloxidase activity can be detected on day 4 (late 2nd instar), and the activity continues to accumulate through day 7 (late 3rd instar). This accumulation was not observed when larvae were irradiated with a minimum dose of 40 Gy before the 3rd instar. However, irradiating larvae in which enzyme activity was already high (days 5 and 6) did not remove activity but only reduced the rate of further accumulation. These results indicate that measuring the activity of this enzyme in C. capitata larvae is a good, sensitive, and reliable indicator of irradiation treatment provided that the limits mentioned above are observed.

Effects of Environmental Factors on Phase Variation in Larval Cotton Leafworms, Alabama argillacea (Lepidoptera: Noctuidae)

Phase variation in cotton leafworm larvae was characterized using six color categories, ranging from green with yellow longitudinal bands to velvety black. A density-dependent relationship was found between percentage of black larvae and degree of crowding in field-collected larvae. Controlled experiments confirmed that crowding affected degree of larval phase variation. Exposure to crowding during the second and third instar had the greatest effect upon melanization expressed in the fifth instar. Phase variation of crowded larvae reared under photoperiods of LD 14:10 or LD 12:12 were similar. However, the degree of melanization in larvae reared at 18°C was greater than that of larvae reared at 27.5°C.

Effects of 25-azasteroids on development and reproduction of the southwestern corn borer Diatraea grandiosella Dyar

25-Azacholesterol and 25-azacoprostane significantly increased the larval period of southwestern corn borer in a dose dependent fashion from 1 to 300 ppm in the diet. Male larvae were much more resistant than female larvae to the growth-inhibiting effects of the azasteroids. Both azasteroids caused melanization of larvae and inhibited moulting, but did not produce larval-pupal intermediates. The azasteroids caused a reduction in pupal and adult weight at higher concentrations, more so in females than in males. Pupal periods and adult longevity were shortened, and adult wing malformation occurred with the highest azasteroid concentrations. Egg production and hatchability decreased with increasing azasteroid concentrations in larval diets.

Role of Oesophageal Connectives in Cuticular Melanization in Larvae of the Armyworm, Leucania separata WALKER (Lepidoptera : Noctuidae)

Transection of ventral nerve cords and implantation of ganglia were performed in crowded Leucania separata larvae which were destined to become black in body colour. Transection of the oesophageal connectives at 21 hr before the 5th-larval ecdysis resulted in pale coloration in the 6th-instar larvae. Implantation of suboesophageal ganglia taken from larvae before the 5th-larval ecdysis into isolatted abdomens resulted in more intensive melanization than implantation of those from the 6th-instar larvae soon after ecdysis. The ganglia taken from the 6th-instar larvae, of which oesophageal connectives had been transected at 21 hr before 5th-larval ecdysis, resulted in intense melanization after implantation into isolated abdomens. It is suggested that during the larval moulting some stimulation transmitted posteriorly through oesophageal connectives promotes release of the hormone(s), which cause(s) melanization, from the suboesophageal ganglion.

Juvenile hormone titers in the hemolymph during late larval development of the tobacco hornworm, Manduca sexta (L.).

1. A sensitive and quantitative bioassay for JH is described based on the JH inhibition of cuticle melanization in larvae of the black mutant of Manduca sexta. The assay is sensitive down to about 2 x 10-5 µg (20 pg) C18JH.2. Using this assay, the JH titers in hemolymph of larvae of M. sexta from ecdysis to the fourth instar through the first third of the fifth instar have been estimated. The JH titer is highest immediately after ecdysis to the fourth instar and reniains relatively high until after initiation of the last larval molt. During the time that molting is initiated, the JH concentration is about 2 x 10-8 M in terms of C18JH equivalents. Following initiation of molting the titer drops about 30-fold.3. Immediately after ecdysis to the fifth instar, the JH titer is again high (nearly the same as seen at the initiation of the molt), then by day 1 has declined sixfold and remains constant through day 2. In mature fifth instar larvae, the titer has dropped again to essentially undetectable levels.4. The rate of degradation of endogenous JH in the hemolymph was estimated following neck- or abdomen-ligation of fourth instar larvae. After either type of ligation, JH activity was lost from the hemolymph with a half-life of about 1.5 hours.

Hemocytic changes associated with the encapsulation and melanization of some insect parasites

The hemocytic changes that attend parasite encapsulation and melanization in larvae of Drosophila, Musca domestica, and Orthellia caesarion are very similar to those changes occurring in noninfected individuals at metamporhosis. Some of the changes include the precocious differentiation and migration of hemocytes. Comparative and quantitative hemocytological data suggest that some stimulus in infected larvae, acting directly on the hemocytes or on the mechanism(s) controlling their activity, causes the cells to leave areas of the body where they are normally found and to encapsulate parasites. Questions concerning the origin and mode of action of the initial stimulus are raised, and as a basis for future experimentation it is proposed that the cellular immune reactions of these insects against internal metazoan parasites result from a hormonal imbalance.