Effectiveness of diatomaceous earth for control of Sitophilus zeamais (Coleoptera: Curculionidae), Tribolium castaneum and Palorus subdepressus (Coleoptera: Tenebrionidae)

The effectiveness of diatomaceous earth (DE) or diatomite has been assessed against three major beetle pests of stored maize: Sitophilus zeamais (the maize weevil), Tribolium castaneum (the red flour beetle) and Palorus subdepressus (the depressed flour beetle). Maize has been treated with four doses of DE (1.5, 3, 4.5 and 6 g/kg) and four doses of Actellic Super™ Dust a chemical insecticide used as a reference (0.25, 0.5, 0.75 and 1 g/kg). The effective mortality was measured for each treatment after 1, 2, 4, 7 and 14 d of exposure. The corrected mortality rates were calculated by considering the mortality in the control group. Diatomaceous earth was as effective as Actellic Super™ Dust but required higher doses. Diatomaceous earth acted faster on S. zeamais and P. subdepressus compared to T. castaneum. The highest dose tested for DE caused the same mortality in T. castaneum as the recommended dose of Actellic Super™ Dust. Diatomaceous earth is a good alternative for the control of these three devastating insect pests of maize stocks and can readily be incorporated into integrated stored products pest management programs.     

Volatile organic compounds from the interaction between Fusarium verticillioides and maize kernels as a natural repellents of Sitophilus zeamais

Maize kernels are exposed to Sitophilus zeamais attack and Fusarium verticillioides infestation during storage, which can result in product deterioration and economic losses. The objective of this study was to evaluate the involvement of the Volatile Organic Compounds (VOCs) emitted by the fungi-corn system in grain-insect interactions. Volatiles emitted by healthy maize kernels were different from those emitted by fungal infected kernels, with the latter being enriched by alcohols, ketones and sesquiterpenes, which were considered early indicators of fungal contamination. The results demonstrated that the kernels exposed to the fungal VOCs and their pure compounds (1-octen-3-ol and 3-octanol) were less attractive and less damaged by S. zeamais than controls. In addition to compound adsorption, other processes may have caused the protective effect of exposed kernels against insect damage. This is the first contribution of the role of the fungal volatiles on the behavior of S. zeamais, and could provide an important contribution to the conservation of stored grains and pest management and an early indicator of fungal contamination.     

Is flint corn naturally resistant to Sitophilus zeamais infestation?

Sitophilus zeamais (maize weevil) is one of the most destructive pests of maize stored in tropical and subtropical regions. This study determined the resistance of flint corn and dent corn to infestation by S. zeamais (Motschulsky), the maize weevil. Improved King Philip hybrid flint corn and Fontanelle 6T-510 hybrid dent corn were used in this experiment. Two temperature conditions (10 °C and 27 °C) and two storage times (15 days and 30 days) were used. Results showed that flint corn was more resistant to insect damage than dent corn at 27 °C and 30 day storage time. After 30 days storage time and 27 °C death rate was significantly higher in flint corn (R² = 0.945) compared to (R² = 0.634) in dent corn. Damaged seed was 10% higher in dent corn then in flint corn at 27 °C and 30 days. However, no significant difference was observed for seed weight loss between flint corn and dent corn at the same storage conditions. Both dent and flint corn were extensively cultivated in developing countries It appears that storage of flint corn may be one promising solution to reducing corn damage infestation problems in the tropics and in developing countries, but more research is needed.     

Evaluation of stirring to suppress weevils in stored maize

The maize weevil (Sitophilus zeamais Motschulsky) is found throughout the world and is among the most destructive pests of stored grain and grain products. Maize weevil suppression is difficult and chemical insecticides are frequently employed. Stored grain insects can also be suppressed by physical disturbance which involves movement of individual kernels with respect to one another. Stirring grain in a silo disturbs individual kernels but we don't know of any study on the effects of stirring on maize weevils. The objective of this research was to determine the effects periodic stirring weevil-infested maize has on maize weevil population density and on maize quality. Six 0.12-m³ (4.2-ft³) steel experimental containers were used in this study. Three of the containers were equipped with Sukup Fastir®™ stirring machines. All containers were loaded with 30 kg of maize and unsexed adult weevils were placed in each container at a density of 25 live weevils per kg of maize. Stirring machines were programmed to travel one length of the stirred containers every 12 h. At 40 days and at 80 days, no live weevils were found in samples from the stirred containers, but at 80 days, reached 18 weevils per kg in control containers. Stirring increased BCFM in the stirred maize by seven percentage points and decreased maize moisture by 0.2 percentage points compared to control containers. Mechanical damage and bulk density changes were inconsequential. Stirring shows promise as an effective non-chemical method for suppression of maize weevils, but studies at silo scale are needed.     

Impact of moisture content and maize weevils on maize quality during hermetic and non-hermetic storage

The objective of this study was to determine the impact of moisture content and Sitophilus zeamais Motschulsky on maize quality during hermetic and non-hermetic storage conditions. Commercial Channel 211-97 hybrid maize kernels were conditioned to 14, 16, 18, and 20% moisture content (wet basis), and then three replications of 300 g of maize grain were stored in glass jars or triple Ziploc^® slider 66-μm(2.6-mil) polyethylene bags at four conditions: hermetic with weevils, hermetic no-weevils, non-hermetic with weevils, non-hermetic no-weevils. All jars and bags were stored in an environmental chamber at 27 °C and 70% relative humidity for either 30 or 60 d. At the end of each storage period, jars and bags were assessed for visual mold growth, mycotoxin levels, gas concentrations, pH level, the numbers of live and dead S. zeamais, and maize moisture content. The maize stored in non-hermetic conditions with weevils at 18 and 20% exhibited high levels of mold growth and aflatoxin contamination (>150 ppb). Conversely, very little mold growth was observed in maize stored in hermetic, and no aflatoxins were detected in any moisture level. CO₂ increased and O₂ gradually decreased as storage time increased for maize stored in hermetic conditions (with or without weevils) in all moisture level. No significant difference in pH was observed in any storage conditions (P < 0.05). Total mortality (100%) of S. zeamais was observed in all hermetically stored samples at the end of 60 days storage. Moisture content for hermetically stored maize was relatively constant. A positive correlation between moisture content and storage time was observed for maize stored in non-hermetic with weevils (r = 0.96, P < 0.05). The results indicate that moisture content and the number of S. zeamais weevils plays a significant role in maize storage, both under hermetic and non-hermetic conditions.     

Resistance of Tripsacorn to Sitophilus zeamais and Oryzaephilus surinamensis

One strategy that has been used to find germplasm for developing improved plant varieties is to test ancestral germplasm for the desired traits. Although the progenitors of commercial maize are not known, a hybrid (called Tripsacorn) developed from a perennial teosinte, Zea diploperennis, and eastern gamagrass, Tripsacum dactyloides, resembles the earliest known samples of primitive domesticated maize. We tested resistance of whole Tripsacorn to the primary storage pest (primary storage pests can infest intact kernels) the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), and resistance of ground Tripsacorn to the secondary storage pest (secondary pests usually cannot infest intact kernels) the sawtoothed grain beetle, Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). Tripsacorn was immune to attack by S. zeamais. The weevils were unable to lay eggs in the Tripsacorn, and we hypothesized that the hardness of the fruitcase was responsible for lack of weevil oviposition. Oryzaephilus surinamensis were able to complete immature development on ground Tripsacorn, but duration of development was longer and weight of emerged adults was less than for beetles developing on wheat. Hardness of the fruitcase may have been a primitive mechanism of defense against insects and other pests, but probably would not be an acceptable trait in commercial varieties. It remains to be determined whether the possible antibiotic effect demonstrated in ground Tripsacorn would be a useful trait in commercial maize hybrids.     

Chemical bases for maize grain resistance to infestation and damage by the maize weevil,Sitophilus zeamais Motschulsky

It was suggested that the factors that confer resistance on a maize variety against Sitophilus zeamais Motschulsky are chemically based. To test this hypothesis, resistance indices of the weevil were assessed using a new scale developed by Nwosu et al. (2015a) after performing detailed chemical analysis of the whole-maize grain using twenty elite maize varieties under ambient temperature and relative humidity of 30.7 °C and 74.5% respectively. Increases in maize varietal crude fibre, phenolic acid and trypsin inhibitor increased significantly mortality of S. zeamais adults and reduced significantly survival rate of S. zeamais adults, percent of grain damage, percent of weight loss, weight of grain flour and oviposition by the adult females. The level of cystein proteinase inhibitor (a natural protectant of plants against insect attack) in the grains was not on its own responsible for increased mortality, reduced grain damage and reduced oviposition. The study identified crude fibre, phenolic acid and trypsin inhibitor of whole-maize grain as the bases for resistance. Their significant increase in grains resulted in low infestation. Whereas, increased protein, zinc, magnesium, calcium, sodium, phosphorus, manganese, iron, cobalt and starch rendered the elite maize grains susceptible to S. zeamais attack. Therefore, significant incorporation of the bases for resistance and significant reduction of the bases for susceptibility in maize grains during breeding programmes is advocated; provided this does not adversely affect palatability and nutritional needs of man. Eighty-five percent of the elite maize varieties were at least resistant to S. zeamais infestation and damage. The resistant varieties, particularly 2000SYNEE-WSTR and TZBRELD3C5 maize with high resistance should be promoted for growing. Antibiosis, antixenosis and preference were the mechanisms of maize grain resistance to S. zeamais attack.     

Radio frequency heating against Sitophilus zeamais Motschulsky in white maize

Radio frequency treatments were evaluated for the control of Sitophilus zeamais Motschulsky in white maize, and their effects on physiological and biochemical properties were evaluated. A 12 kW, 27.12 MHz radio frequency machine was used with an electrode gap of 20 cm; batches of 10 and 20 kg of white maize (11.8% moisture content, w.b.) were treated. Radio frequency heating treatments at 50 °C for 3 min or 60 °C in white maize were effective to achieve 100% mortality of Sitophilus zeamais 4th instar larvae. Significant changes were observed in the moisture content, water activity and color in the corn kernels after the treatments (P < 0.05); however, they were within the range established by the Mexican Standard. As an advantage, the viability and germination of the grain were not affected by the treatments (P > 0.05). Radio frequency has potential to be a postharvest treatment against this pest without damage to white maize.     

Efficacy of filter cake and Triplex powders from Ethiopia applied to wheat against Sitophilus zeamais and Sitophilus oryzae

The efficacy of filter cake and Triplex powders applied to wheat was evaluated in the laboratory against the maize weevil, Sitophilus zeamais Motschulsky and rice weevil, Sitophilus oryzae (Linnaeus)—two most common insect pests associated with stored grain in Ethiopia. Efficacy of these powders was determined by exposing 20 adults of each species to 100 g of wheat treated with 0, 100, 500, 700 and 1000 mg/kg of filter cake and Triplex. Adult mortality was determined 7 and 14 d after exposure. In addition, adult progeny production, percentage of insect damaged kernels, and percentage of grain weight loss at each species-powder-concentration-time combinations were determined after 42 d. The 7 and 14 d mortality was 100% for adults of both species exposed to 1000 mg/kg of filter cake; only the 14 d mortality of Sitophilus species was 100% for adults exposed to 700 mg/kg. Mortality of S. oryzae adults was 100% when exposed for 14 d to1000 mg/kg of Triplex. Mortality of S. zeamais never reached 100% in any Triplex treatments. Adult progeny production of S. zeamais was completely suppressed at filter cake concentrations of 700 and 1000 mg/kg, whereas 1000 mg/kg was necessary for complete suppression of S. oryzae adult progeny production. Complete suppression of adult progeny production was not observed in any Triplex treatments. Complete reduction in percentage of insect damaged kernels and percentage of grain weight loss were obtained when S. zeamais and S. oryzae adults were exposed to 1000 mg/kg of filter cake; similar reductions with S. zeamais occurred only at 1000 mg/kg of Triplex. In the case of S. oryzae, complete reduction of insect damaged kernels and grain weight loss were not achieved at any concentration of Triplex. These powders can be used as alternatives to chemical insecticides for management of Sitophilus species.     

Effect of CO2 modified atmosphere packaging on aflatoxin production in maize infested with Sitophilus zeamais

The weevil Sitophilus zeamais (Motschulsky), the maize weevil, is a pest of stored maize that can cause feeding damage and lead to the proliferation of toxigenic fungi. The application of modified atmospheres with a high concentration of CO₂ is an alternative method for the control of S. zeamais and the inhibition of fungal growth. The objectives of the study were to determine the effect of S. zeamais infestation, grain damage and grain moisture content on aflatoxin production by Aspergillus flavus on maize, and the impact of high CO₂ modified atmosphere packaging on pest infestation and aflatoxin production. Mycotoxin production was only recorded when maize was infested with S. zeamais and had A. flavus inoculum. However, production of mycotoxins was not recorded when the maize was mechanically damaged and stored at 18% moisture content, indicating that the biological activity of the insect was determinant in the production of mycotoxins. The high CO₂ modified atmosphere packaging tested (90% CO₂, 5% O₂ and 5% N₂) prevented mycotoxin production.     

Tolerance of Sitophilus zeamais (Coleoptera: Curculionidae) to heated controlled atmosphere treatments

Combination heat and controlled atmosphere (CA) postharvest phytosanitary treatments are environmentally friendly alternatives to chemical fumigants. A controlled atmosphere/heating block system (CA-HBS) was used to rapidly assess tolerances of adult maize weevil, Sitophilus zeamais, both under regular air (RA) and CA (1% O₂ and 15% CO₂) conditions. In the RA treatment, thermal death kinetics for S. zeamais adults were determined at temperatures between 46 °C and 52 °C at a heating rate of 5 °C/min. The results showed that thermal death curves of S. zeamais adults followed a 0th-order kinetic reaction model. The required holding times for achieving 100% mortality were 165, 40, 14, and 4 min at 46, 48, 50 and 52 °C, respectively. The activation energy for killing S. zeamais adults was 526.7 kJ/mol. The effects of CA at various temperature-time combinations and heating rates on insect mortality were evaluated. The mortality of S. zeamais adults was higher under CA treatment than in the heat treatment alone. The slowest heating rate (0.1 °C/min) achieved the highest insect mortality in CA treatments but lowest mortality in RA treatments. The information obtained from the CA-HBS can be used to develop combination heat and CA treatments against S. zeamais.     

Susceptibility of selected maize seed genotypes to Sitophilus zeamais (Coleoptera: Curculionidae)

Studies were carried out under laboratory conditions of 25 ± 2 °C and 70 ± 5% RH in an incubator to determine the relative susceptibility of eighteen maize genotypes to attack by the maize weevil, Sitophilus zeamais Motschulsky. The experiment was laid out in a Completely Randomized Design (CRD) with three replications. Adult mortality, number of F₁ progeny, weevil development time, susceptibility index, percentage seed damage, percentage weight loss, and weight of powder produced were determined after storage period of three months. The susceptibility index was determined using Dobie’s formula and the genotypes were classified into different susceptibility groups. The genotypes exhibited varying degrees of susceptibility to S. zeamais attack. Only Aseda was regarded as resistant and TZE-Y POP STR as moderately resistant to S. zeamais. Kpari-Faako, Tintim, WACCI-M-1215, WACCI-M-1594 and Wang-Dataa were regarded as moderately susceptible to S. zeamais. However, Abontem, Bihilifa, Ewul-Boyu, Sanzal-Sima, TZE-I 17, WACCI-M-1205, WACCI-M-1508 and WACCI-M-1510 were regarded as susceptible genotypes. Furthermore, Aburohemaa, Obaatanpa and Omankwa were regarded as highly susceptible to S. zeamais. Number of F₁ progeny, seed damage, seed weight loss, weight of dust produced and seed moisture content had positive relationship with varietal susceptibility while adult weevil mortality, median development period and seed germination after infestation had an inverse relationship with susceptibility in maize. The use of insect resistant genotypes would offer a sustainable way of minimizing postharvest losses of seeds in storage especially for smallholder farmers who keep harvested grains for future use as food and seed.     

Degradation of azadirachtin A on treated maize and cowpea and the persistence of Azadirachta indica seed oil on Callosobruchus maculatus and Sitophilus zeamais

Azadirachta indica seed oil has long been used in many parts of the world for the control of various insect pests. The quantification of its known insecticidal compound Azadirachtin A on treated commodities remains a challenge. The degradation of Azadirachtin A in treated cowpea and maize was determined with HPLC-MS as well as the toxicity of A. indica seed oil on their respective major pests is storage between 0 and 180 days. Azadirachtin A degraded slowly on treated maize from 1.31 mg/kg (0-day) to 0.38 mg/kg (180-day) while on cowpea it degraded from 1.14 mg/kg (0-day) to 0.43 mg/kg (180-day). A. indica oil caused a significant day-dependent mortality of adults Callosobruchus maculatus and Sitophilus zeamais and its effectiveness decreased with time. The tested oil was more persistent for inhibiting progeny production than on adult mortality. Further studies are needed to evaluate the quality of treated grains at different storage times.     

Development of Sitophilus zeamais Motschulsky,in maize kernels and pellets made from maize kernel fractions

As a means of studying certain aspects of resistance of maize varieties to Sitophilus zeamais, various types of pellets were prepared using ground maize and compared with whole, pericarpless, and germless kernels. Numbers of weevil progeny (from six females and three males, and usually a 7-day oviposition period) were greatest in pellets made of flour moistened with water containing agar. More progeny was produced in pellets than in whole kernels. Damaged kernels (hot-water treated, pericarpless, germless) were more susceptible than undamaged kernels and fewer weevil progeny were produced in pellets made of germless kernels than from pellets of whole kernels. Additions of small amounts of extra germ tissue to whole maize flour enhanced the susceptibility of pellets to the weevil, but adding larger amounts of germ of pericarp reduced progeny number, weight and developmental speed.     

Efficacy of castor bean oil (Ricinus communis L.) against maize weevils (Sitophilus zeamais Mots.) in northwestern Ethiopia

The maize weevil, Sitophilus zeamais Mots. (Coleoptera: Curculionidae), undermines food security. The biocidal activity of castor bean oil (Ricinus communis L.) against S. zeamais, was studied at various doses at Dembecha, northwestern Ethiopia in 2013/14 (November–April). In the castor bean oil efficacy test, weevil mortality steadily increased with castor bean oil dose. According to the results of the ANOVA, number of dead weevils significantly varied between castor bean oil doses 1 h after treatment (F_{10, 21} = 117.6, p < 0.0001). Just 53% of the weevils were killed in one hour by applying 2 ml of the oil while doses higher than 2 ml killed greater than 85% of the weevils. Using Probit analysis, the LD₅₀ of using castor bean oil against maize weevils was calculated to be 2.04 ml. Therefore, 2 ml of castor bean oil was found sufficient to destroy 50% of the weevils. Higher doses of castor bean oil significantly reduced maize seed germination.     

A comparison of two methods of assessment of maize varietal resistance to the maize weevil, Sitophilus zeamais Motschulsky, and the influence of kernel hardness and size on susceptibility

Fifty-two maize varieties were screened for resistance to infestation by the maize weevil, Sitophilus zeamais, using assessment methods proposed by Dobie (J. Stored Products Res. 10 (1974) 183-197) and Urrelo et al. (J. Stored Products Res. 26 (1990) 100). The two methods gave similar assessments of maize susceptibility to S. zeamais. The Dobie method is preferred due to the lower total time required for assessment of relative susceptibility of maize varieties. The greatest disadvantage of the Urrelo method is the intensive labour requirements in the early stages of a trial, when numbers of eggs have to be counted, although it has the advantage that the assessment may be terminated upon emergence of the first F(1) adult. Two explanatory variables, kernel size and hardness, were investigated to determine whether they may be used as indicators of resistance. Results suggested that kernel size is the more important in determining resistance to attack by S. zeamais, with large kernels appearing to show greater resistance than small ones. Contrary to expectations, of the varieties tested, including local, hybrid and improved open pollinated (IOP) varieties, the local varieties were generally more susceptible. This may be related to kernel size, as all IOPs and hybrids tested had large kernels, whereas the majority of the local varieties had small ones. No clear relationship between weevil susceptibility and kernel hardness could be detected, although there was an indication that differences associated with kernel size varied depending on kernel hardness. None of the varieties tested showed high levels of resistance to attack by S. zeamais.     

Susceptibility of Ethiopian wheat varieties to granary weevil and rice weevil infestation at optimal and sub-optimal temperatures

Integrating varietal resistance with temperature manipulation during storage may provide a better option for protection of stored grains and may decrease reliance on the use of synthetic chemicals. The current study was conducted to determine the susceptibility of different varieties of wheat seed to the infestation by the granary weevil, Sitophilus granarius (L.), and rice weevil, Sitophilus oryzae (L.), at optimal (30 °C) and sub-optimal (19 °C) temperatures. Kernels of six wheat varieties namely, Danda'a, Digalu, ET-13-A2, Kakaba, Millennium, and Pavon-76 were examined over a period of 90 d. Significant interactions were detected between wheat varieties and storage temperature for progeny emergence, percentage of insect damaged kernels, grain weight loss, and amount of powder produced per gram of wheat. Kernels of Danda'a, infested with S. oryzae at 30 °C exhibited significantly lower mean progeny counts (13.3 live insects), lower percentage of grain weight loss (4.2%) and insect-damaged kernels (6.4%), and powder production (1.5 mg/g). Kernel weight and hardness index were negatively associated with percentage of insect damaged kernels and grain weight loss. Kernel diameter was positively associated with both of percentage of insect damaged kernels and grain weight loss. Wheat varieties with high Zeleny sedimentation values had lower percentage of insect-damaged kernels and grain weight loss. These results indicated that kernel weight, hardness index, and protein content are predominant factors contributing to wheat resistance against S. granarius and S. oryzae. The varieties Millennium and Danda'a can be considered with other integrated pest management approaches to reduce stored grain losses of wheat in Ethiopia.     

Terpenoids,DEET and short chain fatty acids as toxicants and repellents for Rhyzopertha dominica (coleoptera: Bostrichidae) and Lasioderma serricorne (Coleoptera: Ptinidae)

Plant-based products and common repellents have been suggested as promising alternatives for management of stored product insects. In this study, contact toxicity and repellent activity of the safe natural products carvacrol, citronella oil, geraniol, nootkatone, ocimene and R-(+)-pulegone, and the synthetic commercial repellents, N,N-Diethyl-3-methylbenzamide (DEET), and the fatty acid mixture of octanoic, nonanoic, and decanoic acids (C8910) were evaluated against the lesser grain borer, Rhyzopertha dominica and the cigarette beetle, Lasioderma serricorne under laboratory conditions. In contact toxicity assays the compounds were tested at concentrations ranging between 0.008 and 0.4 mg/cm². Carvacrol and R-(+)-pulegone exhibited the highest contact toxicity with LC₅₀ values of 0.019 and 0.023 mg/cm² against L. serricorne and LC₅₀ values of 0.012 and 0.019 mg/cm² against R. dominica, respectively. Similarly, C8910, geraniol and citronella oil showed toxic effect against both insects. The repellent activity of compounds was tested using the preference method assay at concentrations ranging between 3.125 and 50.0 μg/cm². The highest repellency percentage (RP) was achieved by C8910 against L. serricorne with a RP value of 76.0% at the lowest concentration (6.25 μg/cm²), while carvacrol showed the highest repellent activity against R. dominica with RP value of 88.0% at 3.125 μg/cm² within 3 h of insect exposure. The tested compounds caused higher repellent activity to R. dominica than L. serricorne. In vitro inhibition studies of acetylcholinesterase (AChE) in adults of both species showed that R-(+) pulegone strongly inhibited AChE activity of R. dominica and L. serricorne with 69.0% and 88.0% inhibition at 40 mM, respectively. Carvacrol caused 41.8% inhibition in AChE activity of R. dominica compared to 66.7% of L. serricorne at 40 mM. The results indicated that the tested natural compounds may be useful alternatives for controlling R. dominica and L. serricorne.     

Evaluation of potential use of nootkatone against maize weevil (Sitophilus zeamais Motschulsky) and rice weevil [S. oryzae (L.)](Coleoptera: Curculionidae)

Nootkatone is a natural sesquiterpene ketone that shows insecticidal activity against insects and ticks. Its contact toxicity and repellency against two major stored-product insect pests, maize weevil (Sitophilus zeamais Motschulsky) and rice weevil [Sitophilus oryzae (L.)], were investigated in the current study. Contact toxicity was evaluated using a no-choice test with treated filter paper, while repellency was evaluated using a choice test with treated corn (for maize weevils) or wheat (for rice weevils). Nootkatone showed low contact toxicity (ranging from 0 to 51%) against the two weevil species at the tested concentrations (ranging from 11.58 μg/cm² to 1158.08 μg/cm²) on filter papers. In choice tests, corn treated with 0.10% or higher and wheat treated with 0.5% nootkatone or higher had significantly fewer maize or rice weevils compared with the solvent only treated control, indicating a repellent effect. The repellency percentage ranged between 46.3 and 93.1% against maize weevils and 39.2-67.2% for rice weevils.