Digestive proteolytic and amylolytic activities in Trogoderma granarium Everts (Dermestidae: Coleoptera)

Characteristics of Trypsin genes and their roles in insecticide resistance based on omics and functional analyses in the malaria vector Anopheles sinensis

Trypsin is one of the most diverse and widely studied protease hydrolases. However, the diversity and characteristics of the Trypsin superfamily of genes have not been well understood, and their role in insecticide resistance is yet to be investigated. In this study, a total of 342 Trypsin genes were identified and classified into seven families based on homology, characteristic domains and phylogenetics in Anopheles sinensis, and the LY-Domain and CLECT-Domain families are specific to the species. Four Trypsin genes, (Astry2b, Astry43a, Astry90, Astry113c) were identified to be associated with pyrethroid resistance based on transcriptome analyses of three field resistant populations and qRT-PCR validation, and the knock-down of these genes significantly decrease the pyrethroid resistance of Anopheles sinensis based on RNAi. The activity of Astry43a can be reduced by five selected insecticides (indoxacarb, DDT, temephos, imidacloprid and deltamethrin); and however, the Astry43a could not directly metabolize these five insecticides, like the trypsin NYD-Tr did in earlier reports. This study provides the overall information frame of Trypsin genes, and proposes the role of Trypsin genes to insecticide resistance. Further researches are necessary to investigate the metabolism function of these trypsins to insecticides.

Direct competition and potential displacement involving managed Trogoderma stored product pests

The establishment of an exotic pest may require displacing local species with a similar niche. The potential of Trogoderma granarium to displace Trogoderma inclusum was explored in a stored product setting. We performed direct competition experiments varying commodity and temperature over different durations. At nine weeks T. inclusum outproduced T. granarium on all commodities at any temperature. However the proportion of T. granarium versus T. inclusum was greater at 32 °C compared to 25 °C. The nine-week production of T. granarium was best on wheat, while rice was optimal for T. inclusum. After 25 weeks, when adults were used at the start of competition, T. inclusum maintained an advantage in the direct competition. If larvae were used to initiate the competition for 25 weeks, the two species coexisted well at 25 °C, but T. granarium nearly excluded T. inclusum at 32 °C. Thus T. inclusum performs better in competition over shorter intervals when resources are plentiful, but T. granarium can be more successful over longer time periods, particularly when late instar larvae are involved. The finding suggests a real threat of introductions of T. granarium larvae to establish populations within grain storage infrastructure where T. inclusum is common.

Development of an array of molecular tools for the identification of khapra beetle (Trogoderma granarium), a destructive beetle of stored food products

Trogoderma granarium Everts, the khapra beetle, native to the Indian subcontinent, is one of the world's most destructive pests of stored food products. Early detection of this pest facilitates prompt response towards the invasion and prevents the need for costly eradication efforts. Such detection requires proper identification of T. granarium, which morphologically resembles some more frequently encountered, non-quarantine congeners. All life stages of these species are difficult to distinguish using morphological characters. Additionally, biosurveillance trapping can result in the capture of large numbers of specimens awaiting identification. To address these issues, we aim to develop an array of molecular tools to rapidly and accurately identify T. granarium among non-target species. Our crude, cheap DNA extraction method performed well for Trogoderma spp. and is suitable for downstream analyses including sequencing and real-time PCR (qPCR). We developed a simple quick assay usingrestriction fragment length polymorphism to distinguish between T. granarium and the closely related, congeneric T. variabile Ballion and T. inclusum LeConte. Based on newly generated and published mitochondrial sequence data, we developed a new multiplex TaqMan qPCR assay for T. granarium with improved efficiency and sensitivity over existing qPCR assays. These new tools benefit regulatory agencies and the stored food products industry by providing cost- and time-effective solutions to enhance the identification of T. granarium from related species. They can be added to the existing pest detection toolbox. The selection of which method to use would depend on the intended application.

Evaluation of artificial diets based on different legume seeds on the nutritional physiology and digestive function of Helicoverpa armigera (Hübner)

Helicoverpa armigera (Hübner) is considered a serious agricultural pest worldwide. We explored the effects of artificial diets containing ten legumes, including broad beans (Shadan, Feyz, Saraziri, Barekat, and Mahta cultivars), white kidney beans (Dehghan cultivar), red kidney beans (Goli cultivar), common beans (Khomein cultivar), cowpeas (Mashhad and Arabi cultivars) on the feeding responses of H. armigera by quantifying specific primary and secondary metabolites in the studied legumes and determining larval nutritional indices and digestive enzyme activities. The results showed that the highest efficiency of conversion of digested food (ECD) and relative growth rate values (RGR) of whole larval instars were obtained in the Dehghan and Goli cultivars. However, the lowest values of ECD and RGR were observed in the larvae fed on the Khomein and Mahta cultivars. The highest proteolytic and amylolytic activities of larvae were found on the Dehghan and Mashhad cultivars. The highest and lowest values of standardized insect-growth index and index of plant quality were observed in larvae feeding on the Dehghan and Khomein cultivars, respectively. Additionally, significant variations in phytochemical metabolites were recorded among the studied legume cultivars. Significant negative or positive correlations were also found between feeding characteristics and enzymatic activities of H. armigera with the biochemical composition of the studied legumes. The cluster analysis results revealed that artificial diets containing Mahta and Khomein cultivars were unsuitable for H. armigera, and can be used as candidates for integrated pest management programs or for screening insect inhibitors to produce genetically modified pest-resistant plants.

Comparative Population Growth of the Khapra Beetle (Coleoptera: Dermestidae) and the Warehouse Beetle (Coleoptera: Dermestidae) on Wheat and Rice

We evaluated the relative population growth of two stored-product insect species in the genus Trogoderma, the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), and the warehouse beetle, Trogoderma variabile Ballion (Coleoptera: Dermestidae). Ten adults of each species were placed in vials containing wheat or paddy rice. These tests were performed at 27 and 32°C and the number of adults in the vials were counted after 35 and 70 days. For all the time intervals and temperatures of both species on wheat, the resulting larval abundances were similar, with the exception of 27°C at 70 days where more T. variabile larvae developed. At the higher temperature, both species had similar population growth on rice. However, the success was mixed at 27°C with T. granarium having a greater abundance after 35 days, while T. variabile dominated after 70 days. Frass production in both commodities was usually similar for the two species, but greater frass production occurred by T. variabile on wheat after 70 days at 27°C, while T. granarium produced more frass on rice after 35 days at 32°C. Both species nearly always caused equivalent commodity damage. Our research suggests that under ideal conditions these two closely, but very differently treated species in commerce from the genus Trogoderma have comparable population growth, and cause similar damage on wheat and rice.

Phytochemical profile and insecticidal activity of Agave americana leaf extract towards Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

The main objective of the present study is to introduce a new and ecologically safe method for managing the rice weevil, Sitophilus oryzae. Therefore, the Agave americana leaf extract's phytochemical profile, and its insecticidal activity against the adults of S. oryzae were evaluated. The A. americana leaf extract was screened for the following phytochemicals: total phenolics (14.70 ± 0.31 mg GAE/g FW), total flavonoids (5.15 ± 0.18 mg RE/g FW) and saponins (10.32 ± 0.20 mg OAE/g FW). The HPLC-ESI/TOF-MS analysis results revealed that flavonoid glycosides (kaempferol, quercetin, and isorhamnetin derivates) were the major phenolic compounds of the A. americana leaf extract. In addition, the GC-MS analysis identified n-alkanes (77.77%) as significant compounds of the lipophilic fraction from the leaf extract. Moreover, the insecticidal potential was assessed through contact and repellent bioassays towards the rice weevil adults. The LD₅₀, LC₅₀, and RC₅₀ values were 10.55 μg/insect, 8.99 μg/cm², and 0.055 μg/cm² for topical application method, treated filter-paper method, and repellent bioassay, respectively. Furthermore, the A. americana leaf extract inhibited digestive enzyme activities, and median inhibition concentrations IC₅₀ were evaluated to be 146.06 ± 1.74 and 86.18 ± 1.08 μg/mL for α-amylase and protease, respectively. Overall, our results highlighted the promising potential of the leaf extract against S. oryzae adults, allowing us to recommend the extract under investigation as an ecofriendly alternative to synthetic insecticides.

Structural and Functional Characterization of Hermetia illucens Larval Midgut

The larvae of Hermetia illucens are among the most promising agents for the bioconversion of low-quality biomass, such as organic waste, into sustainable and nutritionally valuable proteins for the production of animal feed. Despite the great interest in this insect, the current literature provides information limited to the optimization of rearing methods for H. illucens larvae, with particular focus on their efficiency in transforming different types of waste and their nutritional composition in terms of suitability for feed production. Surprisingly, H. illucens biology has been neglected and a deep understanding of the morphofunctional properties of the larval midgut, the key organ that determines the extraordinary dietary plasticity of this insect, has been completely overlooked. The present study aims to fill this gap of knowledge. Our results demonstrate that the larval midgut is composed of distinct anatomical regions with different luminal pH and specific morphofunctional features. The midgut epithelium is formed by different cell types that are involved in nutrient digestion and absorption, acidification of the lumen of the middle region, endocrine regulation, and growth of the epithelium. A detailed characterization of the activity of enzymes involved in nutrient digestion and their mRNA expression levels reveals that protein, carbohydrate, and lipid digestion is associated to specific regions of this organ. Moreover, a significant lysozyme activity in the lumen of the anterior and middle regions of the midgut was detected. This enzyme, together with the strong acidic luminal pH of middle tract, may play an important role in killing pathogenic microorganisms ingested with the feeding substrate. The evidence collected led us to propose a detailed functional model of the larval midgut of H. illucens in which each region is characterized by peculiar features to accomplish specific functions. This platform of knowledge sets the stage for developing rearing protocols to optimize the bioconversion ability of this insect and its biotechnological applications.

Proteolytic Activity in the Midgut of Helicoverpa armigera (Noctuidae: Lepidoptera) Larvae Fed on Wild Relatives of Chickpea, Cicer arietinum

Wild relatives of crops are an important source of resistance genes against insect pests. However, it is important to identify the accessions of wild relatives with different mechanisms of resistance to broaden the basis and increase the levels of resistance to insect pests. Therefore, we evaluated 15 accessions of wild relatives of chickpea belonging to seven species and five genotypes of cultivated chickpea for their resistance to pod borer, Helicoverpa armigera, which is the most damaging pest of chickpea. The test genotypes were evaluated for resistance to H. armigera using detached pod assay. Data were also recorded on activity of the digestive enzymes in the midgut of the larvae fed on different wild relatives of chickpea. All the wild chickpea genotypes suffered lower pod damage and weight gained by the third-instar larvae of H. armigera was lower when fed on them compared with the cultivated chickpea. The accessions, IG 69979 (Cicer cuneatum), PI 599066, IG 70006, IG 70018, IG 70022 (Cicer bijugum), IG 599076 (Cicer chrossanicum), and IG 72933, IG 72953 (Cicer reticulatum), showed high levels of resistance to H. armigera. There were significant differences in protease activity in larval gut of H. armigera fed on different wild relatives of chickpea. Total protease, trypsin, and chymotrypsin activities were lowest in larva fed on PI 599066 (C. bijugum) compared with that in the larvae fed IG 69979 (C. cuneatum) and IG 70022 (C. bijugum). Aminopeptidase activity was highest in the larvae fed on IG 70022 (C. bijugum) and IG 599076 (C. chrossanicum), whereas lowest activity was recorded in the larvae fed on ICC 3137 and KAK 2 (susceptible checks). The variation in protease activities may be due to the presence of protease inhibitors in the wild relatives or hyperproduction of enzymes by the larvae as result of protease inhibitor activity of the wild relatives, resulting in low weight gain by larvae. The results suggested that wild relatives of chickpea with diverse mechanisms of resistance can be exploited to increase the levels and diversify the basis of resistance to H. armigera in cultivated chickpea.

Feeding performance and life table parameters of Khapra Beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) on various barley cultivars

The Khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), is a common pest of cereal grains and other stored products. In this study, the effects of ten barley cultivars (Abidar, Bahman, Line20, Line22, Line30, Lisuei, Lokht11, Makuyi, Sahand, and Sahraa) were evaluated on life table parameters and nutritional indices of T. granarium under the following laboratory conditions: 33 ± 1°C, 60 ± 5% RH, and a photoperiod of 14: 10 (L: D) h. Life history parameters of T. granarium could be appropriate indices in resistance and susceptibility evaluation of barley cultivars. The maximum survival rate of immature stages was observed on Makuyi and Lisuei cultivars and the minimum rate was on Abidar and Line22 cultivars. The shortest development time was on Makuyi cultivar and the longest on Line22 cultivar. Pupal weight was ranged from 2.56 mg on Lokht11 to 4.86 mg on Makuyi. Fecundity and egg-hatching rates were highest on Lisuei cultivar and the adults were long-lived on Makuyi cultivar. The highest r m values were observed on Makuyi and Lisuei cultivars but lower value of it resulted from rearing of T. granarium on Line22 cultivar (0.0350 female per female day-1). The results showed that T. granarium larvae fed on Makuyi cultivar had higher values of relative consumption rate and relative growth rate. The results indicated that Makuyi and Lisuei cultivars were relatively susceptible barley cultivars and Line22 was the most inappropriate cultivar for feeding of T. granarium, which could prove useful in the development of Integrated Pest Management programs for this pest.

Invader Competition with Local Competitors: Displacement or Coexistence among the Invasive Khapra Beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), and Two Other Major Stored-Grain Beetles?

Local potential competitor species are important determinants of the invasibility of an environment even when widely recognized invasive species are concerned since it may compromise its establishment. Thus, the outcome of the direct competition among the invasive khapra beetle, Trogoderma granarium, and the cosmopolitan species lesser grain borer, Rhyzopertha dominica and rice weevil, Sitophilus oryzae, and thus the likelihood of establishment of T. granarium under their co-occurrence, was here explored in paddy rice and wheat, at temperatures between 25 and 35°C and through 200 days of storage. Insect infestations were higher in wheat rather than in paddy rice. Trogoderma granarium was unable to displace any of the competing species under two and three-species competition experiments retaining lower adult population than both local competitors at the lowest temperature level. Rhyzopertha dominica prevailed in paddy rice, while S. oryzae prevailed in wheat. Paradoxically, T. granarium adults retained low population growth but contributed more for the total frass production and grain loss, much more than that recorded for R. dominica. Nonetheless, T. granarium larvae exhibited high population numbers 130 days after the introduction of the parental individuals. At higher temperature levels (30 and 35°C) the numbers of T. granarium larvae were extremely high even after 65 days, while the numbers of the other two species rapidly declined. Interestingly, the simultaneous presence of R. dominica and S. oryzae was beneficial for the population growth of T. granarium. Consequently, T. granarium has the ability to outperform other primary stored-product insects at high temperatures, while its presence at low temperatures remains for long periods apparently unaffected by other co-occurring species. Hence, T. granarium, in wheat, is able to outcompete other major species of stored-product insects at elevated temperatures, while at 25°C this species can maintain low numbers of individuals for long periods, which can rapidly produce population outbursts when the prevailing conditions are suitable for its development.

Wheat cultivars affecting life history and digestive amylolytic activity of Sitotroga cerealella Olivier (Lepidoptera: Gelechiidae)

The life history and digestive α-amylase activity of the Angoumois grain moth, Sitotroga cerealella Olivier (Lepidoptera: Gelechiidae) were studied on six wheat cultivars (Arg, Bam, Nai 60, Pishtaz, Sepahan and Shanghai) at 25 ± 1°C, relative humidity of 65 ± 5% and a photoperiod of 16:8 (L:D) h. A delay in the developmental time of S. cerealella immature stages was detected when larvae were fed on cultivar Sepahan. The maximum survival rate of immature stages was seen on cultivar Bam (93.33 ± 2.10%), and the minimum rates were on cultivars Nai 60 (54.66 ± 2.49%) and Sepahan (49.33 ± 4.52%). The highest realized fecundity and fertility were recorded for females which came from larvae fed on cultivar Bam (93.30 ± 2.10 eggs/female and 91.90 ± 3.10%, respectively); and the lowest ones were observed for females which came from larvae fed on cultivar Sepahan (49.30 ± 4.50 eggs/female and 67.4 ± 11.1%, respectively). The heaviest male and female weights of S. cerealella were observed on cultivar Bam (2.97 ± 0.02 and 4.80 ± 0.01 mg, respectively). The highest amylolytic activity of the fourth instar was detected on cultivar Bam (0.89 ± 0.04 mg maltose min-1), which had the maximum mean hundred-wheat weight (5.92 ± 0.19 g). One α-amylase isozyme was detected in the midgut extracts from the fourth instar larvae fed on different wheat cultivars, and the highest intensity was found in larvae fed on cultivar Bam. Correlation analyses showed that very high correlations existed between the immature period, fecundity and fertility on one side and inhibition of α-amylase, soluble starch content and hundred-wheat weight on the other. According to the obtained results, cultivar Sepahan is an unfavorable host for the feeding and development of S. cerealella.

Three-way interaction among plants, bacteria, and coleopteran insects

MAIN CONCLUSION

Coleoptera, the largest and the most diverse Insecta order, is characterized by multiple adaptations to plant feeding. Insect-associated microorganisms can be important mediators and modulators of interactions between insects and plants. Interactions between plants and insects are highly complex and involve multiple factors. There are various defense mechanisms initiated by plants upon attack by herbivorous insects, including the development of morphological structures and the synthesis of toxic secondary metabolites and volatiles. In turn, herbivores have adapted to feeding on plants and further sophisticated adaptations to overcome plant responses may continue to evolve. Herbivorous insects may detoxify toxic phytocompounds, sequester poisonous plant factors, and alter their own overall gene expression pattern. Moreover, insects are associated with microbes, which not only considerably affect insects, but can also modify plant defense responses to the benefit of their host. Plants are also frequently associated with endophytes, which may act as bioinsecticides. Therefore, it is very important to consider the factors influencing the interaction between plants and insects. Herbivorous insects cause considerable damage to global crop production. Coleoptera is the largest and the most diverse order in the class Insecta. In this review, various aspects of the interactions among insects, microbes, and plants are described with a focus on coleopteran species, their bacterial symbionts, and their plant hosts to demonstrate that many factors contribute to the success of coleopteran herbivory.

Nutritional Physiology of the Khapra Beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) Fed on Various Barley Cultivars

The Khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), is known as one of the mostserious pests of grains in many parts of the world. In this study, the effect of nine barley cultivars (‘Bahman’,‘CB-84-10’, ‘Fajr 30’, ‘Makuyi’, ‘Nosrat’, ‘Yousof’, ‘13A1’, ‘18A1’, and ‘19 A1’) and a wheat cultivar (‘MV17’, as a control) was determined on the nutritional indices and digestive enzymatic activity of T. granarium at 33 6 1C,relative humidity of 6565%, and a photoperiod of 14:10 (L:D) h. The highest and lowest values of larval weight gain of sixth instar were detected on wheat (0.757±0.068 mg) and cultivar Bahman (0.342±0.071 mg). Also, T. granarium larvae fed on cultivar Bahman had the lowest value of efficiency of conversion of ingested food(10.90±2.09%) as compared with wheat and other barley cultivars. Also, the highest midgut amylolytic and proteolytic activities of sixth instar were on cultivar Bahman (0.364±0.024 mU/mg and 80.54±1.73 U/mg, respectively)and the lowest activities were on cultivar Nosrat (0.043±0.004 mU/mg and 7.15±0.01 U/mg, respectively).It is concluded that barley cultivar Bahman was the most unsuitable host for feeding of T. granarium.

Characterization of Bactrocera dorsalis serine proteases and evidence for their indirect role in insecticide tolerance

The oriental fruit fly Bactrocera dorsalis (Hendel) causes devastating losses to agricultural crops world-wide and is considered to be an economically important pest. Little is known about the digestive enzymes such as serine proteases (SPs) in B. dorsalis, which are important both for energy supply and mitigation of fitness cost associated with insecticide tolerance. In this study, we identified five SP genes in the midgut of B. dorsalis, and the alignments of their deduced amino acid sequences revealed the presence of motifs conserved in the SP superfamily. Phylogenetic analyses with known SPs from other insect species suggested that three of them were trypsin-like proteases. Analyses of the expression profiles among the different developmental stages showed that all five genes were most abundant in larvae than in other stages. When larvae were continuously fed on diet containing 0.33 μg/g β-Cypermethrin, expression of all five genes were upregulated in the midgut but the larval development was delayed. Biochemical assays were consistent with the increased protease activity exhibited by SPs in the midgut after treatment with β-Cypermethrin. Taken together, these findings provide evidence for the hypothesis that enhanced SP activity may play an indirect role in relieving the toxicity stress of insecticide in B. dorsalis.

Nutritional performance and activity of some digestive enzymes of the cotton bollworm, Helicoverpa armigera, in response to seven tested bean cultivars

Nutritional performance and activity of some digestive enzymes (protease and α-amylase) of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) in response to feeding on bean (Phaseolus vulgaris L. (Fabales: Fabaceae)) cultivars (Shokufa, Akhtar, Sayyad, Naz, Pak, Daneshkadeh, and Talash) were evaluated under laboratory conditions (25 ± 1°C, 65 ± 5% RH, and a 16:8 L:D photoperiod). The highest and lowest respective values of approximate digestibility were observed when fourth, fifth, and sixth larval instar H. armigera were fed red kidney bean Akhtar and white kidney bean Daneshkadeh. The efficiency of conversion of ingested and digested food was highest when H. armigera was fed red kidney beans Akhtar and Naz and lowest when they were fed white kidney bean Pak. The highest protease activity of fifth instars was observed when they were fed red kidney bean Naz, and the highest amylase activity of fifth instars was observed when they were fed red kidney bean Sayyad. Sixth instar larvae that fed on red kidney bean Sayyad showed the highest protease activity. Larvae reared on common bean Talash and white kidney bean Pak showed the highest amylase activity. Among bean cultivars tested, red kidney bean Sayyad was the most unsuitable host for feeding H. armigera.

A trypsin-like proteinase in the midgut of Ectomyelois ceratoniae Zeller (Lepidoptera: Pyralidae): purification, characterization, and host plant inhibitors

A trypsin-like proteinase was purified and characterized in the midgut of Ectomyelois ceratoniae. A purification process that used Sepharyl G-100 and DEAE-cellulose fast flow chromatographies revealed a proteinase with specific activity of 66.7 μmol/min/mg protein, recovery of 27.04 and purification fold of 23.35. Molecular weight of the purified protein was found to be 35.8 kDa. Optimal pH and temperature were obtained 9 and 20°C for the purified trypsin proteinase, respectively. The purified enzyme was significantly inhibited by PMSF, TLCK, and SBTI as specific inhibitors of trypsins in which TLCK showed the highest inhibitory effect. Trypsin proteinase inhibitors were extracted from four varieties of pomegranate including Brait, Torsh-Sabz, May-Khosh, and Shirin by ion exchange chromatography. It was found that fractions 17-20 of Brait; fractions 18 and 21-26 of Torsh-Sabz; fractions 1-7, 11-17, and 19-21 of May-Khosh and fraction 8 for Shirin showed presence of trypsin inhibitor in these host. Comparison of their inhibitory effects on the purified trypsin proteinase of E. ceratoniae demonstrated that fractions from May-khosh variety had the highest effect on the enzyme among other extracted fractions. Characterization of serine proteinases of insects mainly trypsins is one of the promising methods to decrease population and damages via extracting their inhibitors and providing resistant varieties.

Digestive proteolytic and amylolytic activities and feeding responses of Helicoverpa armigera (Lepidoptera: Noctuidae) on different host plants

Digestive proteolytic and amylolytic activities and feeding responses of fifth instar larvae of Helicoverpa armigera (Hübner) on different host plants including chickpea (cultivars Arman, Hashem, Azad, and Binivich), common bean (cultivar Khomein), white kidney bean (cultivar Dehghan), red kidney bean (cultivar Goli), cowpea (cultivar Mashhad), tomato (cultivar Meshkin), and potato (cultivars Agria and Satina) were studied under laboratory conditions (25 +/- 1 degrees C, 65 +/- 5% RH and a photoperiod of 16:8 [L:D] h). Our results showed that the highest protease activity in optimal pH was on cultivar Dehghan (8.717 U/mg) and lowest one was on Meshkin (3.338 U/mg). In addition, the highest amylase activity in optimal pH was on cultivar Dehghan (0.340 mU/mg) and lowest was on Meshkin (0.088 mU/mg). The larval weight of fifth instar H. armigera showed significant difference, being heaviest on Binivich (125.290 +/- 5.050 mg) and lightest on Meshkin (22.773 +/- 0.575 mg). Furthermore, the highest and lowest values of food consumed were on Goli (362.800 +/- 27.500 mg) and Satina (51.280 +/- 4.500 mg), respectively. In addition, the lowest values of prepupal and pupal weight were on Meshkin (32.413 +/- 0.980 and 41.820 +/- 1.270 mg, respectively). The results indicated that tomato (Meshkin) was unsuitable host for feeding fifth instar larvae of H. armigera.

Larval midgut modifications associated with Bti resistance in the yellow fever mosquito using proteomic and transcriptomic approaches

BACKGROUND

Bacillus thuringiensis var. israelensis (Bti) is a natural larval mosquito pathogen producing pore-forming toxins targeting the midgut of Diptera larvae. It is used worldwide for mosquito control. Resistance mechanisms of an Aedes aegypti laboratory strain selected for 30 generations with field-collected leaf litter containing Bti toxins were investigated in larval midguts at two levels: 1. gene transcription using DNA microarray and RT-qPCR and 2. differential expression of brush border membrane proteins using DIGE (Differential In Gel Electrophoresis).

RESULTS

Several Bti Cry toxin receptors including alkaline phosphatases and N-aminopeptidases and toxin-binding V-ATPases exhibited altered expression levels in the resistant strain. The under-expression of putative Bti-receptors is consistent with Bt-resistance mechanisms previously described in Lepidoptera. Four soluble metalloproteinases were found under-transcribed together with a drastic decrease of metalloproteinases activity in the resistant strain, suggesting a role in resistance by decreasing the amount of activated Cry toxins in the larval midgut.

CONCLUSIONS

By combining transcriptomic and proteomic approaches, we detected expression changes at nearly each step of the ingestion-to-infection process, providing a short list of genes and proteins potentially involved in Bti-resistance whose implication needs to be validated. Collectively, these results open the way to further functional analyses to better characterize Bti-resistance mechanisms in mosquitoes.

Digestive proteolytic and amylolytic activities of Helicoverpa armigera in response to feeding on different soybean cultivars

BACKGROUND

Digestive proteolytic and amylolytic activities of the larvae of Helicoverpa armigera (Hübner) fed either on artificial diet or on different soybean cultivars (356, M4, M7, M9, Clark, Sahar, JK, BP, Williams, L17, Zane, Gorgan3 and DPX) and response of the larvae to feeding on some soybean-based protease inhibitors were studied.

RESULTS

The highest general and specific proteolytic activities were in artificial-diet-fed larvae. Although the highest general proteolytic activity was in the larvae fed on L17, M4 and Sahar cultivars, the lowest tryptic activity was on L17 and Sahar, which may be due to the presence of some serine protease inhibitors in these two cultivars, resulting in hyperproduction of chymotrypsin- and elastase-like enzymes in response to the inhibition of these enzymes. The highest amylolytic activity was on M4, and the lowest was on Williams and DPX. General proteolytic activity of SKTI-fed larvae was the highest compared with SBBI- and STI-fed larvae.

CONCLUSION

The findings demonstrated that the cultivars L17 and Sahar were partially resistant to this pest, probably because of some secondary chemicals or proteinaceous protease inhibitors of these cultivars.