Zeamais Adults Research Articles

Olfactory Response of Sitophilus zeamais Adults to Odours of Semolina Pasta and Semolina Pasta Enriched with Different Amounts of Acheta domesticus Powder.

The behavioural response of adult maize weevil, Sitophilus zeamais, to different types of semolina pasta enriched or not enriched with increasing proportions (5%, 10%, and 15%) of house cricket (Acheta domesticus) powder was investigated in olfactometer arena bioassays by using trap devices. In the five-choice behavioural bioassays, the number of S. zeamais adults attracted to 100% durum wheat semolina pasta was significantly higher than those attracted to the other pasta types enriched with A. domesticus powder. In the two-choice behavioural bioassays, the Response Index for each pasta type was positive and significant. However, although not significant, there was a progressive reduction in the Response Index as the cricket powder content increased. In similar experiments, there were no significant differences between cricket powder alone and the control in the number of attracted S. zeamais, indicating a neutral effect towards insects. These observations suggest that the lower attractiveness of pasta enriched with house cricket powder is mainly due to the masking of host food odours. Solid-phase microextraction coupled to gas chromatography-mass spectroscopy identified a total of 18 compounds in the head-space samples of the different types of pasta, highlighting differences in volatile composition. Some volatile compounds were only present in the pasta produced with cricket powder. In particular, 1-octen-3-ol and phenol were present in the samples containing 5%, 10%, or 15% cricket powder; pentanal, benzaldehyde, and dimethyl disulphide were present in samples containing 10% or 15% cricket powder; and 2,5-dimethyl-pyrazine was present in the sample containing 15% cricket powder. Further investigation with individual compounds and mixtures is needed to define the chemical basis of the differences in the insect olfactory preference observed in this study.

Insecticidal formulation based on essential oil from Ocimum basilicum Linn. Herb supported onto modified kaolinite for stored maize protection

In this study, essential oil was obtained by hydrodistillation from the leaves of Ocimum basilicum and it was analyzed by GC-MS. Eucalyptol (11.19 %), trans-iso eugenol (13.12 %), hexadecanoic acid methyl ester (19.26 %) and 9-octadecenoic acid (z)-methyl ester (25.12 %) had been the leading four main components of the plant leaves of the essential oil. The unmodified and modified kaolin was characterized and analyzed by XRD, FT-IR, TGA and SEM/EDX and thus the principal mineral of the nanoclay was proved to be kaolinite. The hydrodistiled essential oil in the absence of the clay support was evaluated within 24 h of exposure time and the outcome revealed that it was insecticidally active against the maize weevil, S. zeamais adults. Moreover, the exposure time effect, the formulation efficiency, the effect of remnant and stability of the prepared formulations were investigated and the results indicated an enhancement of bioinsecticides for a long period with upgraded persistence against the S. zeamais. Finally, the results recommend that O. basilicum essential oil - modified kaolinite formulations should be used as best options to chemical insecticides in pest control of stored products like stored maize grain insects, S. Zeamais.

Analysis of potential volatile organic compounds in Sitophilus zeamais (Coleoptera: Curculionidae)-infestedwheat based on lipid oxidation-a reference to early and rapid detection method.

The maize weevil, Sitophilus zeamais Motschulsky, is a hidden pest that presents serious risk to grain quality during postharvest storage. Lipid-derived volatile detection is considered a key reference for early prediction of S. zeamais infestation. However, the exact compositions of fatty acids and volatile organic compounds (VOCs) in S. zeamais-infested wheat are yet to be determined. In this study, we aimed to explore the effect of S. zeamais infestation on lipid metabolism in wheat infested with S. zeamais eggs (4 days), larvae (20 days), pupae (35 days), and adults (45 days). Compared to those in the control group, the activities of lipid oxidation enzymes, such as lipase, lipoxygenase, and alcohol dehydrogenase, increased by 82.73%, 105.12%, and 487.86%, respectively, during the storage period of 1 life cycle of S. zeamais. Additionally, the fatty acid composition of S. zeamais-infested wheat was significantly altered (palmitic acid [1.10-fold], oleic acid [1.07-fold], and linoleic acid [0.95-fold]). Furthermore, 91 VOCs were identified in all wheat samples; then, multivariate statistical analyses categorized these samples into 4 groups: uninfested, longer storage, lightly infested, and heavily infested. Moreover, 31, 26, and 45 potential VOCs were identified to distinguish uninfested wheat from those in the other 3 groups. These results demonstrated that S. zeamais infestation induces an elevation in lipid-related enzymatic activities, which potentially leads to a decrease in lipid content alongside the production of specific VOCs (undecan-4-olide, heptaldehyde, and 2-nonenal). These findings provide novel insights for rapidly identifying grains infested by hidden pests and effectively managing these pests during grain storage.

Olfactory Preferences of Sitophilus zeamais to Cereal- and Legume-Based Pasta.

We compared the attractiveness of five commercially available Italian macaroni pastas of different shapes (penne, casarecce, and fusilli) made from cereals and/or legumes [100% Triticum durum; 100% Cicer arietinum; 100% Lens esculenta; 50% Triticum durum + 50% Cicer arietinum; 60% Triticum durum + 40% Lens esculenta] to adults of Sitophilus zeamais (L.). A multiple-choice walking bioassay showed that S. zeamais adults were more attracted to cereal than legume pastas. The modified Flit-Track M2 trap devices baited with pasta made with 100% T. durum captured an average of 61.4% of the adults released into the olfactometric arena after 7 days. Of the insects tested, pasta made with 100% C. arietinum trapped 3.8%, pasta made with 100% L. esculenta trapped 2.7%, pasta made with 50% T. durum + 50% C. arietinum trapped 4.3%, and pasta made with 60% T. durum + 40% L. esculenta trapped 4.2%. When individually compared, 79.6% of S. zeamais adults chose the Triticum durum pasta. Orientation to 100% Cicer pasta or 100% Lens pasta was not observed. In the choice test, only 37% and 25% were attracted to Triticum and Cicer pastas or Triticum and Lens pasta, respectively. Our results confirm that the low attractiveness of legume pasta is mainly due to the lack of attractant stimuli rather than the emission of repellent compounds. From a practical perspective, it is also interesting to note how mixed pasta decreases the risk of S. zeamais infestation.

Entomotoxicity of ZnO NPs synthesized using Clausena anisata Hook.f. ex Benth(ulmaayii) leaf extract against maize weevil, Sitophilus zeamais Mostch (Coleoptera: Curculionidae)

The application of leaf extract to synthesize nanoparticles has been taken as a green method. In this study, the potential for synthesizing zinc oxide nanoparticles (ZnO NPs) from Clausena anisata Hook.f. ex Benth. leaf extract was investigated. The source of zinc was zinc nitrate hexahydrate (Zn(NO3)2.6H2O). The characterization study was done by Ultraviolet–visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), Transmission electron microscope (TEM) and atomic force microscopy (AFM). The crystalline shape of nanoparticles is disclosed inside the XRD result, morphology is confirmed through SEM effects, and consequently, the ZnO NPs scale was predicted. ZnO NPs were synthesized to work against Sitophilus zeamais adults. A mortality count was carried out in 14 days and all the 3 dosages (0.2 g, 0.4 g and 0.6 g) were effective in killing S. zeamais. F1 progeny emergence was highly reduced in comparison to untreated control. Maize seeds were successfully germinated after treatment application with ZnO NPs.

Activity of nanoemulsion botanical insecticides from Myristica fragrans and Jatropha curcas essential oil against Sitophilus zeamais

Abstract. Nuryanti NSP, Budiarti L, Dulbari, Sutrisno H, Sudrajat D, Yuriansyah, Priyadi, Rahmadi R, Rochman F, Sari EY, Maharani JS. 2023. Activity of nanoemulsion botanical insecticides from Myristica fragrans and Jatropha curcas essential oil against Sitophilus zeamais. Biodiversitas 24: 5610-5617. Maize weevils also known as Sitophilus zeamais, are primary pests that decrease in the quality and quantity of grain products. This study aimed to examine the impact of nanoemulsion formulas of Myristica fragrans and Jatropha curcas essential oils on S. zeamais adults. The investigation focused on the toxicity, ability to inhibit population growth, intensity of damage caused, and effect on seed weight loss. The essential oils were extracted using the distillation method, and the toxicity was tested through contact, fumigant, and seed dressing. A probit program was used to analyze the toxicity level (LC50 and LC95). The results showed that M. fragrans essential oil had the highest toxicity in contact treatment and the lowest when applied via fumigation. Furthermore, this method shows an LC50 value for the contact method of 0.53% and fumigation of 1.01%, while the LC95 value is 4.38% and 10.60% respectively. Based on the LC95 botanical insecticide from J. curcas, all three methods were toxic to S. zeamais adults, with contact being the highest, followed by seed dressing, and fumigant, at 5.23, 6.44, and 19.94%, respectively. The botanical insecticides derived from M. fragrans essential oil through contact provided the best inhibitory activity on population development, intensity of damage, and seed weight loss, with values of 18.00, 16.81, and 13.96%. Plant-based pesticides not only cause pest mortality but also maintain seed quality by reducing weight loss, intensity of pest attacks, and inhibiting the development of pest populations in storage.

Effects of Annona squamosa leaf extract on the insects Aedes aegypti, Nasutitermes corniger, and Sitophilus zeamais and the microcrustacean Hyalella sp.

The high environmental toxicity of currently used insecticides and the emergence of resistant insect populations have prompted the search for new agents to control insect pests. In this study, we characterized a saline extract from Annona squamosa L. leaf to determine its chemical constituents and effects on third instar Aedes aegypti L. larvae, Nasutitermes corniger Motsch. workers and soldiers, Sitophilus zeamais Motsch. adults, and Hyalella sp. juveniles. The extract showed a protein concentration of 22.9 mg/mL and included lectins (specific hemagglutinating activity of 21,333.33) and trypsin inhibitors (specific activity of 15.6 U/mg), as well as the secondary metabolites cinnamic acid derivatives, rutin, and chlorogenic acid. The extract killed third instar Ae. aegypti larvae (50 % lethal concentration of 1.9 %, w/v) and increased the permeability of the peritrophic membrane of Ae. aegypti larvae. The extract did not affect the survival of N. corniger workers or soldiers but killed S. zeamais adults with mortality rates of 51.2–63.8 %. A strong deterrent feeding effect was detected, making S. zeamais adults reject an artificial diet containing the extract. Juveniles of the microcrustacean Hyalella sp. were highly sensitive to treatment with the extract at the 50 % lethal concentration for Ae. aegypti. In conclusion, A. squamosa leaf extract kills Ae. aegypti larvae and S. zeamais adults by increasing the peritrophic membrane permeability and exhibiting a strong food deterrent effect, respectively. However, as an insecticide, the extract should be used with caution because of its high non-target toxicity. The effects of A. squamosa leaf extract may be linked to the actions of lectins, trypsin inhibitors, rutin, and chlorogenic acid.

Insecticidal and Repellent Activities of Four Essential Oils Against Sitophilus zeamais (Coleoptera: Curculionidae).

This study aimed to evaluate the efficacy of Corymbia citriodora, Melaleuca alternifolia (Myrtaceae), Mentha × piperita (Lamiaceae), and Schinus terebinthifolius (Anacardiaceae) essential oils as an alternative to manage Sitophilus zeamais (Coleoptera: Curculionidae) adults. Acute contact toxicity, acute toxicity on treated maize grain, fumigation toxicity, repellency bioassays, and GC-MS analysis of the essential oils were carried out. Corymbia citriodora, M. alternifolia, M. × piperita, and S. terebinthifolius oils were toxic at different levels to S. zeamais through residual contact, ingestion and via fumigation, and were also repellent to adults of this pest. Melaleuca alternifolia oil was the most active in contact (LC50 = 18.98μL.mL-1), ingestion (LC50 = 1.03μL.g-1), and fumigant (LC50 = 20.05μL.L-1 air) bioassays. Citronelal (53.6% in C. citriodora), terpinen-4-ol (46.9% in M. alternifolia), menthol (44.8% in M. × piperita), and β-caryophyllene (16.2% in S terebinthifolius) are the major constituents of these oils. Melaleuca alternifolia and M. × piperita essential oils can be used by residual contact, while those of C. citriodora, M. alternifolia, and M. × piperita by mixing with maize grains. Melaleuca alternifolia essential oil can be used as a fumigant, while those of C. citriodora and S. terebinthifolius as repellents for S. zeamais adults.

Assessing the Effects of Microwave Treatments on Rice Quality and Mortality of Adult Maize Weevil, Sitophilus zeamais

Highlights The study provides insight to microwave technology and the effects of Sitophilus zeamais mortality on rough rice and brown rice that has been previously dried. The mortality of S. zeamais was highest at 5 kW at 90 s, with 98 and 100% mortality for rough rice and brown rice, respectively. Using a microwave power of 5 kW for 90 s on rough rice did not affect head rice yield (HRY), color, or pasting characteristics. For brown rice, a shorter duration of 34 or 60 s at 5 kW or 3 kW for 90 s is recommended to avoid a reduction in HRY. Abstract. A laboratory study was conducted to determine if an industrial microwave could kill Sitophilus zeamais infesting rough rice and brown rice. The rough rice and brown rice samples were comprised of previously air-dried long-grain hybrid (RT 7521 FP) cultivars at initial moisture contents of 11.3 and 12.7% wet basis (w.b.), respectively. Samples (250 g) were infested with ten S. zeamais adults and heated with a microwave power of 3 and 5 kW for 34, 60, and 90 s. The effects of microwave treatments on moisture, head rice yield (HRY), rice color, and pasting characteristics were evaluated. The mortality of S. zeamais was highest at 5 kW at 90 s, with 98% and 100% mortality for rough rice and brown rice, respectively. Rough rice treated at 5 kW at 90 s did result in significantly lower moisture content than the control; however, HRY, color, and pasting characteristics were not significantly different than the controls. Brown rice treated at 5 kW for 90 s resulted in lower moisture content, and there was a significant decrease in the HRY (28.4%) compared to the control (56.2%). No differences in color and some variations in pasting characteristics were observed when compared to the controls. For brown rice, we recommended a shorter duration of 34 or 60 s at 5 kW or 3 kW for 90 s be used to avoid a reduction in HRY and pasting characteristics. Keywords: Brown rice, Maize weevil, Microwave drying, Rough rice.

INSECTICIDAL PROPERTY OF TERPENES AGAINST MAIZE WEEVIL, SITOPHILUS ZEAMAIS (MOTSCHULSKY)

Synthetic pesticides are used indiscriminately in insect pest management, which damages the ozone layer and causes resistance in target organisms as well as neurotoxicity, carcinogenicity, teratogenicity and mutagenesis in non-target organisms. Due to these negative consequences, research is now focused on using plant-based techniques to control insect pests. The maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae), was tested in the laboratory to determine the insecticidal effects of two pure essential oil constituents, namely α-pinene and β-caryophyllene. These two terpenes were tested against S. zeamais for their toxic, ovipositional, developmental, and feeding inhibitory effects. When S. zeamais adults were fumigated for 24 and 48hrs, the median lethal concentrations (LC50) of α-pinene and β-caryophyllene were 0.412 and 0.305 μlcm-3 and 0.486 and 0.315 μlcm-3 air respectively. When S. zeamais adults were exposed for 24 and 48hrs in a contact toxicity assay, the LC50 values for α-pinene and β-caryophyllene were 0.388 and 0.256 μlcm-2 and 0.308 and 0.216 μlcm-2 area respectively. Adults exposed to sub-lethal concentrations of both terpenes experienced decreased acetylcholine esterase (AChE) enzyme activity. In S. zeamais, α-pinene and β-caryophyllene decreased oviposition, progeny output and eating. According to this study, α-pinene and β-caryophyllene can be used to make environmentally acceptable formulations and as a substitute for synthetic insecticides.

Fumigant Activity of Tridax procumbens (Asterales: Asteraceae) Essential Oil Against Sitophilus zeamais (Coleoptera: Curculionidae) and Its Effects on Thai Rice Seed Germination

Abstract Fumigant activity of the essential oil extracted from Tridax procumbens L. (Asterales: Asteraceae) by water distillation was assessed against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), together with its effect on the germination of three Thai varieties of rice, Oryza sativa L. (Poales: Poaceae). Tridax procumbens essential oil contains 25 compounds with five principal components as 1,2-cyclooctanediol (11.49%), hexanal (5.34%), 4-heptenal (4.92%), 2,4-nonadienal (3.10%), and 1,6-dimethylhepta-1,3,5-triene (1.67%). Tridax procumbens essential oil was a fumigant toxin to S. zeamais adults with a median lethal concentration (LC50) of 1,509.79 µl/L air 24 h after exposure. The highest concentration of 250 µl/L air of T. procumbens essential oil showed low efficacy in killing adults of S. zeamais at 24 h with 10% mortality. This concentration also affected newly emerged progeny (F1) of S. zeamais compared to the control, with the highest reduction of 92.87%, and also decreased seed germination of the three varieties of Thai rice RD6, Kham Na Sinuan, and KDML at 94.25, 96.0, and 93.25%, respectively, compared with the control (98.0–98.75%). Results indicate that essential oil from T. procumbens has potential for application on stored products to control progeny of S. zeamais that cause seed damage.

Molecular Identification of Beauveria bassiana and Metarhizium anisopliae Isolates and Their Bio-control Potential against Acanthoscelides obtectus and Sitophilus Zeamais


 
 
 Acanthoscelides obtectus and Sitophilus zeamais are among the most damaging stored-product insect pests. This study was carried out to identify Beauveria bassiana and Metarhizium anisopliae and to evaluate their insecticidal potential against A. obtectus and S. zeamais adults. Fungal isolates were characterized molecularly based on ITS1, 5.8S and ITS2 regions of rDNA. B. bassiana YK23 and YK26, and M. anisopliae YK41 and YK45 were sprayed onto adults of A. obtectus and S. zeamais at 1×105, 1×106 and 1×107 conidia mL−1 doses. At the end of the 10th day of application, the numbers of dead adults were counted. Mortality rates (%) and lethal times (LT50 and LT90) were calculated for each isolate. Fungal isolates displayed promising insecticidal activity against A. obtectus and S. zeamais. B. bassiana and M. anisopliae caused 100% mortality against A. obtectus, even at the lowest dose. However, B. bassiana and M. anisopliae caused 100% mortality on S. zeamais at higher doses. Depending on the increasing doses, significant decreases were observed at the lethal times. Median lethal time (LT50) decreased up to 64.24 h (2.67 days) and 53.69 h (2.24 days) in A. obtectus exposed to B. bassiana and M. anisopliae, respectively. LT50 decreased to 61.04 h (2.54 days) and 53.89 h (2.25 days) in S. zeamais exposed to the same fungi. B. bassiana and M. anisopliae can be taken into account in the control of those pests.
 
 

Prolonged repellent activity of Ruta graveolens essential oil adsorbed on different mineral matrices against Sitophilus zeamais (L.) (Coleoptera: Curculionidae)

Plant-derived essential oils (EOs) have been considered as promising alternatives to conventional insecticides. But because of their high biodegradability and rapid volatilization, EOs are not persistent. To overcome this drawback of short protection time, EOs can be adsorbed onto protective mineral matrices to enhance efficiency by slowing down volatilization. This work was aimed at assessing the potential effectiveness of Ruta graveolens L. (Rutaceae) essential oil (RGEO)-adsorbed zeolite (ZEO) and cloisite 20A (C20A) mineral bio-composites in prolonging the odor-driven repellent efficacy of RGEO towards Sitophilus zeamais (L.) (Coleoptera: Curculionidae). Chemical profile of RGEO was identified using GC and GC-MS. Produced bio-composites were physiochemically characterized by FTIR, SEM-EDS, and TGA. The compounds, 2-undecanone (44.7%) and 2-nonanone (30.3%) were the major constituents of RGEO. Repellent action of bio-composites accounting for 50–100% was persisted for 90 d towards S. zeamais adults, whereas the RGEO used without the adsorbents recorded 0% and 44% of repellent potency within 24 h at the lowest and highest concentrations respectively. Given the volatility of RGEO, IR analyses demonstrated successful adsorption and 90-d long persistence of RGEO on both mineral matrices. Micro-/nanostructural architecture of bio-composites ranged from hierarchically porous for ZEO to intercalated platelets for C20A. EDS imaging confirmed the homogenous dispersion of constituent elements of RGEO on both mineral matrices. Bio-composites indicated improved thermal stability in the presence of air flow relative to the neat mineral matrices. Repellent potency of the bio-composites was arranged in the sequence, RGEO-ZEO < RGEO-C20A throughout the 90 d of experimental period. Findings further suggested that formulations based on EOs adsorbed on solid minerals represent a promising strategy in overcoming EOs’ limitations through retaining enough volatility while maintaining their slow release, thereby prolonging the repulsive effect of EOs for use in stored-product protection.

Efficiency of Schinus molle Essential Oil against Bactericera cockerelli (Hemiptera: Triozidae) and Sitophilus zeamais (Coleoptera: Dryophthoridae)

The present study determines the chemical composition of Schinus molle essential oil and its mortality and repellent effect on Bactericera cockerelli immature stage and Sitophilus zeamais adults. Twenty-four compounds were identified and the most abundant were o-Cymene (29.04), 1R-α-Pinene (15.52), camphene (14.00), and β-myrcene (11.54). On the fifth-instar psyllid nymph, the LC50 and LC90 at 48 h were 442.67 and 864.29 ppm, and for the fourth-instar were 273.41 and 534.67 ppm. The maize-weevil registered an LC50 and LC90 of 343.25 and 986.96 ppm for the fifteenth day. A selection index (Si) of 0.37 with 800 ppm was registered, showing the highest repellent activity, while with the lowest concentration (50 ppm), non-repellent activity was recorded. However, all concentrations above 100 ppm showed repellency against the maize weevil. The study reveals, for the first time, the essential oil’s insecticidal effects on the fourth and fifth nymphal stage of the potato/tomato psyllid B. cockerelli and the usefulness of the essential oil as a repellent against adult of S. zeamais. The Si effect on maize weevil was grouped into categories.

Auto‐identification of two Sitophilus sibling species on stored wheat using deep convolutional neural network

Sitophilus oryzae and Sitophilus zeamais are the two main insect pests that infest stored grain worldwide. Accurate and rapid identification of the two pests is challenging because of their similar appearances. The S. zeamais adults are darker and shinier than S. oryzae in visible light. Convolutional neural network (CNN) can be applied for the effective differentiation due to its high effectiveness in object recognition. We propose a multilayer convolutional structure (MCS) feature extractor to extract insect characteristics within each layer of the CNN architecture. A region proposal network is adopted to determine the location of a potential pest in the wheat background. The precision of classification and the robustness of bounding box regression are increased by including deeper layer variables into the classification and bounding box regression subnets, as well as combining loss functions softmax and smooth L1. The proposed multilayer convolutional structure network (MCSNet) achieves the mean average precision of 87.89 ± 2.36% from the laboratory test, with an average detection speed of 0.182 ± 0.005 s per test. The model was further assessed with the field trials, and the obtained accuracy was 90.35 ± 3.12%. For all test conditions, the average precision for S. oryzae was higher than that for S. zeamais. The proposed MCSNet model has demonstrated that it is a fast and accurate method for detecting sibling species from visible light images in both laboratory and field trials. This will ultimately be applied for pest management together with an upgraded industrial camera system, which has been installed in over 100 000 grain depots of China.

Toxicological Stability of Ocimum basilicum Essential Oil and Its Major Components in the Control of Sitophilus zeamais.

Essential oils (EOs) are widely recognized as efficient and safe alternatives for controlling pest insects in foods. However, there is a lack of studies evaluating the toxicological stability of botanical insecticides in stored grains in order to establish criteria of use and ensure your efficiency. The objective of this work was to evaluate the toxicological stability of basil essential oil (O. basilicum) and its linalool and estragole components for Sitophilus zeamais (Motschulsky) adults in corn grains by fumigation. The identification of the chemical compounds of the essential oil was performed with a gas chromatograph coupled to a mass selective detector. Mortality of insects was assessed after 24 h exposure. After storage for six (EO) and two months (linalool and estragole) under different conditions of temperature (5, 20, and 35 °C) and light (with and without exposure to light), its toxicological stability was evaluated. Studies revealed that the essential oil of O. basilicum and its main components exhibited insecticidal potential against adults of S. zeamais. For greater toxicological stability, suitable storage conditions for them include absence of light and temperatures equal to or less than 20 °C.

Function of four mitochondrial genes in fumigation lethal mechanisms of Allyl Isothiocyanate against Sitophilus zeamais adults

Allyl isothiocyanate (AITC) is a promising alternative to chemical fumigants, and mitochondrial dysfunction has been proposed to play a crucial role in its lethal mechanisms; however, the specific lethal mechanisms of AITC remain unknown. Four mitochondrial electron transport chain genes, nd5, nd6, cox1, and cox5, were selected from adult Sitophilus zeamais and processed with RNA interference experiments. Then, the biochemical and biophysical effects were compared between double-stranded RNA (dsRNA)-mediated insects and wild-type insects after AITC fumigation at the concentration of LC50 values. The bioactivity of AITC against dsnd6-mediated insects increased, while the bioactivity against dcox1-mediated insects decreased. Compared with the wild-type insects, the increase of reactive oxygen species (ROS) levels by AITC in mitochondria from dsnd6-mediated insects increased by 18.95%, while that of dscox1-mediated insects decreased by 27.45%. The effects of AITC on mRNA expression levels of detoxifying enzymes including CAT (down-regulation effect) and CuZnSOD (overexpression effect) partly recovered in the dsnd5-mediated insects, while a greater effect was observed for dscox1-mediated insects. Molecular docking results indicated that ASN511 at the cox1 subunit was the binding site of AITC by one hydrogen bond, with a bond distance of 2.1 Å. These findings provide insight for further applications of AITC and could provide a novel strategy to investigate lethal mechanisms of insecticides.

Effects of Essential Oils from 24 Plant Species on Sitophilus zeamais Motsch (Coleoptera, Curculionidae).

Simple SummaryThe maize weevil (Sitophilus zeamais Motsch) is a major pest in stored grain, responsible for significant economic losses and having a negative impact on food security. Due to the harmful effects of traditional chemical controls, it has become necessary to find new insecticides that are both effective and safe. In this sense, plant-derived products such as essential oils (EOs) appear to be appropriate alternatives. Therefore, laboratory assays were carried out to determine the chemical compositions, as well as the bioactivities, of various EOs extracted from aromatic plants on the maize weevil. The results showed that the tested EOs were toxic by contact and/or fumigance, and many of them had a strong repellent effect. Samples of 14 EOs and 17 of their main constituents (monoterpenes) had high fumigant toxicity against S. zeamais adults and might constitute a viable control method of this pest.Chemical control of the maize weevil (Sitophilus zeamais) has been ineffective and presents serious collateral damage. Among plant-derived insecticides, essential oils (EOs) are suitable candidates to control this stored products pest. In this work, the insecticidal activities of 45 natural EOs against S. zeamais adults were screened, and the most promising ones (24 EOs) were characterized by GC–MS. The repellent and toxic effects (contact and fumigant) of these 24 EOs were determined, and by a cluster analysis they were classified into two groups considering its fumigant activity and contact toxicity. For the EOs with the highest fumigant potential (14 oils) and their main active constituents (17 compounds), lethal concentrations were determined. The most active EOs were those obtained from L. stoechas and L. alba, with LC50 values of 303.4 and 254.1 µL/L air and characterized by a high content of monoterpenes. Regarding the major compounds, the oxygenated monoterpenes R-(+)-pulegone (LC50 = 0.580 mg/L air), S-(-)-pulegone (LC50 = 0.971 mg/L air) and R-(-)-carvone (LC50 = 1.423 mg/L air) were the most active, as few variations in their concentrations significantly increased insect mortality.

Insecticidal activity of bis(methylthio)methane based volatile extract of Olax zeylanica (L.) against Sitophilus zeamais (L.) and Corcyra cephalonica (Stainton)

Sri Lankan natives traditionally introduce pungently odorized Olax zeylanica (L.) leaves into their grain storages aiming at the efficient control of insect pests associated with stored grains. The headspace components of O. zeylanica leaves were analyzed by GC–MS, subsequently isolated the major compound being responsible for the plant’s protective effect and laboratory bioassays were conducted to test its lethal activities against Sitophilus zeamais (L.) (Coleoptera: Curculionidae) and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae). A total of 2 headspace sulfur-containing constituents were found consisting the volatilome of O. zeylanica leaves wherein bis(methylthio)methane (BMTM) was identified as the major organosulfur constituent (75.3 %). BMTM provided strong and immediate control against 3–7 days old S. zeamais adults, 1 day old eggs, 15–17 days old larvae and 1 day old adults of C. cephalonica within 24 h of post treatment. In contact and fumigation assays, S. zeamais (LC50(contact) = 0.16 v/v% and LC50(fumigation) = 0.17 v/v%) was more susceptible to BMTM than C. cephalonica (LC50(contact) = 0.19 v/v% and LC50(fumigation) = 0.22 v/v%) in their adult stages. In contact grain assays, adulticidal effects persisted for 84 h. The degree of susceptibility of different C. cephalonica life stages to BMTM was arranged in the order of eggs (LC50 = 0.18 v/v%) > adults (LC50 = 0.19 v/v%) > larvae (LC50 = 0.29 v/v%) producing > 95 % lethal effects at the respective time points of 9, 12, and 24 h. Additionally, it was evidenced that the grain viability and germination were not affected by the uptake of BMTM. BMTM caused substantial toxicities in S. zeamais and C. cephalonica inferring the favorable use of natural BMTM in the successful control of stored grain insect pests, thereby obviating the necessity in sole relying on conventional synthetic insecticides in storage systems.

Insectıcıdal actıvıtıes of Anethum graveolens and Illıcıum verum essentıal oıls agaınst Sıtophılus zeamaıs

Inappropriate use of synthetic insecticides in pest management programs contribute in ozone depletion, neurotoxicity, carcinogenicity, teratogenicity, mutagenesis and resistance. These negative outcomes have diverted attention towards the use of plant products in insect’s population management. In this study, dill (Anethum graveolens) and star anise (Ilicium verum) essential oils were isolated by hydrodistillation method using clevenger apparatus, and evaluated for repellent, toxic and oviposition inhibitory potential against maize weevil Sitophilus zeamais (Coleoptera: Curculionidae) by fumigation and contact methods. In toxicity assay by fumigation method, median lethal concentrations (LC50) recorded were 0.316 and 0.243 μlcm-3 air; 0.362 and 0.284 μlcm-3; and 0.497 and 0.418 μlcm-3 of A. graveolens and I. verum oils and pure limonene after 24 and 48h exposure to S. zeamais adults, respectively. In contact toxicity assay, LC50 were 0.219 and 0.159 μlcm-2 area; 0.269 and 0.226 μlcm-2; and 0.567 and 0.386 μlcm-2 of A. graveolens and I. verum oils and pure limonene after 24 and 48 h exposure to S. zeamais adults, respectively. Both A. graveolens and I. verum oils and limonene reduced progeny production and acetylcholinesterase activity in S. zeamais adults when fumigated with sub-lethal concentrations. The outcomes of this study will help in preparation of essential oil based formulations for stored grain insect pest management.