Adipokinetic hormones control amylase activity in the cockroach (Periplaneta americana) gut

This study examined the biochemical characteristics of α‐amylase and hormonal (adipokinetic hormone: AKH) stimulation of α‐amylase activity in the cockroach (Periplaneta americana) midgut. We applied two AKHs in vivo and in vitro, then measured resultant amylase activity and gene expression, as well as the expression of AKH receptor (AKHR). The results revealed that optimal amylase activity is characterized by the following: pH: 5.7, temperature: 38.4 °C, K_m (Michaelis–Menten constant): 2.54 mg starch/mL, and V_max (maximum reaction velocity): 0.185 μmol maltose/mL/min. In vivo application of AKHs resulted in significant increase of amylase activity: by two‐fold in the gastric caeca and 4–7 fold in the rest of the midgut. In vitro experiments supported results seen in vivo: a 24‐h incubation with the hormones resulted in the increase of amylase activity by 1.4 times in the caeca and 4–9 times in the midgut. Further, gene expression analyses reveal that AKHR is expressed in both the caeca and the rest of the midgut, although expression levels in the former were 23 times higher than levels in the latter. A similar pattern was found for the amylase (AMY) gene. Hormonal treatment did not affect the expression of either gene. This study is the first to provide evidence indicating direct AKH stimulation of digestive enzyme activity in the insect midgut, supported by specific AKHR gene expression in this organ.     

Effect of natural toxins and adipokinetic hormones on the activity of digestive enzymes in the midgut of the cockroach Periplaneta americana

This study examined the effect of two natural toxins (a venom from the parasitic wasp Habrobracon hebetor and destruxin A from the entomopathogenic fungus Metarhizium anisopliae), and one pathogen (the entomopathogenic fungus Isaria fumosorosea) on the activity of basic digestive enzymes in the midgut of the cockroach Periplaneta americana. Simultaneously, the role of adipokinetic hormones (AKH) in the digestive processes was evaluated. The results showed that all tested toxins/pathogens elicited stress responses when applied into the cockroach body, as documented by an increase of AKH level in the central nervous system. The venom from H. hebetor showed no effect on digestive enzyme activities in the ceca and midgut in vitro. In addition, infection by I. fumosorosea caused a decrease in activity of all enzymes in the midgut and a variable decrease in activity in the ceca; application of AKHs did not reverse the inhibition. Destruxin A inhibited the activity of all enzymes in the midgut but none in the ceca in vitro; application of AKHs did reverse this inhibition, and no differences between both cockroach AKHs were found. Overall, the results demonstrated the variable effect of the tested toxins/pathogens on the digestive processes of cockroaches as well as the variable ability of AKH to counteract these effects.     

Structural diversity of adipokinetic hormones in the hyperdiverse coleopteran Cucujiformia

Seventeen species of the coleopteran series Cucujiformia are investigated for the presence and sequence of putative adipokinetic hormones (AKHs). Cucujiformia includes species from the major superfamilies, that is, Chrysomeloidea, Curculionoidea, Cucujoidea, and Tenebrionoidea. The clade Phytophaga in which the Chrysomeloidea and Curculionoidea reside, harbor very detrimental species for agriculture and forestry. Thus, this study aims not only to demonstrate the structural biodiversity of AKHs in these beetle species and possible evolutionary trends but also to determine whether the AKHs from harmful pest species can be used as lead substances for a future putative insecticide that is harmless to beneficial insects. Sequence analysis of AKHs is achieved by liquid chromatography coupled to mass spectrometry. Most of the investigated species contain AKH octapeptides in their corpora cardiaca, although previously published work also found a few decapeptides, which we comment on. The signature and sole AKH in cerambycidae Chrysomeloidea and Curculionoidea is Peram‐CAH‐I (pEVNFSPNW amide), which is also found in the majority of chrysomelidae Chrysomeloidea and in the one investigated species of Cucujoidea albeit in a few cases associated with a second AKH which can be either Peram‐CAH‐II (pELTFTPNW amide), Emppe‐AKH (pEVNFTPNW amide), or Micvi‐CC (pEINFTPNW amide). The most often encountered AKH in Tenebrionoidea, family Meloidae as well as family Tenebrionidae, is Tenmo‐HrTH (pELNFSPNW amide) followed by Pyrap‐AKH (pELNFTPNW amide) and a Tenmo‐HrTH extended decapeptide (in Meloidae). Finally, we examine AKH sequences from 43 species of cucujiform beetles, including the superfamily Coccinelloidea for a possible lead compound for producing a cucujiform‐specific pesticide.     

The adipokinetic hormones of African water bugs of the Heteropteran families Nepidae and Belostomatidae

Four African species of true water bugs (Nepomorpha: Hemiptera: Heteroptera) are studied by mass spectrometry and biological assays to gain information on the presence, structure and function of peptides from the adipokinetic hormone (AKH) family, which are produced in the corpora cardiaca (CC). The water scorpion Laccotrephes fabricii Stål (Nepidae) has the peptide code‐named Peram‐CAH‐I with the sequence pGlu‐Val‐Asn‐Phe‐Ser‐Pro‐Asn‐Trp amide, whereas Appasus grassei Poisson (Belostomatidae) produces Anaim‐AKH, which is a Ser⁷ analogue of Peram‐CAH‐I (pGlu‐Val‐Asn‐Phe‐Ser‐Pro‐Ser‐Trp amide). The giant water bug Hydrocyrius columbiae Spinola (Belostomatidae) has two adipokinetic hormone family members: Anaim‐AKH and Letin‐AKH, which again differ only at position 7 (Ser⁷ versus Tyr⁷). When the sequence data are compared with current molecular phylogenetic analyses of Nepomorpha, they are essentially in agreement with the newest ideas on phylogenetic relationships among the families. Functional investigation of these peptides reveals a mainly lipid‐based energy metabolism in these insects, as demonstrated by a hyperlipaemic response after injecting crude CC extract or the appropriate peptide into the respective species. The carbohydrate concentration in the haemolymph is not affected by such injections, and the carbohydrate level in most cases is lower than that of the circulating lipids. During physical exercise, such as swimming for 1 h, carbohydrates may contribute to some extent to the provision of energy; the substantial increase in the concentration of lipids in the haemolymph, however, is a strong indicator that the peptides are released from the CC and act primarily as true adipokinetic hormones during this period of intense muscular activity.     

The adipokinetic hormone of Mantodea in comparison to other Dictyoptera

Six species of the order Mantodea (praying mantises) are investigated for the presence and sequence of putative adipokinetic hormones (AKHs). The selected species span a wide evolutionary range of various families and subfamilies of the clade Mantodea. The corpora cardiaca of the different species are dissected, methanolic extracts prepared, peptides separated by liquid chromatography, and AKHs detected and sequenced by ion trap mass spectrometry. All six species investigated contain an octapeptide with the primary structure pGlu‐Val‐Asn‐Phe‐Thr‐Pro‐Asn‐Trp amide, which is code‐named Emppe‐AKH and had been found earlier in three other species of Mantodea. Conspecific bioassays with the species Creoboter sp. (family Hymenopodidae) reveal an adipokinetic but not a hypertrehalosemic function of Emppe‐AKH. Comparison with other members of the Dictyoptera (cockroaches, termites) show that Emppe‐AKH is only found in certain termites, which have been recently placed into the Blattaria (cockroaches) as sister group to the family Cryptocercidae. Termites and cockroaches both show biodiversity in the sequence of AKHs, and some cockroach species even contain two AKHs. In contrast, all praying mantises—irrespective of their phylogenetic position—synthesize uniformly only one and the same octapeptide Emppe‐AKH.     

Structure and function of adipokinetic hormones of the large white butterfly Pieris brassicae

The large white butterfly Pieris brassicae L. (also called cabbage white) is very common in Europe, Asia and the northern region of Africa, and has also been found in South Africa during approximately the last 20 years. The species is considered a pest insect, with larvae attacking brassicaceous crops. The adult is a strong migratory flyer and new territory can be infested this way. As a first step to investigate methods for combating this pest species, the present study aims to determine the complement of adipokinetic peptides, here generically referred to as adipokinetic hormones (AKHs), which are required to regulate the mobilization of fuels for insect flight. Biological assays, as well as mass spectrometry, reveal information about the presence, structure and function of AKHs in P. brassicae: a methanolic extract of the corpora cardiaca has hypertrehalosaemic activity in cockroaches, does not cause hyperlipaemia in locusts, and has adipokinetic activity in P. brassicae itself. Liquid‐chromatography electrospray ion trap mass spectrometry reveals three peptides that can be associated with the AKH family: the non‐amidated undecapeptide Vanca‐AKH (pELTFTSSWGGK‐OH), the nonapeptide Manse‐AKH (pELTFTSSWG amide) and the novel octapeptide Piebr‐AKH (pELTFSSGW amide). Sequence confirmation of all three assigned structures is obtained from matching mass spectrometry spectra from synthetic and native peptides. Moreover, the synthetic peptides Manse‐AKH and Piebr‐AKH have significant hyperlipaemic (=adipokinetic) activity when injected into newly‐emerged adult cabbage white butterflies. The non‐amidated Vanca‐AKH is, apparently, incompletely processed Manse‐AKH without hormonal activity. Simulated dispersal flight is able to release AKHs, as indicated by the higher concentration of lipids in the haemolymph of adult P. brassicae after activity and rest periods.     

Digestive morphophysiology of Gryllodes sigillatus (Orthoptera: Gryllidae)

The evolution of the digestive system in the Order Orthoptera is disclosed from the study of the morphophysiology of the digestive process in its major taxa. This paper deals with a cricket representing the less known suborder Ensifera. Most amylase and trypsin activities occur in crop and caeca, respectively. Maltase and aminopeptidase are found in soluble and membrane-bound forms in caeca, with aminopeptidase also occurring in ventriculus. Amaranth was orally fed to Gryllodes sigillatus adults or injected into their haemolymph. The experiments were performed with starving and feeding insects with identical results. Following feeding of the dye the luminal side of the most anterior ventriculus (and in lesser amounts the midgut caeca) became heavily stained. In injected insects, the haemal side of the most posterior ventriculus was stained. This suggested that the anterior ventriculus is the main site of water absorption (the caeca is a secondary one), whereas the posterior ventriculus secretes water into the gut. Thus, a putative counter-current flux of fluid from posterior to anterior ventriculus may propel digestive enzyme recycling. This was confirmed by the finding that digestive enzymes are excreted at a low rate. The fine structure of midgut caeca and ventriculus cells revealed that they have morphological features that may be related to their involvement in secretion (movement from cell to lumen) and absorption (movement from lumen to cell) of fluids. Furthermore, morphological data showed that both merocrine and apocrine secretory mechanisms occur in midgut cells. The results showed that cricket digestion differs from that in grasshopper in having: (1) more membrane-bound digestive enzymes; (2) protein digestion slightly displaced toward the ventriculus; (3) midgut fluxes, and hence digestive enzyme recycling, in both starved and fed insects.     

Adipokinetic hormone functions that are not associated with insect flight

Abstract This review deals with some lesser known functions of adipokinetic hormones (AKHs), specifically those that are not associated directly with flight activity. The data summarized and discussed relate to AKHs in insects that have lost the ability to fly and use exclusively and/or mostly walking for their locomotion; and to activation of pathways that do not lead directly to production and subsequent rapid consumption of energy, but help the insect to combat stress situations. Emphasis is placed on AKH‐stimulated walking activities in Pyrrhocoris apterus, Gryllus bimaculatus, Periplaneta americana and Drosophila mellanogaster; diel fluctuations in AKH activities; the actions of AKH in alternative stress situations in which infection, toxins and other kinds of stressors interact; and the role of AKHs in anabolic processes and egg production. Possible mechanisms of action are proposed when justified by available knowledge.     

Biochemical response between insects and plants: an investigation of enzyme activity in the digestive system of Leucoptera coffeella (Lepidoptera: Lyonetiidae) and leaves of Coffea arabica (Rubiaceae) after herbivory

Plant defence mechanisms can reduce the digestive enzyme activity of insect pests. The aim of this study was to determine the relationship between the production of proteinase inhibitors, lipoxygenase and polyphenol oxidase activity in Coffea arabica (Catuai IAC 15) plants, and the digestive enzyme activity in the pest Leucoptera coffeella (Lepidoptera: Lyonetiidae) after feeding on the plant. The production of proteinase inhibitors was evaluated with L‐BApNA as a substrate. We studied lipoxygenase activity with linoleic acid and polyphenol oxidase activity with catechol substrates, in coffee plants damaged (T1) and not damaged (T2) by L. coffeella. L. coffeella digestive enzyme activity was verified by trypsin‐like (substrate l ‐BApNA and l ‐TAME), chymotrypsin‐like (BTpNA and ATEE), cysteine proteases (l ‐BApNA) and total protease (azocasein). Proteinase inhibitor production and lipoxygenase and polyphenol oxidase activity in C. arabica increases (P ≤ 0.05) with L. coffeella damage. Our results provide important information that these enzymatic activities may play a role in plant defence processes in C. arabica. Trypsin‐like activity increases, whereas chymotrypsin‐like and cysteine protease activity decrease in the midgut of L. coffeella, which acts as a defence mechanism.     

The adipokinetic hormones of Heteroptera: a comparative study

The adipokinetic hormones (AKHs) from 15 species of heteropteran Hemiptera (encompassing eight families, six superfamilies and three infraorders) have been isolated and structurally identified using liquid chromatography coupled with mass spectrometry. None of the structures are novel and all are octapeptides. These peptide sequence data are used, together with the previously available AKH sequence data on Heteroptera, to create a larger dataset for comparative analyses. This results, in total, in AKH sequences from 30 species (spanning 13 families), which are used in a matrix confronted with the current hypotheses on the phylogeny of Heteroptera. The expanded dataset shows that all heteropterans have octapeptide AKHs; three species have two AKHs, whereas the overwhelming majority have only one AKH. From a total of 11 different AKH peptides known from Heteroptera to date, three AKHs occur frequently: Panbo‐red pigment‐concentrating hormone (RPCH) (×10), Schgr‐AKH‐II (×6) and Anaim‐AKH (×4). The heteropteran database also suggests that particular AKH variants are family‐specific. The AKHs of Heteroptera: Pentatomomorpha (all terrestrial) are not present in Nepomorpha (aquatic) and Gerromorpha: Gerridae (semiaquatic); AKHs with a Val in position 2 are absent in the Pentatomomorpha (only AKHs with Leu² are present), whereas Val² predominates in the nonterrestrial species. An unexpected diversity of AKH sequences is found in Nepomorpha, Nepoidea, Nepidae and Nepinae, whereas Panbo‐RPCH (which has been identified in all infraorders of decapod crustaceans) is present in all analysed species of Pentatomidae and also in the only species of Tessaratomidae investigated. The molecular evolution of Heteroptera with respect to other insect groups and to crustaceans is discussed     

Control of the release of digestive enzymes in the caeca of the cricket Gryllus bimaculatus

Abstract In Gryllus bimaculatus, more digestive enzymes (amylase, trypsin, aminopeptidase) are secreted in the caecum of fed crickets than in unfed crickets, but the enzymes are released continuously at a basal rate in unfed animals. The rate of synthesis of the enzymes appears to parallel their rate of release. Digestive enzymes are released in response to a specific ratio of nutrients, although a high nutrient component in the food does not necessarily induce a high digestive enzyme release for that component. Rinsed flat‐sheet preparations of the caecum are incubated with specific nutrients (carbohydrates and proteins) and various concentrations of a neuropeptide (type‐A allatostatin), which affects generally the basal rates of secretion. Both maltose and glucose increase the release of amylase in vitro, but starch produces an inhibition of amylase release at lower concentrations. Bovine serum albumin (BSA), peptone and a mixture of amino acids have almost no effect on the release of aminopeptidase or carboxypeptidase, and only low concentrations of peptone increase trypsin release. High concentrations of both BSA and peptone strongly inhibit trypsin activity, perhaps by excess substrate binding to the trypsin active site. The allatostatin Grybi‐AST 5 elevates the release of amylase in vitro, but not of trypsin or aminopeptidase, in 2‐day‐old fed females. In the caeca from 1‐day‐old unfed crickets, both amylase and the trypsin release are stimulated in the presence of AST 5. The paracrine AST 5 is probably released from the gut endocrine cells and binds to the enzyme‐producing caecal cells.     

Locust corpora cardiaca contain an inactive adipokinetic hormone

A neuropeptide from the migratory locust, Locusta migratoria, has been identified as a novel member of the family of adipokinetic hormones (AKHs). The peptide is probably synthesised in the brain because it is the first AKH found in the storage lobe, whilst the three 'classic' Locusta AKHs are present in the glandular lobe of the corpora cardiaca. In locusts, the peptide has no biological activity usually associated with AKHs. There is only 36-56% sequence identity with the three Lom-AKHs, but 78% identity with the Drosophila melanogaster AKH, Drm-HrTH. The new peptide is active in the American cockroach, Periplaneta americana, and was provisionally named 'L. migratoria hypertrehalosaemic hormone', Lom-HrTH; its biological role in locusts remains to be established. The high degree of identity with Drm-HrTH suggests that Lom-HrTH is an ancient molecule.     

Identification of the adipokinetic hormone of the large milkweed bug Oncopeltus fasciatus

Abstract The adipokinetic hormone (AKH) of the large milkweed bug Oncopeltus fasciatus is isolated from an acidified methanolic extract of 200 corpora cardiaca, purified by single step reversed phase high‐performance liquid chromatography (HPLC) and N‐terminally deblocked using pyroglutamate aminopeptidase. The sequence is identified by Edman degradation and matrix assisted laser desorption/ionization‐time of flight mass spectroscopy as pGlu‐Leu‐Asn‐Phe‐Ser‐Pro‐Asn‐Trp amide. This structure is confirmed by chemical synthesis and coelution of native and synthetic peptide on HPLC. The AKH of O. fasciatus is identical to Tenmo‐HrTH, a member of the adipokinetic/red pigment‐concentrating hormone peptide family that had been isolated earlier from several tenebrionid beetles. Tenmo‐HrTH causes a significant rise in the concentration of haemolymph lipids when injected into adult male and female O. fasciatus, but displays no hyperglycaemic activity. There is no indication of the presence of other AKHs in O. fasciatus. The large milkweed bug represents the first member of the seed bugs (Lygaeidae) for which the endogenous AKH has been identified.     

The flow and fate of digestive enzymes in the field cricket,Gryllus bimaculatus

The flow of enzymes, the ratio of bound to unbound enzymes, and their inactivation in the cricket Gryllus bimaculatus was studied. The digestive enzymes are forced forward into the crop by caecal contraction and then they are mixed with freshly chewed food and saliva, forming a crop‐chyme. This chyme is blended by crop peristalsis, and periodic opening of the preproventricular valve (PPV) allows posterior movement into the proventriculus and further into the midgut. The contraction of the crop is modulated by Grybi‐AST and Grybi‐SK peptides, which are partially secreted by the caecal endocrine cells. Most of the aminopeptidase and the four disaccharidases examined are membrane bound (62–80%); the remaining (20–38%) as well all trypsin, chymotrypsin, lipase, and amylase are secreted free into the caecal lumen. Cricket trypsin loses only 30% of its activity in 4 h and very little thereafter. The presence of digestive products in the lumen appears to retard further trypsin autolysis. Cricket trypsin digests 42% of the chymotrypsin, 37% of the lipase, and 45% of the amylase in the caecal fluids over 24 h in vitro no significant difference. Without Ca ion amylase was almost completely digested. About 50% of the membrane bound and free aminopeptidase was digested in the caecal lumen, and about 30–38% of the bound and free maltase. This loss of digestive enzyme activity is possible, because enzyme secretion rates are high, the unbound enzymes are effectively recycled, and the time of nutrient passage is short.     

Identification of the Mamestra configurata (Lepidoptera: Noctuidae) peritrophic matrix proteins and enzymes involved in peritrophic matrix chitin metabolism

The peritrophic matrix (PM) is essential for insect digestive system physiology as it protects the midgut epithelium from damage by food particles, pathogens, and toxins. The PM is also an attractive target for development of new pest control strategies due to its per os accessibility. To understand how the PM performs these functions, the molecular architecture of the PM was examined using genomic and proteomic approaches in Mamestra configurata (Lepidoptera: Noctuidae), a major pest of cruciferous oilseed crops in North America. Liquid chromatography‐tandem mass spectrometry analyses of the PM identified 82 proteins classified as: (i) peritrophins, including a new class with a CBDIII domain; (ii) enzymes involved in chitin modification (chitin deacetylases), digestion (serine proteases, aminopeptidases, carboxypeptidases, lipases and α‐amylase) or other reactions (β‐1,3‐glucanase, alkaline phosphatase, dsRNase, astacin, pantetheinase); (iii) a heterogenous group consisting of polycalin, REPATs, serpin, C‐Type lectin and Lsti99/Lsti201 and 3 novel proteins without known orthologs. The genes encoding PM proteins were expressed predominantly in the midgut. cDNAs encoding chitin synthase‐2 (McCHS‐2), chitinase (McCHI), and β‐N‐acetylglucosaminidase (McNAG) enzymes, involved in PM chitin metabolism, were also identified. McCHS‐2 expression was specific to the midgut indicating that it is responsible for chitin synthesis in the PM, the only chitinous material in the midgut. In contrast, the genes encoding the chitinolytic enzymes were expressed in multiple tissues. McCHS‐2, McCHI, and McNAG were expressed in the midgut of feeding larvae, and NAG activity was present in the PM. This information was used to generate an updated model of the lepidopteran PM architecture.     

Responses of midgut amylases of Helicoverpa armigera to feeding on various host plants

Midgut digestive amylases and proteinases of Helicoverpa armigera, a polyphagous and devastating insect pest of economic importance have been studied. We also identified the potential of a sorghum amylase inhibitor against H. armigera midgut amylase. Amylase activities were detected in all the larval instars, pupae, moths and eggs; early instars had lower amylase levels which steadily increased up to the sixth larval instar. Qualitative and quantitative differences in midgut amylases of H. armigera upon feeding on natural and artificial diets were evident. Natural diets were categorized as one or more members of legumes, vegetables, flowers and cereals belonging to different plant families. Amylase activity and isoform patterns varied depending on host plant and/or artificial diet. Artificial diet-fed H. armigera larvae had comparatively high amylase activity and several unique amylase isoforms. Correlation of amylase and proteinase activities of H. armigera with the protein and carbohydrate content of various diets suggested that H. armigera regulates the levels of these digestive enzymes in response to macromolecular composition of the diet. These adjustments in the digestive enzymes of H. armigera may be to obtain better nourishment from the diet and avoid toxicity due to nutritional imbalance. H. armigera, a generalist feeder experiences a great degree of nutritional heterogeneity in its diet. An investigation of the differences in enzyme levels in response to macronutrient balance and imbalance highlight their importance in insect nutrition.     

CARBOHYDRASES IN THE DIGESTIVE SYSTEM OF THE SPINED SOLDIER BUG,Podisus maculiventris (SAY) (HEMIPTERA: PENTATOMIDAE)

The spined soldier bug, Podisus maculiventris, is a generalist predator of insects and has been used in biological control. However, information on the digestion of food in this insect is lacking. Therefore, we have studied the digestive system in P. maculiventris, and further characterized carbohydrases in the digestive tract. The midgut of all developmental stages was composed of anterior, median, and posterior regions. The volumes of the anterior midgut decreased and the median midgut increased in older instars and adults, suggesting a more important role of the median midgut in food digestion. However, carbohydrase activities were predominant in the anterior midgut. In comparing the specific activity of carbohydrases, α‐amylase activity was more in the salivary glands (with two distinct activity bands in zymograms), and glucosidase and galactosidase activities were more in the midgut. Salivary α‐amylases were detected in the prey hemolymph, demonstrating the role of these enzymes in extra‐oral digestion. However, the catalytic efficiency of midgut α‐amylase activity was approximately twofold more than that of the salivary gland enzymes, and was more efficient in digesting soluble starch than glycogen. Midgut α‐amylases were developmentally regulated, as one isoform was found in first instar compared to three isoforms in fifth instar nymphs. Starvation significantly affected carbohydrase activities in the midgut, and acarbose inhibited α‐amylases from both the salivary glands and midgut in vitro and in vivo. The structural diversity and developmental regulation of carbohydrases in the digestive system of P. maculiventris demonstrate the importance of these enzymes in extra‐oral and intra‐tract digestion, and may explain the capability of the hemipteran to utilize diverse food sources.     

Digestive anatomy of Halella azteca (Crustacea,Amphipoda)

The digestive tract of the freshwater amphipod Hyalella azteca is a straight but differentiated tube consisting of foregut, midgut, and hindgut divisions. The foregut is subdivided into a tubular esophagus, a cardiac stomach, and a pyloric stomach. The cuticular lining of the cardiac stomach is elaborated into a set of food-crushing plates and ossicles, the gastric mill, while the pyloric cuticle forms a complex straining and pressing mechanism. Nine caeca arise from the midgut, seven anteriorly and two posteriorly. Four of the anterior caeca, the hepatopancreatic caeca, are believed to be the primary sites of digestion and absorption. The remaining caeca may be absorptive, secretory, or both. The much-folded hindgut wall is capable of great distention by extrinsic muscle action for water intake to aid in flushing fecal material out of the anus; such action also may stimulate antiperistalsis by intrinsic rectal muscles.     

Fine structure of the larval midgut of the fly Rhynchosciara and its physiological implications

The midgut of Rhynchosciara americana larvae consists of a cylindrical ventriculus from which protrudes two gastric caeca formed by polyhedral cells with microvilli covering their apical faces. The basal plasma membrane of these cells is infolded and displays associated mitochondria which are, nevertheless, more conspicuous in the apical cytoplasm. The anterior ventricular cells possess elaborate mitochondria-associated basal plasma membrane infoldings extending almost to the tips of the cells, and small microvilli disposed in the cell apexes. Distal posterior ventricular cells with long apical microvilli are grouped into major epithelial foldings forming multicellular crypts. In these cells the majority of the mitochondria are dispersed in the apical cytoplasm, minor amounts being associated with moderately-developed basal plasma membrane infoldings. The proximal posterior ventriculus represents a transition region between the anterior ventriculus and the distal posterior ventriculus. The resemblance between the gastric caeca and distal posterior ventricular cells is stressed by the finding that their microvilli preparations display similar alkaline phosphatase-specific activities. The results lend support to the proposal, based mainly on previous data on enzyme excretion rates, that the endo-ectoperitrophic circulation of digestive enzymes is a consequence of fluid fluxes caused by the transport of water into the first two thirds of midgut lumen, and its transference back to the haemolymph in the gastric caeca and in the distal posterior ventriculus.     

The adipokinetic hormone of the coleopteran suborder Adephaga: Structure,function, and comparison of distribution in other insects

The aim of the current study is to identify the adipokinetic hormone(s) (AKHs) of a basal suborder of the species‐rich Coleoptera, the Adephaga, and possibly learn more about the ancestral AKH of beetles. Moreover, we wanted to compare the ancestral AKH with AKHs of more advanced beetles, of which a number are pest insects. This would allow us to assess whether AKH mimetics would be suitable as insecticides, that is, be harmful to the pest species but not to the beneficial species. Nine species of the Adephaga were investigated and all synthesize only one octapeptide in the corpus cardiacum, as revealed by Edman degradation sequencing techniques or by mass spectrometry. The amino acid sequence pGlu‐Leu‐Asn‐Phe‐Ser‐Thr‐Gly‐Trp corresponds to Schgr‐AKH‐II that was first identified in the desert locust. It is assumed that Schgr‐AKH‐II—the peptide of a basal beetle clade—is the ancestral AKH for beetles. Some other beetle families, as well as some Hymenoptera (including honey bees) also contain this peptide, whereas most of the pest beetle species have different AKHs. This argues that those peptides and their receptors should be explored for developing mimetics with insecticidal properties. A scenario where Schgr‐AKH‐II (the only AKH of Adephaga) is used as basic molecular structure to derive almost all other known beetle AKHs via single step mutations is very likely, and supports the interpretation that Schgr‐AKH‐II is the ancestral AKH of Coleoptera.