Insecticidal activity of extracts of handroanthus impetiginosus on Plutella xylostella (Lepidoptera: plutellidae) larvae

Plutella xylostella is considered the main pest of cabbage in Brazil and the world, causing damage of up to 100%. Thus, this study evaluated the insecticidal activity of extracts obtained from the fruits, seeds, bark, leaves, and flowers of Handroanthus impetiginosus against the diamondback moth, P. xylostella larvae. The seed extract showed the highest mortality (97.0%) compared to the control treatment. The LC50 values indicated that the seed and flower extracts (0.01003 and 0.01288 mg/L respectively) assumed the highest toxicity to P. xylostella larvae after 24 h of exposure. The results of this study indicated that the seeds extract is the most promising toxic extract, with measured mortality of approximately 97.0% for P. xylostella larvae after 144 h of exposure in kale plants. Seed extract showed the best insecticidal activity. Thus, this extract can be applied to develop an insecticide based on H. impetiginosus seed.

Lytic Polysaccharide Monooxygenase Activity of Tma12 Is Critical for Its Toxicity to Whitefly

Lytic polysaccharide monooxygenases (LPMOs) are powerful redox enzymes that transform complex carbohydrates through oxidation and make them suitable for saccharification by canonical hydrolases. Due to this property, LPMOs are considered to be a valuable component of enzymatic consortia for industrial biorefineries. Tma12 is a fern entomotoxic protein that kills whitefly and has structural similarities with chitinolytic LPMO. However, its enzymatic activity is poorly understood. Studying the role of the LPMO-like activity in the insecticidal function of Tma12 can be of considerable importance. Our results show that Tma12 preferentially binds and digests β-chitin. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis shows that the digestion of chitin produces chitin oligosaccharides of various lengths (DP2-DP7). The Michaelis constant (km) and catalytic constant (kcat) for hydrocoerulignone are 0.022 mM and 0.044 s-1, respectively. The attenuation of catalytic activity through diethylpyrocarbonate modification abolishes the insecticidal activity of the protein. Our findings reveal that (a) Tma12 is an active LPMO and (b) LPMO activity is indispensable for its function as a bioinsecticide.

Design, Synthesis, and Insecticidal Evaluation of N-Pyridylpyrazole Amide Derivatives Containing 4,5-Dihydroisoxazole Amide as Potential Ryanodine Receptor Activators

Using the 4,5-dihydroisoxazol amide structure to expand the aliphatic amide moiety of chlorantraniliprole, a series of 28 novel N-pyridylpyrazolecarboxamide derivatives containing 4,5-dihydroisoxazol amide fragment were designed and synthesized. All target compounds had been properly characterized and confirmed by 1H NMR, 13C NMR, and HRMS, and the effects were evaluated against Mythimna separata (M. separata) and Plutella xylostella (P. xylostella). The bioassay results indicated that most of the target compounds exhibited good insecticidal activities against M. separata and P. xylostella at 50 mg/L; especially, compound A4 showed an LC50 value of 3.27 mg/L against M. separata. Calcium imaging experiments indicated that the target compound A4 had a similar mechanism of action to chlorantraniliprole, causing an increase in the cytoplasmic Ca2+ concentration. The molecular docking revealed the possible binding mode of compound A4 with a ryanodine receptor.

Structural modification of (3E)-4,8-dimethyl-1,3,7-nontriene enhances its ability to kill Plutella xylostella insect pests

BACKGROUND

Plant secondary metabolites and their modified derivatives play an important role in the discovery and development of novel insecticides. The natural plant product (3E)-4,8-dimethyl-1,3,7-nontriene (DMNT) has been proven to be able to effectively repel and kill the lepidopteran insect pest Plutella xylostella.

RESULTS

In this study, four oxygenated derivatives of DMNT were synthesized by allylic hydroxylation and subsequent etherification or esterification. Bioassays on P. xylostella larvae showed that the compounds DMNT-OCH3 (2), DMNT-OCy (3) and DMNT-OAc (4) were more toxic to the larvae than DMNT alone. The most pronounced effect was observed for compound 2, which showed a 22.23% increase in lethality at a concentration of 0.25 μm. Moreover, the peritrophic matrix (PM) barrier in the insect midgut was more severely damaged by compounds 2, 3 and 4 than by DMNT. The median lethal concentration (LC50 , 48 h) of compounds 2, 3 and 4 on P. xylostella was determined to be 0.98, 1.13 and 1.11 mg mL-1 , respectively, which is much lower than the commercial insecticides eucalyptol (2.89 mg mL-1 ) and thymol (2.45 mg mL-1 ).

CONCLUSION

These results suggested that oxygenated DMNT derivatives offer a significantly improved killing effect over DMNT on P. xylostella. This work has provided a basis for further design, structural modification and development of DMNT as botanical insecticides. © 2023 Society of Chemical Industry.

Synergism in Two-Component Insecticides with Dillapiole against Fall Armyworm

The fall armyworm (Spodoptera frugiperda), a polyphagous insect pest, is a major threat to food production, rapidly spreading through all the tropical areas in the world. Resistance has developed to the control protocols used so far (pyrethroids, organophosphorus, and genetically modified plants), and alternative strategies must be found. The bioactivity in essential oils is usually associated with the major constituents, but synergistic interactions among the constituents (even minor ones) can improve the levels of activity considerably. Herein, we tested the insecticidal activity of several constituents of the essential oil from Piper aduncum, an Amazonian Piperaceae, both separately and as binary mixtures, through their application on the dorsal side of the larva pronotum. Dillapiole proved to be, isolated, the most active compound in this oil (LD50 = 0.35 ppm). In binary mixtures, a strong synergistic effect was observed for the pairs of dillapiole with β-caryophyllene (LD50 = 0.03 ppm), methyl eugenol (LD50 = 0.05 ppm), and α-humulene (LD50 = 0.05 ppm). In some cases, however, antagonism was recorded, as for dillapiole + β-pinene (LD50 = 0.44 ppm). The use of binary mixtures of essential oil constituents as low-environmental-toxicity insecticides allows a fine tuning of the insecticidal activity, and the exploitation of synergy effects.

Mediterranean Plants as Potential Source of Biopesticides: An Overview of Current Research and Future Trends

The development and implementation of safe natural alternatives to synthetic pesticides are urgent needs that will provide ecological solutions for the control of plant diseases, bacteria, viruses, nematodes, pests, and weeds to ensure the economic stability of farmers and food security, as well as protection of the environment and human health. Unambiguously, production of botanical pesticides will allow for the sustainable and efficient use of natural resources and finally decrease the use of chemical inputs and burden. This is further underlined by the strict regulations on pesticide residues in agricultural products and is in harmony with the Farm to Fork strategy, which aims to reduce pesticide use by 50% by 2030. Thus, the present work aims to compile the scientific knowledge of the last 5 years (2017-February 2023) regarding the Mediterranean plants that present biopesticidal effects. The literature review revealed 40 families of Mediterranean plants with at least one species that have been investigated as potential biopesticides. However, only six families had the highest number of species, and they were reviewed comprehensively in this study. Following a systematic approach, the extraction methods, chemical composition, biopesticidal activity, and commonly used assays for evaluating the antimicrobial, pesticidal, repellant, and herbicidal activity of plant extracts, as well as the toxicological and safety aspects of biopesticide formulation, are discussed in detail. Finally, the aspects that have not yet been investigated or are under-investigated and future perspectives are highlighted.

Potential insecticidal extracts from Artocarpus lacucha against Spodoptera litura (Lepidoptera: Noctuidae) larvae

Artocarpus lacucha, a plant in the Moraceae family, has traditionally been used in Southeast Asian medicine to treat various ailments. This study investigated the insecticidal potential against Spodoptera litura of several compounds extracted from A. lacucha using a topical application method. A sequential extraction method was employed with A. lacucha stems to identify the most toxic crude extract by using hexane, dichloromethane, ethyl acetate, and methanol solvents. Subsequently, the most toxic crude extract was analyzed for chemical composition by HPLC, followed by the isolation process. Among these crude extracts, the ethyl acetate crude extract was the most toxic to second-instar S. litura larvae (24-h LD50 value of ~9.07 µg/larva). Our results showed that the catechin isolated from the ethyl acetate crude extract exhibited the highest toxicity against this insect (24-h LD50 value of ~8.37 µg/larva). Additionally, catechin significantly decreased the activities of acetylcholinesterase, carboxylesterases, and glutathione S-transferase in the larvae. These findings suggest that catechin isolated from A. lacucha could be a potential insecticidal agent against S. litura. However, the toxicity and persistence of catechin under field conditions need to be further investigated to develop this novel insecticide.

A review of extraction and quantification of capsaicin and its bio insecticidal activity in food grains

Chili peppers pungent and spicy flavor is caused by capsaicin, which is one of their active components. As well as being an important aspect of fruit quality, the hot sensation is a key attribute linked to members of the Capsicum genus. Extraction is one of the most popular techniques for separating and purifying organic materials, but the technique must be quick, affordable, adaptable, efficient, and high performing. This review formulates the extraction of Capsaicin from chili peppers. The extraction methods used were solvent extraction (SE), ultrasound assisted extraction (UAE), microwave assisted extraction (MAE), enzymatic treatment, supercritical fluid extraction (SFE), solid phase microextraction (SPME), aqueous two phase system (ATPS) and liquid under pressure (PLE). The content of capsaicin in the extract was evaluated by using Thin Layer Chromatography (TLC), Fourier Transform Infrared Spectroscopy (FTIR) and High performance Liquid Chromatography (HPLC). The insecticidal activity of capsaicin in storage insects in food grains for shelf life enhancement and bio availability of capsaicinoids in terms of absorption, distribution, metabolism, and elimination were also discussed.

Bruceine D Acts as a Potential Insecticide by Antagonizing 20E-EcR/USP Signal Transduction

Bruceine D (BD) is an effective insecticidal compound found in the Chinese herb Brucea javanica (L.) Merr. BD inhibits the growth and metamorphosis of Plutella xylostella and Drosophila melanogaster; however, its target protein and the molecular mechanism of insecticidal activity remain unclear. In this study, proteins with high affinity for BD were screened using surface plasmon resonance and high-performance liquid chromatography coupled with matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, revealing the ecdysone receptor (EcR) is the main target of BD. In vivo results showed that BD inhibited insect growth and metamorphosis through inhibition of the expression of 20E response genes. In vitro dual luciferase and enhanced green fluorescent protein (EGFP) fluorescence experiments indicated that BD suppressed the transcriptional activation activity of EcR by blocking the ecdysone response element (EcRE)-triggered transcriptional cascade, suggesting that BD inhibits the formation of the 20E-EcR-USP-EcRE complex. Moreover, molecular docking demonstrated that BD bound well to EcR. Elucidating the insecticidal mechanism of BD will be helpful in the development of green pesticides to control pests.

Design, Synthesis, and Biological Activities of Novel Phenylpyrazole Derivatives Containing a Trifluoromethylselenyl Moiety

Phenylpyrazole insecticides are widely used for crop protection and public sanitation by blocking gamma-aminobutyric acid (GABA)-gated chloride channels and glutamate-gated chloride (GluCl) channels. Herein, 36 novel phenylpyrazole derivatives containing a trifluoromethylselenyl moiety were designed and synthesized based on the strategy of introducing a selenium element. All derivative structures were characterized by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). The insecticidal activity results indicated that some derivatives had good insecticidal activities against Aedes albopictus (A. albopictus) and Plutella xylostella (P. xylostella). The larvicidal activity against mosquitos of compounds 5, 5a, 5k, and 5l at 0.5 mg/L was 60-80%. At a concentration of 500 mg/L, compounds 5, 5a, 5h, 5k, 5l, 5r, 6, 6j, 6k, and 7 showed a 70-100% mortality against P. xylostella. Among them, derivatives 5 and 6 had a better insecticidal effect with mortality rates of 87 and 93% at 50 mg/L, respectively. It was summarized that the different binding poses of fipronil and compounds 5 and 6 in the Musca domestica (M. domestica) GABARs might lead to the disparity in bioactivity from docking studies. Toxicity tests on zebrafish suggested that compound 6 may be slightly less toxic to the embryos than fipronil on hatching rate.

Synthesis, Bioactivity and Molecular Docking of Nereistoxin Derivatives Containing Phosphonate

Novel nereistoxin derivatives containing phosphonate were synthesized and characterized via ³¹P, ¹H and ¹³C NMR and HRMS. The anticholinesterase activity of the synthesized compounds was evaluated on human acetylcholinesterase (AChE) using the in vitro Ellman method. Most of the compounds exhibited good inhibition of acetylcholinesterase. All of these compounds were selected to assess their insecticidal activity (in vivo) against Mythimna separata Walker, Myzus persicae Sulzer and Rhopalosiphum padi. Most of the tested compounds displayed potent insecticidal activity against these three species. Compound 7f displayed good activity against all three insect species, showing LC₅₀ values of 136.86 μg/mL for M. separata, 138.37 μg/mL for M. persicae and 131.64 μg/mL for R. padi. Compound 7b had the highest activity against M. persicae and R. padi, with LC₅₀ values of 42.93 μg/mL and 58.19 μg/mL, respectively. Docking studies were performed to speculate the possible binding sites of the compounds and explain the reasons for the activity of the compounds. The results showed that the compounds had lower binding energies with AChE than with the acetylcholine receptor (AchR), suggesting that compounds are more easily bound with AChE.

Design, Synthesis, and Biological Activity of Novel Benzo[d][1,3]dioxole-6-benzamide Derivatives: Multichitinase Inhibitors as Potential Insect Growth Regulator Candidates

Insect growth regulators (IGRs) disrupt normal development of physiological processes in insects and are recognized as green insecticides. Insect chitinases play a crucial role in cuticle degradation during molting, and OfChtI, OfChtII, and OfChi-h are the prospective targets for discovering new insecticides as IGRs. In our previous study, we identified the lead compound a12 as a promising multitarget inhibitor. Herein, we used the binding modes of a12 with three chitinases to recognize the critical interactions and residues favorable to the bioactivity. Subsequently, to improve the bioactivity of inhibitors via enhanced the interactions with important residues, a series of benzo[d][1,3]dioxole-6-benzamide derivatives were rationally designed and synthesized, and their inhibitory activities against Ostrinia furnacalis (O. furnacalis) chitinases, as well as insecticidal activities against O. furnacalis and Plutella xylostella (P. xylostella) were investigated. Among them, compound d29 acted simultaneously on OfChtI, OfChtII, and OfChi-h with K_i values of 0.8, 11.9, and 2.3 μM, respectively, a significant improvement over the inhibitory activity of the lead compound a12. Moreover, d29 exhibited superior activity than a12 against two lepidopteran pests by interfering with normal insect growth and molting, indicating that d29 is a potential lead candidate for novel IGRs with a multichitinase mechanism. The present study revealed that simultaneous inhibition on multiple chitinases could achieve excellent insecticidal activity. The elucidation of inhibition mechanisms and molecular conformations illustrated the interactions with the three chitinases, as well as the discrepancy in bioactivity, which will be beneficial for future work to improve the potency of bioactivity as IGRs for pest control in sustainable agriculture.

Design, Synthesis, and Insecticidal Activity of Mesoionic Pyrido[1,2-a]pyrimidinone Containing Isoxazole/Isoxazoline Moiety as a Potential Insecticide

Bean aphid (Aphis craccivora) resistance to commonly used insecticides has made controlling these pests increasingly difficult. In this study, we introduced isoxazole and isoxazoline, which possess insecticidal activity, into pyrido[1,2-a]pyrimidinone through a scaffold hopping strategy. We designed and synthesized a series of novel mesoionic compounds that exhibited a range of insecticidal activities against A. craccivora. The LC₅₀ values of compounds E1 and E2 were 0.73 and 0.88 μg/mL, respectively, better than triflumezopyrim (LC₅₀ = 2.43 μg/mL). Proteomics and molecular docking analyses showed that E1 might influence the A. craccivora nervous system by interacting with neuronal nicotinic acetylcholine receptors (nAChRs). This research offers a new approach to the advancement of novel mesoionic insecticides.

Design, Synthesis and Various Bioactivity of Acylhydrazone-Containing Matrine Analogues

Compounds with acylhydrazone fragments contain amide and imine groups that can act as electron donors and acceptors, so they are easier to bind to biological targets and thus generally exhibit significant biological activity. In this work, acylhydrazone fragments were introduced to the C-14 or C-11 position of matrine, a natural alkaloid, aiming to enhance their biological activities. The result of this bioassay showed that many synthesized compounds exhibited excellent anti-virus activity against the tobacco mosaic virus (TMV). Seventeen out of 25 14-acylhydrazone matrine derivatives and 17 out of 20 11-butanehydrazone matrine derivatives had a higher inhibitory activity against TMV than the commercial antiviral agent Ribavirin (the in vitro activity, in vivo inactivation, curative and protection activities at 500 µg/mL were 40.9, 36.5 ± 0.9, 38.0 ± 1.6 and 35.1 ± 2.2%, respectively), and four 11-butanehydrazone matrine derivatives even had similar to or higher activity than the most efficient antiviral agent Ningnanmycin (55.4, 57.8 ± 1.4, 55.3 ± 0.5 and 60.3 ± 1.2% at 500 µg/mL for the above four test modes). Among them, the N-benzyl-11-butanehydrazone of matrine formed with 4-bromoindole-3-carboxaldehyde exhibited the best anti-TMV activity (65.8, 71.8 ± 2.8, 66.8 ± 1.3 and 69.5 ± 3.1% at 500 µg/mL; 29, 33.5 ± 0.7, 24.1 ± 0.2 and 30.3 ± 0.6% at 100 µg/mL for the above four test modes), deserving further investigation as an antiviral agent. Other than these, the two series of acylhydrazone-containing matrine derivatives were evaluated for their insecticidal and fungicidal activities. Several compounds were found to have good insecticidal activities against diamondback moth (Plutella xylostella) and mosquito larvae (Culex pipiens pallens), showing broad biological activities.

Discovery of Novel Isoxazoline Derivatives Containing Diaryl Ether against Fall Armyworms

With the continuous evolution of insect resistance, it is a tremendous challenge to control the fall armyworm (Spodoptera frugiperda) with traditional insecticides. To solve this pending issue, a series of novel isoxazoline derivatives containing diaryl ether structures were designed and synthesized, and most of the target compounds exhibited excellent insecticidal activity. Based on the three-dimensional quantitative structure-activity relationship (3D-QSAR) model analysis, we further optimized the molecular structure with compound L35 obtained and tested for its activity. Compound L35 (LC₅₀ = 1.69 mg/L) exhibited excellent insecticidal activity against S. frugiperda, which was better than those of commercial fipronil (LC₅₀ = 70.78 mg/L) and indoxacarb (LC₅₀ = 5.37 mg/L). The enzyme-linked immunosorbent assay showed that L35 could upregulate the levels of GABA in insects. In addition, molecular docking and transcriptomic results also indicated that compound L35 may affect the nervous system of S. frugiperda by acting on GABA receptors. Notably, through high-performance liquid chromatography (HPLC), we were able to obtain the two enantiomers of compound L35, and the insecticidal activity test revealed that S-(+)-L35 was 44 times more active than R-(-)-L35 against S. frugiperda. This study established the chemistry basis and mechanistic foundations for the future development of pesticide candidates against fall armyworms.

Synthesis, insecticidal activity, and ensembled docking of nitroguanidines bearing S- and R-proline

BACKGROUND

The amino acids R- and S-proline were used to synthesize novel neonicotinoid derivatives that, after being characterized by ¹ H, DEPTQ 135, and HRMS-QTOF, were evaluated for use as insecticides against Galleria mellonella (caterpillar), Sitophilus zeamais, Xylosandrus morigerus, Xyleborus affinis, and Xyleborus ferrugineus.

RESULTS

Comparisons of biological activity and absolute configuration showed that the R enantiomer had excellent and outstanding insecticidal activity against the insects tested, with up to 100% mortality after 12 h compared with dinotefuran at the same concentration.

CONCLUSIONS

The results suggest that compound R6 is an excellent lead enantiopure insecticide for future development in the field of crop protection. Furthermore, intermolecular interactions between nicotinic acetylcholine receptors and the R enantiomer displays a lower score which mean a higher affinity to the nAChR receptor and the π-π interactions are more stable than the S derivative. © 2023 Society of Chemical Industry.

Preparation and Characterization of Insecticide/Calix[4]arene Complexes and Their Enhanced Insecticidal Activities against Plutella xylostella

Applications of supramolecular materials in plant protection have attracted significant interest in recent years. To develop a feasible method to improve the efficacy and reduce the usage of chemical pesticides, the effect of calix[4]arene (C4A) inclusion on enhancing the insecticidal activity of commercial insecticides was investigated. Results showed that all three tested insecticides (chlorfenapyr, indoxacarb, and abamectin) with distinct molecular sizes and modes of action were able to form stable 1:1 host-guest complexes with C4A through simple preparation steps. The insecticidal activities of the complexes against Plutella xylostella were effectively enhanced compared to the guest molecule, with the synergism ratio being up to 3.05 (for indoxacarb). An obvious correlation was found between the enhanced insecticidal activity and the high binding affinity between insecticide and C4A, while the improvement in water solubility may not be a determining factor. The work would provide hints for the further development of functional supramolecular hosts as synergists in pesticide formulations.

Discovery of Novel Isoxazoline Compounds that Incorporate a para-Diamide Moiety as Potential Insecticidal Agents against Fall Armyworm (Spodoptera frugiperda)

Spodoptera frugiperda is a major migratory agricultural pest, which seriously impedes agricultural production around the world. To discover potent compounds against S. frugiperda, a number of novel isoxazoline derivatives were designed and synthesized and created on account of the identified lead compound F32 (4-(5-(3,5-dichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)-2-methyl-N-(3-propionamidophenyl)benzamide). Based on the three-dimensional quantitative structure-activity relationship of those compounds, the compound G22 (N-(4-acetamidophenyl)-4-(5-(3,5-dichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)-2-methylbenzamide) was developed. A bioassay showed that G22 is highly lethal to S. frugiperda (LC₅₀ = 1.57 mg/L), a more effective control than insecticides fipronil (LC₅₀ = 78.8 mg/L) and chlorantraniliprole (LC₅₀ = 1.60 mg/L). Field trials were also implemented to identify candidate agents. Furthermore, from the insect γ-aminobutyric acid (GABA) enzyme-linked immunosorbent assay, it is obvious that G22 could up-regulate the expression of GABA of insects, which showed a similar result to fipronil. The analysis of molecular docking exhibited that the hydrophobic effect and hydrogen bonds play key roles in the combination between G22 with GABA receptors. This study provides a potent isoxazoline candidate compound for the S. frugiperda control.

Natural Products for Pesticides Discovery: Structural Diversity Derivation and Biological Activities of Naphthoquinones Plumbagin and Juglone

Plant diseases and insect pests seriously affect the yield and quality of crops and are difficult to control. Natural products are an important source for the discovery of new pesticides. In this work, naphthoquinones plumbagin and juglone were selected as parent structures, and a series of their derivatives were designed, synthesized and evaluated for their fungicidal activities, antiviral activities and insecticidal activities. We found that the naphthoquinones have broad-spectrum anti-fungal activities against 14 types of fungus for the first time. Some of the naphthoquinones showed higher fungicidal activities than pyrimethanil. Compounds I, I-1e and II-1a emerged as new anti-fungal lead compounds with excellent fungicidal activities (EC₅₀ values: 11.35-17.70 µg/mL) against Cercospora, arachidicola Hori. Some compounds also displayed good to excellent antiviral activities against the tobacco mosaic virus (TMV). Compounds I-1f and II-1f showed similar level of anti-TMV activities with ribavirin, and could be used as new antiviral candidates. These compound also exhibited good to excellent insecticidal activities. Compounds II-1d and III-1c displayed a similar level of insecticidal activities with matrine, hexaflumuron and rotenone against Plutella xylostella. In current study, plumbagin and juglone were discovered as parent structures, which lays a foundation for their application in plant protection.

Discovery of a Novel Class of Acylthiourea-Containing Isoxazoline Insecticides against Plutella xylostella

Isoxazoline structures are widely found in natural products and are rich in biological activities. This study discloses the development of a series of novel isoxazoline derivatives by introducing acylthiourea fragments to access insecticidal activity. All synthetic compounds were examined for their insecticidal activity against Plutella xylostella, with results showing moderate to strong activity. Based on this, the structure-activity relationship analysis was carried out via the constructed three-dimensional quantitative structure-activity relationship model to further guide the structure optimization, resulting in the optimal compound 32. The LC₅₀ of compound 32 against Plutella xylostella was 0.26 mg/L, demonstrating better activity than the positive control, ethiprole (LC₅₀ = 3.81 mg/L), avermectin (LC₅₀ = 12.32 mg/L), and compounds 1-31. The insect GABA enzyme-linked immunosorbent assay demonstrated that compound 32 might act on the insect GABA receptor, and the molecular docking assay further illustrated the mode of action of compound 32 with the GABA receptor. In addition, the proteomics analysis indicated that the action of compound 32 on Plutella xylostella was multi-pathway.

Design, Synthesis, and Insecticidal and Fungicidal Activities of Ether/Oxime-ether Containing Isoxazoline Derivatives

The existing agricultural insecticides have developed drug resistance from long-term use. Isoxazoline derivatives are new insecticides discovered in the 21st century. Because of their unique insecticidal mechanism, high selectivity, safety, and no significant cross resistance with the existing pesticides on the market, they have become a hot spot in the field of pesticide research. Herein, a series of novel isoxazoline derivatives containing ether and oxime-ether structures were designed and synthesized by a scaffold-hopping strategy using the pesticide fluralaner as a template structure. Through the investigation of insecticidal activity and the systematic structure-activity relationship, a series of compounds with high insecticidal activities were found, and compounds I-4, II-9, and II-13 with LC₅₀ values of 0.00008-0.00036 mg/L against diamondback moth emerged as novel insecticide candidates. These compounds also exhibited broad spectrum fungicidal activities against 14 plant fungi. The current work provides a reference for the design of new isoxazoline compounds based on the scaffold-hopping strategy.

The insecticidal activity and mechanism of tebuconazole on Nilaparvata lugens (Stål)

BACKGROUND

Previous studies have shown that fungicides have insecticidal activity that can potentially be used as an insecticide resistance management strategy in the brown planthopper Nilaparvata lugens (Stål). However, the mechanism that induces mortality of N. lugens remains elusive.

RESULTS

In the present study, the insecticidal activities of 14 fungicides against N. lugens were determined, of which tebuconazole had the highest insecticidal activity compared with the other fungicides. Furthermore, tebuconazole significantly inhibited the expression of the chitin synthase gene NlCHS1; the chitinase genes NlCht1, NlCht5, NlCht7, NlCht9, and NlCht10; and the β-N-acetylhexosaminidase genes NlHex3, NlHex4, NlHex5 and NlHex6; it significantly suppressed the expression of ecdysteroid biosynthetic genes as well, including SDR, CYP307A2, CYP307B1, CYP306A2, CYP302A1, CYP315A1 and CYP314A1 of N. lugens. Additionally, tebuconazole affected the diversity, structure, composition, and function of the symbiotic fungi of N. lugens, as well as the relative abundance of saprophytes and pathogens, suggesting that tebuconazole reshapes the diversity and function of symbiotic fungi of N. lugens.

CONCLUSION

Our findings illustrate the insecticidal mechanism of tebuconazole, possibly by inhibiting normal molting or disrupting microbial homeostasis in N. lugens, and provide an important rationale for developing novel insect management strategies to delay escalating insecticide resistance. © 2023 Society of Chemical Industry.

Design, synthesis and insecticidal activities of 4-propargyloxybenzene sulfonamide derivatives substituted with amino acids

Sixty-nine 4-propargyloxybenzene sulfonamide derivatives with different amino acids as amino substituent were synthesized and evaluated for their insecticidal activity against third-instar Mythimna separate. The bioassay results revealed that some derivatives bearing amino acid ester group performed good insecticidal activity against third-instar M.separata, such as the LC₅₀ values of D18 and D19 were 4.28 and 2.96 mg/ml after 48 h, in particular, the LC₅₀ of D16 was 2.38 mg/ml and the activity was improved by 14 times compared to celangulin V (34.48 mg/ml). The above results provided theoretical and experimental basis for the discovery of novel insecticidal active compounds.

Insecticidal effects of two Tunisian diatomaceous earth loaded with Thymus capitatus (L.) Hoffmans and Links as an ecofriendly approach for stored coleopteran pest control

This study investigated composition and toxicity of Thyme EOs against two main stored grain insect pests. Carvacrol was distinguished as a major compound (78.34%). In laboratory tests, EOs applied by both direct contact and fumigant tests was more toxic to L. serricorne than T. castaneum. The EOs were also tested combined with two Tunisian Diatomaceous earths (DEs) against T. castaneum. The LC₅₀ was 6.28 µL/L air for natural preparation EO/R1, 5.90 µL/L air for EO/R2 and 121.17 for crude EOs by fumigant test, respectively. While, contact test revealed that natural DEs; dust act as an insecticide with 'LC₅₀' values of 3.22 and 0.29 µL/cm²f or R1 and R2, respectively. Moreover, a significant difference was noted between crude EO, EO/R1 and EO/R2. Overall, the enhancement of the Tunisian DEs' insecticidal activity by its mix with EOs may be a promising active substance as a stored grain protectant.

Design, Synthesis, and Insecticidal Activities of Novel meta-Diamide Compounds Containing Ethyl Acetate and Their Derivatives

In this study, a series of meta-diamide compounds containing ethyl acetate group and their derivatives were designed and synthesized. Their insecticidal activities against Plutella xylostella, Spodoptera frugiperda and Alfalfa sprouts were evaluated. Preliminary bioassays showed that some of the title compounds exhibited excellent insecticidal activities. Especially compound ethyl N-(3-((2-bromo-4-(perfluoropropan-2-yl)-6-(trifluoromethyl)phenyl)carbamoyl)-2-fluorophenyl)-N-(4-cyanobenzoyl)glycinate and ethyl N-(3-((2-bromo-4-(perfluoropropan-2-yl)-6-(trifluoromethyl)phenyl)carbamoyl)-2-fluorophenyl)-N-(6-fluoronicotinoyl)glycinate showed 100 % mortality at 0.1 mg/L against Plutella xylostella and Spodoptera frugiperda, same to broflanilide. Their LC₅₀ against Plutella xylostella is 0.286 mg/L and 0.0218 mg/L, respectively. Moreover, compound ethyl N-(3-((2-bromo-4-(perfluoropropan-2-yl)-6-(trifluoromethyl)phenyl)carbamoyl)-2-fluorophenyl)-N-(6-fluoronicotinoyl)glycinate displayed faster control efficacy than broflanilide at 0.1 mg/L. The results indicated that meta-diamide compounds containing ethyl acetate group could be developed as novel and promising insecticides.