Evolutionary trends of digestion and absorption in the major insect orders

Integrating water balance mechanisms into predictions of insect responses to climate change

Efficient water balance is key to insect success. However, the hygric environment is changing with climate change; although there are compelling models of thermal vulnerability, water balance is often neglected in predictions. Insects survive desiccating conditions by reducing water loss, increasing their total amount of water (and replenishing it) and increasing their tolerance of dehydration. The physiology underlying these traits is reasonably well understood, as are the sources of variation and phenotypic plasticity. However, water balance and thermal tolerance intersect at high temperatures, such that mortality is sometimes determined by dehydration, rather than heat (especially during long exposures in dry conditions). Furthermore, water balance and thermal tolerance sometimes interact to determine survival. In this Commentary, we propose identifying a threshold where the cause of mortality shifts between dehydration and temperature, and that it should be possible to predict this threshold from trait measurements (and perhaps eventually a priori from physiological or -omic markers).

Clogmia albipunctata (Williston, 1893) midgut physiology: pH control and functional relationship with Lower Diptera (nematoceran) especially with hematophagous species

Clogmia albipunctata (Williston, 1893) is a non-hematophagous insect belonging to the order Diptera, suborder Nematocera (Lower Diptera) and family Psychodidae. In the present work, we investigated how C. albipunctata control their midgut pH under different physiological conditions, comparing their midgut physiology with some nematoceran hematophagous species. The C. albipunctata midgut pH was measured after ingestion of sugar, protein and under the effect of the alkalinizing hormone released in the hemolymph of the hematophagous sand fly Lutzomyia longipalpis obtained just after a blood meal. The midgut pH of unfed or sugar-fed C. albipunctata is 5.5-6, and its midgut underwent alkalinization after protein ingestion or under treatment with hemolymph collected from blood fed L. longipalpis. These results suggested that in nematocerans, mechanisms for pH control seem shared between hematophagous and non-hematophagous species. This kind of pH control is convenient for successful blood digestion. The independent evolution of many hematophagous groups from the Lower Diptera suggests that characteristics involved in midgut pH control were already present in non-hematophagous species and represent a readiness for adaptation to this feeding mode.

Ultrastructural Changes in the Midgut of Brazilian Native Stingless Bee Melipona scutellaris Exposed to Fungicide Pyraclostrobin

Melipona scutellaris is a Brazilian stingless bee that is important for pollinating wild flora and agriculture crops. Fungicides have been widely used in agriculture, and floral residues can affect forager bees. The goal of our study was to evaluate the effects of sublethal concentrations of pyraclostrobin on the midgut ultrastructure of M. scutellaris forager workers. The bees were collected from three non-parental colonies and kept under laboratory conditions. The bees were orally exposed continuously for five days to pyraclostrobin in syrup at concentrations of 0.125 ng a.i./µL (FG1) and 0.005 ng a.i./µL (FG2). The control bees (CTL) were fed a no-fungicide sucrose solution, and the acetone solvent control bees (CAC) received a sucrose solution containing acetone. At the end of the exposure, the midguts were sampled, fixed in Karnovsky solution, and routinely processed for transmission electron microscopy. Ultrastructural analysis demonstrated that both the fungicide concentrations altered the midgut, such as cytoplasmic vacuolization (more intense in FG1), the presence of an atypical nuclear morphology, and slightly dilated mitochondrial cristae in the bees from the FG1 and FG2 groups (both more intense in FG1). Additionally, there was an alteration in the ultrastructure of the spherocrystals (FG1), which could be the result of cellular metabolism impairment and the excretion of toxic metabolites in the digestive cells as a response to fungicide exposure. The results indicate that ingested pyraclostrobin induced cytotoxic effects in the midgut of native stingless bees. These cellular ultrastructural responses of the midgut are a prelude to a reduced survival rate, as observed in previous studies.

The common bed bug Cimex lectularius synthesizes hemozoin as an essential defense against the toxic effects of heme

The common bed bug Cimex lectularius (Linnaeus 1758) is an ectoparasite that feeds preferably on human blood, being considered an important public health issue. Blood-feeding is a challenging process for hematophagous organisms, and one of the inherent risks with this kind of diet is the liberation of high doses of free heme after the digestion of hemoglobin. In order to deal with this potent cytotoxic agent, such organisms have acquired different defense mechanisms. Here, we use UV-visible spectrophotometry and infrared spectroscopy to show that C. lectularius crystalizes free heme to form the much less dangerous compound, hemozoin. According to our results, the peak of formation of hemozoin in the intestinal contents occurred 4-5 days after the blood meal, primarily in the posterior midgut. The quantification of the rate of conversion of heme to hemozoin revealed that at the end of digestion all the heme was in the form of hemozoin. Inhibition of the synthesis of hemozoin using the anti-malarial drug quinine led to an increase in both catalase activity in the intestinal epithelium and the mortality of the bed bugs, indicating that the insects were unable to cope with the oxidative stress generated by the overload of free heme. The data presented here show for the first time how C. lectularius deals with free heme, and how the process of formation of hemozoin is essential for the survival of these insects. Since resistance to insecticides is a common feature among field populations of bed bugs, there is an urgent need to develop alternative control methods. Thus, targeting the synthesis of hemozoin emerges as a possible novel strategy to fight bed bugs.

Novel Insights into the circRNA-Modulated Developmental Mechanism of Western Honey Bee Larval Guts

Circular RNAs (circRNAs) are a class of novel non-coding RNAs (ncRNAs) that play essential roles in the development and growth of vertebrates through multiple manners. However, the mechanism by which circRNAs modulate the honey bee gut development is currently poorly understood. Utilizing the transcriptome data we obtained earlier, the highly expressed circRNAs in the Apis mellifera worker 4-, 5-, and 6-day-old larval guts were analyzed, which was followed by an in-depth investigation of the expression pattern of circRNAs during the process of larval guts development and the potential regulatory roles of differentially expressed circRNAs (DEcircRNAs). In total, 1728 expressed circRNAs were detected in the A. mellifera larval guts. Among the most highly expressed 10 circRNAs, seven (novel_circ_000069, novel_circ_000027, novel_circ_000438, etc.) were shared by the 4-, 5-, and 6-day-old larval guts. In addition, 21 (46) up-regulated and 22 (27) down-regulated circRNAs were, respectively, screened in the Am4 vs. Am5 (Am5 vs. Am6) comparison groups. Additionally, nine DEcircRNAs, such as novel_circ_000340, novel_circ_000758 and novel_circ_001116, were shared by these two comparison groups. These DEcircRNAs were predicted to be transcribed from 14 and 29 parental genes; these were respectively annotated to 15 and 22 GO terms such as biological regulation and catalytic activity as well as 16 and 21 KEGG pathways such as dorsoventral axis formation and apoptosis. Moreover, a complicated competing endogenous RNA (ceRNA) network was observed; novel_circ_000838 in the Am4 vs. Am5 comparison group potentially targeted ame-miR-6000a-3p, further targeting 518 mRNAs engaged in several developmental signaling pathways (e.g., TGF-beta, hedgehog, and wnt signaling pathway) and immune pathways (e.g., phagosome, lysosome, and MAPK signaling pathway). The results demonstrated that the novel_circ_000838-ame-miR-6000a-3p axis may plays a critical regulatory part in the larval gut development and immunity. Furthermore, back-splicing sites of six randomly selected DEcircRNAs were amplified and verified by PCR; an RT-qPCR assay of these six DEcircRNAs confirmed the reliability of the used high-throughput sequencing data. Our findings provide a novel insight into the honey bee gut development and pave a way for illustration of the circRNA-modulated developmental mechanisms underlying the A. mellifera worker larval guts.

Histochemistry and transcriptomics of mucins and peritrophic membrane (PM) proteins along the midgut of a beetle with incomplete PM and their complementary function

The midgut of Zabrotes subfasciatus (Coleoptera) and other insects may have regions lacking a peritrophic membrane (matrix, PM) and covered with a jelly-like material known as peritrophic gel. This work was undertaken to test the hypothesis that the peritrophic gel is a vertebrate-like mucus. By histochemistry we identified mucins along the whole midgut, which contrasts with the known occurrence of PM only at the posterior midgut. We also analyzed the expression of the genes coding for mucus-forming mucins (Mf-mucins), peritrophins, chitin synthases and chitin deacetylases along the midgut and carcass (insect without midgut) by RNA-seq. Mf-mucins were identified as proteins with high O-glycosylation and multiple tandem repeats of Pro/Thr/Ser residues. Peritrophins were separated into PM proteins, cuticular proteins analogous to peritrophins (CPAPs) and ubiquitous-chitin-binding domain-(CBD)-containing proteins (UCBPs). PM proteins have at least 3, CPAP one or 3, and UCBPs have a varied number of CBDs. PM proteins are more expressed at midgut, CPAP at the carcass, and UCBP at both. The results showed that most PM proteins are mainly expressed at the posterior midgut, together with midgut chitin synthase and chitin deacetylase, and in agreement with the presence of PM only at the posterior midgut by visual inspection. The excretion of most midgut chitinase is avoided, suggesting that the shortened PM is functional. Mf-mucins are expressed along the whole midgut, probably forming the extracellular mucus layer observed by histochemistry. Thus, the lack of PM at anterior and middle midgut causes the exposure of a mucus, which may correspond to the previously described peritrophic gel. The putative functional interplay of mucus and PM is discussed. The major role of mucus is proposed to be tissue protection and of PM to enhancing digestive efficiency by allowing enzyme recycling.

Identification of 14 glutathione S-transferase genes from Lasioderma serricorne and characterization of LsGSTe1 involved in lambda-cyhalothrin detoxification

In insects, glutathione S-transferases (GSTs) play a pivotal role in the detoxification of a wide range of pesticides. The cigarette beetle, Lasioderma serricorne, is an economically important pest insect of stored products. Recently, pyrethroid insecticides have been used to control this pest. However, little is known concerning the responses and functions of GSTs in L. serricorne under pyrethroid exposure. In this study, transcriptome sequencing was performed on L. serricorne, and a total of 14 GSTs were identified by retrieving the unigene dataset. Of these, 13 predicted GSTs fell into six cytosolic classes, namely, delta, epsilon, omega, sigma, theta, and zeta, and one was assigned to an "unclassified" group. The GST genes were differentially expressed in various larval tissues and at different developmental stages. Exposure to the pyrethroid insecticide lambda-cyhalothrin (LCT) caused oxidative stress in L. serricorne larvae and led to significantly elevated expression levels of six genes, among which LsGSTe1 was the most upregulated. Recombinant LsGSTE1 protein displayed LCT-metabolizing activity. Furthermore, LsGSTE1 protects cells against oxidative stress. Moreover, knockdown of LsGSTe1 by RNA interference dramatically increased the susceptibility of L. serricorne larvae to LCT treatment. The results from this study provide sequence resources and expression data for GST genes in L. serricorne. Our findings indicate that LsGSTE1 plays a dual role in LCT detoxification by metabolizing the pesticide and by preventing LCT-induced oxidative stress. Thus, the LsGSTe1 gene could be used as a potential target for sustainable management of the cigarette beetle.

Anatomical changes of the beetle digestive tract during metamorphosis correspond to dietary changes

During pupation, the tissues of holometabolous insects change in preparation for the adult lifestyles, although little literature exists examining this hidden process in detail. Using beetles as a model, we hypothesized that species where the adult and larva have the same diets will show less pronounced changes of the digestive tract during metamorphosis than species where the adults diets differ. We also wanted to observe these changes and document them at a level of detail missing from the current record. We compared the structure of the digestive tracts of scarab beetles Oryctes rhinoceros, Thaumastopeus shangaicus, and Protaetia spp. (Coleoptera: Scarabaeidae)-where the larvae eat wood, soil, or compost while the adults feed on soft plant matter, tree sap, and rotting fruits-with the tortoise beetle, Cassida circumdata (Coleoptera: Chrysomelidae), which feeds on leaves as both larva and adult. In the scarab beetles we observed considerable changes in the digestive tracts during the pupal stage, which we could divide into distinct stages, while in the leaf beetle pupae, the gut did not change. This information can provide new insight into metamorphosis, and the illustrations of what occurs during pupation are novel contributions to this field that will facilitate future work.

Overexpression of soybean trypsin inhibitor genes decreases defoliation by corn earworm (Helicoverpa zea) in soybean (Glycine max) and Arabidopsis thaliana

Trypsin inhibitors (TIs) are widely distributed in plants and are known to play a protective role against herbivores. TIs reduce the biological activity of trypsin, an enzyme involved in the breakdown of many different proteins, by inhibiting the activation and catalytic reactions of proteins. Soybean (Glycine max) contains two major TI classes: Kunitz trypsin inhibitor (KTI) and Bowman-Birk inhibitor (BBI). Both genes encoding TI inactivate trypsin and chymotrypsin enzymes, which are the main digestive enzymes in the gut fluids of Lepidopteran larvae feeding on soybean. In this study, the possible role of soybean TIs in plant defense against insects and nematodes was investigated. A total of six TIs were tested, including three known soybean trypsin inhibitors (KTI1, KTI2 and KTI3) and three genes encoding novel inhibitors identified in soybean (KTI5, KTI7, and BBI5). Their functional role was further examined by overexpression of the individual TI genes in soybean and Arabidopsis. The endogenous expression patterns of these TI genes varied among soybean tissues, including leaf, stem, seed, and root. In vitro enzyme inhibitory assays showed significant increase in trypsin and chymotrypsin inhibitory activities in both transgenic soybean and Arabidopsis. Detached leaf-punch feeding bioassays detected significant reduction in corn earworm (Helicoverpa zea) larval weight when larvae fed on transgenic soybean and Arabidopsis lines, with the greatest reduction observed in KTI7 and BBI5 overexpressing lines. Whole soybean plant greenhouse feeding bioassays with H. zea on KTI7 and BBI5 overexpressing lines resulted in significantly reduced leaf defoliation compared to non-transgenic plants. However, bioassays of KTI7 and BBI5 overexpressing lines with soybean cyst nematode (SCN, Heterodera glycines) showed no differences in SCN female index between transgenic and non-transgenic control plants. There were no significant differences in growth and productivity between transgenic and non-transgenic plants grown in the absence of herbivores to full maturity under greenhouse conditions. The present study provides further insight into the potential applications of TI genes for insect resistance improvement in plants.

Hemp Waste as a Substrate for Hermetia illucens (L.) (Diptera: Stratiomyidae) and Tenebrio molitor L. (Coleoptera: Tenebrionidae) Rearing

The proper treatment of cannabis agricultural wastes can reduce the environmental impact of its cultivation and generate valuable products. This study aimed to test the potential of cannabis agricultural wastes as a substrate for the rearing of black soldier fly larvae (BSFL) and yellow mealworms (MW). In the case of BSFL, replacing the fibre component (straw) in the substrate with the hemp waste can increase the nutritional value of the substrate and led to bigger larvae. The bigger larvae had lower P and Mg, and higher Fe and Ca. Crude protein also varied based on the size of larvae and/or the content of protein in the initial substrate, which was boosted by replacing straw with hemp material. No other cannabinoids than cannabidiolic acid (CBDA), cannabigerolic acid (CBGA), and cannabidiol (CBD) were found in significant amounts in the larvae. In the case of MW, the larvae grew less on the hemp material in comparison to wheat bran. Replacing wheat bran with the hemp material led to smaller larvae with higher Ca, Fe, K, and crude protein content, but lower Mg and P values. No cannabinoids were detected in the MW fed with the hemp material.

Larval and adult digestive tract of the carrion beetle Oxelytrum discicolle (Brullé, 1840) (Coleoptera: Silphidae)

Oxelytrum discicolle is a necrophagous beetle occurring in Central and South America, with potential use in forensic entomology for investigations in the context of legal medicine. The present work aimed to describe the morphology of the digestive tract of larvae and adults and contributes to the knowledge about the digestion associated with necrophagy. In the three larval instars, the foregut is short and narrow, the midgut is a dilated tube, elongated with a smooth surface, and the hindgut is narrow and long, with small lateral projections and a dilated terminal region. The gut epithelium in the second and third instar larvae is vacuolated in the mid- and hindgut, with high production of apocrine secretions in the midgut lumen. In adults, the foregut is short, with small spines in the cuticular intima that covers the flattened epithelium. The midgut is dilated, with many short gastric caeca with regenerative cells in the blind portion, which differentiate in digestive columnar cells towards the midgut lumen. The hindgut is long and narrow, with an enlarged distal portion with folded epithelium lined by a thin cuticle. The histochemical tests reveal the absence of protein storage granules in the gut epithelium of larvae and adults. The gut characteristics of the carrion beetle O. discicolle are similar to those of other predatory and phytophagous Coleoptera, which may indicate that ancestry may influence the alimentary canal morphology more than the feeding habits.

Alteration of Manure Antibiotic Resistance Genes via Soil Fauna Is Associated with the Intestinal Microbiome

Livestock wastes contain high levels of antibiotic resistance genes (ARGs) and a variety of human-related pathogens. Bioconversion of livestock manure using larvae of the beetle Protaetia brevitarsis is an effective technique for waste reduction and value creation; however, the fate of manure ARGs during gut passage and interaction with the gut microbiome of P. brevitarsis remains unclear. To investigate this, we fed P. brevitarsis with dry chicken manure for 6 days and measured bacterial community dynamics and ARG abundance and diversity along the P. brevitarsis gut tract using high-throughput quantitative PCR and metagenomics approaches. The diversity of ARGs was significantly lower in larval midgut, hindgut, and frass than in raw chicken manure, and around 80% of pathogenicity-related genes (PRGs) exhibited reduced abundance. Network analysis demonstrated that Bacteroidetes and Firmicutes were the key bacterial phyla associated with ARG reduction. Metagenomic analysis further indicated that ARGs, mobile genetic elements (MGEs), and PRGs were simultaneously attenuated in the hindgut, implicating a decreased likelihood for horizontal gene transfer (HGT) of ARGs among bacteria and pathogens during manure bioconversion. Our findings demonstrated that the attenuation of ARGs is strongly associated with the variation of the gut microbiome of P. brevitarsis, providing insights into mechanisms of risk mitigation of ARG dissemination during manure bioconversion. IMPORTANCE Saprophagous fauna like the oriental edible beetle (P. brevitarsis) plays a fundamental role in converting organic wastes into biofertilizer. Accumulating evidence has shown that soil fauna can reduce the abundance of ARGs, although the underlying mechanism of ARG reduction is still unclear. In our previous research, we found a large reduction of ARGs in vegetable roots and leaves from frass compared with raw manure, providing a promising biofertilizer for soil-vegetable systems. Therefore, in this study, temporal dynamic changes in the microbiomes of the donor (chicken manure) and host (P. brevitarsis) were investigated, and we found a close association between the gut microbiome and the alteration of ARGs. These results shed new light on how the insect gut microbiome can mitigate manure-borne ARGs and provide insights into the bioconversion process via a typical member of the saprophagous fauna, P. brevitarsis.

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.

Exposure to insecticides causes effects on survival, prey consumption, and histological changes in the midgut of the predatory bug, Podisus nigrispinus (Hemiptera: Pentatomidae)

The control of defoliating caterpillars in forestry includes the use of insecticides and releases of the predatory bug Podisus nigrispinus, but some compounds may affect non-target natural enemies, which need evaluation of risk assessment. This research investigates the survival, preference, and prey consumption of P. nigrispinus adults fed with prey treated with the lethal concentration (LC₅₀) of Bacillus thuringiensis (Bt), permethrin, tebufenozide, and thiamethoxam. Moreover, midgut histopathology of P. nigrispinus fed with preys treated with LC₅₀ of each insecticide was investigated. The insecticides Bt, permethrin, and thiamethoxam reduce the survival and the prey consumption in P. nigrispinus fed with preys contaminate with these chemicals. However, the four tested insecticides, including tebufenozide, cause histological changes such as irregular epithelial architecture, cytoplasm vacuolization, and release of cell fragments in the midgut lumen of P. nigrispinus. The sublethal effects of Bt, permethrin, tebufenozide, and thiamethoxam to the natural enemy suggest that they should be better evaluated to be used together with P. nigrispinus for integrated pest management in forestry.

Cuticle melanization and the expression of immune-related genes in the honeybee Apis mellifera (Hymenoptera: Apidae) adult workers

The global decline of bee populations has several factors, including pathogens, which need overcome the insect defenses such as the physical barriers, the body cuticle and peritrophic matrix (primary defenses), as well as the secondary defenses with antimicrobial peptides (AMPs) and the enzyme lysozyme. The regulation of immune defenses according to the infection risks raises questions about the immunity of social bees due to their exposition to different pathogens pressures during the adult lifespan and tasks performed. This study evaluated the primary (body cuticle melanization, peritrophic matrix and cpr14 expression) and secondary (AMPs and lysozyme expression) defenses of the honeybee Apis mellifera workers according to the age and tasks. The expression of malvolio was used to detect precocious forage tasks outside the colony. Forager workers have higher amount of cuticular melanization in the body cuticle than nurse, but not when the age effect is retired, indicating the gradual acquisition of this compound in the integument of adult bees. The relative value of chitin in the peritrophic matrix and cpr14 mRNA are similar in all bees evaluated, suggesting that these components of primary defenses do not change according to the task and age. Differential expression of genes for AMPs in workers performing different tasks, within the same age group, indicates that the behavior stimulates expression of genes related to secondary immune defense. The expression of malvolio gene, accelerating the change in workers behavior, and those related to immune defense suggest the investment in secondary defense mechanisms when the primary defense of the body cuticle is not yet completed.

A toxicological perspective of plastic biodegradation by insect larvae

Larvae of some insect species (Coleoptera and Lepidoptera) can consume and biodegrade synthetic polymers, including polyethylene, polystyrene, polyvinyl chloride, and polypropylene. Multiple chemical (polymer mass loss and shift of the molecular weight, alterations in chemical functionality, formation of biodegraded intermediates, CO₂ production), physical (surface hydrophobicity, thermal analysis), and biological approaches (antibiotic treatment, gut dysbiosis, isolation of plastic microbial degraders) have provided evidence for polymer biodegradation in the larva digestive tract. However, the extent and rate of biodegradation largely depend on the physicochemical structure of the polymer as well as the presence of additives. Additionally, toxicology associated with plastic biodegradation has not been investigated. This knowledge gap is critical to understand the gut symbiont-host interaction in the biodegradation process, its viability in the long term, the effects of plastic additives and their metabolites, and the phenotypic traits linked to a plastic-rich diet might be transferred in successive generations. Likewise, plastic-eating larvae represent a unique case study for elucidating the mechanisms of toxic action by micro- and nanoplastics because of the high concentration of plastics these organisms may be intentionally exposed to. This perspective review graphically summarizes the current knowledge on plastic biodegradation by insect larvae and describes the physiological processes (digestive and immune systems) that may be disrupted by micro- and nanoplastics. It also provides an outlook to advance current knowledge on the toxicity assessment of plastic-rich diets and the environmental risks of plastic-containing by-products (e.g., insect manure used as fertilizer).

Molecular and biological features of Culex quinquefasciatus homozygous larvae for two cqm1 alleles that confer resistance to Lysinibacillus sphaericus larvicides

BACKGROUND

Culex quinquefasciatus resistance to the binary toxin from Lysinibacillus sphaericus larvicides can occur because of mutations in the cqm1 gene that prevents the expression of the toxin receptor, Cqm1 α-glucosidase. In a resistant laboratory-selected colony maintained for more than 250 generations, cqm1_REC and cqm1_REC-2 resistance alleles were identified. The major allele initially found, cqm1_REC , became minor and was replaced by cqm1_REC-2 . This study aimed to investigate the features associated with homozygous larvae for each allele to understand the reasons for the allele replacement and to generate knowledge on resistance to microbial larvicides.

RESULTS

Homozygous larvae for each allele were compared. Both larvae displayed the same level of resistance to the binary toxin (3500-fold); therefore, a change in phenotype was not the reason for the replacement observed. The lack of Cqm1 expression did not reduce the total specific α-glucosidase activity for homozygous cqm1_REC and cqm1_REC-2 larvae, which were statistically similar to the susceptible strain, using artificial or natural substrates. The expression of eight Cqm1 paralog α-glucosidases was demonstrated in resistant and susceptible larvae. Bioassays in which cqm1_REC or cqm1_REC-2 homozygous larvae were reared under stressful conditions showed that most adults produced were cqm1_REC-2 homozygous (69%). Comparatively, in the offspring of a heterozygous sub-colony reared under optimal conditions for 20 generations, the cqm1_REC allele assumed a higher frequency (0.72).

CONCLUSION

Homozygous larvae for each allele exhibited a similar resistant phenotype. However, they presented specific advantages that might favor their selection and can be used in designing resistance management practices. © 2021 Society of Chemical Industry.

Nano-Medicines a Hope for Chagas Disease!

Chagas disease, is a vector-mediated tropical disease whose causative agent is a parasitic protozoan named Trypanosoma cruzi. It is a very severe health issue in South America and Mexico infecting millions of people every year. Protozoan T. cruzi gets transmitted to human through Triatominae, a subfamily of the Reduviidae, and do not have any effective treatment or preventative available. The lack of economic gains from this tropical parasitic infection, has always been the reason behind its negligence by researchers and drug manufacturers for many decades. Hence there is an enormous requirement for more efficient and novel strategies to reduce the fatality associated with these diseases. Even, available diagnosis protocols are outdated and inefficient and there is an urgent need for rapid high throughput diagnostics as well as management protocol. The current advancement of nanotechnology in the field of healthcare has generated hope for better management of many tropical diseases including Chagas disease. Nanoparticulate systems for drug delivery like poloxamer coated nanosuspension of benzimidazole have shown promising results in reducing toxicity, elevating efficacy and bioavailability of the active compound against the pathogen, by prolonging release, thereby increasing the therapeutic index. Moreover, nanoparticle-based drug delivery has shown promising results in inducing the host’s immune response against the pathogen with very few side effects. Besides, advances in diagnostic assays, such as nanosensors, aided in the accurate detection of the parasite. In this review, we provide an insight into the life cycle stages of the pathogen in both vertebrate host and the insect vector, along with an overview of the current therapy for Chagas disease and its limitations; nano carrier-based delivery systems for antichagasic agents, we also address the advancement of nano vaccines and nano-diagnostic techniques, for treatment of Chagas disease, majorly focusing on the novel perspectives in combating the disease.

Synchrotron X-ray phase contrast micro tomography to explore the morphology of abdominal organs in Pterostichus melas italicus Dejean, 1828 (Coleoptera, Carabidae)

Micro-computer tomography imaging is a fast and non-destructive data acquisition technique which can replace or complement the traditional investigation methodologies used in entomology to study morphology. In this paper, Synchrotron Radiation X-ray Phase-Contrast micro tomography (SR-PhC micro-CT) was combined with histology and scanning electron microscopy (SEM) observations to describe the abdominal organs of Pterostichus melas italicus Dejean, 1828 (Coleoptera, Carabidae). This species was used as a representative model because of its ecological role as a generalist predator in agroecosystems. SR-PhC micro-CT allowed us to identify in situ abdominal structures including dorsal vessel, digestive tract with Malpighian tubules, male reproductive system, ganglia, fat bodies, pygidial glands, muscles and tracheae. The histology was performed to define the tissue organization of the digestive and reproductive systems. SR-PhC micro-CT and 3D rendering provided more accurate information on shape and size of organs than histological and SEM analyses, respectively. The finding of this study was to describe the anatomy and histology of organs involved in crucial life history traits, such as reproduction, nutrition and excretion. High quality images and the supplementary video represent a significant advance in knowledge of the carabid anatomy and are a baseline for future research.

Description of the larval and adult hindgut tract of the common spider crab Maja brachydactyla Balss, 1922 (Brachyura, Decapoda, Malacostraca)

Arthropods are the most diversified animals on Earth. The morphology of the digestive system has been widely studied in insects; however, crustaceans have received comparatively little attention. This study describes the hindgut tract of the common spider crab Maja brachydactyla Balss, 1922, in larvae and adults using dissection, light and electron microscopical analyses. The hindgut tract maintains a similar general shape in larvae and adults. Major differences among stages are found in the morphology of epithelial cells and microspines, the thickness of the cuticle and connective-like tissue, and the presence of rosette glands (only in adults). Here, we provide the description of the sub-cellular structure of the folds, epithelium (conformed by tendon cells), musculature, and microspines of the hindgut of larvae and adults of M. brachydactyla. The morphological features of the hindgut of M. brachydactyla are compared with those of other arthropods (Insecta, Myriapoda and Arachnida). Our results suggest that the morphology of the hindgut is associated mainly with transport of faeces. In adults, the hindgut may also exert an osmoregulatory function, as described in other arthropods. At difference from holometabolous insets, the hindgut of M. brachydactyla (Decapoda) does not undergo a true metamorphic change during development, but major changes observed between larval and adult stages might respond to the different body size between life stages.

Development of Monoxenous Trypanosomatids and Phytomonads in Insects

In this review, we summarize the current data on development of monoxenous trypanosomatids and phytomonads in various insects. Of these, Diptera and Hemiptera are the main host groups, and, consequently, most available information concerns their parasites. Within the insect body, the midgut and hindgut are the predominant colonization sites; in addition, some trypanosomatids can invade the foregut, Malpighian tubules, hemolymph, and/or salivary glands. Differences in the intestinal structure and biology of the host determine the variety of parasites' developmental and transmission strategies. Meanwhile, similar mechanisms are used by unrelated trypanosomatids, reflecting the limited range of options to achieve the same goal.

The salivary glands of Brontocoris tabidus (Heteroptera: Pentatomidae): Morphology and secretory cycle

Brontocoris tabidus (Signoret) (Heteroptera: Pentatomidae) is a zoophytophagous insect used for biological control in agriculture and forest systems because its nymphs and adults feed on insects and plants. The predatory Pentatomidae insert the mouthparts into the prey, releasing saliva to paralysis and kills the insect, as well as digest body parts to be sucked in a preliminary extra-oral digestion. In a short period of time, this insect shows the ability to feed again, suggesting the existence of a constant and abundant secretory cycle in the salivary glands. This study evaluated the morphological, histochemical and ultrastructural changes of the salivary glands of B. tabidus in fed and starved insects. The salivary complex of this predatory bug has a pair of bilobed salivary glands and a pair of tubular accessory salivary glands. The accessory glands have the lumen lined by a thick non-cuticular layer rich in glycoproteins. The secretory cells of the B. tabidus principal salivary glands have constant secretory activity, with each lobe producing different substances. The physiological processes that occur in the salivary gland of B. tabidus indicate that the insect needs to feed constantly, corroborating the potential of this insect to be used in biological control programs.

Exposure to chlorantraniliprole reduces locomotion, respiration, and causes histological changes in the midgut of velvetbean caterpillar Anticarsia gemmatalis (Lepidoptera: Noctuidae)

The anthranilic diamide, chlorantraniliprole is a systemic insecticide affecting ryanodine receptors. This insecticide is used to control caterpillars in soybean crops because it has low toxicity to non-target organisms. The objective was to identify side-effects of chlorantraniliprole on midgut histopathology, respiration and behavior of the velvetbean caterpillar Anticarsia gemmatalis in laboratoty. Chlorantraniliprole has LC50 = 0.61 (0.58-0.64) mg mL-1 for A. gemmatalis fourth instar caterpillars after 96 h. The insecticide causes severe histopathological effects in the midgut with epithelial disorganization, microvilli degeneration, cytoplasm vacuolization, cell fragmentation, and peritrophic matrix disorganization. The respiratory rate and the walking speed decrease, whereas the resting period increase for caterpillars exposed to this insecticide. Chlorantraniliprole is toxic to A. gemmatalis at median lethal concentrations causing severe histological and ultrastructural changes with degeneration of the midgut epithelium, reduction of respiratory rates and inducing an arresting behavioral response of this insect.

Challenges and physiological implications of wood feeding in termites

Termites are fascinating insects for a number of reasons, one of which being their specialization on diets of wood lignocellulose. The goal of this review is to consider stress-inducing characteristics of wood and apparent molecular-physiological adaptations in termite guts to overcome these stressors. Defensive factors present in wood include extractive secondary plant metabolites, lignin and related phenolics, crystalline cellulose, and low nitrogen content. Molecular-physiological adaptations of the termite gut to deal with these factors include robust detoxification and antioxidant machinery, the production of a peritrophic matrix and a wide range of cellulases from host and symbiotic sources, and creation of niches available to nitrogen-fixing bacterial symbionts. Considering termite gut physiology and symbioses in the context of stress-response has applied implications. These outcomes can include development of efficient biomass breakdown strategies, protection of microbes during industrial processing applications, and safeguarding wooden structures from termite damage.