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Pyrethrum is a botanical insecticide derived from pyrethrum flowers. Feeding deterrence caused by pyrethrum has been reported in several sucking insects; however, there is no account of the cause of deterrence—whether from a single component or the combination of six active ingredients, called pyrethrins. We determined the feeding deterrence of natural pyrethrins, their two main components (pyrethrins I and II), and pyrethroid insecticides on the blowfly, Phormia regina. In a dual-choice feeding assay that minimized tarsal contact with food sources but allowed feeding through proboscises, natural pyrethrins, synthetic pyrethrins I/II, and allethrin were observed to induce deterrence at a concentration 16 times lower than the lowest concentration at which the knockdown rate increased. Feeding bouts were interrupted by intensive grooming of the proboscis at the deterring concentration, but no such grooming was observed to occur while feeding on the unpalatable tastants—NaCl, quinine, and tartaric acid. The underlying mode of action for the feeding deterrence of pyrethrins at sub-lethal concentrations probably occurs on the fly oral gustatory system, while differing from that of unpalatable tastants. The potent feeding deterrence of pyrethrins may provide effective protection for pyrethrum plants by rapidly deterring insects from feeding, before insecticidal activities occur.

• Glucosinolates are plant secondary metabolites used in host plant recognition by insects specialized on Brassicaceae, such as the diamondback moth (DBM), Plutella xylostella. Their perception as oviposition cues by females would seem to require their occurrence on the leaf surface, yet previous studies have reached opposite conclusions about whether glucosinolates are actually present on the surface of crucifer leaves. DBM oviposits extensively on Barbarea vulgaris, despite its larvae not being able to survive on this plant because of its content of feeding‐deterrent saponins. • Glucosinolates and saponins in plant tissue and mechanically removed surface waxes from leaves of Barbarea spp. were analyzed with high‐performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC‐MS). • Surface waxes from leaves of Barbarea spp. contained glucosinolates, but not feeding‐deterrent saponins. • Our research is the first to show that glucosinolates are present on the leaf surface of Barbarea spp., but not in other crucifers investigated, resolving some conflicting results from previous studies. Our research is also the first to quantify glucosinolates on the leaf surface of a crucifer, and to show that the concentrations of glucosinolates found on the leaf surface of Barbarea spp. are sufficient to be perceived by ovipositing DBM.

Insecticidal action of plant essential oils has been an area of intensive research in the new millennium, according to a recent bibliometric analysis. Despite this overwhelming research effort, commercialization of bioinsecticides based on essential oils has lagged far behind, although such products have now been used in the USA for over a decade, and in the EU in the last 4–5 years. Recent progress in commercialization of these products is reviewed here. Essential oils and their mono- and sesquiterpenoid constituents are fast-acting neurotoxins in insects, possibly interacting with multiple receptor types. These compounds also display potentially important sublethal behavioural effects in pest insects, including feeding and oviposition deterrence and repellence. Synergy among essential oil terpenoids appears to be a common phenomenon, and a mechanism for this action in rosemary oil has recently been demonstrated. Commercial development of bioinsecticides based on plant essential oils can follow several different pathways producing products with active ingredients differing in their genesis. These include products whose active ingredients consist of (1) a mixture of essential oils; (2) a single essential oil, or a single terpenoid constituent; (3) a blend of terpenoids, synthetically produced, that emulate those in a plant essential oil; and (4) a novel (non-natural) blend of terpenoids obtained from different plant sources. Examples of each of these are provided.

The rise in global temperature also favors the multiplication of pests and pathogens, which calls into question global food security. Plants have developed special coping mechanisms since they are sessile and lack an immune system. These mechanisms use a variety of secondary metabolites as weapons to avoid obstacles, adapt to their changing environment, and survive in less-than-ideal circumstances. Plant secondary metabolites include phenolic compounds, alkaloids, glycosides, and terpenoids, which are stored in specialized structures such as latex, trichomes, resin ducts, etc. Secondary metabolites help the plants to be safe from biotic stressors, either by repelling them or attracting their enemies, or exerting toxic effects on them. Modern omics technologies enable the elucidation of the structural and functional properties of these metabolites along with their biosynthesis. A better understanding of the enzymatic regulations and molecular mechanisms aids in the exploitation of secondary metabolites in modern pest management approaches such as biopesticides and integrated pest management. The current review provides an overview of the major plant secondary metabolites that play significant roles in enhancing biotic stress tolerance. It examines their involvement in both indirect and direct defense mechanisms, as well as their storage within plant tissues. Additionally, this review explores the importance of metabolomics approaches in elucidating the significance of secondary metabolites in biotic stress tolerance. The application of metabolic engineering in breeding for biotic stress resistance is discussed, along with the exploitation of secondary metabolites for sustainable pest management.

Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is one of the most destructive pests of various crops cultivated in Thailand. Spodoptera litura larvae, at early stages, attack the leaves and feed on every part of infested crops in later stages. Acorus calamus essential oil contains toxic asarones, which are generalistic cytotoxic compounds. However, the present study is the first attempt to look at safer metabolites from the rhizomes that could deter insect feeding. The objective was to use such compounds as safer residues on crops that would prevent the feeding of herbivorous lepidopterans. Accordingly, phenolic metabolites were isolated and evaluated to establish the feeding deterrence against polyphagous S. litura larvae. Methanol extract of A. calamus, chrysin, and 4-hydroxy acetophenone compounds were the most effective feeding deterrents with FD50 of 87.18, 10.33, and 70.77 µg/cm2, respectively, after 4 h of feeding on treated kale leaves in a no-choice leaf disc assay. Chrysin also reduced carboxylesterase activities (1.37-fold), whereas A. calamus methanol extract reduced glutathione-S-transferase activities (1.44-fold). Some larvae were also seen dead if they consumed the treated kale leaves. Feeding deterrent activity in the methanol extract of A. calamus was due to chrysin and 4-hydroxy acetophenone. The large-scale utilization of such compounds could help develop feeding deterrent strategies in the integrated pest management of lepidopterans. Graphical Abstract

Tribolium castaneum is a challenging pest of stored products, causing significant economic losses. The present study explored the efficacy of Coridothymus capitatus essential oil and its primary constituent, carvacrol, as eco-friendly alternatives for managing this pest. To evaluate their insecticidal potential, repellency, fumigant toxicity, and antifeedant properties, progeny inhibition assays were performed. Carvacrol exhibited superior repellency compared to the essential oil, achieving a 92% repellency rate at 2 mg/cm2. Both compounds demonstrated significant fumigant toxicity against T. castaneum, with LC50 values of 168.47 and 106.5 μL/L for the essential oil and carvacrol, respectively, after 24 h. Carvacrol also outperformed the essential oil in antifeedant activity, inducing an 80.7% feeding deterrence at 1.17 mg/g. Moreover, both treatments effectively suppressed the development of the pest’s progeny. These results collectively underscore the potent insecticidal properties of C. capitatus essential oil and carvacrol, particularly carvacrol, as promising candidates for the sustainable management of T. castaneum in stored product protection.

Insect kinins (leucokinins) are multifunctional peptides acting as neurohormones and neurotransmitters. In females of the mosquito vector Aedes aegypti (L.), aedeskinins are known to stimulate fluid secretion from the renal organs (Malpighian tubules) and hindgut contractions by activating a G protein-coupled kinin receptor designated “Aedae-KR.” We used protease-resistant kinin analogs 1728, 1729, and 1460 to evaluate their effects on sucrose perception and feeding behavior. In no-choice feeding bioassays (capillary feeder and plate assays), the analog 1728, which contains α-amino isobutyric acid, inhibited females from feeding on sucrose. It further induced quick fly-away or walk-away behavior following contact with the tarsi and the mouthparts. Electrophysiological recordings from single long labellar sensilla of the proboscis demonstrated that mixing the analog 1728 at 1 mM with sucrose almost completely inhibited the detection of sucrose. Aedae-KR was immunolocalized in contact chemosensory neurons in prothoracic tarsi and in sensory neurons and accessory cells of long labellar sensilla in the distal labellum. Silencing Aedae-KR by RNAi significantly reduced gene expression and eliminated the feeding-aversion behavior resulting from contact with the analog 1728, thus directly implicating the Aedae-KR in the aversion response. To our knowledge, this is the first report that kinin analogs modulate sucrose perception in any insect. The aversion to feeding elicited by analog 1728 suggests that synthetic molecules targeting the mosquito Aedae-KR in the labellum and tarsi should be investigated for the potential to discover novel feeding deterrents of mosquito vectors.

Synthetic pesticides pose a risk to the environment and human health by contaminating soil, water, and food chains. Natural plant-based alternatives offer a safer and more sustainable solution by reducing pollution, supporting biodiversity, and minimising pesticide resistance. This study evaluated the antifeedant activity of methanolic leaves extracts from invasive black cherry ( Prunus serotina Erhr.) against a storage pest, the granary weevil ( Sitophilus granarius L.). Chromatographic analysis of P. serotina leaves methanolic extracts identified 10 main phenolic compounds, with ursolic acid, p-coumaric acid o-coumaric acid, and caffeic acid exceeding 10%. LC-MS/MS analysis detected 12 compounds above the limit of quantification (LOQ), with luteolin-7-O-glucoside, caffeic acid, and chlorogenic acid at the highest concentrations. The antifeedant activity of P. serotina leaves methanolic extract was tested using the wheat wafer method, showing medium antifeedant effects at all extract concentrations (3.5, 5.0, and 12.0 mg/mL). Both males and females fed significantly less extract-treated wafers, with the inhibition of female feeding being stronger at 12.0 mg/ml. The extracts of P. serotina effectively discourage feeding of S. granarius , and the potency increases with concentration. Their flavonoids, phenolic acids, and cyanogenic glycosides suggest a complex mode of action, making them a promising natural alternative to synthetic insecticides. Further research should isolate key active compounds and evaluate their efficacy as botanical pesticides.

Phytoecdysteroids are analogs of insect hormones that control various vital functions, in particular, molting and metamorphosis. These phytoecdysteroids form part of the plant’s defenses against insect pests. In the present work, we studied the effect of five phytoecdysteroids (20-hydroxyecdysone, Makisterone A, Ponasterone A, Polypodine B, Ecdysone) on larvae of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). It is the most common pest of stored products. This study aimed to determine if small structural changes between these molecules could change their activity as antifeedants and growth disruptors in insect pests. Initially, we studied their effects on larval feeding behavior using a non-choice test by observing the presence of those larvae on the food pellets. Then we studied their toxicity on the insect development parameters by observing mortality percentages, pupation, and the emergence of adults. Our results indicate that all phytoecdysteroids possess antifeedant properties against T. castaneum larvae. This activity differs depending on the molecule and the concentration used. Compared to the control, 20-hydroxyecdysone exhibited a significant antifeedant activity, while polypodine B showed the lowest effect when incorporated to T. castaneum diet at the highest doses. Phytoecdysteroids caused significant disturbances in the growth and development parameters of T. castaneum , manifested by an inducted mortality, delayed pupation, reduced pupation, and reduced emergence of adults. From the study, we could conclude that the susceptibility of T. castaneum against phytoecdysteroids differs depending on the analog used. The minimal structural differences between these molecules could significantly affect their efficacy against this insect pest.

Lonicera maackii is an invasive shrub in North America for which allelopathic effects toward other plants or herbivores have been suspected. We characterized the major phenolic metabolites present in methanol extracts of L. maackii leaves. In addition, we examined the effects of methanol-water extracts of L. maackii leaves on seed germination of a target plant species and on feeding preference and growth rate of a generalist insect herbivore. A total of 13 individual major and minor compounds were detected in crude leaf extracts by high-performance liquid chromatography coupled to electronspray ionization-tandem mass spectrometry (ESI-MS/MS). Extracts were dominated by two major flavones, apigenin and luteolin, and their glucoside derivatives, apigenin-7-glucoside and luteolin-7-glucoside. Quantities of these compounds, along with chlorogenic acid, varied between two sampling points. Leaf extracts that contained these compounds were inhibitory to seed germination of Arabidopsis thaliana. In addition, treatment of artificial diet with leaf extracts deterred feeding of the generalist herbivore, Spodoptera exigua, in choice experiments but had no effect on growth rate in short-term no-choice bioassays. Purified apigenin tended to deter feeding by S. exigua and inhibited seed germination of A. thaliana. We conclude that leaves of L. maackii contain phenolic compounds, including apigenin and chlorogenic acid, capable of having biological effects on other plants and insects.