Interaction of salivary and midgut proteins of Helicoverpa armigera with soybean trypsin inhibitor

Design, Synthesis of Dienthiazole Derivatives, and Evaluation of Aphicidal Activity

Nitrogen-containing heterocycles have attracted attention for the development of chemicals because of their many types, high physiological activities, and ease of synthesis. Aphids are severe pests found worldwide that cause serious losses in crop yield and quality every year. In this study, a series of novel dienolone thiazole derivatives were synthesized using dienolone acetate as the parent molecule. The synthesis involved bromination, Hantzsch reaction, esterification, deprotection, and other reactions. The structure of the compounds was determined using proton and carbon-13 nuclear magnetic resonance, high-resolution mass spectrometry, and single-crystal diffraction. The synthesized compounds exhibited excellent insecticidal activities against five species of aphids, including Schizaphis graminum, Brevicoryne brassicae, Aphis gossypii, Aphis citricola Van der, and Myzus persicae. The median lethal concentration values of the compound H-13 for S. graminum, B. brassicae, A. gossypii, A. citricola Van der, and M. persicae were 8.72, 13.77, 14.17, 12.96, and 12.35 μg/mL, respectively. The mode of action test results indicated that compound H-13 had superior contact and systemic activity against M. persicae, similar to the positive control flonicamid. Furthermore, a field trial showed that the control effect of compound H-13 at 100 μg/mL concentration was comparable to that of flonicamid against M. persicae. The mortality was 85.6% and 90.3% after 7 and 14 days, respectively. Finally, to further explore the action mechanism of these compounds, the insecticidal activity of compounds H-13 (strong) and H-24 (weak) on aphid protease was determined. Compound H-13 was found to have a significant inhibitory effect on the strong alkaline tryptase activity. Compound H-13 might cause aphid poisoning and death by inhibiting the trypsin activity. This study provided important insights for the discovery and development of new insecticides.

Allelochemical Interactions in the Trophic System «Henosepilachna vigintioctomaculata Motschulsky-Solanum tuberosum Linneus»

Henosepilachna vigintioctomaculata is an intrinsic element in the agroecosystem of potato fields. The issues of relationships in the system "potato ladybird beetle-potato plant" have not yet been studied. To study the effect of potato varieties on the potato ladybird beetle, only hatched and active larvae with a hatching rate close to 100% were selected from a laboratory colony. Larvae of the first summer generation collected in potato fields were used in our study to determine the level of adrenaline in the bodies of insects, fresh potato leaves were used to study the content of glycoalkaloids, the content and activity of proteinase inhibitors. The larvae that fed on plants of varieties Belmonda, Queen Anne, Lilly, Dachny, Kazachok, Yubilyar, and Avgustin demonstrated the highest level of stress while the stress level in those that fed on variety Smak was the lowest. The damage inflicted by potato ladybird beetles on leaves of some studied potato varieties led to a progressive increase in the content of glycoalkaloids already within 24 h after the phytophages had been transferred. In most cases, the content of glycoalkoloids increased by 20% within five days. Potato ladybird beetles feeding on plants of different potato varieties caused a progressive increase in proteinase inhibitors (% of the control). Plants of variety Smak did not show a significant increase in the content of alkaloids in the herbage in response to the damage. A correlation was established between the mortality rate, the activity of proteinase inhibitors, the dynamics of glycoalkaloids, and the level of adrenaline, which could be formulated as follows: the higher the content of glycoalkaloids and the activity of proteinase inhibitors in the tissues of potato plants, the higher the level of stress in the potato ladybird beetles that feed on them.

Inhibitory Effect of Protease Inhibitors on Larval Midgut Protease Activities and the Performance of Plutella xylostella (Lepidoptera: Plutellidae)

Plutella xylostella L. (diamondback moth) is a pest of cruciferous plants. To understand the relationship among protease inhibitors, protease activities and the growth and development of this insect, the activities of midgut proteases of P. xylostella larvae were determined in this study. Protease samples were extracted from the midguts of P. xylostella larvae, and the protease activities were determined using enzyme specific substrates. The results showed that CaCl₂, EDTA, and EGTA inhibited only the trypsin. Among the common protease inhibitors, phenylmethyl sulfonyl fluorine (PMSF), Nα-p-methyl sulfonyl-L-lysine chloromethylketone (TLCK), Nα-methyl sulfonyl-L- phenylalanine chloromethyl ketone (TPCK), soybean trypsin inhibitor (STI), and PMSF inhibited the total protease, high-alkaline trypsin (a trypsin subtype with highly alkaline pH optimum), low-alkaline trypsin (another trypsin subtype with slightly alkaline pH optimum), and chymotrypsin; TLCK inhibited the total protease and high-alkaline trypsin, whereas TPCK only activated the high-alkaline trypsin activities. STI had an inhibitory effect on all the proteases. These results showed that protease inhibitors had a certain extent inhibition to protease activities in the larval midgut of P. xylostella and that STI can potentially be used for effective pest control. The development of P. xylostella was delayed in the presence of different inhibitors. These effects were also related to the concentration of the inhibitor. A higher STI concentration showed a longer lasting effect but lower effect in this study compared to that of TLCK. The protease inhibitors had some inhibitory effect on the synthesis and secretion of proteases, and interfered with the protease activity, thereby inhibiting the absorption of nutrients and delaying the growth and development of P. xylostella and reducing their ability to reproduce. These findings should provide the baseline information about using for effective pest management in the future.

Molecular Mechanism Underlying the Entomotoxic Effect of Colocasia esculenta Tuber Agglutinin against Dysdercus cingulatus

Colocasia esculenta tuber agglutinin (CEA), a mannose binding lectin, exhibits insecticidal efficacy against different hemipteran pests. Dysdercus cingulatus, red cotton bug (RCB), has also shown significant susceptibility to CEA intoxication. However, the molecular basis behind such entomotoxicity of CEA has not been addressed adequately. The present study elucidates the mechanism of insecticidal efficacy of CEA against RCB. Confocal and scanning electron microscopic analyses documented CEA binding to insect midgut tissue, resulting in an alteration of perimicrovillar membrane (PMM) morphology. Internalization of CEA into insect haemolymph and ovary was documented by western blotting analyses. Ligand blot followed by mass spectrometric identification revealed the cognate binding partners of CEA as actin, ATPase and cytochrome P450. Deglycosylation and mannose inhibition assays indicated the interaction to probably be mannose mediated. Bioinformatic identification of putative glycosylation or mannosylation sites in the binding partners further supports the sugar mediated interaction. Correlating entomotoxicity of CEA with immune histological and binding assays to the insect gut contributes to a better understanding of the insecticidal potential of CEA and endorses its future biotechnological application.

Differential peroxidase activities in three different crops upon insect feeding

Peroxidases are the ubiquitous enzyme and reported to be present in all living genera. They catalyses reduction of peroxide and generate reactive oxygen species. In the present study we demonstrated that insect infestation induces peroxidase activity in sap and total soluble protein (TSP) of plant leaves. Three important crop plants viz. tomato, cowpea and cotton were used for this study. After infestation of chewing insect, Peroxidase activity in the sap and TSP of all the studied plants were enhanced in the range of 1.6 to 3.14 fold. Similar observations were also obtained with feeding of sap sucking insects, in which increment in peroxidase activity of sap and TSP was in the range of 1.8 to 2.53 fold. Enhanced peroxidase activity was reconfirmed by in-gel peroxidase assay. Enzyme kinetic study showed turn over efficiency of peroxidase from cotton (~101.3 min(-1)) was almost similar to tomato (~100.8 min(-1)) but higher than cowpea (~98.21 in(-1)). MS/MS analysis of observed band showed significant similarity with the reported peroxidases in database.