Phytochemical screening and insecticidal activities of some medicinal plants against the maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae).

This study emphasizes the phytochemical study of some locally available botanicals against maize weevils. Nine plant parts were collected from six plant species. The test plant powder (200 g) was suspended sequentially in 600 ml of petroleum ether, chloroform, acetone, methanol, and distilled water for 72 h with frequent agitation. Different concentrations of the crude extracts were applied to maize seeds at rates of 10 ml, 15 ml and 20 ml per 100 g. All treatments with different extracts at different rates of application showed significant differences (p < 0.05) in the cumulative mean percentage mortality of the maize weevil. The seed extract of Maesa lanceolata and Croton macrostachyus and the leaf extract of Clausena anisata showed cumulative percent mortality ranged 95.32-98.02% in 28 days after treatment application. There was no significant difference (p > 0.05) among all treatments for the prevention of F1 progeny emergence. In all extracts, Clausena anisata showed 100% inhibition of F1 progeny emergence. All treatments significantly reduced seed weight loss and damage. The treated maize seeds were germinated with an acceptable germination quality. In conclusion, an increased dosage of the extract resulted in significant mortality in maize weevils. The seed extracts of Maesa lanceolata and Croton macrostachyus and Clausena anisata leaf extract were observed to be the most promising botanical in protecting stored maize against maize weevil.

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.

Insecticidal toxicity of essential oil of Nepalese Acorus calamus (Acorales:Acoraceae) against Sitophilus zeamais (Coleoptera:Curculionidae).

Maize weevil (Sitophilus zeamais) (Coleoptera:Curculionidae) is an economic stored grain pest that causes significant damage to various stored products, including maize (Zea mays). In this study, we extracted essential oil from the rhizome of sweet flag (Acorus calamus) (Acorales:Acoraceae) by hydro-distillation and tested insecticidal property of the oil at 7 concentrations (10, 5, 2.5, 1.25, 0.625, 0.3125, 0.15625 and control) against maize weevil (Sitophilus zeamais) at the National Entomology Research Center, Nepal Agricultural Research Council in the year 2020/2021. Three different experiments were conducted: scintillating vial bioassay, repellency test, and exposing weevils to oil treated maize grains. Scintillating vial bioassay showed that higher the concentration of essential oil, lower the time required to cause 50 % maize weevil mortality. Median lethal concentration (LC50) at 3 and 24 h was calculated as 2.29 and 0.16 % of oil concentration in scintillating vial bioassay. When oil is treated to maize grain, LC50 for 10 and 16 days was calculated as 2.77 and 0.23 % of oil concentrations. In the same way, at 10 % concentration maize weevil showed highest repellent activity (98.75 %) as compared to 5, 2.5 and 1.25 % concentrations after 24 h of treatment. Weight loss and grain damage were significantly less in the oil treatments than the control. However, from the perspective of health benefits, Acorus calamus treated maize is still questionable for feed and food purpose. As ß asarone has carcinogenic effects at certain level, it needs further residue tests of treated maize to know allowable maximum residue limit (MRL) before consumption as food or feed.

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

Objective: 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. Methods: Acute contact toxicity, acute toxicity on treated maize grain, fumigation toxicity, repellency bioassays, and GC-MS analysis of the essential oils were carried out. Results: 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 = 18.98 µL.mL-1), ingestion (LC50 = 1.03 µL.g-1), and fumigant (LC50 = 20.05 µL.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 ß-caryophyllene (16.2% in S terebinthifolius) are the major constituents of these oils. Conclusions: 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.

Medicinal Plants as a Natural Greener Biocontrol Approach to "The Grain Destructor" Maize Weevil (Sitophilus zeamais) Motschulsky.

According to the United Nations (UN), the global population may skyrocket to 9.8 billion people in 2050 and 11.2 billion in 2100, placing an overwhelming burden on food security as the world will have to meet this growing demand. Maize is the largest staple grain crop produced in developing countries. The maize weevil, Sitophilus zeamais, is one of the most destructive post-harvest pests of stored cereals and grains. The maize weevil contributes up to 40% of total food-grain losses during storage, mainly in developing countries. Current synthetic pesticides are ineffective, and, moreover, they raise serious environmental safety concerns as well as consumer health hazards. Drawing from past oversights and current environmental realities and projections, the global population has been switching to green living by developing sustainable strategies. In our context, these new greener strategies include the utilization of medicinal plants to control maize weevil infestation, which unlocks unlimited innovative possibilities, and, thus, improves the yield, quality, and safety of maize. Medicinal plants are less toxic, easily biodegradable, and capable of protecting grain from pests. This paper systematically outlines the literature on host plants as well as the feeding and associated diseases of the maize weevil. In light of this, we cement medicinal plants as excellent candidates in the pursuit of greener, sustainable, more potent, and cost-effective pesticides.

On-farm storage loss estimates of maize in Kenya using community survey methods.

Maize is the most important staple in sub-Saharan Africa (SSA), with highly seasonal production. High storage losses affect food security, but good estimations are lacking. A new method using focus group discussions (FGDs) was tested with 121 communities (1439 farmers, 52% women) in Kenya's six maize-growing zones, to estimate the maize losses to storage pests and analyze farmer practices. As control strategies, half of the farmers used chemical pesticides (49%), while hermetic bags (16%) and botanicals (15%) were also popular. Relative loss from weevils in the long rains was estimated at 23%, in the short rains 18%, and annually 21%. Fewer farmers were affected by the larger grain borer (LGB) than by maize weevils: 42% in the long rainy season and 32% in the short rainy season; losses from LGB were also smaller: 19% in the long season, 17% in the short season, and 18% over the year. Total storage loss, from both species combined, was estimated at 36%, or 671,000 tonnes per year. The greatest losses occur in the humid areas, especially the moist mid-altitudes (56%), and with smaller loss in the drylands (20-23%). Extrapolating the point data and overlaying with the maize production map shows the geographic distribution of the losses, with the most important area found around Lake Victoria. FGDs provide convenient and cheap tools to estimate storage losses in representative communities, but a total loss estimate of 36% is higher than is found in other studies, so its accuracy and framing effects need to be assessed. We conclude that storage pests remain a major problem, especially in western Kenya, and that the use of environmentally friendly technologies such as hermetic storage and botanicals needs more attention, both by the public extension service and private agrodealers.

Development of the first high-density linkage map in the maize weevil, Sitophilus zeamais.

The maize weevil, Sitophilus zeamais, is a worldwide pest that disproportionately affects subsistence farmers in developing countries. Damage from this pest threatens food security in these communities as widely available and effective control methods are lacking. With advances over the last decade in the development of genetic pest management techniques, addressing pest issues at the ecosystem level as opposed to the farm level may be a possibility. However, pest species selected for genetic management techniques require a well-characterized genome and few genomic tools have been developed for S. zeamais. Here, we have measured the genome size and developed the first genetic linkage map for this species. The genome size was determined using flow cytometry as 682 Mb and 674 Mb for females and males, respectively. The linkage map contains 11 linkage groups, which correspond to the 10 autosomes and 1 X-chromosome found in the species and it contains 1,121 SNPs. This linkage map will be useful for assembling a complete genome for S. zeamais.

Efficacy of deltamethrin and pirimiphos-methyl in proportionally layer-treated maize against the larger grain borer and the maize weevil.

Two insecticides (deltamethrin and pirimiphos-methyl) were evaluated in laboratory assays as grain protectants when applied as a total percentage of a maize mass to control adult Prostephanus truncatus and Sitophilus zeamais. All experiments were conducted at the University of Thessaly in Greece at 30°C and 65% RH under continuous darkness. Either insecticide was applied to 20 g of maize placed in a vial or to the upper one half, one fourth, or one-eighth layer of the maize, then insects were either added to the vials before or after the maize in a completely randomized block design CRBD with n = 9 replicates. Mortality, progeny production, and insect damaged kernels (IDK) were then evaluated for each vial. Insect introduction method (before or after) did not have any impact on any of the variables. Mortality was nearly 100% for all treatments for both insecticides for P. truncatus. Subsequently, progeny production and the number of insect damaged kernels were very low or zero for P. truncatus. Mortality of S. zeamais remained low across layer treatments for deltamethrin. However, S. zeamais was easily controlled by pirimiphos-methyl. The results of this laboratory study show that while deltamethrin and pirimiphos-methyl have some effectiveness as a layer treatment on a column of maize, efficacy will be dependent on the target species, and the depth of the treated layer, as well as the location on which the insects are present.

Novel Approach for a Controlled Delivery of Essential Oils during Long-Term Maize Storage: Clove Bud and Pennyroyal Oils Efficacy to Control Sitophilus zeamais, Reducing Grain Damage and Post-Harvest Losses.

Maize grains represent a significant contribution for assuring food safety all over the globe. Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), also known as the maize weevil, is one of the most destructive pests in stored maize, causing qualitative and quantitative losses. To control S. zeamais populations in maize storage sites, synthetical chemical insecticides are applied. However, these are often used wastefully, have environmental implications, and can induce the development of resistant populations. In this work, the insecticidal and grain protecting efficacy of an innovative macro-capsule delivery device, loaded with essential oils from Clove bud and Pennyroyal, as well as their combined solutions, was tested against naturally S. zeamais-infested maize grains. The blend of both compounds incorporated in a controlled release device reduced losses by more than 45% over a long storage period of twenty weeks, diminishing the survivability of maize weevils by over 90%. The usage of the blend at a concentration of 370 µL⋅Lair-1 with an antioxidant showed the best results, however, by halving the concentration (185 µL⋅Lair-1), a significant control of S. zeamais populations was still achieved.

Preliminary Assessment of Repellency and Toxicity of Essential Oils against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) on Stored Organic Corn Grains.

Insect infestation of cereal grains during post-harvest storage not only causes significant grain loss, but also reduces grain quality and makes grains more susceptible to mold infection. Synthetic pesticides are banned from being used in organic grain storage setting due to their high toxicity. The main insect damaging stored corn grains is maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). The purpose of this study was to evaluate insect repellency and insecticidal potentials of some generally recognized as safe (GRAS) essential oils (EOs) (including cinnamon, clove, thyme, oregano, and orange terpene oils) at concentrations of 1-20% against the maize weevil using an olfactometer and a simulated fumigation method, respectively. The olfactory tests show that cinnamon oil had the highest repellency (90%) to the weevils among the EOs tested. The insecticidal activity study indicates that maize weevil mortality increased with EO concentration and storage time with cinnamon, clove, and thyme oils being more effective. No weevil death was observed at 1% EOs; weevil mortality was 3.3-36% at 5%, which varied with the type of EO and storage time. At 10% or higher concentrations, all tested EO showed comparable or higher insecticidal activity than pirimiphos methyl-positive control at its recommended concentration (5 mg/kg corn). No significant increase in weevil mortality was observed with further increase in EO concentration, with exceptions of oregano oil and thyme oil. The highest weevil mortality levels were observed at week 7 for 15% cinnamon oil (100%) and eugenol (100%), followed by 20% thyme oil (93%). The study indicates that some EOs have great potential to serve as synthetic insecticide alternatives to protect organic corn grains from maize weevil damage during storage. This is important to food security, safety and environmental health.

Repellency and Reduction of Offspring Emergence Potential of Some Botanical Extracts against Sitophilus zeamais (Coleoptera: Curculionidae) in Stored Maize.

Botanical repellents are, usually, considered safe to control Sitophilus zeamais, the main pest of stored maize, as they do not leave toxic residues in food, in addition to having lower costs than chemical insecticides. The aim of this study was to evaluate the repellency potential and the reduction of emerged offspring of botanical extracts, of Schinus terebinthifolius, Ludwigia sericea, L. tomentosa, L. nervosa, L. longifolia, and use them as botanical insecticides for S. zeamais. For the repellency test, arenas were set up, containing 50 g of maize kernels exposed to aqueous extract, besides a control treatment. At the center of each arena, 100 insects were released. After 48 h, the proportion of insects in the treated grains was determined. To test the effects of the extracts on insect mating and egg-laying, free-choice and no-choice tests were performed. Insects in both tests remained for ten days for mating and egg-laying. After this period, insects were removed to evaluate the offspring emergence. Sixty days after grain infestation, the number of emerged insects was counted. All selected botanical extracts demonstrated repellent action against S. zeamais, even after 48 h of application. The L. nervosa aqueous extract significantly reduced the emergence of S. zeamais.

Chemical vs. Enzymatic Refining to Produce Peanut Oil for Edible Use or to Obtain a Sustainable and Cost-Effective Protector for Stored Grains against Sitophilus zeamais (Coleoptera: Curculionidae).

Among the various existing techniques, enzymatic degumming represents a process that is establishing itself as a valid alternative to the more classic chemical processes. Moreover, vegetable oils of various origins have been gaining more consideration as sustainable and affordable protectants for cereals and pulses against the attack of several insect pests. Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) is one of the key pests of cereal crops in the field and in stored and processed cereal products. Based on these highlighted issues, the overall aim of this research was twofold: (i) firstly, the effectiveness of the enzymatic degumming process was evaluated through the use of three different enzymes in order to verify the possible industrial application within the SALOV company as an alternative to the conventional chemical process; (ii) in a second phase, the possible use of the innovative refined oils was explored for sustainable stored grain protection towards S. zeamais. The results obtained confirm the strong possibility of applying the enzymatic process, which is innovative and, in a chemical way, more sustainable than the classical one. Regarding the toxicity towards S. zeamais, the crude peanut oil and the chemically refined peanut oil had lower LC50 values (1.836 and 1.372 g kg-1, respectively) than the oils rectified through enzymatic degumming (LC50 from 2.453 to 4.076 g kg-1), and, therefore, they can be suggested as sustainable stored grain protectants.

Insecticidal activities of long pepper (Piper retrofractum Vahl) fruit extracts against seed beetles (Callosobruchus maculatus Fabricius, Callosobruchus chinensis Linnaeus, and Sitophilus zeamais Motschulsky) and their effects on seed germination.

Bruchid beetles (Callosobruchus maculatus and Callosobruchus chinensis), and maize weevil (Sitophilus zeamais) are important insect pests during the postharvest period. Botanical insecticide is an alternative solution for controlling these insects, and long pepper (Piper retrofractum) has been reported as having insecticidal potential against general insect pests. Film seed coatings with various concentrations of hexane extracts were made for mung bean (Vigna radiata) and corn (Zea mays) seeds. Insecticidal activities of these treatments were assessed at before and after storage period of six months, and seed germination was also evaluated. The hexane extract was subjected to analysis of the bioactive components by using Gas Chromatography-Mass Spectrometry (GC-MS). Results revealed that the hexane extract presented extreme toxicity to both bruchid beetles higher compared to maize weevil at 24 h with LC50 values of 5.57-6.75 and 58.04 µg⋅cm-2, respectively. Bruchid beetles presented significant response to ethanol, acetone and hexane extracts, whereas maize weevil showed relatively low responsibility. Film seed coating with hexane extract at 1% and 3% concentrations with six-month storage presented high insecticidal activity against bruchid beetles by more than 88% mortality but had low kill rates against maize weevil. The coated mung bean seeds presented non-seed germination effect, whereas high effect was observed on coated corn. Isolation of bioactive components demonstrated that there were 74 compounds, where pentadecane was the main compound. Film seed coating technology for mung bean seed preservation by using 1% hexane extract from long pepper fruit presented to be an extremely effective method to control bruchid beetles without any seed germination effect. It could serve as one of the green insecticides of the future.

Insecticidal activity of a chemotype VI essential oil from Lippia alba leaves collected at Caatinga and the major compound (1,8-cineole) against Nasutitermes corniger and Sitophilus zeamais.

Lippia alba is an aromatic shrub known to produce a diversity of essential oils, which can be classified into chemotypes. This study reports on the insecticidal activity of essential oil from L. alba leaves collected at Caatinga and its major compound against termite Nasutitermes corniger and maize weevil Sitophilus zeamais. The chromatographic analysis revealed the presence of 19 compounds, with 1,8-cineole being the most common (70.01%). When ingested, the oil promoted the mortality of N. corniger (LC50: 18.25 and 8.4 nL/g for workers and soldiers, respectively). The compound 1,8-cineole was also termiticidal for workers (LC50: 13.7 nL/g). The oil inhibited the activity of N. corniger exoglucanase, xylanase, and proteases. Toxicity by ingestion to S. zeamais was detected for the oil (LC50: 0.297 µL/g) but not for 1,8-cineole; however, both the oil and 1,8-cineole showed anti-nutritional effects. Fumigant effects of the oil and 1,8-cineole against S. zeamais (LC50 of 78.0 and 13.64 µL/L in air, respectively) were detected. This is the first record of a chemotype VI oil from L. alba collected at Caatinga and the first report of the insecticidal activity of a chemotype VI oil. Our study demonstrates that essential oil from L. alba and 1,8 cineole have the potential for the development of natural insecticides.

Convolutional Neural Networks Using Enhanced Radiographs for Real-Time Detection of Sitophilus zeamais in Maize Grain.

The application of artificial intelligence (AI) such as deep learning in the quality control of grains has the potential to assist analysts in decision making and improving procedures. Advanced technologies based on X-ray imaging provide markedly easier ways to control insect infestation of stored products, regardless of whether the quality features are visible on the surface of the grains. Here, we applied contrast enhancement algorithms based on peripheral equalization and calcification emphasis on X-ray images to improve the detection of Sitophilus zeamais in maize grains. In addition, we proposed an approach based on convolutional neural networks (CNNs) to identity non-infested and infested classes using three different architectures; (i) Inception-ResNet-v2, (ii) Xception and (iii) MobileNetV2. In general, the prediction models developed based on the MobileNetV2 and Xception architectures achieved higher accuracy (≥0.88) in identifying non-infested grains and grains infested by maize weevil, with a correct classification from 0.78 to 1.00 for validation and test sets. Hence, the proposed approach using enhanced radiographs has the potential to provide precise control of Sitophilus zeamais for safe human consumption of maize grains. The proposed method can automatically recognize food contaminated with hidden storage pests without manual features, which makes it more reliable for grain inspection.

Evaluation of early-generation tropical maize testcrosses for grain-yield potential and weevil (Sitophilus zeamais Motschulsky) resistance.

Smallholder maize farmers in Africa experience pre- and post-harvest production stresses either individually or in combination at different stages of the crop cycle. The maize weevil is among the major post-harvest storage pests. A strategy to address this problem is to develop and promote high yielding maize germplasm with resistance to multiple stresses. A study was conducted to: 1) assess yield and agronomic performance of testcross hybrids developed from early generation lines; and 2) assess the response of the testcross hybrids to infestation with Sitophilus zeamais. Fifty-eight drought-tolerant testcross hybrids were evaluated for agronomic performance and weevil resistance at four environments in Uganda in 2016. Hybrid G39 (L2/T2) had the best grain yield performance; it significantly out-performed the best check by 11.4% in all environments. Hybrid grain from field trials was subjected to Sitophilus zeamais infestation in a choice and no choice test under laboratory conditions. Hybrids G56 (L49/T2) and G58 (L51/T2) had the least weevil damage and were rated as resistant to Sitophilus zeamais. The numbers of damaged kernels, number of exit holes and ear aspect were positively correlated with the grain weight loss. The results suggest possibilities for simultaneous selection for high grain yield and storage insect pest resistance among drought-tolerant genotypes. Use of high-yielding and resistant maize hybrids to storage insect pest should be promoted for increased maize production and managing post-harvest losses due to the maize weevil in smallholder farming communities in Africa.

Characterization of the complete mitochondrial genome of the maize weevil, Sitophilus zeamais (Insecta: Coleoptera: Curculionidae) from Guizhou province.

The complete mitochondrial genome of the maize weevil Sitophilus zeamais (GenBank accession number: MN905575) from Guizhou Province consists of a circular DNA molecule of 18,421 bp (with 75.69% A + T content), which is longer by 316 bp than that of the mitogenome of S. zeamais from Nigeria. The mitogenome comprises 13 protein-coding, 22 tRNA, and two rDNA genes. The protein-coding genes have typical ATN (Met) initiation codons and are terminated by typical TAN stop codons.

Evaluation of the Insecticidal Activities of α-Pinene and 3-Carene on Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae).

Pest management in most sub-Saharan subsistence agriculture involves mainly the use of botanicals that are either applied as powders, solvent extracts, ash or essential oils. Two hydrogenated monoterpenes (α-pinene and 3-carene) from Cupressus sempervirens were tested against Sitophilus zeamais in the laboratory to evaluate the contact and fumigation effects on the mortality of adult and immature weevils, progeny production, and grain damage. Contact toxicity of the terpenes was investigated at these concentrations: 0.08, 4, 8 and 12 ppm (terpene/maize), while fumigant action was studied at the following doses: 1, 2, 3, and 4 ppm. The results indicate that insecticidal effects were concentration-dependent since mortality increased with dosage and exposure periods. After a 14-day exposure period at the concentration of 12 ppm of α-pinene and 3-carene/grain, more than 98% mortality of the mature weevils was observed at concentrations of 4.1333 and 1.642 ppm respectively and progeny production was reduced by 98% and 100%, respectively. When α-pinene and 3-carene were applied as fumigants, LC50s (lethal concentrations that generate 50% mortality) of 1.402 and 0.610 ppm were obtained after 24 h of exposure, respectively. At concentrations above 3 ppm, both monoterpenes acted as repellents to weevils and reduced grain damage by 80%. Both monoterpenes inhibited the development of immature stages of the weevil and reduced progeny by up to 94%. These compounds are very promising and effective and could be exploited as novel phytoinsecticides against the maize weevil.

Insecticidal Activity of 28 Essential Oils and a Commercial Product Containing Cinnamomum cassia Bark Essential Oil against Sitophilus zeamais Motschulsky.

Maize weevils, Sitophilus zeamais, are stored product pests mostly found in warm and humid regions around the globe. In the present study, acute toxicity via contact and residual bioassay and fumigant bioassay of 28 essential oils as well as their attraction-inhibitory activity against the adults of S. zeamais were evaluated. Chemical composition of the essential oils was analyzed by gas chromatography-mass spectrometry, and a compound elimination assay was conducted on the four most active oils (cinnamon, tea tree, ylang ylang, and marjoram oils) to identify major active constituents. Amongst the oils examined, cinnamon oil was the most active in both contact/residual and fumigant bioassays, and exhibited strong behavioral inhibitory activity. Based on the compound elimination assay and chemical analyses, trans-cinnamaldehyde in cinnamon oil, and terpinen-4-ol in tea tree and marjoram oils were identified as the major active components. Although cinnamon oil seemed promising in the lab-scale bioassay without rice grains, it failed to exhibit strong insecticidal activity when the container was filled with rice. When a cinnamon oil-based product was applied both in an empty glass jar and a rice-filled container, all weevils in the empty jar were killed, whereas fewer than 15% died in the rice-filled container.

Genetic Basis of Maize Resistance to Multiple Insect Pests: Integrated Genome-Wide Comparative Mapping and Candidate Gene Prioritization.

Several species of herbivores feed on maize in field and storage setups, making the development of multiple insect resistance a critical breeding target. In this study, an association mapping panel of 341 tropical maize lines was evaluated in three field environments for resistance to fall armyworm (FAW), whilst bulked grains were subjected to a maize weevil (MW) bioassay and genotyped with Diversity Array Technology's single nucleotide polymorphisms (SNPs) markers. A multi-locus genome-wide association study (GWAS) revealed 62 quantitative trait nucleotides (QTNs) associated with FAW and MW resistance traits on all 10 maize chromosomes, of which, 47 and 31 were discovered at stringent Bonferroni genome-wide significance levels of 0.05 and 0.01, respectively, and located within or close to multiple insect resistance genomic regions (MIRGRs) concerning FAW, SB, and MW. Sixteen QTNs influenced multiple traits, of which, six were associated with resistance to both FAW and MW, suggesting a pleiotropic genetic control. Functional prioritization of candidate genes (CGs) located within 10-30 kb of the QTNs revealed 64 putative GWAS-based CGs (GbCGs) showing evidence of involvement in plant defense mechanisms. Only one GbCG was associated with each of the five of the six combined resistance QTNs, thus reinforcing the pleiotropy hypothesis. In addition, through in silico co-functional network inferences, an additional 107 network-based CGs (NbCGs), biologically connected to the 64 GbCGs, and differentially expressed under biotic or abiotic stress, were revealed within MIRGRs. The provided multiple insect resistance physical map should contribute to the development of combined insect resistance in maize.