Stored-product Insect Pests Research Articles

High concentrations of piperonyl butoxide (PBO) enhance toxicity of S-methoprene against the lesser grain borer, Rhyzopertha dominica.

Insect growth regulators (IGRs) have been playing a major role in the effective management of a range of stored product insect pests including species that have developed resistance to major groups of insecticides, such as organophosphates (OPs) and synthetic pyrethroids (SPs). In the present study, we evaluated the efficacy of S-methoprene alone and in combination with piperonyl butoxide (PBO), an adjuvant component of insecticides for synergy, against two strains, Lab-S (susceptible) and Met-R (Methoprene resistant) of an economically important pest species, the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae). Adults of both Lab-S and Met-R strains were exposed to wheat treated with multiple concentrations of S-methoprene ranging from 0.001 to 0.01 and 10 to 60 mg/kg, respectively, alone and in combination with PBO. A variety of concentrations, including 0.27, 0.53, 0.80, and 1.07 g/kg, were evaluated for PBO. Mortality of adults and percent reduction in progeny were assessed after 14 and 65 days of treatment, respectively. As anticipated, the adult mortality rates of both strains were not significantly affected by S-methoprene alone. However, the number of progeny produced confirmed that the Met-R strain exhibited a high level of resistance to S-methoprene alone, with over 50 F1 progeny adults surviving in wheat treated with the maximal rate, 10 mg/kg. In contrast, the toxicity of S-methoprene was increased against the same resistant strain (Met-R), by 0.80 or 1.07 g/kg of PBO in combination treatment, resulting in a significant reduction in progeny numbers (25 adults per container). Although the tested concentrations of S-methoprene and PBO were well above the currently registered rate globally, our results highlight the fact that PBO enhances the toxicity of S-methoprene to some extent, reaffirming that the mode of action of the latter involves the inhibition of mixed-function oxidases (MFOs) and highlights the need for further research into developing potential binary or triplet formulations containing these two active ingredients (AIs).

Effects of nutrition on recovery, mortality, and mobility of adult Tribolium castaneum after exposure to long-lasting insecticide-incorporated netting.

Long-lasting insecticide-incorporated netting (LLIN) has been used to deliver contact insecticides as an integrated pest management tool for stored product insect pests in food facilities. Although the presence of food is known to improve insect recovery after exposure, it is not clear whether food nutritional quality plays a role. Here, the red flour beetle Tribolium castaneum adults were exposed to two commercially available LLINs, Carifend (active ingredient α-cypermethrin) and D-Terrence (deltamethrin), then transferred to Petri dishes with foods with varying nutritional quality (e.g., 0-100% ratios of flour to non-nutritive cellulose). We investigated the effects of nutrition, LLIN type, and exposure time on post-exposure recovery, mortality, and mobility. After exposure for 2-168 h, the immediate mortality of T. castaneum adults ranged from 0.5% to 91.0% with Carifend and 0% to 75.3% with D-Terrence. Adult recovery and delayed mortality were significantly affected by nutritional quality, LLIN type, exposure time, and recovery time. For both LLINs, adult recovery increased over time, with a trend for higher recovery and lower mortality with increasing nutritional quality and decreasing exposure time. In addition, adult mobility decreased multiple-fold after Carifend or D-Terrence exposure for 30, 60 or 90 min compared to 10 min. This study shows nutrition significantly modulates the efficacy of LLIN against T. castaneum, and thus strengthens the rationale for implementing stringent sanitation protocols for food facility managers. © 2024 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Evaluation of the crude chitinases toxicity on the reproductive system of Callosobruchus maculatus (Coleoptera: Bruchidae)

Insecticides represent the most used control method against the insect pests of stored food products. But there are strains of insects which are resistant to these insecticides: it is the case of the beetle of the chickpea Callosobruchus maculatus. The present study has for objective the evaluation of the biological activity of chitinolytic enzymes extracted from the fish offals Scorpaena scrofa (scorpion fish) on this beetle at different doses (3%, 6%, 9%, 12%, 15% and 21%) prepared with the buffer solution. The results obtained from three treatments (T1, T2 and T3) realized according to the dose of the crude enzyme and the time of exposure were compared with those of the controls and have showed a very significant efficiency of our crude enzyme on the reduction of the fertility rate of 100% by treating the couple (T1) at the same time as to treat the male (T3) and the female (T2) separately with the strongest dose (21%) for 48 h of exposure. It would be thus desirable to demonstrate the activity of these enzymes in the real conditions of storage.

Effects of Some Plant Powders on Immatures of Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) on Stored Cocoa Beans

Rice moth, Corcyra cephalonica, an important insect pest of many stored food products has been reported as one of the most important pest of cocoa bean, which causes significant reduction in weight and quality of beans. High pesticides level in cocoa beans pose danger to human health and may hinder its acceptance in the global market due to regulations on Maximum Residue Limit (MRL). This study therefore, evaluated the insecticidal effects of the powders of Piper guineense, Aframomum melegueta, Eugenia aromatica and Rice husk on egg hatchability and larva mortality of C. cephalonica. Powder efficacies as insecticides were tested by applying varying rates (0.0, 0.1, 0.2, 0.3 and 0.4g) on petri dish lined with filter paper and the developmental stages (20 eggs and 10 larvae) of the insect were introduced in a Completely Randomized Design experiment. Egg hatchability was recorded at 24 h interval for 96 h. Larvae mortality was recorded at every 24 and 48 h of introduction. All powders completely inhibited egg hatchability at 0.3 and 0.4g rates. P. guineense and A. melegueta recorded 60% and 50% larva mortality at 48hour post treatment. Mean adult emergence was zero at higher rates in all treatments. Powders of P. guineense and A. melegueta were effective as contact bio-insecticide against C. cephalonica immature stages

The Evaluation of Toxicity Effects of Synthetic Volatile Compounds and Essential Oils on Callosbruchus maculatus L. and its Biology

The biology studies and contact toxicity of synthetic volatile compounds, namely Propionic acid and Benzaldehyde, and essential oils namely, Ocimum basilicum and Mentha piperita, and their different possible combinations evaluated against Callosobruchus maculatus and were carried out at the Department of Entomology, Annamalai University to develop an economically viable and effective alternative to chemical insecticides to manage the stored product insect pests. In the biology study, the egg period was 5±0.07 days. The larval and pupal period together was 21.24±0.67. The total development period recorded from the day of oviposition to adult emergence was 35.03±0.35 days. The maximum contact toxicity was observed in Propionic acid + Benzaldehyde with 8.73 µl LC50. Therefore, in addition to being incorporated into the storage pest management to prevent the development of resistance, combinations of essential oils and synthetic volatiles, such as propionic acid and benzaldehyde, could be used as an alternative to the chemical fumigants that are mostly used to control pests of stored products.

Toxicity of Essential Oil from Plectranthus amboinicus (Lamiales: Lamiaceae) against Sitophilus zeamais (Coleoptera: Curculionidae)

Abstract Maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), is a major insect pest of stored grain products, causing extensive damage to both grain quantity and quality. The application of synthetic insecticides to control this insect has a negative impact on human health and the environment. Essential oils derived from natural plants are recognized as user- and environmentally friendly alternatives. The use of essential oils from Lamiaceae, which exhibit toxic properties through contact, fumigation, and repellency, provides another option for protecting stored products from various insect pests. The aim of this research was to study the chemical constituents and insecticidal activity of essential oil extracted from the leaves of Indian borage, Plectranthus amboinicus (Lour.) (Lamiales: Lamiaceae), against S. zeamais adults.The chemical composition of the essential oil was analyzed using gas chromatography–mass spectrometry, and the insecticidal activity against adult maize weevils was investigated in the laboratory. The experimental plan followed a completely randomized design with five replications of seven treatments or concentrations of the essential oil: 0, 0.5, 1, 1.5, 2, 2.5, and 3 µl/ml air. The results revealed that the essential oil from the leaves of P. amboinicus contained 23 chemical constituents (97.51%). Thymol (49.96%) was identified as the main compound followed by caryophyllene, trans-α-bergamotene, 3-methyl-4-isopropylphenol, γ-terpinene, p-cymene, caryophyllene oxide, humulene, 4-hydroxy-2-methylacetophenone, 2-hydroxy-2-phenylbutyramide, (2-oxazolidinylidene)malononitrile, hexestrol, terpinen-4-ol, 1-octen-3-ol, (1R,7S,E)-7-isopropyl-4,10-dimethylenecyclodec-5-enol, α-bisabolene, isoaromadendrene epoxide, α-farnesene, 4-carene, α-muurolene, 3-hexen-1-ol, ledene oxide-(II), and α-myrcene, respectively. The fumigation toxicity (median lethal concentration) to maize weevil adults at 48 h was 292.53 µl/ml air. The essential oil from the leaves of P. amboinicus, when applied at a concentration of 2 µl/ml air for 144 and 168 h, resulted in adult maize weevil mortality exceeding 90%. The highest concentration tested (3 µl/ml air) led to exceptionally high mortality rates, with 99–100% of the maize weevils succumbing to the treatment. These findings demonstrate that essential oil from P. amboinicus leaves holds promise as a fumigation insecticide for reducing the population of maize weevils, a significant pest in stored products.

Influence of molecular descriptors of plant volatilomics on fumigant action against the three major stored product beetle pests.

Plant volatilomics such as essential oils (EOs) and volatile phytochemicals (PCs) are known as potential natural sources for the development of biofumigants as an alternative to conventional fumigant pesticides. This present work was aimed to evaluate the fumigant toxic effect of five selected EOs (cinnamon, garlic, lemon, orange, andpeppermint) and PCs (citronellol, limonene, linalool, piperitone, andterpineol) against the Callosobruchus maculatus, Sitophilus oryzae, and Tribolium castaneum adults. Furthermore, for the estimation of the relationship between molecular descriptors and fumigant toxicity of plant volatiles, quantitative structural activity relationship (QSAR) models were developed using principal component analysis and multiple linear regression. Amongst the tested EOs, garlic EO was found to be the most toxic fumigant. The PCs toxicity analysis revealed that terpineol, limonene, linalool, and piperitone as potential fumigants to C. maculatus (< 20 µL/L air of LC50), limonene and piperitone as potential fumigants to T. castaneum (14.35 and 154.11 µL/L air of LC50, respectively), and linalool and piperitone as potential fumigants to S. oryzae (192.27 and 69.10 µL/L air of LC50, respectively). QSAR analysis demonstrated the role of various molecular descriptors of EOs and PCs on the fumigant toxicity in insect pest species. In specific, dipole and Randic index influence the toxicity in C. maculatus, molecular weight and maximal projection area influence the toxicity in S. oryzae, and boiling point and Dreiding energy influence the toxicity in T. castaneum. The present findings may provide insight of a new strategy to select effective EOs and/or PCs against stored product insect pests.

Efficacy of Botanical Oils on Adult Mortality, Egg Laying, Hatchability and Adult Emergence of Callosobruchus. Maculatus (F.) (Coleoptera: Chrysomelidae: Bruchidae)

The cowpea weevil Callosobruchus maculatus Fabricius, is the major insect pest that threatens effective legume storage. The laboratory experiment was conducted to assess the efficacy of four different botanical oils (Clove, Eucalyptus, Jojoba and Lemon) against the cowpea weevil, C. maculatus by using residual film technique. All the botanical oils were applied at two different concentration levels (0/50 and 0.75%). The results showed that all used oils significantly increased the mortality and reduced the mean number of eggs laying, hatchability and emergence percentages compared to the untreated control. The treatment of cowpea seeds with oils reduced slightly the germination but swelling percentage was higher in treated seeds than control. The results also indicated variation in the activity of botanical oils regarding the stage of the insect, the plant origin of the oils and concentration level. The present study suggested that botanical oils (Clove, Eucalyptus, Jojoba and Lemon) may be preferred option than conventional pesticides far the protecting stored pulse grains against stored products insect pests’ infestation, especially C. maculatus.

Physicochemical comparison of chitin characteristics in three major stored-product beetle pests: Implications for biofumigant toxicity

The present study investigates the chitin properties of stored-product insect pests and their association with the fumigant toxicity of garlic essential oil. Chitin isolates of Callosobruchus maculatus, Sitophilus oryzae, and Tribolium castaneum adults were characterized using FT-IR, XRD, EA, SEM-EDS, and NMR techniques. Fumigant toxicity assay was performed under airtight condition in glass vial. The S. oryzae contains highest chitin content (19 %), followed by T. castaneum (10 %) and C. maculatus (8 %). The degree of crystallinity was lower in C. maculatus (67.13 %) than in S. oryzae (77.05 %) and T. castaneum (76.56 %). Morphologically, C. maculatus chitin displayed a flat lamellar surface with pores, while S. oryzae and T. castaneum exhibited densely arranged microfibrils based surfaces. Fumigant toxicity assays revealed varied susceptibility levels, C. maculatus exhibited higher susceptibility (0.27 μL/L air of LC50) compared to S. oryzae and T. castaneum (14.35 and 3.74 μL/L air of LC50, respectively) to garlic essential oil. The higher chitin content, greater crystallinity, and densely arranged structures in S. oryzae might contribute to its tolerance towards fumigant. Additionally, physico-chemical properties and penetration potentiality of the bioactive constituents might be linked to the toxicity in insects. Understanding these relations can enrich knowledge of chitin's role in fumigant toxicity mechanism.

Stored products insects in Portugal – New data and overview

The introduction of stored product insect pests to new areas is facilitated by food trade among countries, and effective detection and monitoring programs are crucial for food security. The khapra beetle, Trogoderma granarium Everts is one of the most destructive insect species. In Portugal, T. granarium has been detected in 1988. However, no new data has been added to this information since that date. Floor traps with pheromones specific to T. granarium were used and placed inside ports, mills, and storage facilities, including warehouses and silos, between June and September in 2017, 2019, 2021, and 2022.Previous results from other sampling programs conducted between 2002 and 2008 are also referred here to add more evidence for the presence or absence of T. granarium in Portugal. Here, various types of traps, including some generalists and others with pheromones (such as T. granarium), were used. The collected insects were identified to species, or genus.Surveys conducted identified approximately 40 insect species that are associated with stored products, in a total of 23.725 insects, and among them, the weevils belonging to the genus Sitophilus C.J.Schoenherr have been recognized as the main pests that affects stored cereals. Regarding the surveys made between 2017 and 2022 and previous surveys done in Portugal (between 2002 and 2008; n = 26.719 insects identified), no T. granarium individuals were detected in any of the entomological samples, and only a few Dermestidae specimens were found across all surveys, one of them belonging to the same genus, identified as Trogoderma inclusum LeConte. With the predicted changes in climate, there is a risk of introducing T. granarium and other destructive insect pests that could displace Sitophilus weevils as the key stored products pest in Portugal. Therefore, it is crucial to monitor and implement measures to prevent the spread of invasive pests for effective pest management and food security purposes, using proper trapping methods and accurate and rapid identification tools.

Plant‐Based Products as Control Agents of Stored Product Insect Pests: Prospects, Applications and Challenges

Stored product insect pests pose a significant threat to global food security and economic stability, as they cause substantial damage to stored grains and other food commodities. Traditional pest control methods often rely on chemical insecticides, which can have adverse effects on the environment, human health, and food safety. In light of these concerns, there is growing interest in exploring sustainable and eco-friendly alternatives for managing stored product insect pests. This abstract highlights the potential of plant-based products as a viable and environmentally friendly approach to control stored product insect pests. Plant-based products, such as botanical extracts and essential oils, are derived from various plant sources and have shown promise in repelling, deterring, and even killing insect pests. These products offer several advantages, including biodegradability, reduced chemical residues, and minimal harm to non-target organisms. This review summarizes recent research on the efficacy of plant-based products against a range of stored product insect pests, including but not limited to beetles, weevils, and moths. It discusses the mechanisms through which these products exert their pest control effects, such as disrupting insect behavior, affecting their reproduction, or inducing mortality. Moreover, the potential synergistic effects of combining plant-based products with other pest management strategies, like hermetic storage and modified atmospheres, are explored. In addition, this abstract examines the challenges and limitations associated with the use of plant-based products in pest management, including issues related to formulation, stability, and the need for further research to standardize application protocols. The economic feasibility and scalability of plant-based pest control methods are also considered. The findings presented in this abstract emphasize the importance of incorporating plant-based products into integrated pest management strategies for stored product insect pests. These products have the potential to contribute to a more sustainable and environmentally friendly approach to safeguarding global food reserves, while minimizing the risks associated with chemical pesticides. Further research and collaboration between the scientific community, agricultural industry, and policymakers are essential to harness the full potential of plant-based products in the fight against stored product insect pests.

Infestation and storages in Balochistan during 2019-2020

The present study was aimed to inspect the stored product insect pests from different godowns (Governmental and Private) of four districts namely Quetta, Pishin, Loralai and Sibi (two from cold and two from hot climatic regions). Insect pests damaging cereals were collected from godowns of these localities. The collections were made on a monthly basis from five (Private/Govt./Plinth) godowns of each district. All insect pests were collected during January -December 2019-2020. These samples were identified by using the standard identification keys [1–3]. Tribolium castaneum showed the highest increase, from 10.28% in 2019 to 13.54% in 2020. Trogoderma granarium also had a significant increase from 9.28% to 12.25%, followed by Rhizopertha dominica with an increase from 7.18% to 9.83%. Sitophylus oryzae showed a smaller increase from 7.18% to 8.40%, while Angoumois grain moths had the smallest increase from 1.06% to 1.59% in Sibi while least population was noticed in Quetta as Tribolium castaneum were found with 5.03% and increased to 7.25% in 2020. Trogoderma granarium from 3.80% to 5.56%, Rhizopertha dominica were from 2.67% to 3.48%, Sitophylus oryzae from 1.75% to 1.49% and Angoumois grain moths were collected from 0.51% to 0.41%. The collected data also reveal that in governmental godowns the population of stored product insect pests were found higher than the private godowns due to their basic facilities. The values in Sibi showed an increase from 11.74% to 16.42% in 2020 for government godowns and an increase from 6.95% to 12.30% in open areas. Private godowns had 15.34% in 2019 and increased to 16.89% in 2020. Similarly, Loralai and Pishin government godowns also showed an increase in insect pests in 2020. In contrast, Quetta government godowns had a relatively stable percentage of insect pests in 2019 and 2020, while private godowns showed an increase from 2.88% to 4.04%. The present study is the first of its kind and is helped full for the identification and prevalence of different stored product pests in different storages of Balochistan during 2019-2020 in Covid condition.

Efficiency of Utilizing Citrullus colocynthis (L) Essential Oil Alone and When it Mixed with Diatomaceous Earth Against some Stored Products Insect Pests

Efficiency of Utilizing Citrullus colocynthis (L) Essential Oil Alone and When it Mixed with Diatomaceous Earth Against some Stored Products Insect Pests

Phosphine resistance among stored product insect pests: A global meta-analysis-based perspective

Phosphine resistance among stored product insect pests: A global meta-analysis-based perspective

Current status of phosphine resistance in Indian field populations of Tribolium castaneum and its influence on antioxidant enzyme activities

Resistance to phosphine is widely reported in several stored product insect pests globally. However, knowledge of its prevalence and the association of antioxidant enzymes with phosphine resistance is limited. Herein, we assessed the levels of phosphine susceptibility and estimated the antioxidant enzyme activities viz., superoxide dismutase (SOD), peroxidase (POX), and catalase (CAT) in selected Indian populations of red flour beetle Tribolium castaneum (Herbst). Dose–response probit assays revealed that the LC50 values ranged from 0.038 to 1.277 mg L−1 showing 2.11 to 70.94-fold resistance to phosphine compared to susceptible check. Activities of antioxidant enzymes varied significantly between the T. castaneum populations following phosphine exposure. The magnitude of SOD activity ranged from 8.77 to18.82 U mg−1 protein, while, the activities of POX and CAT varied between 52.42 and 408.32 and 61.11 to 247.49 µM H2O2 reduced min−1 mg−1 of protein, respectively. The correlation analysis revealed a significant positive association of SOD (r = 0.89) and POX (r = 0.98) with increased resistance ratio, while the CAT (r = − 0.98) is negatively linked with resistance to phosphine. A principal component analysis identified phosphine resistance was closely associated with POX and SOD activities but was unrelated to the CAT activity. Our results throw light on the varied association of antioxidant enzyme activities in response to phosphine fumigation in field populations of T. castaneum. Further studies on the biochemical and molecular basis of phosphine stress in insects may help to devise suitable strategies to safeguard storage commodities and ensure a sustainable environment.

Antioxidant and detoxifying enzymes response of stored product insect pests to bioactive fractions of botanical extracts used as stored grains protectant

Recurrent exposure of stored product insects to synthetic insecticides resulted in the development of resistance which occurs due to changes in insect metabolic enzymes. The inhibitory effect of ethyl acetate active fraction of Mitracarpus villosus, Bridelia micrantha, and Clerodendrum capitatum on antioxidant and detoxifying enzymes of stored product insects was investigated in this study. Sitophilus oryazae, Tribolium castaneum, and Rhizopertha dominica were exposed to 5 and 20 μl concentrations of ethyl acetate active fraction VI 50:50 derived from glass column chromatography in a fumigation chamber and were homogenized separately. The results showed that SOD, CAT, GPx, GSH, and GST activities were dosage-time-dependent. Adult insects exposed to different dosages of C. capitatum active fractions significantly inhibited GST and GPx activities, and SOD, CAT, and GSH activities were induced in comparison to insects in control. While, M. villosus and B. micrantha extracts exhibited a significant increase (p &lt; 0.05) in SOD, CAT, and GSH in contrast to the inhibitory effects on GST and GPx. These results clearly show that stored beetles differ in their response to different enzymatic activities and that the evaluated plant materials may be used as an eco-friendly biopesticide in the IPM strategy for safeguarding stored food grains against stored produced insect pests.

Identifying common stored product insects using automated deep learning methods

Monitoring stored product insect pests is a common practice for post-harvest management of stored grain and grain-based commodities, which helps ensure product quality from harvest to final consumer. Current methods of sampling and monitoring can be time-consuming, labor-intensive, expensive and require expertise in insect identification. Therefore, this study aims to develop an image-based automated identification system for common stored product insect species using deep-learning methods. Top-down images of the common stored product adult insect species of Rhyzopertha dominica, Cryptolestes ferrugineus, Tribolium castaneum, Sitophilus oryzae, and Oryzaephilus surinamensis were acquired and analyzed. Deep learning-based, state-of-the-art Convolutional Neural Networks (CNN) models (ResNet-50, MobileNet-v2, DarkNet-53, and EfficientNet-b0) were fine-tuned with a transfer learning approach to classify the insect species. All models were able to correctly identify the insect species with at least 96% accuracy and with few misclassifications. One issue with trained CNNs is that they do not explain the reasoning for the classification and are often called a “black box”. Therefore, visualization methods called Gradient-weighted Class Activation Mapping (Grad-CAM) were implemented to explore the black box network. The Grad-CAM uses heat maps to highlight the major image features that the network focused on to make insect species predictions. The Grad-CAM verifies the network's prediction and also helps improve network performance. This study contributes to the overall goal of developing a camera-based system for monitoring stored grain insects. The developed system would empower warehouse, flour mills, and other food facilities with a tool to quickly and accurately identify insect species in stored product environments and could be implemented as part of a close to real-time monitoring system.

Fabrication of Carum copticum essential oil-loaded chitosan nanoparticles and evaluation its insecticidal activity for controlling Rhyzopertha dominica and Tribolium confusum.

Plant essential oils (EOs) can be used as a feasible tool for insect pest control. Nanoparticle formulations of plant EOs can improve the efficiency and stability of EOs, as well as insecticidal potential. In this study, Carum copticum L. essential oil-loaded nanoparticles (OLNs) were prepared via an oil-in-water emulsion, followed by droplet solidiffication via ionic gelation using a cross-linker, sodium tripolyphosphate (TPP). The nanoparticles were characterized by ultraviolet and visible (UV-Vis) spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), laser light scattering (LS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Moreover, the insecticidal activity of C. copticum EO and OLNs was evaluated against Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Tribolium confusum Jacquelin du Val. (Coleoptera: Tenebrionidae). In addition, their effectiveness was assessed on the progeny production of tested insect species. The loading efficiency ranged from 34.33 to 84.16% when the chitosan to EO weight ratio was 1:1.25 and 1:0.5, respectively. The loading efficiency decreased with increasing EO content in the nanoparticles. The OLN particles exhibited spherical shape. The particle size was in the range 120-223.6 nm and increased with the increase of EO to chitosan ratio. So that the largest mean particle size (223.6 nm) was reported in the 1:1.25 weight ratio of chitosan to the EO. The mortality percentage of R. dominica and T. confusum adults were 74 and 57% when exposed for 7 days to 2000 mg/kg of OLNs at the 1:1.25 weight ratio, while EO caused 62 and 44% mortality on both insect species, respectively. Therefore, OLNs can potentially improve the insecticidal activity of C. copticum EO and could be applied to facilitate control of stored-product insect pests.

MicroR-9c-5p and novel-mir50 co-target Akt to regulate Lasioderma serricorne reproduction.

High fecundity is a common characteristic of insect pests which increases the difficulty of population control. Serine/threonine kinase Akt is an indispensable component of the insulin signaling pathway. Silencing of LsAkt severely hinders reproduction in Lasioderma serricorne, a stored product insect pest. However, the post-transcriptional pathway of LsAkt in L. serricorne remains unknown. This study identified 2 binding sites of miR-9c-5p and novel-mir50 in the coding sequences of LsAkt. The expression profiles of 2 microRNAs (miRNAs) and LsAkt displayed an opposite pattern during the adult stages. Luciferase reporter assay showed that novel-mir50 and miR-9c-5p could downregulate the expression of LsAkt. Overexpression of miR-9c-5p and novel-mir50 by injection of mimics inhibited the expression of LsAkt and reduced oviposition, decreased egg hatchability, and blocked ovarian development. It also decreased the expression of genes involved in ovarian development (LsVg and LsVgR) and the nutritional signaling pathway (LsTOR, LsS6K, and Ls4EBP), and reduced the phosphorylation of Akt. Conversely, injection of miR-9c-5p and novel-mir50 inhibitors induced the expressions of LsAkt, LsVg, LsVgR, LsTOR, LsS6K, and Ls4EBP, enhanced Akt phosphorylation level, and accelerated ovarian development. Injection of bovine insulin downregulated the expression of miR-9c-5p and novel-mir50 and upregulated the LsAkt expression. It also rescued the reproductive development defects associated with miR-9c-5p/novel-mir50 overexpression, forming a positive regulatory loop of insulin signaling. These results indicate that miR-9c-5p/novel-mir50 regulates the female reproduction of L. serricorne by targeting Akt in response to insulin signaling. The data also demonstrate the effects of the insulin/miRNA/Akt regulatory axis in insect reproduction.

Numerical responses of the predatory mites, Cheyletus eruditus (Trombidiformes: Cheyletidae) and Cheyletus malaccensis, to Liposcelis decolor (Psocodea: Liposcelididae).

Predatory mites display diverse ecological mechanisms to suppress pest population density below certain thresholds known to cause economic loss. The current study explored the numerical responses of the predatory mites, Cheyletus eruditus (Schrank) (Trombidiformes: Cheyletidae) and Cheyletus malaccensis Oudemans, to Liposcelis decolor (Pearman) (Psocodea: Liposcelididae). The numerical responses of these 2 cheyletid mites to nymphs, adult males, and adult females of L. decolor were determined under laboratory conditions at 24 ± 1 °C, 85 ± 5 RH, and 0:24 (L:D) photoperiod. Oviposition rate, oviposition efficiency, and efficiency of conversion of ingested (ECI) food resources were the key numerical response parameters assessed. The present study revealed a general trend of a strong negative and positive correlation between oviposition rates and increase in prey densities (number of prey per 16.98 cm2) for C. eruditus and C. malaccensis, respectively. The oviposition efficiency was mostly similar for both predatory mites and was inversely related to prey density. Generally, ECI (%) decreased considerably with increasing prey density across different prey types for both predators, however, C. malaccensis was more efficient than C. eruditus in utilizing prey biomass. Given the relatively weak numerical responses, we recommended further assessment of these predatory mites before recommending their use for managing stored-product insect pests in the United States.