Diflubenzuron stimulates phosphorylation of a 39 kDa integumental protein from newly molted American cockroach (Periplaneta americana)

Chitin is a component of the Rhodnius prolixus midgut

Chitin is an essential component of the peritrophic matrix (PM), which is a structure that lines the insect's gut and protects against mechanical damage and pathogens. Rhodnius prolixus (Hemiptera: Reduviidae) does not have a PM, but it has an analogous structure, the perimicrovillar membrane (PMM); chitin has not been described in this structure. Here, we show that chitin is present in the R. prolixus midgut using several techniques. The FTIR spectrum of the KOH-resistant putative chitin-material extracted from the midgut bolus showed peaks characteristic of the chitin molecule at 3500, 1675 and 1085 cm(1). Both the midgut bolus material and the standard chitin NMR spectra showed a peak at 1.88 ppm, which is certainly due to methyl protons in the acetamide a group. The percentages of radioactive N-acetylglucosamine (CPM) incorporated were 2 and 4% for the entire intestine and bolus, respectively. The KOH-resistant putative chitin-material was also extracted and purified from the N-acetylglucosamine radioactive bolus, and the radioactivity was estimated through liquid scintillation. The intestinal CHS cDNA translated sequence was the same as previously described for the R. prolixus cuticle and ovaries. Phenotypic alterations were observed in the midgut of females with a silenced CHS gene after a blood meal, such as retarded blood meal digestion; the presence of fresh blood that remained red nine days after the blood meal; and reduced trachea and hemozoin content compared with the control. Wheat germ agglutinin (a specific probe that detects chitin) labeling proximal to the intestine (crop and midgut) was much lower in females with a silenced CHS gene, especially in the midgut region, where almost no fluorescence signal was detected compared with the control groups. Midguts from females with a CHS gene silenced by dsRNA-CHS and control midguts pre-treated with chitinase showed that the chitin-derived fluorescence signal decreased in the region around the epithelium, the region facing the midgut and projections towards the intestinal lumen when evaluated microscopically. The relative reduction in CHS transcripts by approximately 80% using an RNAi assay supports the phenotypical alterations in the midgut observed using fluorescence microscopy assays. These data show that chitin is present in the R. prolixus midgut epithelium and in its surface projections facing the lumen. The CHS gene expression and the presence of chitin in the R. prolixus midgut may suggest a target for controlling Chagas disease vectors and addressing this public health problem.

Benzoylurea Chitin Synthesis Inhibitors

Benzoylurea chitin synthesis inhibitors are widely used in integrated pest management (IPM) and insecticide resistance management (IRM) programs due to their low toxicity to mammals and predatory insects. In the past decades, a large number of benzoylurea derivatives have been synthesized, and 15 benzoylurea chitin synthesis inhibitors have been commercialized. This review focuses on the history of commercial benzolyphenylureas (BPUs), synthetic methods, structure-activity relationships (SAR), action mechanism research, environmental behaviors, and ecotoxicology. Furthermore, their disadvantages of high risk to aquatic invertebrates and crustaceans are pointed out. Finally, we propose that the para-substituents at anilide of benzoylphenylureas should be the functional groups, and bipartite model BPU analogues are discussed in an attempt to provide new insight for future development of BPUs.

Effects of sublethal concentrations of the chitin synthesis inhibitor, hexaflumuron, on the development and hemolymph physiology of the cutworm, Spodoptera litura

The effects of sublethal concentrations 0.1, 0.5, and 1.2 µg mL(-1)of the chitin synthesis inhibitor, hexaflumuron, on larval growth and development, the count and proportion of hemocytes, and carbohydrate content (trehalose and glyceride) in hemolymph were investigated in the cutworm, Spodoptera litura (Fabricious) (Lepidoptera: Noctuidae). When 3(rd) instar larvae were subjected to the sublethal concentrations, there were dose-dependent effects on larval weight and length of each instar larvae, percent pupation and the duration of development. Most of the larvae died during the molting process at all concentrations. Few individuals from 0.5 and 1.2 µg mL(-1)concentrations could develop to the 6(th) instar, while the pupae emerging from the 0.1 µg mL(-1)concentrations did not exceed 16% of the number of the initial larvae. In 5(th)instar S. litura, the total number of hemocytes was significantly increased at 24 hours post-treatment, whereas the proliferation of hemocytes was inhibited, plasmatocyte pseudopodia contracted, and granulocyte expanded at 96 hours post-treatment. The increases of plasmatocyte count and the decreases of granulocyte count were dose-dependent. The longer treatment time of the sublethal concentrations increased the content of total carbohydrate and trehalose in hematoplasma, and was dose-dependent in hemocytes. The content of glyceride in hemolymph was significantly higher at 24 hours post-treatment, but gradually returned to normal levels at 96 hours post-treatment as compared with the control. The results suggested that sublethal concentrations of hexaflumuron reduced S. litura larval survival and interfered with hemolymph physiological balances.

3-D QSAR analysis of inhibition of murine soluble epoxide hydrolase (MsEH) by benzoylureas, arylureas, and their analogues

Two hundred and seventy-one compounds including benzoylureas, arylureas and related compounds were assayed using recombinant murine soluble epoxide hydrolase (MsEH) produced from a baculovirus expression system. Among all the insect growth regulators assayed, 18 benzoylphenylurea congeners showed weak activity against MsEH. Newly synthesized cyclohexylphenylurea, 1-benzyl-3-phenylurea, and 1,3-dibenzylurea analogues were rather potent. The introduction of a methyl group at the para-position of the phenyl ring of cyclohexylphenylurea enhanced the activity 6-fold, though similar substituent effects were not seen for any of the benzoylphenylureas. The activities of these compounds, including several previously reported compounds, such as dicyclohexylurea, diphenylurea, and their related analogues (Morisseau et al., Proc. Natl. Acad. Sci., 1999, 96, 8849), were quantitatively analyzed using comparative molecular field analysis (CoMFA), a three-dimensional quantitative structure-activity relationship (3-D QSAR) method. Both steric and electrostatic factors contributing to variations in the activity were visualized using CoMFA. CoMFA results showed that one side of the cyclohexylurea moiety having a trans-amide conformation (A-ring moiety) is surrounded by large sterically unfavorable fields, while the other side of A-ring moiety and the other cyclohexyl group (B-ring moiety) is encompassed by sterically favored fields. Electrostatically negative fields were scattered around the entire molecule, and a positive field surrounds the carbon of the carbonyl group. Hydrophobic fields were visualized using Kellogg's hydropathic interaction (HINT) in conjunction with CoMFA. Hydrophobically favorable fields appeared beside the 4- and 4'-carbon atoms of the cyclohexyl groups, and hydrophobically unfavorable fields surrounded the urea bridge. The addition of the molecular hydrophobicity, log P [corrected], to CoMFA did not improve the correlation significantly. The ligand-binding interactions shown by X-ray crystallographic data were rationalized using the results of the CoMFA and HINT analyses, and the essential physicochemical parameters for the design of new MsEH inhibitors were disclosed.