Silkworm and Silk: Traditional and Innovative Applications

The various subjects covered in the present Special Issue "Silkworm and Silk: Traditional and Innovative Applications" demonstrate how sericulture, a practice deeply rooted in human history, can act as a bridge to bring together an exceptionally wide range of scientific and technical expertise in both conventional topics and cutting-edge technologies [...]

Mechanical Processing of Hermetia illucens Larvae and Bombyx mori Pupae Produces Oils with Antimicrobial Activity

The aim of this work was to develop processing methods that safeguard the quality and antimicrobial properties of H. illucens and B. mori oils. We adopted a vegetable diet for both insects: leftover vegetables and fruit for H. illucens and mulberry leaves for B. mori. First, alternative techniques to obtain a good oil extraction yield from the dried biomass of H. illucens larvae were tested. Traditional pressing resulted to be the best system to maximize the oil yield and it was successfully applied to B. mori pupae. Oil quality resulted comparable to that obtained with other extraction methods described in the literature. In the case of B. mori pupae, different treatments and preservation periods were investigated to evaluate their influence on the oil composition and quality. Interestingly, agar diffusion assays demonstrated the sensitivity of Gram-positive Bacillus subtilis and Staphylococcus aureus to H. illucens and B. mori derived oils, whereas the growth of Gram-negative Pseudomonas aeruginosa and Escherichia coli was not affected. This study confirms that fat and other active compounds of the oil extracted by hot pressing could represent effective antimicrobials against bacteria, a relevant result if we consider that they are by-products of the protein extraction process in the feed industry

A soil fungus confers plant resistance against a phytophagous insect by disrupting the symbiotic role of its gut microbiota

Plants generate energy flows through natural food webs, driven by competition for resources among organisms, which are part of a complex network of multitrophic interactions. Here, we demonstrate that the interaction between tomato plants and a phytophagous insect is driven by a hidden interplay between their respective microbiotas. Tomato plants colonized by the soil fungus Trichoderma afroharzianum, a beneficial microorganism widely used in agriculture as a biocontrol agent, negatively affects the development and survival of the lepidopteran pest Spodoptera littoralis by altering the larval gut microbiota and its nutritional support to the host. Indeed, experiments aimed to restore the functional microbial community in the gut allow a complete rescue. Our results shed light on a novel role played by a soil microorganism in the modulation of plant-insect interaction, setting the stage for a more comprehensive analysis of the impact that biocontrol agents may have on ecological sustainability of agricultural systems

The amazing complexity of insect midgut cells: types, peculiarities, and functions

The insect midgut epithelium represents an interface between the internal and the external environment and it is the almost unique epithelial tissue by which these arthropods acquire nutrients. This epithelium is indeed able to produce digestive enzymes and to support vectorial transport of small organic nutrients, ions, and water. Moreover, it plays a key role in the defense against pathogenic microorganisms and in shaping gut microbiota. Another important midgut function is the ability to produce signaling molecules that regulate its own physiology and the activity of other organs. The two main mature cell types present in the midgut of all insects, i.e., columnar and endocrine cells, are responsible for these functions. In addition, stem cells, located at the base of the midgut epithelium, ensure the growth and renewal of the midgut during development and after injury. In insects belonging to specific orders, midgut physiology is deeply conditioned by the presence of unique cell types, i.e., goblet and copper cells, which confer peculiar features to this organ. This review reports current knowledge on the cells that form the insect midgut epithelium, focusing attention on their morphological and functional features. Notwithstanding the apparent structural simplicity of this organ, the properties of the cells make the midgut a key player in insect development and homeostasis

Functional characterization of sugar transport in the intestinal epithelium of an insect (Aphidius ervi, Hymenoptera)

Aphidius ervi is an entomophagous wasp, widely used in biological control because adult females lay the eggs in the haemocoel of several aphid species. After hatching, A. ervi larvae develop in the living host feeding on its haemolymph and, just before metamorphosis, kill the host by devouring its internal tissues and pupating inside the body wall, from which the adult will finally emerge. Like many other parasitoids, A. ervi finely redirects host metabolism in order to optimize haemolymph nutrient contents to support larval specific needs. In aphid haemolymph, sugar titre is extremely high, reaching a concentration of 129 and 60 mM for fructose and glucose respectively. The peculiar sugar-rich environment in which A. ervi larvae develop, suggestive of a critical role of these nutrients for the insect survival, stimulated us to identify the transporters involved in glucose and fructose intestinal absorption, especially considering that information on sugar transport in insect midgut is scanty. The study performed in larval A. ervi intestine, isolated and incubated in vitro, allowed us to detect, with functional, immunohistochemical and immunoblotting approaches, the transport proteins responsible for glucose and fructose uptake and to characterise their basic properties. The results unequivocally show that the cellular model for sugar transport in the larval stage of this insect is surprisingly similar to that conventionally described for mammals (i.e. SGLT1-like and GLUT5-like transporters on the apical membrane of the intestinal epithelial cell, and GLUT2-like transporters on the basolateral one), with the expression, apparently constitutive, of GLUT2 transporters also in the apical membrane, in agreement with the model for the transcellular absorption of hexoses recently proposed (Kellett, J. Physiol. 531, 585, 2001)

A morphological and functional characterization of Bombyx mori larval midgut cells in culture

Recent studies have shown that Bombyx mori larval midgut can transport proteins unaltered following the transcellular pathway by transcytosis. The numerous steps involved in this complex process are still unknown in the insect midgut, and a promising tool to elucidate this aspect is the availability of single midgut cells in culture suitable for transport experiments. Mature midgut cells in culture were obtained from stem cells isolated from B. mori larvae cultured in Grace’s medium supplemented with 20-hydroxyecdysone (20-HE) and α-arylphorin. After three weeks, up to 60 % of the cultured cells were differentiated into columnar and goblet cells, the two predominant cell types in the midgut epithelium. These cells presented in vitro the same shape, morphology and polarity recorded in vivo, even if their dimensions were slightly reduced. Columnar cells displayed a well developed cytoskeletal arrangement, with actin filaments highly organized within the thick brush border and distributed in faint filaments in the cell cytoplasm. Microtubules formed a substantial net just beneath the brush border and ran longitudinally from the apical to the basal pole of the cell. Cultured cells homogenates displayed aminopeptidase N and alkaline phosphatase activity, proving that these two enzymes, involved in vivo in the intermediate and final digestion, are expressed also in vitro. The columnar cells differentiated in culture were able to internalize two model proteins with quite different transport rate