Insecticidal and Antifeedant Activities of Malagasy Medicinal Plant (Cinnamosma sp.) Extracts and Drimane-Type Sesquiterpenes against Aedes aegypti Mosquitoes

Exploring Ocimum basilicum's Secondary Metabolites: Inhibition and Molecular Docking against Rhynchophorus ferrugineus for Optimal Action

The objective of our work is to create a practical procedure to produce in vitro cell suspensions of O. basilicum and to ascertain the factors that encourage enhanced secondary metabolite production. We investigated the impact of these metabolites on Rhynchophorus ferrugineus's adult and larval target enzymes. The explants were cultivated on Murashige and Skoog (MS) media with 0.1 to 1 mg/L plant growth regulators (PGRs) to create calluses. 2,4-Dichlorophenoxyacetic acid (2,4-D), kinetin, 1-naphthylacetic acid (NAA), and indole-3-butryic acid (IBA) at 0.5, 0.5, 0.1, and 1 mg/L, respectively, with 3% sucrose led to the highest biomass accumulation. In cell suspensions, the total phenolic content (TPC) and total flavonoid content (TFC) were 39.68 and 5.49 mg/g DW, respectively, with abiotic Verticillium dahliae as an activator. Rosmarinic acid, ursolic acid, nepetoidin A and B, salvigenin, and quercetin-3-O-rutinoside as flavonoids and phenolics were analyzed using UPLC-I TQD MS, with the highest concentrations reached after 40 days. The extract demonstrates insecticidal activity against the fourth-instar larvae of R. ferrugineus, with adults at 1197 µg/mL and 12.5 µg/larvae as LC50 and LD50 values. The extract inhibited acetylcholine esterase (AChE), acid phosphatases (ACPs), alkaline phosphatases (ALPs), and gamma-aminobutyric acid-transaminase (GABA-T) in larval tissue in vitro, with IC50 values of 124.2, 149.3, 157.8, and 204.8 µg/mL, and in vivo, with IC50 values of 157.2, 179.4, 185.3, and 241.6 µg/mL, after 24 h. Pure compounds identified the activity of the extract, showing the inhibition of AChE, ACPs, ALPs, and GABA-T with IC50 values ˂ 200 µg/mL (in vitro). The ABMET examination revealed good oral permeability, and docking tests showed that the compounds bind AChE, ACPs, ALPs, and GABA-T. These findings show that a green bioprocessing method such as an O. basilicum cell suspension is a quick and straightforward technique for producing phenolic compounds, and it may be used to develop sustainable bio-insecticides and new green procedures.

Immunomodulatory, cyto-genotoxic, and growth regulatory effects of nerolidol on melon fruit fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae)

Insects have evolved a robust immune system consisting of humoral and cellular branches and their orchestrated response enables insect to defend against exogenous stressors. Exploration of underlying immune mechanisms of insect pest under allelochemical stress can give us new insights on insect pest management. In this study, nerolidol, a plant sesquiterpene was evaluated for its insecticidal, growth regulatory, immunomodulatory, and cyto-genotoxic effects against melon fruit fly, Zeugodacus cucurbitae (Coquillett). First, second, and third instar larvae of Z. cucurbitae were fed on artificial diet containing different concentrations (5, 25, 125, 625, and 3125 ppm) of nerolidol. Results revealed a significant reduction in pupation and adult emergence as well as prolongation of developmental duration of treated larvae. Decline in growth indices showed remarkable growth inhibitory effects of nerolidol. Pupal weight and nutritional parameters viz. Larval weight gain, food assimilated, and mean relative growth rate declined after treatment. Immunological studies on second instar larvae depicted a drop in total hemocyte count and variations in proportions of plasmatocytes and granulocytes of LC30 and LC50 treated larvae. Phenoloxidase activity in nerolidol treated larvae initially increased but was suppressed after 72 h of treatment. The frequency of viable hemocytes decreased and that of apoptotic and necrotic hemocytes increased with both the lethal concentrations of nerolidol. Comet assay revealed a significant damage to DNA of hemocytes. The findings of the current study indicate that nerolidol exerts its insecticidal action through growth regulation, immunomodulation, and cyto-genotoxicity thus revealing its potential to be used as biopesticide against Z. cucurbitae.

Bioactive Molecules Derived from Plants in Managing Dengue Vector Aedes aegypti (Linn.)

Mosquitoes are the potential vectors of several viral diseases such as filariasis, malaria, dengue, yellow fever, Zika fever and encephalitis in humans as well as other species. Dengue, the most common mosquito-borne disease in humans caused by the dengue virus is transmitted by the vector Ae. aegypti. Fever, chills, nausea and neurological disorders are the frequent symptoms of Zika and dengue. Thanks to various anthropogenic activities such as deforestation, industrialized farming and poor drainage facilities there has been a significant rise in mosquitoes and vector-borne diseases. Control measures such as the destruction of mosquito breeding places, a reduction in global warming, as well as the use of natural and chemical repellents, mainly DEET, picaridin, temephos and IR-3535 have proven to be effective in many instances. Although potent, these chemicals cause swelling, rashes, and eye irritation in adults and children, and are also toxic to the skin and nervous system. Due to their shorter protection period and harmful nature towards non-target organisms, the use of chemical repellents is greatly reduced, and more research and development is taking place in the field of plant-derived repellents, which are found to be selective, biodegradable and harmless to non-target species. Many tribal and rural communities across the world have been using plant-based extracts since ancient times for various traditional and medical purposes, and to ward off mosquitoes and various other insects. In this regard, new species of plants are being identified through ethnobotanical surveys and tested for their repellency against Ae. aegypti. This review aims to provide insight into many such plant extracts, essential oils and their metabolites, which have been tested for their mosquitocidal activity against different life cycle forms of Ae. Aegypti, as well as for their efficacy in controlling mosquitoes.

Hydrazone modification of non-food natural product sclareolide as potential agents for plant disease

Plant diseases and their drug resistance pose a serious threat to agricultural production. One way to solve this problem is to discover new and efficient botanical pesticides. Herein, a series of novel hydrazide-hydrazone-containing sesquiterpenoid derivatives were synthesized by simply modifying the structure of the non-food natural product sclareolide. The biological activity results illustrated that compared to ningnanmycin (39.2 μg/mL), compound Z28 had the highest antiviral activity against tobacco mosaic virus (TMV), and the concentration for 50% of maximal effect (EC₅₀) of its inactivation activity was 38.7 μg/mL, followed by compound Z14 (40.6 μg/mL). Transmission electron microscopy (TEM) demonstrated that TMVs treated with compounds Z14 and Z28 were broken into rods of different lengths, and their external morphology was fragmented or even severely fragmented. Autodocking and molecular dynamics (MD) simulations indicated that compound Z28 had a strong affinity for tobacco mosaic virus coat protein (TMV-CP), with a higher binding energy of -8.25 kcal/mol compared to ningnanmycin (-6.79 kcal/mol). The preliminary mechanism revealed that compound Z28 can achieve an antiviral effect by targeting TMV-CP, rendering TMV unable to self-assemble and replicate, and might be a candidate for a novel plant antiviral agent. Furthermore, the curative and protective activities of compound Z22 (EC₅₀ = 16.1 μg/mL) against rice bacterial blight were 51.3% and 50.8%, respectively. Its control effect was better than that of bismerthiazol (BT) and thiadiazole copper (TC), compound Z22 that can be optimized as an active molecule.

Anticancer Activity of Natural and Semi-Synthetic Drimane and Coloratane Sesquiterpenoids

Drimane and coloratane sesquiterpenoids are present in several plants, microorganisms, and marine life. Because of their cytotoxic activity, these sesquiterpenoids have received increasing attention as a source for new anticancer drugs and pharmacophores. Natural drimanes and coloratanes, as well as their semi-synthetic derivatives, showed promising results against cancer cell lines with in vitro activities in the low micro- and nanomolar range. Despite their high potential as novel anticancer agents, the mode of action and structure–activity relationships of drimanes and coloratanes have not been completely enlightened nor systematically reviewed. Our review aims to give an overview of known structures and derivatizations of this class of sesquiterpenoids, as well as their activity against cancer cells and potential modes-of-action. The cytotoxic activities of about 40 natural and 25 semi-synthetic drimanes and coloratanes are discussed. In addition to that, we give a summary about the clinical significance of drimane and coloratane sesquiterpenoids.

1,3,4-Oxadiazole Contained Sesquiterpene Derivatives: Synthesis and Microbiocidal Activity for Plant Disease

A series of 1,3,4-oxadiazole contained sesquiterpene derivatives were synthesized, and the activity of the target compounds against Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac), and tobacco mosaic virus (TMV) were evaluated. The biological activity results showed that the EC₅₀ values of compounds H4, H8, H11, H12, H14, H16, and H19 for Xac inhibitory activity were 33.3, 42.7, 56.1, 74.5, 37.8, 43.8, and 38.4 μg/ml, respectively. Compounds H4, H8, H15, H19, H22, and H23 had inhibitory effects on Xoo, with EC₅₀ values of 51.0, 43.3, 43.4, 50.5, 74.6, and 51.4 μg/ml, respectively. In particular, the curative and protective activities of compound H8 against Xoo in vivo were 51.9 and 49.3%, respectively. In addition, the EC₅₀ values of the inactivation activity of compounds H4, H5, H9, H10, and H16 against TMV were 69.6, 58.9, 69.4, 43.9, and 60.5 μg/ml, respectively. The results of molecular docking indicated that compound H10 exhibited a strong affinity for TMV-coat protein, with a binding energy of −8.88 kcal/mol. It may inhibit the self-assembly and replication of TMV particles and have an anti-TMV effect, which supports its potential usefulness as an antiviral agent.

Growth inhibition of Spodoptera frugiperda larvae by camptothecin correlates with alteration of the structures and gene expression profiles of the midgut

Background

Spodoptera frugiperda is a serious pest that causes devastating losses to many major crops, including corn, rice, sugarcane, and peanut. Camptothecin (CPT) is a bioactive secondary metabolite of the woody plant Camptotheca acuminata, which has shown high toxicity to various pests. However, the effect of CPT against S. frugiperda remains unknown.

Results

In this study, bioassays have been conducted on the growth inhibition of CPT on S. frugiperda larvae. Histological and cytological changes were examined in the midgut of larvae fed on an artificial diet supplemented with 1.0 and 5.0 µg/g CPT. The potential molecular mechanism was explored by comparative transcriptomic analyses among midgut samples obtained from larvae under different treatments. A total of 915 and 3560 differentially expressed genes (DEGs) were identified from samples treated with 1.0 and 5.0 µg/g CPT, respectively. Among the identified genes were those encoding detoxification-related proteins and components of peritrophic membrane such as mucins and cuticle proteins. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses indicated that part of DEGs were involved in DNA replication, digestion, immunity, endocrine system, and metabolism.

Conclusions

Our results provide useful information on the molecular basis for the impact of CPT on S. frugiperda and for future studies on potential practical application.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07726-8.

Stop the crop: Insights into the insecticidal mode of action of cinnamodial against mosquitoes

Cinnamodial (CDIAL) is a drimane sesquiterpene dialdehyde found in the bark of Malagasy medicinal plants (Cinnamosma species; family Canellaceae). We previously demonstrated that CDIAL was insecticidal, antifeedant, and repellent against Aedes aegypti mosquitoes. The goal of the present study was to generate insights into the insecticidal mode of action for CDIAL, which is presently unknown. We evaluated the effects of CDIAL on the contractility of the ventral diverticulum (crop) isolated from adult female Ae. aegypti. The crop is a food storage organ surrounded by visceral muscle that spontaneously contracts in vitro. We found that CDIAL completely inhibited spontaneous contractions of the crop as well as those stimulated by the agonist 5-hydroxytryptamine. Several derivatives of CDIAL with known insecticidal activity also inhibited crop contractions. Morphometric analyses of crops suggested that CDIAL induced a tetanic paralysis that was dependent on extracellular Ca²⁺ and inhibited by Gd³⁺, a non-specific blocker of plasma membrane Ca²⁺ channels. Screening of numerous pharmacological agents revealed that a Ca²⁺ ionophore (A23187) was the only compound other than CDIAL to completely inhibit crop contractions via a tetanic paralysis. Taken together, our results suggest that CDIAL induces a tetanic paralysis of the crop by elevating intracellular Ca²⁺ through the activation of plasma membrane Ca²⁺ channels, which may explain the insecticidal effects of CDIAL against mosquitoes. Our pharmacological screening experiments also revealed the presence of two regulatory pathways in mosquito crop contractility not previously described: an inhibitory glutamatergic pathway and a stimulatory octopaminergic pathway. The latter pathway was also completely inhibited by CDIAL.

Phytochemical Screening and Bioactivity of Ludwigia spp. in the Control of Plutella xylostella (Lepidoptera: Plutellidae)

Simple Summary

Ludwigia species have several pharmacological applications, but their insecticidal proprieties have not been tested. This research thus aimed to study the effects of aqueous extracts on the biological characteristics of Plutella xylostella. We noted that the L. tomentosa, L. longifolia and L. sericea extracts were active. These species showed the best results regarding their ability to control P. xylostella populations, due to the presence of substances that inhibit food consumption and interfere in the morphological and physiological transformations of the offspring and adult oviposition.

Abstract

We tested the bioactivity of aqueous extracts of Ludwigia spp. (Myrtales: Onagraceae) on the biological cycle of Plutella xylostella. We assessed the duration of and viability during the larval, pupal and adult phases, as well as the influence of the extracts on the fecundity and hatching of P. xylostella eggs. Subsequently, we phytochemically screened the extracts. The extracts of L. tomentosa and L. longifolia reduced the pupal weight instead of prolonging the larval stage of P. xylostella. The L. tomentosa effect caused higher larval mortality and reduced the fecundity and hatching of P. xylostella eggs, and L. sericea reduced the egg survival. The phenolic compounds—flavonoids, condensed tannins and alkaloids—were more abundant in L. nervosa, L. tomentosa, L. sericea and L. longifolia. The L. tomentosa, L. longifolia and L. sericea extracts were bioactive, and these species showed the best results regarding their ability to control P. xylostella populations, because these plants produce substances able to inhibit food consumption and interfere with the morphological and physiological transformations of the offspring and the oviposition of adults.

Phenolic Fingerprinting, Antioxidant, and Deterrent Potentials of Persicaria maculosa Extracts

Persicaria maculosa (Polygonaceae) (known as lady’s thumb) is an annual morphologically variable weed that is widely distributed in Chile. The purpose of this study was to investigate the antifeedant potential of methanolic (MeOH), ethanolic (EtOH), and dichloromethane (DCM) extracts from the aerial parts of this plant collected in the Valparaíso and Curicó provinces (Chile) and relate this activity to the antioxidant capacity and the presence of phenolic compounds in the extracts. A phenolic profile based on HPLC-ESI-MS/MS allowed the identification of 26 phenolic compounds, most of them glycosyl derivatives of isorhamnetin, quercetin, and kaempferol. In addition, the total phenolic content (TP), total flavonoids (TF), and antioxidant activity measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH), superoxide anion scavenging (O₂⁻), ferric-reducing antioxidant power (FRAP), and cupric-reducing antioxidant capacity (CUPRAC) of the extracts are reported. The antifeedant potentials of the plant extracts were tested against Epilachna paenulata, Pseudaletia adultera, Macrosiphum euphorbiae, and Diaphorina citri insects for the first time. The activity against the aphid M. euphorbiae was significant for the DCM extracts of plants from Valparaíso and Curicó (settling % = 23% ± 4% and 23% ± 5%, respectively). The antifeedant activities against the beetle E. paenulata and the lepidoptera P. adultera were significant for Valparaíso extracts, especially when tested against E. Paenulata (IFP = 1.0 ± 0.0). Finally, the MeOH and EtOH extracts from Valparaíso plants reduced the diet consumption of the psilid D. citri (p < 0.05). The results showed that P. maculosa is a good source of flavonoids with some antioxidant capacities and has potential interest as botanical eco-friendly alternative with deterrent activity.

Total Synthesis of Cinnamodial-Based Dimer (-)-Capsicodendrin

We describe the first total synthesis of cinnamodial-based dimer (-)-capsicodendrin. First, we developed a 12-step synthetic route to access (-)-cinnamodial from 1-vinyl-2,6,6-trimethylcyclohexene. We then showed that (-)-cinnamodial can selectively dimerize to (-)-capsicodendrin under kinetically controlled basic conditions. Our observations regarding a facile conversion of (-)-capsicodendrin back to (-)-cinnamodial hint at the possibility that (-)-capsicodendrin is a chemical reservoir of insecticidal (-)-cinnamodial and Cinnamosma genus plants release it upon environmental stresses.