Fine structure of the alimentary canal of the larval blow fly Chrysomya megacephala (Diptera: Calliphoridae)

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.

Morphological description of the midgut tract and midgut-hindgut junction in the larvae of the spider crab Maja brachydactyla Balss, 1922 (Malacostraca: Decapoda)

The midgut tract of decapods is a digestive organ involved in the synthesis of peritrophic membrane, food transport, absorption of nutrients, and osmoregulation. The midgut tract has been described in detail in adult decapods, but little information is available regarding the morphology and ultrastructure of the midgut tract in larval stages. The present study describes the midgut tract and the midgut-hindgut junction of the larvae of the common spider crab Maja brachydactyla Balss, 1922 using techniques that included dissection, light microscopy, and electron microscopy. The study is mainly focused on the stages of zoea I and megalopa. The results obtained in this study show that the larval midgut tract is a short and simple tube positioned anteriorly, between the stomach and the hindgut tract. During larval development, the maximum length of the midgut tract increases significantly, but no differences were found on either the maximum diameter or the morphological traits of the organ. The midgut tract is active at least ca. 12 h after hatching, as suggested by the presence of the peritrophic membrane in the lumen, the presence of abundant electro-dense vesicles in the cell apex, and the release of the vesicle content on the organ lumen. The midgut-hindgut junction forms an abrupt transition between the midgut tract and the hindgut tract in which epithelial cells with mixed features of midgut and hindgut do not occur.

Major differences in the larval anatomy of the digestive and excretory systems of three Oestridae species revealed by micro-CT

Oestrid flies (Diptera: Oestridae) do not feed during the adult stage, so they depend on an efficient assimilation and storage of nutrients during their parasitic larval stage. We describe the general morphology and provide volumetric data for the digestive and excretory organs of the three larval instars of the nasal bot fly Oestrus ovis L., using micro-computed tomography. The size of the digestive and excretory organs greatly increased across larval instars. In all instars, the two salivary glands were remarkably large and formed a 'glandular band' by coming together, but without lumina uniting, at their posterior ends. The distal region of the anterior Malpighian tubules was greatly enlarged and full of highly radio-opaque concretions. Moreover, the anatomy of O. ovis third-instar larva was compared to that of two species of, respectively, similar and different feeding habits: Cephenemyia stimulator (Clark) and Hypoderma actaeon Brauer. Whereas the general morphology and arrangement of the digestive and excretory systems of C. stimulator was similar to that of O. ovis, some differences were observed in H. actaeon: a swollen anterior region of the midgut, salivary glands shorter and not forming a 'band' and anterior Malpighian tubules narrowly uniform throughout their entire length.

Neurochemical regulation of Aedes aegypti salivary gland function

The salivary gland of hematophagous arthropods is critical for blood meal acquisition, blood vessel localization, and secretion of digestive enzymes. Thus, there is significant interest in the regulation of salivary gland function and mechanisms driving the secretion of saliva and digestive proteins. We aimed to gain a broader understanding of the regulatory role of aminergic, cholinergic, and octopaminergic neuromodulators to saliva and protein secretion from the female A. aegypti salivary gland. Quantification of saliva after injection with neuromodulators showed that dopamine, serotonin, and pilocarpine increased the secretory activity of the salivary gland with potency rankings dopamine = serotonin > pilocarpine. No change in saliva secretion was observed with octopamine or ergonovine, which indicates the A. aegypti salivary gland may be regulated by dopaminergic, serotonergic, and cholinergic systems, but are not likely regulated by octopaminergic or tryptaminergic systems. Next, we studied the regulatory control of dopamine-mediated salivation. Data indicate extracellular calcium flux, but not neural function, is critical for dopamine-mediated salivation, which suggests epithelial transport of ions and not neuronal control is responsible for dopamine-mediated salivation. For regulation of protein secretion, data indicate dopamine or serotonin exposure facilitates amylase secretion, whereas serotonin but not dopamine exposure increased apyrase concentrations in the secreted saliva. General immunoreactivity to anti-rat D1-dopamine receptor antibody was observed, yet immunoreactivity to the anti-rat D2-receptor antibody was identified in the proximal regions of the lateral lobes and slight immunoreactivity in the distal portion of the lateral lobe, with no expression in the medial lobe.

Effects of Methamphetamine on the Development and Its Determination in Aldrichina grahami (Diptera: Calliphoridae)

Age determination of necrophagous flies serves as an important tool for postmortem interval (PMI) estimation in forensic investigations. Drugs or toxins in cadavers may alter the developmental time of larvae, and lead to deviation in PMI estimation. Methamphetamine (MA), as one of the most abused psychostimulant drugs in Asia and North America, is often involved in forensic entomotoxicological cases. This study investigated the effects of MA (0, 45, 90, and 180 ng/mg) on the developmental rate, morphology, and survival of Aldrichina grahami (Aldrich, 1930). The results showed that 1) the developmental time to reach the pupal instar was statistically slower for the larvae reared on rabbit mince containing MA than for the control; 2) the mean length of the larvae exposed to MA concentrations was longer than those of the control; 3) the mean weight of the pupae exposed to the highest concentration of MA was significantly lighter than those of the control; 4) the GC-MS method can detect the content of MA in A. grahami immatures and empty puparia (EP).

Bioprospection of immature salivary glands of Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae)

Larval therapy (LT) comprises the application of sterile Calliphoridae larvae for wound debridement, disinfection, and healing in humans and animals. Larval digestion plays a key role in LT, where the salivary glands and gut produce and secrete proteolytic and antimicrobial substances. The objective of this work was to bioprospect the salivary glands of Chrysomya megacephala (Fabricius, 1794) larvae, using ultrastructural, morphological, and histological observations, and the total protein electrophoretic profile. The salivary glands present a deferent duct, originating from the buccal cavity, which bifurcates into efferent ducts that insert through a slight dilatation to a pair of tubular-shaped tissues, united in the region of fat cells. Histologically, the secretion had protein characteristics. Cell cytoplasm presented numerous free ribosomes, autophagic vacuoles, spherical and elongated mitochondria, atypical Golgi complexes, and dilated rough endoplasmic reticulum. In the apical cytoplasm, secretory granules and microvilli secretions demonstrated intense protein synthesis, basal cytoplasm with trachea insertions, and numerous mitochondria. The present work described the ultrastructure and morphology of C. megacephala third instar salivary glands, confirming intense protein synthesis and the molecular weight of soluble proteins.

Response of the common cutworm Spodoptera litura to lead stress: changes in sex ratio, Pb accumulations, midgut cell ultrastructure

When cutworm Spodoptera litura larvae were fed on the diets with different lead (Pb) concentrations for one or five generations, changes in growth and food utilization were recorded; Pb accumulations were detected by Atomic Absorption Spectrophotometer; changes in midgut cell ultrastructure were observed by Transmission Electron Microscopy (TEM). The effects of Pb stress on S. litura growth and food utilization differed significantly between insects of the 1st and 5th generation. The male-female rate of 200mgkg(-1) Pb treatment from the 1st generation and 50mgkg(-1) Pb treatment from the 5th generation was significantly higher than control. No significant difference of Pb accumulations was found in larvae, pupae and adults between the 1st and 5th generation. No significant difference of Pb accumulations in corresponding tissues of larvae was found between male and female. Compared to fat body, hemolymph, head, foregut and hindgut, the highest Pb accumulation was found in migut of larvae exposed to 200mgkg(-1) Pb. TEM showed that expanded intercellular spaces were observed in Pb-treated midgut cells. The nuclei were strongly destroyed by Pb stress, evidenced by chromatin condensation and destroyed nuclear envelope. Mitochondria became swollen with some broken cristae after exposure to Pb. Therefore, neither gender nor progeny difference was present in Pb accumulations of S. litura, although effects of Pb stress on S. litura growth and food utilization differed from different generations and genders. Pb accumulations in midgut caused pathological changes in cells ultrastructure, possibly reflected the growth and food utilization of S. litura.

Sarcophaga (Liosarcophaga) dux (Diptera: Sarcophagidae): A flesh fly species of medical importance

BACKGROUND

Although tropical climate of Thailand is suitably endowed with biodiversity of insects, flies of medical importance is not well investigated. Using information from literature search, fly survey approach and specialist's experience, we review database of Sarcophaga (Liosarcophaga) dux Thomson (Diptera: Sarcophagidae), one of the priorities flesh fly species of medical importance in Thailand.

RESULTS

This review deals with morphology, bionomics and medical involvement. Important morphological characteristics of egg, larva, puparia and adult were highlighted with illustration and/or micrographs. Search pertaining to molecular analysis used for fly identification and developmental rate of larvae were included. Medical involvement of larvae was not only myiasis-producing agent in humans and animals, but associated with human death investigations.

CONCLUSIONS

This information will enable us to accurate identify this species and to emphasis the increase medically important scene in Thailand.

Alimentary Canal of the Adult Blow Fly, Chrysomya megacephala (F.) (Diptera: Calliphoridae)-Part I: Ultrastructure of Salivary Glands

The salivary gland ultrastructure of the adult male blow fly, Chrysomya megacephala (F.) (Diptera: Calliphoridae), was investigated at the ultrastructural level using light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The salivary glands are paired structures composed of a single median deferent duct bifurcated into two long, narrow efferent ducts connected to the coiled tubular glands. The SEM image of the gland surface revealed that the basal lamina is relatively smooth in general, but the whole surface appeared as a trace of rough swollen insertion by intense tracheal ramification. Ultrastructurally, the salivary gland is enclosed within the basal lamina, and interdigitation cytoplasmic extensions were apparent between the adjacent gland cells. The basement membrane appeared infoldings that is similar to the complex of the labyrinth channel. The cytoplasm characteristic of the gland revealed high activity, based on the abundance of noticeable secretory granules, either singly or in an aggregated reservoir. In addition, mitochondria were found to intersperse among rich parallel of arrays rough endoplasmic reticulum. Thick cuticle, which was well-delineated and electron dense, apically lined the gland compartments, with discontinuity of the double-layer cuticle revealing a trace of secretion discharged into the lumen. Gross anatomy of the adult salivary gland was markedly different from that of the third instar of the same species, and structural dissimilarity is discussed briefly.

Immunohistological localization of serotonin in the CNS and feeding system of the stable fly Stomoxys calcitrans L. (Diptera: Muscidae)

Serotonin, or 5-hydroxytryptamine (5-HT), plays critical roles as a neurotransmitter and neuromodulator that control or modulate many behaviors in insects, such as feeding. Neurons immunoreactive (IR) to 5-HT were detected in the central nervous system (CNS) of the larval and adult stages of the stable fly, Stomoxys calcitrans, using an immunohistological technique. The location and pattern of the 5-HT IR neurons are described and compared for these two different developmental stages. Anatomical features of the fly feeding system were analyzed in third instar larvae and adult flies using a combination of histological and immunohistological techniques. In third instar larvae, the cibarial dilator muscles were observed within the cibarial pump skeleton and innervated by 5-HT IR neurons in nerves arising from the brain. There were four pairs of nerves arising from the frontal surface of the larval brain that innervate the cibarial pump muscles, pharynx, and muscles controlling the mouth hooks. A strong serotoninergic innervation of the anterior stomatogastric system was observed, which suggests 5-HT may play a role in the coordination of different phases of food ingestion by larvae. Similarly, many 5-HT IR neurons were found in both the brain and the thoracico-abdominal ganglia in the adult, some of which innervate the cibarial pump dilator muscles and the stomatogastric muscles. This is tnhe first report describing neuromuscular structures of the stable fly feeding system. The results reported here suggest 5-HT may play a critical role in feeding behaviors of stable fly larvae and adults.

Alimentary canal of the blow fly Chrysomya megacephala (F.) (Diptera: Calliphoridae): an emphasis on dissection and morphometry

The alimentary canal is a major organ system that is often involved in the transmission of pathogens to humans from insects that serve as vectors of disease. In this study, we investigated the alimentary canal of the blow fly, Chrysomya megacephala (F.) (Diptera: Calliphoridae), highlighting the description for dissection and morphometric analysis of each organ. Dissection was performed in a phosphate buffer solution (pH=7.4) on 3(rd) instar larvae (three to four days old) and on both male and female adults (seven days old). Larval dissection was accomplished using two fine forceps to open the specimens from the posterior end and proceed anteriorly toward the cephalic segment. Meticulous dissection of the anterior end was vital for observation of the delicate salivary ducts, crop duct, and esophagus. Overall length of the 3(rd) instar alimentary canal measured 89.15 mm (range 81.40-99.70 mm). The midgut comprised the longest portion, measuring 46.35 mm (range 40.00-52.00 mm; n = 30) of the entire canal. Adult dissection was also performed from abdomen to head. Morphometric analyses revealed that the alimentary canal of males and females were relatively similar. No statistical differences were found between the entire length of the alimentary canal from mouth to anus (excluding all branches of the salivary glands, crop, and Malpighian tubules) of males and females. The alimentary canals of males measured 36.23 mm (range 32.60-41.20 mm) in length; whereas, those of females measured 37.23 mm (range 32.70-42.15 mm). Two-thirds of the entire canal length was comprised of midgut in each sex.