TMOF-like factor controls the biosynthesis of serine proteases in the larval gut of Heliothis virescens

Heliothis virescens chymotrypsin is translationally controlled by AeaTMOF binding ABC putative receptor

Heliothis virescens larval chymotrypsin (GenBank accession number AF43709) was cloned, sequenced and its three dimensional (3D) conformation modeled. The enzyme's transcript was first detected 6 days after larval emergence and the transcript level was shown to fall between larval ecdysis periods. Comparisons between the activities of larval gut chymotrypsin and trypsin shows that chymotrypsin activity is only 16% of the total trypsin activity and the pH optimum of the larval chymotrypsin is between pH 9-10, however the enzyme also exhibited a broad activity between pH 4-6. Injections of AeaTMOF and several shorter analogues into 3rd instar larvae followed by Northern blot analyses showed that although the chymotrypsins activities were inhibited by 60%-80% the transcript level of the sequenced chymotrypsin was not reduced and was similar to controls in which the chymotrypsin activity was not inhibited, indicating that AeaTMOF and its analogues exert a translational control. Based on these observations a putative AeaTMOF receptor (ABCC4) homologous to the Ae. aegypti ABC receptor sequence was found in the H. virescens genome. 3D molecular modeling and docking of the AeaTMOF and several of its analogues to the ABCC4 receptor showed that it can bind AeaTMOF and its analogues as was shown before for the Ae. aegypti receptor.

Silicon-based induced resistance in maize against fall armyworm [Spodoptera frugiperda (Lepidoptera: Noctuidae)]

The fall armyworm (Spodoptera frugiperda) is a major economic pest in the United States and has recently become a significant concern in African and Asian countries. Due to its increased resistance to current management strategies, including pesticides and transgenic corn, alternative management techniques have become more necessary. Currently, silicon (Si) is being used in many pest control systems due to its ability to increase plant resistance to biotic and abiotic factors and promote plant growth. The current experiments were carried out at the College of Plant Protection, Gansu Agricultural University, Lanzhou, China, to test the effect of Si on lifetable parameters and lipase activity of fall armyworm and vegetative and physiological parameters of maize plants. Two sources of Si (silicon dioxide: SiO2 and potassium silicate: K2SiO3) were applied on maize plants with two application methods (foliar application and soil drenching). The experiment results revealed that foliar applications of SiO2 and K2SiO3 significantly (P≤0.05) increased mortality percentage and developmental period and decreased larval and pupal biomass of fall armyworm. Similarly, both Si sources significantly (P≤0.05) reduced lipase activity of larvae, and fecundity of adults, whereas prolonged longevity of adults. Among plant parameters, a significant increase in fresh and dry weight of shoot, stem length, chlorophyll content, and antioxidant activity was observed with foliar applications of Si. Root fresh and dry weight was significantly (P ≤ 0.05) higher in plants treated with soil drenching of SiO2 and K2SiO3. Moreover, SiO2 performed better for all parameters as compared to K2SiO3 and control treatment. The study conclusively demonstrated a significant negative effect on various biological parameters of fall armyworm when plants were treated with Si, so it can be a promising strategy to control this pest.

Integrated Transcriptomic and Proteomic Analyses Suggest the Participation of Endogenous Protease Inhibitors in the Regulation of Protease Gene Expression in Helicoverpa armigera

Insects adapt to plant protease inhibitors (PIs) present in their diet by differentially regulating multiple digestive proteases. However, mechanisms regulating protease gene expression in insects are largely enigmatic. Ingestion of multi-domain recombinant Capsicum annuum protease inhibitor-7 (CanPI-7) arrests growth and development of Helicoverpa armigera (Lepidoptera: Noctuidae). Using de novo RNA sequencing and proteomic analysis, we examined the response of H. armigera larvae fed on recombinant CanPI-7 at different time intervals. Here, we present evidence supporting a dynamic transition in H. armigera protease expression on CanPI-7 feeding with general down-regulation of protease genes at early time points (0.5 to 6 h) and significant up-regulation of specific trypsin, chymotrypsin and aminopeptidase genes at later time points (12 to 48 h). Further, coexpression of H. armigera endogenous PIs with several digestive protease genes were apparent. In addition to the differential expression of endogenous H. armigera PIs, we also observed a distinct novel isoform of endogenous PI in CanPI-7 fed H. armigera larvae. Based on present and earlier studies, we propose potential mechanism of protease regulation in H. armigera and subsequent adaptation strategy to cope with anti-nutritional components of plants.

Trypsin of Litopenaeus vannamei is required for the generation of hemocyanin-derived peptides

Hemocyanin is a copper containing respiratory glycoprotein in arthropods and mollusks, which also have multiple functions in vivo. Recent studies have shown that hemocyanin could generate several peptides, which play important roles in shrimp innate immunity. However, how these hemocyanin-derived peptides are generated is still largely unknown. In this study, we report for the first time that the generation of hemocyanin-derived peptides was closely correlated with trypsin expression in shrimp hepatopancreas following infection with different bacteria. RNA interference (RNAi) mediated knockdown of trypsin or treatment with the serine protease inhibitor, aprotinin, resulted in significant decrease in the levels of hemocyanin-derived peptides. Moreover, recombinant trypsin (rTrypsin) was able to hydrolyse hemocynin in vitro with the hydrolysate having a high bacterial agglutination activity while the denatured hemocynin untreated with rTrypsin lost its agglutination activity. Taken together, our current results showed that the generation of hemocyanin-derived peptides correlates with an increase trypsin expression.

Enzyme Activity, Cold Hardiness, and Supercooling Point in Developmental Stages of Acrosternum arabicum (Hemiptera: Pentatomidae)

Several species of pentatomid bugs feed on pistachio fruits in Iran. Acrosternum arabicum Wagner (Hemiptera: Pentatomidae) is one of the most important pests of pistachio in Rafsanjan, Iran. This study was carried out to investigate the carbohydrase activities, supercooling points, and cold hardiness profiles of different developmental stages of A. arabicum under laboratory conditions. The midgut amylolytic of A. arabicum showed an optimal pH at 7.0. The highest amylolytic activity was found in the female adults (35.41 ± 0.90 nmol/min/gut). The mean amylolytic activity measured in first instar nymph was 6.75 ± 0.54 nmol/min/gut. Midgut α- and β-glucosidase showed an optimal activity at pH 5 and 7, respectively. These activities increased from first (83 ± 5 and 54 ± 5 nmol/min, respectively) to fifth (881 ± 17 and 237 ± 14 nmol/min, respectively) instar nymphs. The enzyme activities increased in the adults. Midgut α- and β-galactosidase showed an optimal activity at pH 5. α- and β-galactosidase activities were low in the first instar nymphs (73 ± 5 and 21 ± 3 nmol/min, respectively). The level of α- and β-galactosidase activities in the female adults (533 ± 18 and 246 ± 6 nmol/min, respectively) was higher than the nymphs. The lowest super cooling points (-19 and -18.2 °C, respectively) and the highest cold hardiness (22 and 18% following 24 h exposure at - 20 °C, respectively) were recorded for the eggs and adult females.

In-depth characterization of trypsin-like serine peptidases in the midgut of the sugar fed Culex quinquefasciatus

BACKGROUND

Culex quinquefasciatus is a hematophagous insect from the Culicidae family that feeds on the blood of humans, dogs, birds and livestock. This species transmits a wide variety of pathogens between humans and animals. The midgut environment is the first location of pathogen-vector interactions for blood-feeding mosquitoes and the expression of specific peptidases in the early stages of feeding could influence the outcome of the infection. Trypsin-like serine peptidases belong to a multi-gene family that can be expressed in different isoforms under distinct physiological conditions. However, the confident assignment of the trypsin genes that are expressed under each condition is still a challenge due to the large number of trypsin-coding genes in the Culicidae family and most likely because they are low abundance proteins.

METHODS

We used zymography for the biochemical characterization of the peptidase profile of the midgut from C. quinquefasciatus females fed on sugar. Protein samples were also submitted to SDS-PAGE followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis for peptidase identification. The peptidases sequences were analyzed with bioinformatics tools to assess their distinct features.

RESULTS

Zymography revealed that trypsin-like serine peptidases were responsible for the proteolytic activity in the midgut of females fed on sugar diet. After denaturation in SDS-PAGE, eight trypsin-like serine peptidases were identified by LC-MS/MS. These peptidases have structural features typical of invertebrate digestive trypsin peptidases but exhibited singularities at the protein sequence level such as: the presence of different amino acids at the autocatalytic motif and substrate binding regions as well as different number of disulfide bounds. Data mining revealed a group of trypsin-like serine peptidases that are specific to C. quinquefasciatus when compared to the culicids genomes sequenced so far.

CONCLUSION

We demonstrated that proteomics approaches combined with bioinformatics tools and zymographic analysis can lead to the functional annotation of trypsin-like serine peptidases coding genes and aid in the understanding of the complexity of peptidase expression in mosquitoes.

Expression of active trypsin-like serine peptidases in the midgut of sugar-feeding female Anopheles aquasalis

BACKGROUND

Anopheles aquasalis is a dipteran of the family Culicidae that is widely distributed in the coastal regions of South and Central America. This species acts as a vector of Plasmodium vivax, an important etiological agent of malaria, which represents a serious public health problem. In mosquitoes, trypsin-like serine proteases are important in blood meal digestion, immune responses and reproductive functions. The study of peptidases expressed in the mosquito midgut is essential to understanding the mechanisms of parasite-host interaction and the physiological process of nutrient digestion.

METHODS

Our study aimed to identify and characterize the proteolytic activities in the midgut of sugar-fed An. aquasalis females using zymographic analyses (substrate-SDS-PAGE), in-solution assays and mass spectrometry.

RESULTS

Here, we used a zymographic analysis to further biochemically characterize the proteolytic profile of the midgut of sugar-feeding An. aquasalis females. The trypsin peptidases migrated between ~17 and ~76 kDa and displayed higher proteolytic activities between pH 7.5 and 10 and at temperatures between 37 °C and 50 °C. Four putative trypsin-like serine peptidases were identified using mass spectrometry and data mining. The molecular masses of these peptidases were similar to those observed using zymography, which suggested that these peptidases could be responsible for some of the observed proteolytic bands.

CONCLUSIONS

Taken together, our results contribute to the gene annotation of the unknown genome of this species, to the tissue location of these peptidases, and to the functional prediction of these crucial enzymes, which all impact further studies of this species.

Adaptive regulation of digestive serine proteases in the larval midgut of Helicoverpa armigera in response to a plant protease inhibitor

Protease inhibitors (PIs) are direct defenses induced by plants in response to herbivory. PIs reduce herbivore digestive efficiency by inhibiting insects' digestive proteases; in turn insects can adapt to PIs by generally increasing protease levels and/or by inducing the expression of PI-insensitive proteases. Helicoverpa armigera, a highly polyphagous lepidopteran insect pest, is known for its ability to adapt to PIs. To advance our molecular and functional understanding of the regulation of digestive proteases, we performed a comprehensive gene expression experiment of H. armigera exposed to soybean Kunitz trypsin inhibitor (SKTI) using a custom-designed microarray. We observed poor larval growth on the SKTI diet until 24 h, however after 48 h larvae attained comparable weight to that of control diet. Although initially the expression of several trypsins and chymotrypsins increased, eventually the expression of some trypsins decreased, while the number of chymotrypsins and their expression increased in response to SKTI. Some of the diverged serine proteases were also differentially expressed. The expression of serine proteases observed using microarrays were further validated by qRT-PCR at different time points (12, 24, 48, 72 and 96 h) after the start of SKTI ingestion. There were also large changes in transcriptional patterns over time in the control diet. Carbohydrate metabolism and immune defense genes were affected in response to SKTI ingestion. Enzyme assays revealed reduced trypsin-specific activity and increased chymotrypsin-specific activity in response to SKTI. The differential regulation of trypsins and chymotrypsins at the transcript and protein levels accompanying a rebound in growth rate indicates that induction of SKTI-insensitive proteases is an effective strategy of H. armigera in coping with this protease inhibitor in its diet.

Insect response to plant defensive protease inhibitors

Plant protease inhibitors (PIs) are natural plant defense proteins that inhibit proteases of invading insect herbivores. However, their anti-insect efficacy is determined not only by their potency toward a vulnerable insect system but also by the response of the insect to such a challenge. Through the long history of coevolution with their host plants, insects have developed sophisticated mechanisms to circumvent antinutritional effects of dietary challenges. Their response takes the form of changes in gene expression and the protein repertoire in cells lining the alimentary tract, the first line of defense. Research in insect digestive proteases has revealed the crucial roles they play in insect adaptation to plant PIs and has brought about a new appreciation of how phytophagous insects employ this group of molecules in both protein digestion and counterdefense. This review provides researchers in related fields an up-to-date summary of recent advances.

Short and long-term antinutritional effect of the trypsin inhibitor ApTI for biological control of sugarcane borer

Plant-derived trypsin inhibitors have been shown to have potent anti-insect effects and are a promising alternative for the biological control of pests. In this work, we tested the anti-insect activity of Adenanthera pavonina trypsin inhibitor (ApTI) against Diatraea saccharalis larvae, a major insect pest in sugarcane. The addition of 0.1% ApTI in short-term assays resulted in 87% and 63% decreased trypsin and chymotrypsin activities respectively. ApTI was not digested after 60h incubation with D. saccharalis midgut proteases. The chronic effects of ApTI on F0 and F1 generations of D. saccharalis were also analyzed. The larvae from the F0 generation showed 55% and 21% decreased larval and pupal viability, respectively. ApTI-fed larvae from the F1 generation showed a decrease of 33% in survival rate and 23% in the average larval weight. Moreover, ApTI treatment reduced trypsin and chymotrypsin activities in F1 larvae. Thus, the anti-insect effects of ApTI on consecutive generations (F0 and F1) of D. saccharalis larvae demonstrate its potential for long-term control of this pest.

The impact of ingested potato type II inhibitors on the production of the major serine proteases in the gut of Helicoverpa armigera

The flowers of the ornamental tobacco produce high levels of a series of 6 kDa serine protease inhibitors (NaPIs) that are effective inhibitors of trypsins and chymotrypsins from lepidopteran species. These inhibitors have a negative impact on the growth and development of lepidopteran larvae and have a potential role in plant protection. Here we investigate the effect of NaPIs on the activity and levels of serine proteases in the gut of Helicoverpa armigera larvae and explore the adaptive mechanisms larvae employ to overcome the negative effects of NaPIs in the diet. Polyclonal antibodies were raised against a Helicoverpa punctigera trypsin that is a target for NaPIs and two H. punctigera chymotrypsins; one that is resistant and one that is susceptible to inhibition by NaPIs. The antibodies were used to optimize procedures for extraction of proteases for immunoblot analysis and to assess the effect of NaPIs on the relative levels of the proteases in the gut and frass. We discovered that consumption of NaPIs did not lead to over-production of trypsins or chymotrypsins but did result in excessive loss of proteases to the frass.

Oostatic peptides

Oostatic peptides are organic molecules, which influence an insect reproduction due to a regulation of the eggs development. It was proved that decapeptide-H-Tyr-Asp-Pro-Ala-Pro-Pro-Pro-Pro-Pro-Pro-OH (YDPAPPPPPP)-isolated from mosquito Aedes aegypti, inhibits trypsin activity in the midgut of the mosquito. Therefore, it was named trypsin-modulating oostatic factor (Aea-TMOF). Feeding the recombinant cells with cloned and expressed TMOF on the coat protein of tobacco mosaic virus (TMV) to mosquito larvae, caused larval mortality. The TMOF was therefore designed for usage as a new biorational insecticide against mosquito. Similarly, a hexapeptide-H-Asn-Pro-Thr-Asn-Leu-His-OH (NPTNLH)-was isolated from the grey flesh fly Neobellieria bullata. This peptide and some of its analogs inhibited trypsin-like synthesis by the midgut in female flies and was therefore entitled Neb-TMOF. Interestingly, the synthetic Aea-TMOF and mainly its C-terminus shorten analogs, including those containing D-amino acids or methylene-oxy isosteric bond, quickly and strongly inhibited the hatchability and egg development in the flesh fly N. bullata.

Proteolytic profiling and comparative analyses of active trypsin-like serine peptidases in preimaginal stages of Culex quinquefasciatus

Background

The mosquito Culex quinquefasciatu s, a widespread insect in tropical and sub-tropical regions of the world, is a vector of multiple arboviruses and parasites, and is considered an important risk to human and veterinary health. Proteolytic enzymes play crucial roles in the insect physiology including the modulation of embryonic development and food digestion. Therefore, these enzymes represent important targets for the development of new control strategies. This study presents zymographic characterization and comparative analysis of the proteolytic activity found in eggs, larval instars and pupae of Culex quinquefasciatus.

Methods

The proteolytic profiles of eggs, larvae and pupa of Cx. quinquefasciatus were characterized by SDS-PAGE co-polymerized with 0.1% gelatin, according to the pH, temperature and peptidase inhibitor sensitivity. In addition, the proteolytic activities were characterized in solution using 100 μM of the fluorogenic substrate Z-Phe-Arg-AMC.

Results

Comparison of the proteolytic profiles by substrate-SDS-PAGE from all preimaginal stages of the insect revealed qualitative and quantitative differences in the peptidase expression among eggs, larvae and pupae. Use of specific inhibitors revealed that the proteolytic activity from preimaginal stages is mostly due to trypsin-like serine peptidases that display optimal activity at alkaline pH. In-solution, proteolytic assays of the four larval instars using the fluorogenic substrate Z-Phe-Arg-AMC in the presence or absence of a trypsin-like serine peptidase inhibitor confirmed the results obtained by substrate-SDS-PAGE analysis. The trypsin-like serine peptidases of the four larval instars were functional over a wide range of temperatures, showing activities at 25°C and 65°C, with an optimal activity between 37°C and 50°C.

Conclusion

The combined use of zymography and in-solution assays, as performed in this study, allowed for a more detailed analysis of the repertoire of proteolytic enzymes in preimaginal stages of the insect. Finally, differences in the trypsin-like serine peptidase profile of preimaginal stages were observed, suggesting that such enzymes exert specific functions during the different stages of the life cycle of the insect.

Enhanced activity of an insecticidal protein, trypsin modulating oostatic factor (TMOF), through conjugation with aliphatic polyethylene glycol

BACKGROUND

Trypsin modulating oostatic factor (TMOF), a decapeptide (Tyr-Asp-Pro-Ala-Pro(6)) isolated from the ovaries of the adult yellow fever mosquito, Aedes aegypti, regulates trypsin biosynthesis. TMOF per os is insecticidal to larval mosquitoes and a good model for the development of technologies to enhance protein insecticide activity by reduced catabolism and/or enhanced delivery to the target.

RESULTS

TFA-TMOF-K (TFA = trifluoro acetyl) allowed the specific conjugation of monodispersed, aliphatic polyethylene glycol (PEG) to the amino group of lysine-producing TMOF-K-methyl(ethyleneglycol)(7)-O-propionyl (TMOF-K-PEG(7) P). The addition of lysine to TMOF reduced its per os larval mosquitocidal activity relative to the parent TMOF, but conjugation of TMOF-K with methyl(ethyleneglycol)(7)-O-propionyl increased its toxicity 5.8- and 10.1-fold above that of TMOF and TMOF-K for Ae. aegypti. Enhanced insecticidal activity was also found for larval Ae. albopictus and for neonates of Heliothis virescens and Heliocoverpa zea. Only TMOF-K was found by MS/MS in the hemolymph for H. virescens fed on TMOF-K-PEG(7) P. No TMOF, TMOF-K or PEGylated TMOF-K was detected in the hemolymph after topical applications.

CONCLUSIONS

This research suggests that aliphatic PEG polymers can be used as a new method for increasing the activity of insecticidal proteins.

The effect of adipokinetic hormone on midgut characteristics in Pyrrhocoris apterus L. (Heteroptera)

Digestive processes and the effect of adipokinetic hormone (Pyrap-AKH) on the amount of nutrients (lipids, proteins, and carbohydrates), and on the activity of digestive enzymes (lipases, peptidases, and carbohydrases) were studied in the midgut of the firebug, Pyrrhocoris apterus. The analyses were performed on samples of anterior (AM), middle (MM) and posterior (PM) midgut parts. The results revealed that the digestion of lipids, carbohydrates and proteins take place in the acidic milieu. The Pyrap-AKH treatment increased significantly the level of lipids and proteins in the midgut, and also the level of triacylglycerols (TGs) predominantly in the AM, and the level of diacylglycerols (DGs) in the MM. The increase was not uniform for all present TG and DG species - those containing the linoleic fatty acid were predominant. No hormonal effect on lipase activity was recorded, while peptidase and glucosidase activity was increased in the MM and PM. All these facts indicate that the Pyrap-AKH probably stimulates digestion by more intensive food ingestion or turnover, and perhaps by the stimulation of metabolite absorption; the activation of digestive enzymes seems to be secondary or controlled by other mechanisms.

Identification and transcription profiling of trypsin in Aedes taeniorhynchus (Diptera: Culicidae): developmental regulation, blood feeding, and permethrin exposure

The cDNA of a trypsin gene from Aedes (Ochlerotatus) taeniorhynchus (Weidemann) was cloned and sequenced. The full-length mRNA sequence (890 bp) for trypsin from Ae. taeniorhynchus (AetTryp1) was obtained, which encodes an open reading frame of 765 bp (i.e., 255 amino acids). To detect whether AetTryp is developmentally regulated, a quantitative real-time polymerase chain reaction was used to examine AetTrypl mRNA expression levels in different developmental stages of Ae. taeniorhynchus. AetTryp1 was expressed at low levels in egg, larval, and pupal stages, but was differentially expressed in adult Ae. taeniorhynchus, with highest levels found in 5-d-old female adults when compared with teneral adults. In addition, AetTryp1 mRNA expression differed between sexes, with expression levels much lower in males. However, in both males and females, there was a significant increase in AetTryp1 transcription levels as age increased and peaked in 5-d-old adults. AetTrypl expressed in 5-d-old female Ae. taeniorhynchus significantly increased after 30 min postblood feeding compared with the control. The AetTryp1 mRNA expression in 5-d-old female Ae. taeniorhynchus was affected by different concentrations of permethrin.

Expression of trypsin-like serine peptidases in pre-imaginal stages of Aedes aegypti (Diptera: Culicidae)

This study reports the biochemical characterization and comparative analyses of highly active serine proteases in the larval and pupal developmental stages of Aedes aegypti (Linnaeus) using substrate-SDS-PAGE. Zymographic analysis of larval stadia detected proteolytic activity in 6-8 bands with apparent molecular masses ranging from 20 to 250 kDa, with activity observed from pH 5.5 to 10.0. The pupal stage showed a complex proteolytic activity in at least 11 bands with apparent Mr ranging from 25 to 250 kDa, and pH optimum at 10.0. The proteolytic activities of both larval and pupal stages were strongly inhibited by phenyl-methyl sulfonyl-fluoride and N-α-Tosyl-L-lysine chloromethyl ketone hydrochloride, indicating that the main proteases expressed by these developmental stages are trypsin-like serine proteases. The enzymes were active at temperatures ranging from 4 to 85°C, with optimal activity between 37 and 60°C, and low activity at 85°C. Comparative analysis between the proteolytic enzymes expressed by larvae and pupae showed that substantial changes in the expression of active trypsin-like serine proteases occur during the developmental cycle of A. aegypti.

Toward a consensus nomenclature for insect neuropeptides and peptide hormones

The nomenclature currently in use for insect neuropeptide and peptide hormone families is reviewed and suggestions are made as to how it can be rationalized. Based upon this review, a number of conventions are advanced as a guide to a more rationale nomenclature. The scheme that is put forward builds upon the binomial nomenclature scheme proposed by Raina and Gäde in 1988, when just over 20 insect neuropeptides had been identified. Known neuropeptides and peptide hormones are assigned to 32 structurally distinct families, frequently with overlapping functions. The names given to these families are those that are currently in use, and describe a biological function, homology to known invertebrate/vertebrate peptides, or a conserved structural motif. Interspecific isoforms are identified using a five-letter code to indicate genus and species names, and intraspecific isoforms are identified by Roman or Arabic numerals, with the latter used to signify the order in which sequences are encoded on a prepropeptide. The proposed scheme is sufficiently flexible to allow the incorporation of novel peptides, and could be extended to other arthropods and non-arthropod invertebrates.

Control of the release of digestive enzymes in the larvae of the fall armyworm, Spodoptera frugiperda

There is a basal level of enzyme activity for trypsin, aminopeptidase, amylase, and lipase in the gut of unfed larval (L6) Spodoptera frugiperda. Trypsin activity does not decrease with non-feeding, possibly because of the low protein levels in plants along with high amino acid requirements for growth and storage (for later reproduction in adults). Therefore, trypsin must always be present so that only a minimal protein loss via egestion occurs. Larvae, however, adjust amylase activity to carbohydrate ingestion, and indeed amylase activity is five-fold higher in fed larvae compared to unfed larvae. Gut lipase activity is low, typical of insects with a high carbohydrate diet. A flat-sheet preparation of the ventriculus was used to measure the release of enzymes in response to specific nutrients and known brain/gut hormones in S. frugiperda. Sugars greatly increase (>300%) amylase release, but starch has no effect. Proteins and amino acids have little or no effect on trypsin or aminopeptidase release. The control of enzyme release in response to food is likely mediated through neurohormones. Indeed, an allatostatin (Spofr-AS A5) inhibits amylase and trypsin, and allatotropin (Manse- AT) stimulates amylase and trypsin release. Spofr-AS A5 also inhibits ileum myoactivity and Manse-AT stimulates myoactivity. The epithelial secretion rate of amylase and trypsin was about 20% of the amount of enzyme present in the ventricular lumen, which, considering the efficient counter-current recycling of enzymes, suggests that the secretion rate is adequate to replace egested enzymes.

The intestinal barrier in lepidopteran larvae: permeability of the peritrophic membrane and of the midgut epithelium to two biologically active peptides

Endogenous peptide regulators of insect physiology and development are presently being considered as potential biopesticides, but their efficacy by oral delivery cannot be easily anticipated because of the limited information on how the insect gut barrier handles these kind of molecules. We investigated, in Bombyx mori larvae, the permeability properties of the two components of the intestinal barrier, the peritrophic membrane (PM) and the midgut epithelium, separately isolated and perfused in conventional Ussing chambers. The PM discriminated compounds of different dimensions but was easily crossed by two small peptides recently proposed as bioinsecticides, the neuropeptide proctolin and Aedes aegypti Trypsin Modulating Oostatic Factor (Aea-TMOF), although their flux values indicated that the permeability was highly affected by their steric conformation. To date, there is very little functional data available on how peptides cross the insect intestinal epithelium, but it has been speculated that peptides could reach the haemocoel through the paracellular pathway. We characterized the permeability properties of this route to a number of organic molecules, showing that B. mori septate junction was highly selective to both the dimension and the charge of the permeant compound. Confocal images of whole-mount midguts incubated with rhodamine(rh)-proctolin or fluorescein isothiocyanate (FITC)-Aea-TMOF added to the mucosal side of the epithelium, revealed that rh-proctolin did not enter the cell and crossed the midgut only by the paracellular pathway, while FITC-Aea-TMOF did cross the cell apical membrane, permeating also through the transcellular route.

Effect of ace inhibitors and TMOF on growth, development, and trypsin activity of larval Spodoptera littoralis

Angiotensin converting enzyme (ACE) is a zinc metallopeptidase capable of cleaving dipeptide or dipeptideamide moieties at the C-terminal end of peptides. ACE is present in the hemolymph and reproductive tissues of insects. The presence of ACE in the hemolymph and its broad substrate specificity suggests an important role in processing of bioactive peptides. This study reports the effects of ACE inhibitors on larval growth in the cotton leafworm Spodoptera littoralis. Feeding ACE inhibitors ad lib decreased the growth rate, inhibited ACE activity in the larval hemolymph, and down-regulated trypsin activity in the larval gut. These results indicate that S. littoralis ACE may influence trypsin biosynthesis in the larval gut by interacting with a trypsin-modulating oostatic factor (TMOF). Injecting third instar larvae with a combination of Aea-TMOF and the ACE inhibitor captopril, down-regulated trypsin biosynthesis in the larval gut indicating that an Aea-TMOF gut receptor analogue could be present. Injecting captopril and enalapril into newly molted fifth instar larvae stopped larval feeding and decreased weight gain. Together, these results indicate that ACE inhibitors are efficacious in stunting larval growth and ACE plays an important role in larval growth and development.

Insect gonadotropic peptide hormones: some recent developments

Gonadotropic peptides are a new generation of peptide hormone regulators of insect reproduction. They have been isolated from ovaries, oviducts, or brains of insects. The subject of this paper is insect peptides that exert stimulatory or inhibitory effects on ovarian development and oocyte maturation. On the basis of the literature data and the results of our investigations, the structure and biological properties of different groups of peptides are presented.

Delivery methods for peptide and protein toxins in insect control

Since the introduction of DDT in the 1940s, arthropod pest control has relied heavily upon chemical insecticides. However, the development of insect resistance, an increased awareness of the real and perceived environmental and health impacts of these chemicals, and the need for systems with a smaller environmental footprint has stimulated the search for new insecticidal compounds, novel molecular targets, and alternative control methods. In recent decades a variety of biocontrol methods employing peptidic or proteinaceous insect-specific toxins derived from microbes, plants and animals have been examined in the laboratory and field with varying results. Among the many interdependent factors involved with the production of a cost-effective pesticide--production expense, kill efficiency, environmental persistence, pest-specificity, pest resistance-development, public perception and ease of delivery--sprayable biopesticides have not yet found equal competitive footing with chemical counterparts. However, while protein/peptide-based biopesticides continue to have limitations, advances in the technology, particularly of genetically modified organisms as biopesticidal delivery systems, has continually progressed. This review highlights the varieties of delivery methods currently practiced, examining the strengths and weaknesses of each method.

Expression of Aedes trypsin-modulating oostatic factor on the virion of TMV: A potential larvicide

We report the engineering of the surface of the tobacco mosaic virus (TMV) virion with a mosquito decapeptide hormone, trypsin-modulating oostatic factor (TMOF). The TMV coat protein (CP) was fused to TMOF at the C terminus by using a read-through, leaky stop codon that facilitated expression of CP and chimeric CP-TMOF (20:1 ratio) that were coassembled into virus particles in infected Nicotiana tabacum. Plants that were infected with the hybrid TMV RNA accumulated TMOF to levels of 1.3% of total soluble protein. Infected tobacco leaf discs that were fed to Heliothis virescens fourth-instar larvae stunted their growth and inhibited trypsin and chymotrypsin activity in their midgut. Purified CP-TMOF virions fed to mosquito larvae stopped larval growth and caused death. Because TMV has a wide host range, expressing TMV-TMOF in plants can be used as a general method to protect them against agricultural insect pests and to control vector mosquitoes.

Biochemical and cytoimmunological evidence for the control of Aedes aegypti larval trypsin with Aea-TMOF

Trypsin and chymotrypsin-like enzymes were detected in the gut of Aedes aegypti in the four larval instar and pupal developmental stages. Although overall the amount of trypsin synthesized in the larval gut was 2-fold higher than chymotrypsin, both enzymes are important in food digestion. Feeding Aea-Trypsin Modulating Oostatic Factor (TMOF) to Ae. aegypti and Culex quinquefasciatus larvae inhibited trypsin biosynthesis in the larval gut, stunted larval growth and development, and caused mortality. Aea-TMOF induced mortality in Ae. aegypti, Cx. quinquefasciatus, Culex nigripalpus, Anopheles quadrimaculatus, and Aedes taeniorhynchus larvae, indicating that many mosquito species have a TMOF-like hormone. The differences in potency of TMOF on different mosquito species suggest that analogues in other species are similar but may differ in amino acid sequence or are transported differently through the gut. Feeding of 29 different Aea-TMOF analogues to mosquito larvae indicated that full biological activity of the hormone is achieved with the tetrapeptide YDPA. Using cytoimmunochemical analysis, intrinsic TMOF was localized to ganglia of the central nervous system in larvae and male and female Ae. aegypti adults. The subesophageal, thoracic, and abdominal ganglia of both larval and adult mosquitoes contained immunoreactive cells. Immunoreactive cells were absent in the corpus cardiacum of newly molted 4th instar larvae but were found in late 4th instar larvae. In both males and females, the intrinsic neurosecretory cells of the corpus cardiacum were filled with densely stained immunoreactive material. These results indicate that TMOF-immunoreactive material is synthesized in sugar-fed male and female adults and larvae by the central nervous system cells.

Trypsin-modulating oostatic factor: a potential new larvicide for mosquito control

Trypsin-modulating oostatic factor (TMOF), a mosquito decapeptide,terminates trypsin biosynthesis in the mosquito gut. The hormone is secreted from the ovary, starting 18 h after the blood meal, circulates in the hemolymph, binds to a gut receptor and stops trypsin biosynthesis by exerting a translational control on trypsin mRNA. Because of the unique primary amino acid sequence of the hormone (YDPAPPPPPP) and its stable three-dimensional conformation, TMOF is not degraded by gut proteolytic enzymes and can traverse the gut epithelial cells into the hemolymph of adults and larvae. Using this unique property, hormone fed to different species of mosquito larvae stops food digestion and causes larval mortality. To determine the shortest amino acid sequence that can bind to the gut receptor and still cause high larval mortality, 25 analogues of TMOF were synthesized and tested. The tetrapeptide(YDPA) was as effective as the decapeptide, indicating that the binding to the gut receptor is at the N-terminus of the molecule. Cloning and expressing the hormone on the coat protein of tobacco mosaic virus (TMV) in Chlorella sp. and Saccharomyces cerevisiae cells and feeding the recombinant cells to mosquito larvae caused larval mortality. These results indicate that TMOF can be used as a new biorational insecticide against mosquito larvae.

Insect peptide hormones: a selective review of their physiology and potential application for pest control

Our knowledge on primary structure, synthesis, release, receptor binding, structure-activity relationships, mode of action and degradation of, mainly, neuropeptides from insects has increased dramatically during the last 10 years or so. Here, five case studies are presented, which deal selectively with effects on: reproduction (trypsin modulating oostatic factor in mosquito); energy metabolism, locomotion and the immune system (adipokinetic hormones); water and ion balance, and feeding behaviour (diuretic hormones, kinins, sulfakinins); sex attraction (pheromone biosynthesis activating neuropeptide); and growth and development, and muscle activity (allatostatins). The literature is reviewed in the context of how the knowledge on neuropeptides has been and can be used for the design of novel, safe and selective compounds to control pest insects in the foreseeable future.