Toxicity of Plant Secondary Metabolites Modulating Detoxification Genes Expression for Natural Red Palm Weevil Pesticide Development

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.

Identification and potential application of key insecticidal metabolites in Tilia amurensis, a low-preference host of Hyphantria cunea

Developing effective insecticidal strategies is an important means of reducing the spread and host plant damage by Hyphantria cunea. In this study, key metabolites with insecticidal activity against H. cunea were screened by targeted metabolomics in Tilia amurensis, a low-preference host plant. Subsequently, the potential of key metabolites that could be used as botanical pesticides was evaluated. The results showed that coumarin was the key insecticidal metabolite of T. amurensis and had a significant insecticidal effect and weight inhibition effect on H. cunea larvae. Coumarin treatment significantly decreased the larval nutrient content and the gene expression of rate-limiting enzymes in the glycolytic pathway and tricarboxylic acid cycle. A significantly enhanced detoxification enzyme activity (CarE and GST), antioxidant oxidase activity (SOD and CAT), non-enzymatic antioxidant levels (GSH), and total antioxidant capacity were observed in coumarin-treated larvae. Coumarin treatment resulted in a significant increase in the expression levels of detoxification enzyme genes (CarE1, CarE2, CarE3, GST2, and GST3) and antioxidant oxidase genes (SOD1, CAT1, and CAT2) in H. cunea larvae. Coumarin treatment significantly increased the levels of MDA and H2O2 in larvae but did not cause pathological changes in the ultrastructure of the larval midgut. Coumarin solution sprayed directly or as a microcapsule suspension formulation with coumarin as the active ingredient had significant insecticidal activity against the H. cunea larvae. Overall, coumarin, a key anti-insect metabolite identified from T. amurensis, can significantly inhibit the growth and survival of H. cunea larvae and has the potential to be developed as a botanical pesticide.

Taxonomy, Biology, Symbionts, Omics, and Management of Rhynchophorus Palm Weevils (Coleoptera: Curculionidae: Dryophthorinae)

Palm weevils, Rhynchophorus spp., are destructive pests of native, ornamental, and agricultural palm species. Of the 10 recognized species, two of the most injurious species, Rhynchophorus ferrugineus and Rhynchophorus palmarum, both of which have spread beyond their native range, are the best studied. Due to its greater global spread and damage to edible date industries in the Middle East, R. ferrugineus has received more research interest. Integrated pest management programs utilize traps baited with aggregation pheromone, removal of infested palms, and insecticides. However, weevil control is costly, development of resistance to insecticides is problematic, and program efficacy can be impaired because early detection of infestations is difficult. The genome of R. ferrugineus has been sequenced, and omics research is providing insight into pheromone communication and changes in volatile and metabolism profiles of weevil-infested palms. We outline how such developments could lead to new control strategies and early detection tools.

Sustainable Pest Management in Date Palm Ecosystems: Unveiling the Ecological Dynamics of Red Palm Weevil (Coleoptera: Curculionidae) Infestations

The red palm weevil (RPW) poses a significant threat to date palm ecosystems, highlighting the necessity of sustainable pest management strategies that carefully consider the delicate ecological balance within these environments. This comprehensive review delves into innovative approaches to sustainable pest management, specifically focusing on date palm, and seeks to unravel the intricate ecological dynamics underlying RPW infestations. We thoroughly analyze biocontrol methods, eco-friendly chemical interventions, and integrated pest management (IPM) strategies, aiming to minimize the ecological impact while effectively addressing RPW infestations. By emphasizing the interplay of both living organisms (biotic) and environmental factors (abiotic) in shaping RPW dynamics, we advocate for a holistic and sustainable management approach that ensures the long-term resilience of date palm ecosystems. This review aims to contribute to an ecologically sound framework for pest management, promoting the sustainability and vitality of date palm ecosystems amidst the challenges posed by the RPW.

A Review on Digestive System of Rhynchophorus ferrugineus as Potential Target to Develop Control Strategies

Rhynchophorus ferrugineus, commonly known as red palm weevil (RPW), is a high-risk insect pest that has become a threat to many important palm species. There are several dominant factors that lead to the successful infestation of RPW, including its stealthy lifestyle, highly chitinized mouthpart, and high fecundity rate. Due to that, millions of dollars of losses have been suffered by many countries invaded by RPW. Several methods have been designed to control its invasion, including the usage of insecticides, but many cause resistance and environmental pollution. Therefore, an environmentally friendly insecticide that targets specific systems or pathways in RPW is urgently needed. One of the potential targets is the digestive system of RPW, as it is the major interface between the insect and its plant host. The related knowledge of RPW's digestive system, such as the anatomy, microflora, transcriptomic analysis, and proteomic analysis, is important to understand its effects on RPW's survival. Several data from different omics regarding the digestive systems of RPW have been published in separate reports. Some of the potential targets have been reported to be inhibited by certain potential insecticides, while other targets have not yet been tested with any inhibitors. Hence, this review may lead to a better understanding on managing infestations of RPW using the system biology approach for its digestive system.

Plant Secondary Metabolites: The Weapons for Biotic Stress Management

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.

Insecticidal properties of Ocimum basilicum and Mentha piperita essential oils against South American Tomato moth, Phthorimaea absoluta (Meyrick) (Lepidoptera: Gelichiidae)

Phthorimaea absoluta (Meyrick) is one of the most destructive pests of tomato, causing 100% yield loss in the absence of control measures. The important method of managing the pest is by using synthetic insecticides. However, intermittent and indiscriminate uses of certain insecticides have negative effect on the environment. Use of herbal insecticides such as secondary metabolites and essential oils is a key for sustainable long term crop protection. Investigation on the insecticidal properties of Ocimum basilicum, Mentha piperita essential oils (EOs) and their constituents was carried out against P. absoluta. The M. piperita EO showed highest mortality (100%) of P. absoluta with LC₅₀ 1.78 μl/ml due to alloaromadendrene (27.99%), levomenthol (18.31%) and santolina triene (9.78%). The O. basilicum EO also had significant mortality (90%) effect with LC₅₀ 3.58 μl/ml due to humulene (32.31%), alpha farnesense (27.22%), estragole (19.24%) and 4-cerene (10.61%). Among binary compounds, levomenthol showed highest mortality (100%) having LC₅₀ 13.18 μl/ml followed by alpha-pinene (100%) with LC₅₀ 16.10 μl/ml, 4-cerene (95%) with LC₅₀ 38.20 μl/ml and alpha-phellandrene (90%) having LC₅₀ 46.83 μl/ml. The observed toxicity in all compounds was due to significant changes in the activity of esterases, glutathione S-transferase and acetylcholine esterases over the time. The present study suggests that O. basilium and M. piperita EOs would provide an additional approach for the management of P. absoluta over synthetic insecticides.

Effects of Methyl Jasmonate Fumigation on the Growth and Detoxification Ability of Spodoptera litura to Xanthotoxin

Methyl jasmonate (MeJA) is a volatile substance derived from jasmonic acid (JA), and it responds to interbiotic and abiotic stresses by participating in interplant communication. Despite its function in interplant communication, the specific role of MeJA in insect defense responses is poorly understood. In this study, we found that carboxylesterase (CarE) activities, glutathione-S-transferase (GSTs) activities, and cytochrome mono-oxygenases (P450s) content increased more after the feeding of diets containing xanthotoxin, while larvae exposed to MeJA fumigation also showed higher enzyme activity in a dose-dependent manner: lower and medium concentrations of MeJA induced higher detoxification enzyme activities than higher concentrations of MeJA. Moreover, MeJA improved the growth of larvae fed on the control diet without toxins and diets with lower concentrations of xanthotoxin (0.05%); however, MeJA could not protect the larvae against higher concentrations of xanthotoxin (0.1%, 0.2%). In summary, we demonstrated that MeJA is effective at inducing S. litura defense response, but the enhanced detoxifying ability could not overcome the strong toxins.

Cap 'n' Collar C and Aryl Hydrocarbon Receptor Nuclear Translocator Facilitate the Expression of Glutathione S-Transferases Conferring Adaptation to Tannic Acid and Quercetin in Micromelalopha troglodyta (Graeser) (Lepidoptera: Notodontidae)

Micromelalopha troglodyta (Graeser) (Lepidoptera: Notodontidae) is a notorious pest of poplar. Coevolution with poplars rich in plant secondary metabolites prompts M. troglodyta to expand effective detoxification mechanisms against toxic plant secondary metabolites. Although glutathione S-transferases (GSTs) play an important role in xenobiotic detoxification in M. troglodyta, it is unclear how GSTs act in response to toxic secondary metabolites in poplar. In this study, five GST gene core promoters were accurately identified by a 5' loss luciferase reporter assay, and the core promoters were significantly induced by two plant secondary metabolites in vitro. Two transcription factors, cap 'n' collar C (CncC) and aryl hydrocarbon receptor nuclear translocator (ARNT), were cloned in M. troglodyta. MtCncC and MtARNT clustered well with other insect CncCs and ARNTs, respectively. In addition, MtCncC and MtARNT could bind the MtGSTt1 promoter and strongly improve transcriptional activity, respectively. However, MtCncC and MtARNT had no regulatory function on the MtGSTz1 promoter. Our findings revealed the molecular mechanisms of the transcription factors MtCncC and MtARNT in regulating the GST genes of M. troglodyta. These results provide useful information for the control of M. troglodyta.

Effects of spinetoram and glyphosate on physiological biomarkers and gut microbes in Bombus terrestris

The sublethal effects of pesticide poisoning will have significant negative impacts on the foraging and learning of bees and bumblebees, so it has received widespread attention. However, little is known about the physiological effects of sublethal spinetoram and glyphosate exposure on bumblebees. We continuously exposed Bombus terrestris to sublethal (2.5 mg/L) spinetoram or glyphosate under controlled conditions for 10 days. The superoxide dismutase, glutathione-S-transferase, carboxylesterase, prophenoloxidase, α-amylase and protease activities, and changes in gut microbes were measured to understand the effects of sublethal pesticide exposure on the physiology and gut microbes of bumblebees. Sublethal pesticide exposure to significantly increased superoxide dismutase activity and significantly decreased gut α-amylase activity in bumblebees but had no significant effect on glutathione-S-transferase, carboxylesterase or gut protease activities. In addition, glyphosate increased the activity of prophenoloxidase. Interestingly, we observed that neither of the two pesticides had a significant effect on dominant gut bacteria, but glyphosate significantly altered the structure of the dominant gut fungal community, and reduced the relative abundance of Zygosaccharomyces associated with fat accumulation. These results suggest that sublethal spinetoram and glyphosate do not significantly affect the detoxification system of bumblebees, but may affect bumblebee health by inhibiting energy acquisition. Our results provide information on the sublethal effects of exposure to low concentrations of glyphosate and spinetoram on bumblebees in terms of physiology and gut microbes.

Larvicidal and repellent potential of Ageratum houstonianum against Culex pipiens

Mosquitoes are unquestionably the most medic arthropod vectors of disease. Culex pipiens, usually defined as a common house mosquito, is a well-known carrier of several virus diseases. Crude ethanol extracts of different organs of Agratum houstonianum are tested with Culex pipiens Linnaeus (Diptera: Culicidae) to determine their larvicidal, antifeedant, and repellency effects. Alongside biochemical analysis, the activity of the AChE, ATPase, CarE, and CYP-450 is detected in the total hemolymph of the C. pipiens larvae to examine the enzymatic action on the way to explain their neurotoxic effect and mode of action. Through HPLC and GC-MS analysis of the phytochemical profile of A. houstonianum aerial parts is identified. The larvicidal activity of aerial parts; flower (AF), leaf (AL), and stem (AS) of A. houstonianum extracts are evaluated against the 3rd instar larvae of C. pipiens at 24-, 48- and 72-post-treatment. A. houstonianium AF, AL, and AS extracts influenced the mortality of larvae with LC50 values 259.79, 266.85, and 306.86 ppm, respectively after 24 h of application. The potency of AF and AL extracts was 1.69- and 1.25-folds than that of AS extract, respectively. A high repellency percentage was obtained by AF extract 89.10% at a dose of 3.60 mg/cm². A. houstonianium AF prevailed inhibition on acetylcholinesterase and decrease in carboxylesterase activity. Moreover, a significant increase in the ATPase levels and a decrease in cytochrome P-450 monooxegenase activity (- 36.60%) are detected. HPLC analysis prevailed chlorogenic and rosmarinic acid as the major phenolic acids in AL and AF, respectively. GC-MS analysis of A. houstonianum results in the identification of phytol as the major makeup. Precocene I and II were detected in AF. Linoleic, linolenic, and oleic acid were detected in comparable amounts in the studied organs. Overall, results suggest that the A. houstonianum flower extract (AF) exhibits significant repellent, antifeedant, and larvicidal activities.

Rosa chinensis Cultivars Affect Fitness-Related Characteristics and Digestive Physiology of the Western Flower Thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae)

Host plant species will influence the population and physiological performance of insects. Frankliniella occidentalis is a well-known invasive pest commonly found on flowering plants. Herein, the population development of F. occidentalis was investigated on the flowers of different Rosa chinensis cultivars (Ruby, Love, Parade, Pink Peace, and Mohana), and the digestive enzyme activities in thrips were measured after feeding on these flowers. The developmental times of F. occidentalis from egg to adult were 10.07, 10.37, 11.64, 10.66, and 10.90 d on Ruby, Love, Parade, Pink Peace, and Mohana, respectively. Significant differences in fecundity were also observed, with the greatest fecundity levels of F. occidentalis on Ruby (82.96) and the lowest on Mohana (63.40). F. occidentalis showed the greatest R0 on Ruby (43.57), followed by Love (36.46), Parade (33.00), Pink Peace (27.97), and Mohana (23.21). The rm showed a similar trend, with values of 0.156, 0.145, 0.141, 0.134, and 0.130, respectively. There were significant differences in digestive enzyme activities in F. occidentalis on different flowers, and different digestive enzymes showed different performance among these plants. The highest amylase and lipase activities in F. occidentalis were on Ruby, on which F. occidentalis had the fastest development rate and the highest R0, whereas the highest trypsin activity was on Pink Peace. All three digestive enzymes in thrips showed the lowest activities on Mohana. The varied population development of F. occidentalis associated with R. chinensis cultivars may be related to their digestive enzyme performance, which plays important roles in nutrient metabolism and insect growth.

Metabolization and sequestration of plant specialized metabolites in insect herbivores: Current and emerging approaches

Herbivorous insects encounter diverse plant specialized metabolites (PSMs) in their diet, that have deterrent, anti-nutritional, or toxic properties. Understanding how they cope with PSMs is crucial to understand their biology, population dynamics, and evolution. This review summarizes current and emerging cutting-edge methods that can be used to characterize the metabolic fate of PSMs, from ingestion to excretion or sequestration. It further emphasizes a workflow that enables not only to study PSM metabolism at different scales, but also to tackle and validate the genetic and biochemical mechanisms involved in PSM resistance by herbivores. This review thus aims at facilitating research on PSM-mediated plant-herbivore interactions.

The sweet wormwood essential oil and its two major constituents are promising for a safe control measure against fall webworm

The fall webworm, Hyphantria cunea (Drury), is a harmful polyphagous global defoliator. The major chemical components of Artemisia annua essential oil (EO) was found to contain (±)-camphor (16.42%), 1,8-cineole (6.22%), α-pinene (6%), caryophyllene (5.19%), and α-selinene (5.17%). The highest toxicity was recorded for EO of A. annua (LD₅₀ = 305.05 μg/larva), followed by (±)-camphor (LD₅₀ = 465.03 μg/larva) and 1,8-cineole (LD₅₀ = 573.49 μg/larva). The binary mixtures of compounds expressed a weaker activity compared to individuals. The (±)-camphor was found to be antagonistic to 1,8-cineole. The biochemical compounds of treated larvae were also determined. The activity level of alanin and aspartate aminotransferase decreased sharply while acid and alkaline phosphatase increased. Activity of lactate dehydrogenase was significantly higher than the control group at 24 h, but decreased significantly after 48 h in all treatments. The activity of esterases were decreased in the treated larvae. The glutathione S-transferase significantly increased in all time intervals. Overall the current results suggest that the sweet wormwood (A. annua) EO and its components could be a safe and environmentally friendly approach in possible control of fall webworm (H. cunea).

Two Apriona Species Sharing a Host Niche Have Different Gut Microbiome Diversity

The adaptability of herbivorous insects to toxic plant defense compounds is partly related to the structure of the gut microbiome. To overcome plant resistance, the insect gut microbiome should respond to a wide range of allelochemicals derived from dietary niches. Nevertheless, for sibling herbivorous insect species, whether the gut microbiome contributes to success in food niche competition is unclear. Based on 16S rDNA high-throughput sequencing, the gut microbiomes of two Apriona species that share the same food niche were investigated in this study to determine whether the gut microbiome contributes to insect success in food-niche competition. Our observations indicated that the gut microbiome tended to play a part in host niche competition between the two Apriona species. The gut microbiome of Apriona swainsoni had many enriched pathways that can help degrade plant toxic secondary compounds, including xenobiotic biodegradation and metabolism, terpenoid and polyketide metabolism, and secondary metabolite biosynthesis. Meanwhile, A. swainsoni hosted a much greater variety of microorganisms and had more viable bacteria than A. germari. We conclude that gut microbes may influence the coevolution of herbivores and host plants. Gut bacteria may not only serve to boost nutritional relationships, but may also play an important role in insect food niche competition.

Secondary Metabolites in Basil, Bio-Insecticide, Inhibition Effect, and In Silico Molecular Docking against Proteolytic Enzymes of the Red Palm Weevil (Rhynchophorus ferrugineus)

The purpose of this work was to determine the secondary metabolites generated by O. basilicum cell suspensions, as well as their insecticide and inhibitory activity against R. ferrugineus. The growth kinetics with inoculation Verticillium dahliae were determined and identified using LC-MS. Determination of total phenolic components (TFC), flavonoids (TF), and condensed tannins (TCT) were measured. Insecticidal activity of O. basilicum extract against R. ferrugineus (larva and adult) and proteolytic enzymes activity were assessed (in vitro and in vivo). The O.basilicum extract had an LC₅₀ of 1238 µg/mL and an LD₅₀ of 13.4 µg/larva. The LC₅₀ of chicoric acid, ursolic acid, salvigenin, quercetin-3-O-rutinoside, rosmarinyl glucoside, and nepetoidin B demonstrated activity at an LC₅₀ of 1132, 1167, 1189, 1214, 1275, and 1317 µg/mL, respectively. Chicoric acid, salvigenin, nepetoidin B, and rosmarinic acid demonstrated an LD₅₀ activity of 10.23, 11.4, 11.9, and 12.4 µg/larva, respectively. The active extract of O. basilicum inhibited total protease, trypsin-like serine proteinases, elastase, cysteine, and metalloprotease activity with an IC₅₀ (in vitro) of 119.4, 91, 102.4, 76.4, and 52.4 µg/mL, respectively. In silico studies of compounds were conducted, such as molecular docking and ADMET analysis. The study proposes using an efficient cell suspension technique to produce O. basilicum extract containing active secondary metabolites and accessible using as bio-insecticide.

Broccoli (Brassica oleracea L. var. italica) cultivars, Palam Samridhi and Palam Vichitra affect the growth of Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)

Effect of the ethyl acetate seed extracts of two cultivars of broccoli, Brassica oleracea Italica, Palam Samridhi (PS) and Palam Vichitra (PV) on growth, development and nutritional physiology of an economically important insect pest, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) was evaluated by conducting bioassays and nutritional assays. The insect larvae were fed on diets amended with the seed extracts of two cultivars at different concentrations viz. 5, 25, 125, 625 and 3125 ppm and taking water as control. The response of the insect varied with plant varieties. The extracts disrupted the developmental cycle of the pest. Larval mortality and total adult emergence were negatively affected. Larval period and total development period were also negatively influenced. Nutritional indices of S. litura also showed considerable decrease in the RGR, RCR, ECI and ECD as compared to control. The AD values were also enhanced with both the cultivars. The findings of the study revealed a considerable anti-insect potential of the two extracts and needs to be further explored for identification and isolation of bioactive constituents from broccoli for efficient management of the pest population.

Eugenol and Thymol Derivatives as Antifeedant Agents against Red Palm Weevil, Rhynchophorus ferrugineus (Coleoptera: Dryophthoridae) Larvae

Simple Summary

Rhynchophorus ferrugineus or the red palm weevil (RPW) is a major invasive insect pest that causes severe problems for palm cultivations and, in turn, for the palm industries worldwide. The current practice for controlling RPW in Malaysia mainly involves the use of synthetic pesticides. However, synthetic pesticides should not be encouraged because they are highly toxic and persistent in the environment and as such, can cause deterioration to the ecosystem and human health. Essential oil (EO) derivatives from eugenol and thymol were tested as potential natural compounds for controlling RPW. We evaluated the effect of eight EO derivatives from eugenol and thymol against the fourth instar larvae of RPW. Feeding contact bioassay was conducted for 14 days with different concentrations of these derivatives, in three replications for each treatment. All the derivatives showed feeding deterrent effects against RPW larvae, particularly 4-allyl-2-methoxy-1-(4-trifluoromethyl-benzyloxy)-benzene and 2-isopropyl-4-methyl-2-((4-nitrobenzyl) oxy) benzene, which demonstrated the most effective antifeedant properties in the eugenol and thymol derivative group. Overall, our findings revealed that both eugenol and thymol derivatives showed similar antifeedant activity against RPW larvae. However, the ether derivatives showed a stronger antifeedant effect than that of esters. Both eugenol and thymol are effective against RPW and have the potential to be investigated further as botanical insecticides for the management of RPW in the future.

Abstract

Coconut palms in Malaysia are infested by a destructive invasive pest, RPW since 2007, and the pest’s population is difficult to control. At present, RPW control management mainly relies on the use of monocrotophos, which is administered by the trunk injection method. However, this pesticide can negatively impact human health and the ecosystem. Plant EO that can be used as a bio-pesticide is highly recommended as an alternative to monocrotophos because of its target-specific and eco-friendly properties. The antifeedant activity of eight eugenol and thymol derivatives from clove and thyme EOs were tested against the fourth instar larvae of RPW through oral bioassay for 14 days. Relative growth rate (RGR), relative consumption rate (RCR), the efficiency of conversion of ingested food (ECI), and the feeding deterrent index (FDI) were compared and analyzed. All of the derivatives showed antifeedant activity, particularly the eugenol derivative, 4-allyl-2-methoxy-1-(4-trifluoromethyl-benzyloxy)-benzene (FDI = 54.14%) and the thymol derivative, 2-isopropyl-4-methyl-2-((4-nitrobenzyl) oxy) benzene (FDI = 53.88%). Both of them showed promising results on their ability to be the most effective antifeedant agents in each derivative group. There was no significant difference in the effectiveness of the eugenol-based and thymol-based derivatives, but the ether derivative group (FDI = 45.63%) had a significantly stronger effect than the ester derivative group (FDI = 39.71%). This study revealed that the compound in ether form is more effective than the compound in ester form as an antifeedant agent against RPW larvae, regardless of the plant EO that the compound is derived from.

The high adaptability of Hyphantria cunea larvae to cinnamic acid involves in detoxification, antioxidation and gut microbiota response

Hyphantria cunea is one of the most destructive invasive agricultural and forest pests worldwide. In order to better understand the adaptation mechanism of H. cunea larvae to secondary metabolites of their highly diversified host plants, the physiological function and detoxification ability of midgut, as well as the gut microbial community were investigated in H. cunea larvae fed with cinnamic acid-treated artificial diets. Our results showed that cinnamic acid treatment could not affect the growth and food utilization of H. cunea larvae, as evidenced by a non-significantly altered larval body weight and efficiency of conversion of ingested food. Evaluation of oxidative stress-related parameters (e.g. malondialdehyde and hydrogen peroxide) and midgut histopathology also clearly confirmed that cinnamic acid treatment caused no significant oxidative damage and pathological changes in the larval midgut. Variance analysis showed that cinnamic acid treatment significantly increased the content of non-enzymatic antioxidants (ascorbic acid and glutathione), the activity of antioxidant enzymes (superoxide dismutase and peroxidase) and detoxification enzyme (carboxylate esterase), as well as the abundance of several gut microbiota at the genus level (Hydrogenophaga and Acinetobacter) involved in the organic substance degradation in larval midgut. Further Pearson's correlation analysis revealed that these strongly altered gut microbiota at the genus level appeared to be significantly correlated with the detoxification and antioxidation parameters. These findings demonstrate the high adaptability of H. cunea larvae to cinnamic acid involves in detoxification, antioxidation and gut microbiota response, and indicate the existence of an extremely effective counter-defense mechanism for H. cunea larvae against the secondary metabolites of host plants.

Bio-Insecticide of Thymus vulgaris and Ocimum basilicum Extract from Cell Suspensions and Their Inhibitory Effect against Serine, Cysteine, and Metalloproteinases of the Red Palm Weevil (Rhynchophorus ferrugineus)

The current study was designed to investigate the insecticide role of volatile constituents produced from cell suspensions of T. vulgaris and O. basilicum against R. ferrugineus. Constituents were extracted from cell suspension after 40 days. Growth kinetics were measured with an inoculation of Verticillium dahliae and identified by GC-MS. Total volatile phenolic constituents were measured. Insecticidal activity against R. ferrugineus (adult) and proteolytic enzyme activity in larvae were assessed. GC-MS showed that the T. vulgaris extract has higher amounts of thymol, p-cymene, γ-terpinene, β-caryophyllene, and linalool in comparison to the O. basilicum extract, which is rich in estragole, β-terpineol, (E)-β-ocimene, 1,8-cineole, germacrene D, and eugenol. The T. vulgaris extract showed an LC₅₀ of 1032 µg/mL, followed by O. basilicum with an LC₅₀ of 1246 µg/mL. The IC₅₀ values against the total proteases were 110.8 and 119.4 µg/mL for T. vulgaris and O. basilicum, respectively. The IC₅₀ for the trypsin-like serine proteinase assessment was 81.6 and 91 µg/mL for T. vulgaris and O. basilicum, respectively. Cysteine, chymotrypsin, and metalloproteinase assessment showed an IC₅₀ above 5000 µg/mL for both extracts. The study is proposed as a potential approach to use T. vulgaris and O. basilicum extract as a bio-insecticide against R. ferrugineus using an accessible and efficient cell suspension technique.

Compatibility of Beauveria bassiana and a Plant Secondary Metabolite: A Novel Modeling Approach to Invade Host Defense for Effective Control of Oligonychus afrasiaticus (McGregor) on Date Palms

Oligonychus afrasiaticus (McGregor) is an important pest causing substantial economic losses to date palm fruits (dates). The application of mycopathogens with plant secondary metabolites, which may proceed synergistically is thus essential to augment sustainable management strategy for O. afrasiaticus. In this regard, extensive laboratory experimentation involving compatibility, synergism, and host defense was performed to develop stable pest management option. The toxin-pathogen compatibility assay results revealed compatible interaction (biological index = 79–95) of B. bassiana ARSEF 8465 against each tested concentration of commercially available (+)-α-Pinene that provide the opportunity to further explore the time and concentration dependent mortality and defense related enzymatic regulation analysis. The time-mortality response assays that mainly comprised of various proportions of B. bassiana ARSEF 8465 and (+)-α-Pinene revealed that the sole application of B. bassiana ARSEF 8465 (LC₅₀ = 19.16 mg/mL), and (+)-α-Pinene (3.41 mg/mL) found to be least lethal compared with joint applications (LC₅₀ ranged from 1.32–7.06 mg/mL). The treatments complied under Scheme IV (80% (+)-α-Pinene: 20% B. bassiana ARSEF 8465 Conidia) led to strong synergistic interaction (joint toxicity = 755). In addition, synergistic interactions greatly induced enzymatic activities of the studied antioxidants (CAT and SOD), and defense-related enzymes (GST and AchE). We concluded that join application of B. bassiana ARSEF 8465 and (+)-α-Pinene is a promising option for controlling Oligonychus afrasiaticus populations.

Sustainable Management of the Red Palm Weevil: The Nexus between Farmers’ Adoption of Integrated Pest Management and Their Knowledge of Symptoms

The red palm weevil (RPW) (Rhynchophorus ferruginous) is one of the most serious pest insects threatening the sustainability of the date palm sector (Phoenix dactylifera L.). Nevertheless, a gap exists in the body of knowledge regarding patterns in farmers’ adoption of integrated pest management (IPM) for RPW control and how their knowledge of RPW symptomology influences IPM adoption. Data were collected using structured questionnaires from 183 palm growers in Al-Ahsa Governorate, Saudi Arabia. The results indicate that most farmers had insufficient knowledge to visually diagnose RPW symptoms and damage. Farmers moderately adopted preventive measures recommended for protection from RPW infestation. Only 13.11% of the farmers exhibited a high rate of adoption of pest management practices for RPW control and eradication. The findings revealed a strong positive association (0.8, p < 0.01) between the knowledge level regarding symptoms and IPM adoption level, whereby the respondents with more knowledge of RPW symptoms showed a higher level of adoption in all IPM categories. This study contributes to the development of our understanding of the social behaviors and risks associated with RPW. This might enhance the quality of awareness campaigns and extension programs and assist in developing a visual inspection protocol for RPW infestation for farmers.

Potential Synergy between Spores of Metarhizium anisopliae and Plant Secondary Metabolite, 1-Chlorooctadecane for Effective Natural Acaricide Development

Date palm dust mites are important pests severely infesting valuable nutritious fruits (dates) of date palm. In search of an alternative to acaricides, joint action of Metarhizium anisopliae EBCL 02049 spores and 1-Chlorooctadecane was evaluated as a potential candidate for the management of Oligonychus afrasiaticus through natural products. In this regard, in vitro tests were performed to evaluate the interaction of M. anisopliae spores with multiple doses of 1-Chlorooctadecane (0.8, 1.6, 2.4, 3.2, and 4.0 mg/mL). Compatibility bioassay results evidenced from vegetative growth (77.7–84.40 mm), sporulation (5.50–7.30 × 10⁶ spores/mL), and germination (96.70–98.20%), revealed that all the tested doses are compatible (biological index > 82) with the spores of M. anisopliae. The impact of combined treatment of spores with 1-Chlorooctadecane in different proportions (Scheme I, II, III, and IV) compared to their sole application against O. afrasiaticus was evaluated by concentration–mortality response bioassays. Results showed that all the combined treatments revealed high mortality compared to the sole application, which showed relatively slow mortality response over time. Toxicity recorded from Scheme IV combinations (80% 1-Chlorooctadecane: 20% Spores), exhibited strong synergistic interaction (joint toxicity = 713). Furthermore, potent interactions have overcome the host antioxidant defense at the final stage of infection by tremendously reducing catalase, and superoxide dismutase activities. These experiments demonstrated fungal–toxin joint synergistic interaction as a promising date palm dust mite management option.

Effect of Tannic Acid on Nutrition and Activities of Detoxification Enzymes and Acetylcholinesterase of the Fall Webworm (Lepidoptera: Arctiidae)

Plant tannins, polyphenolic plant secondary metabolites are involved in important chemical defense processes in plants. In this study, tannic acid was used as the standard of plant tannins to determine the effects on nutritional indices and activities of glutathione S-transferases (GSTs), cytochrome P450 monooxygenase (CYP450), carboxylesterase (CarE), and acetylcholinesterase (AChE) in fourth-instar larvae of Hyphantria cunea (Drury) by feeding on an artificial diet containing tannic acid under different treatments. We found that tannic acid significantly affected the digestive capacity and food utilization rate of H. cunea larvae. A tannic acid concentration of less than 2.0% promoted feeding and the utilization of undesirable food by H. cunea larvae, while inhibitory effects were observed at high concentrations (>2.5%). Tannic acid had a significant effect on the activity of detoxification enzymes and AChE in H. cunea larvae in concentration-dependent and time-dependent manners (P < 0.05). These results provide new insights into the potential mechanisms underlying detoxification in H. cunea larvae against tannic acid in host plants.

De novo transcriptome analysis and identification of genes associated with immunity, detoxification and energy metabolism from the fat body of the tephritid gall fly, Procecidochares utilis

The fat body, a multifunctional organ analogous to the liver and fat tissue of vertebrates, plays an important role in insect life cycles. The fat body is involved in protein storage, energy metabolism, elimination of xenobiotics, and production of immunity regulator-like proteins. However, the molecular mechanism of the fat body's physiological functions in the tephritid stem gall-forming fly, Procecidochares utilis, are still unknown. In this study, we performed transcriptome analysis of the fat body of P. utilis using Illumina sequencing technology. In total, 3.71 G of clean reads were obtained and assembled into 30,559 unigenes, with an average length of 539 bp. Among those unigenes, 21,439 (70.16%) were annotated based on sequence similarity to proteins in NCBI's non-redundant protein sequence database (Nr). Sequences were also compared to NCBI's non-redundant nucleotide sequence database (Nt), a manually curated and reviewed protein sequence database (SwissProt), and KEGG and gene ontology annotations were applied to better understand the functions of these unigenes. A comparative analysis was performed to identify unigenes related to detoxification, immunity and energy metabolism. Many unigenes involved in detoxification were identified, including 50 unigenes of putative cytochrome P450s (P450s), 18 of glutathione S-transferases (GSTs), 35 of carboxylesterases (CarEs) and 26 of ATP-binding cassette (ABC) transporters. Many unigenes related to immunity were identified, including 17 putative serpin genes, five peptidoglycan recognition proteins (PGRPs) and four lysozyme genes. In addition, unigenes potentially involved in energy metabolism, including 18 lipase genes, five fatty acid synthase (FAS) genes and six elongases of very long chain fatty acid (ELOVL) genes, were identified. This transcriptome improves our genetic understanding of P. utilis and the identification of a numerous transcripts in the fat body of P. utilis offer a series of valuable molecular resources for future studies on the functions of these genes.

Development-Disrupting Chitin Synthesis Inhibitor, Novaluron, Reprogramming the Chitin Degradation Mechanism of Red Palm Weevils

Disruption in chitin regulation by using chitin synthesis inhibitor (novaluron) was investigated to gain insights into the biological activity of chitinase in red palm weevils, an invasive pest of date palms in the Middle East. Impact of novaluron against ninth instar red palm weevil larvae was examined by dose-mortality response bioassays, nutritional indices, and expression patterns of chitinase genes characterized in this study. Laboratory bioassays revealed dose-dependent mortality response of ninth-instar red palm weevil larvae with LD₅₀ of 14.77 ppm of novaluron. Dietary growth analysis performed using different doses of novaluron (30, 25, 20, 15, 10, and 5 ppm) exhibited very high reduction in their indexes such as Efficacy of Conversion of Digested Food (82.38%) and Efficacy of Conversion of Ingested Food (74.27%), compared with control treatment. Transcriptomic analysis of red palm weevil larvae characterized numerous genes involved in chitin degradation including chitinase, chitinase-3-like protein 2, chitinase domain-containing protein 1, Endochitinase-like, chitinase 3, and chitin binding peritrophin-a domain. However, quantitative expression patterns of these genes in response to novaluron-fed larvae revealed tissue-specific time-dependent expression patterns. We recorded overexpression of all genes from mid-gut tissues. Growth retarding, chitin remodeling and larvicidal potential suggest novaluron as a promising alternate for Rhynchophorus ferrugineus management.

Bioactivity-guided isolation of rosmarinic acid as the principle bioactive compound from the butanol extract of Isodon rugosus against the pea aphid, Acyrthosiphon pisum

Aphids are agricultural pest insects that transmit viruses and cause feeding damage on a global scale. Current pest control practices involving the excessive use of synthetic insecticides over many years have resulted in aphid resistance to a number of pesticides. In nature, plants produce secondary metabolites during their interaction with insects and these metabolites can act as toxicants, antifeedants, anti-oviposition agents and deterrents towards the insects. In a previous study, we demonstrated that the butanol fraction from a crude methanolic extract of an important plant species, Isodon rugosus showed strong insecticidal activity against the pea aphid, Acyrthosiphon pisum. To further explore this finding, the current study aimed to exploit a bioactivity-guided strategy to isolate and identify the active compound in the butanol fraction of I. rugosus. As such, reversed-phase flash chromatography, acidic extraction and different spectroscopic techniques were used to isolate and identify the new compound, rosmarinic acid, as the bioactive compound in I. rugosus. Insecticidal potential of rosmarinic acid against A. pisum was evaluated using standard protocols and the data obtained was analyzed using qualitative and quantitative statistical approaches. Considering that a very low concentration of this compound (LC90 = 5.4 ppm) causes significant mortality in A. pisum within 24 h, rosmarinic acid could be exploited as a potent insecticide against this important pest insect. Furthermore, I. rugosus is already used for medicinal purposes and rosmarinic acid is known to reduce genotoxic effects induced by chemicals, hence it is expected to be safer compared to the current conventional pesticides. While this study highlights the potential of I. rugosus as a possible biopesticide source against A. pisum, it also provides the basis for further exploration and development of formulations for effective field application.

Lethality of Sesquiterpenes Reprogramming Red Palm Weevil Detoxification Mechanism for Natural Novel Biopesticide Development

Natural biopesticide development for invasive populations of red palm weevils is mainly responsible for the destruction of date palms and demands an extensive screening program of plant secondary metabolites. In the current study, the pesticidal potential of sesquiterpenes (C₁₅ H₂₄), an important class of plant secondary metabolites primarily composed of three isoprene units, was evaluated by laboratory toxicity, feeding performance bioassays, and host detoxification gene expression patterns. Dose-mortality response bioassays performed against mid-aged eighth-instar red palm weevil larvae revealed dose-dependent mortality. Only three sesquiterpenes, including Farnesol (LD₅₀ = 6559 ppm) and Farnesyl acetate (LD₅₀ = 7867 ppm), are considered to have significant toxicity, with Picrotoxin (LD₅₀ = 317 ppm) being the most toxic. Furthermore, highly toxic sesquiterpene (Picrotoxin) established in the current study tremendously reduced the feeding performance indices, including the efficacy of conversion of digested food (ECD) (81.74%) and the efficacy of conversion of ingested food (ECI) (73.62%). The least toxic sesquiterpenes, including β-Caryophyllene, (+)-Cedrol, Nerolidol, (+)-Nootkatone, and Parthenolide, observed in the current study failed to impart significant reductions of ECI and ECD indices. Lethality of the least toxic sesquiterpenes was overcome by greatly inducing gene expressions of Glutathione S transferase (GST) and Cytochrome P450. These encouraging results enabled us to suggest Picrotoxin as a promising biopesticide for the control of red palm weevil infestations.

Effect of crude extracts and purified compounds of Alpinia galanga on nutritional physiology of a polyphagous lepidopteran pest, Spodoptera litura (Fabricius)

Secondary plant metabolites play an important role in providing protection to plants against herbivore insect pests. Keeping in view the increasing importance of biopesticides, the crude extracts from different plants are being investigated for insecticidal activities. Alpinia galanga, a medicinal plant belonging to family Zingiberaceae exhibits a wide range of biological activities. In the present study, crude extracts of A. galanga and its purified compounds i.e. 1'-acetoxychavicol acetate and galangin were evaluated for their effect on various nutritional parameters of Spodoptera litura (Fab.). All the extracts exhibited a significant influence on relative growth and consumption rates as well as efficiency of conversion of ingested and digested food. Ethyl acetate extract was found to be the most effective causing significant reduction in values of RGR, RCR, ECI and ECD of S. litura larvae in comparison to control larvae. The highest concentration of the ethyl acetate extract (2500 ppm) resulted in 44.95%, 10.99%, 38.08% and 37.04% decrease respectively in RGR, RCR, ECI and ECD in comparison to control. The purified compounds also showed inhibitory effects on various nutritional parameters. 1'-Acetoxychavicol acetate was found to be more effective in comparison to galangin.

De novo transcriptomic analysis of the alimentary tract of the tephritid gall fly, Procecidochares utilis

The tephritid gall fly, Procecidochares utilis, is an important obligate parasitic insect of the malignant weed Eupatorium adenophorum which biosynthesizes toxic secondary metabolites. Insect alimentary tracts secrete several enzymes that are used for detoxification, including cytochrome P450s, glutathione S-transferases, and carboxylesterases. To explore the adaptation of P. utilis to its toxic host plant, E. adenophorum at molecular level, we sequenced the transcriptome of the alimentary tract of P. utilis using Illumina sequencing. Sequencing and de novo assembly yielded 62,443 high-quality contigs with an average length of 604 bp that were further assembled into 45,985 unigenes with an average length of 674 bp and an N50 of 983 bp. Among the unigenes, 30,430 (66.17%) were annotated by alignment against the NCBI non-redundant protein (Nr) database, while 16,700 (36.32%), 16,267 (35.37%), and 11,530 (25.07%) were assigned functions using the Clusters of Orthologous Groups (COG), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Ontology (GO) databases, respectively. Using the comprehensive transcriptome data set, we manually identified several important gene families likely to be involved in the detoxification of toxic compounds including 21 unigenes within the glutathione S-transferase (GST) family, 22 unigenes within the cytochrome P450 (P450) family, and 16 unigenes within the carboxylesterase (CarE) family. Quantitative PCR was used to verify eight, six, and two genes of GSTs, P450s, and CarEs, respectively, in different P. utilis tissues and at different developmental stages. The detoxification enzyme genes were mainly expressed in the foregut and midgut. Moreover, the unigenes were higher expressed in the larvae, pupae, and 3-day adults, while they were expressed at lower levels in eggs. These transcriptomic data provide a valuable molecular resource for better understanding the function of the P. utilis alimentary canal. These identified genes could be pinpoints to address the molecular mechanisms of P. utilis interacting with toxic plant host.

Toxin-Pathogen Synergy Reshaping Detoxification and Antioxidant Defense Mechanism of Oligonychus afrasiaticus (McGregor)

Current study reveals the likelihood to use pathogen and toxin mutually as an effective and eco-friendly strategy for Oligonychus afrasiaticus (McGregor) management, which could reduce toxicant dose and host killing time. Therefore, phytol and Beauveria bassiana in different proportions were evaluated to determine their effectiveness. Prior to ascertaining host mortality and defense mechanisms, we have recorded in vitro action of phytol using different concentrations (0.70, 1.40, 2.10, 2.80, and 3.50 mg/mL) against B. bassiana suspension. In vitro compatibility assays revealed that growth parameters (vegetative growth, sporulation, and viability) of B. bassiana were least affected by the action of phytol at all tested concentrations. Biological Index of B. bassiana exhibited compatibility with phytol allowed us to conduct Joint toxicity bioassays in which phytol and spores mixed in different proportions in order to attain maximum treatment effect in terms of high mortality at low concentration under short time. Results revealed that joint-application exhibited both synergistic (treatments with higher proportions of phytol), and antagonistic interaction (treatments with higher proportions of spores) interactions. Biochemical mechanisms involved in host antioxidant and detoxification response were explored by quantifying their respective enzymatic activities. Lethality of different treatments induced different patterns of detoxification enzymes including glutathione S-transferase (GST) and acetylcholinesterase (AchE). Overall, the least potent treatments (20% phytol:80% spores, and 40% phytol:60% spores) established in the current study induced relatively higher GST and AchE activities. On the other hand, the most potent treatment (80% phytol:20% spores) at its maximum concentration exhibited negligible relative GST and AchE activities. Antioxidant enzyme activities of CAT and SOD measured in the current study showed moderate to complex interaction might because of toxin-pathogen remarkable synergy. This study suggested that joint application of phytol with B. bassiana spores have shown tremendous acaricidal potential and found to be promising new strategy for controlling old world date mites.

Sub-Chronic Toxicity of the Hydroethanolic Leaf Extract of Telfairia occidentalis Hook. f. (Cucurbitaceae) in Male Rats

Background: Due to its nutritional and medicinal values, the leaf of Telfairia occidentalis Hook f. (Cucurbitaceae) is consumed in different parts of Nigeria. Acute and sub-chronic toxicity of the hydroethanolic leaf extract of Telfairiaoccidentalis were investigated in this study. Methods: Sixty-four male rats were randomized into four different groups of 16 animals each and were separately administered 80, 400 and 2000 mg/kg T. occidentalis orally (p.o.) for 60 days. Animals were sacrificed and blood samples were collected for hematological and biochemical analyses. Vital organs were harvested and evaluated for in vivo antioxidants and histopathological changes. Results: A significant (p < 0.05) reduction in weight of the testes, compared to the control group, was observed in the group treated with 2000 mg/kg extract. No significant change was observed in the weight of other vital organs relative to the control group. There were significant (p < 0.01) increases in sperm motility and count in the group administered 80 mg/kg extract and significant (p < 0.001) reductions in both parameters at 2000 mg/kg. There were significant increases in the levels of hemoglobin and packed cell volume at 80 and 2000 mg/kg of the extract. In respect of liver function parameters, significant reductions in aspartate aminotransferase and alanine aminotransferase levels at doses of 400 and 2000 mg/kg relative to control were observed. Compared to control, the extract significantly reduced (p < 0.05) the level of total cholesterol (400 mg/kg) and caused a significant increase in the level of high-density lipoprotein (80, 400 and 2000 mg/kg). Significant (p < 0.05) increase in the level of malondialdehyde, decrease in superoxide dismutase level and histopathological abnormalities were observed in the testes at 2000 mg/kg. Upon cessation of treatment with T. occidentalis for 30 days, the observed effects were reversed. Conclusions: The findings showed that the hydroethanolic leaf extract of Telfairia occidentalis is relatively non-toxic on acute and sub-chronic exposures at low to moderate doses, with the potential to elicit anti-anemic effects, reduce the risk of atherosclerosis and cardiovascular disease, and enhance antioxidant status in the brain and liver. Although possibly beneficial at low to moderate doses, the extract could be harmful to the testes with prolonged oral exposure at high dose.

Toxicity and Detoxification Mechanism of Black Pepper and Its Major Constituent in Controlling Rhynchophorus ferrugineus Olivier (Curculionidae: Coleoptera)

The survival, feeding response, and detoxification mechanism of Rhynchophorus ferrugineus Olivier, a key pest responsible for destruction of date palm, was examined with different extracts of Piper nigrum and its major constituent (piperine) identified by GC-MS. In the present study, toxicity of different extracts of black pepper was evaluated by incorporating diffferent doses of extracts into the artificial diet of red palm weevil larvae. All extracts showed dose-dependent insecticidal activity to the tested eighth-instar red palm weevil larvae. Among all the extracts, maximum larvicidal activity was exhibited by chloroform (LD₅₀ = 342.62 mg/l), followed by dichloromethane (LD₅₀ = 357.78 mg/l), acetone (LD₅₀ = 372.57 mg/l), and ethanol (LD₅₀ = 408.88 mg/l). However, piperine, a major constituent of all black pepper extracts identified by GC-MS in the present work, was found to be the most potent treatment exhibiting the least LD₅₀ (219.88 mg/l). In addition, nutritional indices evaluated by calculating the efficiency of the conversion of ingested food (ECI) and digested food (ECD) at the same dose (219.88 mg/l) showed that there was maximum reduction in the ECI (49.90%) and ECD (62.21%) index of larvae fed diets incorporated with piperine. Larvae that were fed diets incorporated with different black pepper extracts experienced increases in the expression of detoxification genes (glutathione S-transferase and cytochrome P450), and this upregulation in detoxification genes (glutathione S-transferase, cytochrome P450 and esterase) was tremendously high in larvae fed diets incorporated with piperine. Results suggest that piperine is a promising bio-pesticide agent for the control of R. ferrugineus Olivier.