Susceptibility of varieties of stored rough rice to losses caused by storage insects

Losses caused by Sitophilus oryzae (L.), Rhyzopertha dominica (F.), and Sitotroga cerealella (Olivier) in 6 commercial varieties of rough rice from the Southern United States were assessed as weight loss of rough rice, loss of milling yield, and loss of monetary value. Over 3 insect generations, S. oryzae caused the least damage, probably because this species requires grains with gross hull defects and the proportion of such grains was relatively small. Damage attributable to S. cerealella or R. dominica was approximately equal. The varieties Vista and Lebonnet were the most susceptible and the variety Dawn the most resistant after 3 generations.     

Grain loss caused by Tribolium castaneum, Sitophilus oryzae and Acanthoscelides obtectus in stored durum wheat and beans treated with Beauveria bassiana

The effect of the fungal entomopathogen Beauveria bassiana (Balsamo) Vuillemin (Hyphomycete) on the losses caused to durum wheat and beans by storage insects was investigated. Grains were infested with Tribolium castaneum (Herbst), Sitophilus oryzae (L.) and Acanthoscelides obtectus (Say). Beauveria bassiana was produced in inoculated autoclaved rice. The spore formulation (ground rice and B. bassiana) was applied to grain (wheat or bean) and shaken to evenly cover the grain. Adults of T. castaneum or S. oryzae were added to wheat and adults of A. obtectus to bean. Five replicates were set up for each treatment and controls (milled rice but no conidia). The insecticidal effect of B. bassiana was tested by measuring the fresh weight and weight loss of grains after four months of storage. Wheat grains infested with S. oryzae without the conidia was significantly more damaged by weevils than grains treated with B. bassiana. The mean fresh weight of grains with the conidia was significantly greater (18.4%) than the corresponding mean without the fungus when S. oryzae were present. Percentage weight loss decreased by 81.5% and was significantly smaller than the loss from the untreated grain. Significant differences were not found in the fresh weight of seed infested with T. castaneum or A. obtectus in treated or untreated grain nor in the percentage weight loss of grains infested with these insects, with and without B. bassiana.     

Status of glycemic index of paddy rice grain (Oryza sativa L.) on infestation by storage pest Sitotroga cerealella

The harvested paddy rice grains are normally stored by growers under normal conditions. Paddy rice grains are natural food for storage pests like Sitotroga. cerealella, a major insect that appears during paddy storage. The changes in grain composition due to such insect infestation in relation to human health especially the alteration in their Glycemic Index (GI) value have not been studied so far. The present investigation was aimed at studying the effect of S. cerealella infestation on rice grain quality and glycemic index of stored paddy grains. Five diverse rice genotypes with different quality traits were evaluated for grain quality after S. cerealella infestation. The tolerance to insect and variation of grain quality varied with rice genotype significantly. The glycemic index, glycemic load, total carbohydrate, amylose content and resistant starch were affected to a great extent. The consumption of affected grains may create health issue due to imbalance in nutrition and unhygienic condition. Improper storage of paddy after harvesting and processing results in infestation by pests at a large scale. Thus, the grain quality needs to be evaluated to judge the suitability of affected grain for consumption.     

An investigation into the use of an X-ray technique in the study of pre-emergent stages of Sitophilus oryzae (L.) developing in Manitoba wheat

The suitability of using an X-ray technique to study pre-emergent stages of Sitophilus oryzae (L.) developing in Manitoba wheat was investigated. A sample of grain was radiographed once every other working day subsequent to exposure to adult S. oryzae for 24 hr, until the emergence of the F1 generation. Eggs and small larvae were not detected in this manner, but after 13 days larvae were detected with increasing efficiency. Pupae and adults within the grain could be detected and were easily distinguished from larvae and pupae.The development of S. oryzae in individual wheat grains was investigated by sticking each grain of wheat to the Sellotape base of an aluminium cell prior to exposure to one female S. oryzae adult, and subsequently radiographing every other day for 23 days. Larvae were positively identified in grains as early as 9 days after oviposition by tracing back their development in the developed X-ray films, and seven suspected (although not positively identified) eggs were seen on the first day after oviposition.A quantity of grain was X-rayed immediately prior to fumigation and at intervals after fumigation. The efficiency with which dead insects were detected decreased with time after fumigation.     

Weight loss of wheat infested with gamma-radiated Sitophilus oryzae (L.) and Rhyzopertha dominica (F.)

Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) adults were treated with 2·5, 5, 10, 25 or 50 krad of gamma radiation and confined on samples of uninfested wheat. Except for those treated at 2·5 krad the amounts of wheat consumed by the adults and their progeny were much less than that eaten by the controls. Five weeks after treatment with 25 krad, total feeding damage by R. dominica and S. oryzae was 11 and 3 per cent, respectively, of the control and most of this feeding occurred during the first week after treatment. The amount of damage caused by live but sterile insects in bulk grain treated with gamma radiation would probably not be a serious problem because of the great reduction in feeding brought about by the radiation.     

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.     

Maize storage insects (Sitophilus zeamais and Prostephanus truncatus) prefer to feed on smaller maize grains and grains with color,especially green

Maize is the major food staple in Eastern and Southern Africa, and since production is seasonal, on-farm storage is practiced by farmers. Because stored maize is susceptible to pests, improved storage methods are being developed which need to be evaluated for their effectiveness in reducing losses. The standard count and weigh method (CWM) assumes storage insects attack grains of different sizes in equal measure, although this has not been tested. This study therefore analyzed storage insects’ feeding preferences for maize grains of different sizes. Maize grain was sieved and split into four size categories, colored with food dyes, remixed, and distributed into 48 jars, each with about 300 g of grain, artificially infested with maize weevils (Sitophilus zeamais) or larger grain borers (Prostephanus truncatus), 40 insects per jar. After two months, the grains were separated into their size categories (visually, by color), and grain damage and weight loss was estimated with the CWM. Results show that storage insects have a preference for feeding on smaller, rather than larger grains; and on colored rather than uncolored grains. Small-sized and colored grains were more likely to be perforated by insects and suffered more weight loss. This preference, observed for both species, is more pronounced in S. zeamais, who also distinguish between different colors, and prefer green. The size effect is, however, comparatively small and the average weight loss calculated by a size-adjusted formula is not significantly different from that calculated by the standard CWM. However, the resulting differences in weight losses between grains of different sizes are small. Weight loss calculated by weighted CWM, while in principle more accurate, does not in practice lead to significantly different estimates. Therefore, the results do not warrant a change in the conventional CWM for weight loss in stored grain.     

The occurrence of a strain of Sitophilus oryzae (L.) (Coleoptera: Curculionidae) breeding in Portuguese kibbled carobs

Sitophilus oryzae (L.), a major pest of cereal grains, was found on a number of Portuguese consignments of dried carob pod, imported into Britain for animal feed. These unexpected occurrences prompted an investigation into the breeding potential of two strains of S. oryzae and one strain of Sitophilus granarius (L.) on this leguminaceous food. It was found that of the three strains tested only the strain of S. oryzae from Portugal was able to breed, at a slow rate, on carob pod. Carobs used as animal feed may therefore be a source of direct introduction to farms of a major grain storage pest.     

Field trials to control insect pests of farm-stored maize in Zambia

Severe infestations of Sitophilus zeamais Motsch and Sitotroga cerealella Oliv. occur in maize cobs stored under farm conditions in Zambia causing up to 92% damaged grains 8 months after harvest. Shelling the maize reduced S. cerealella damage to low levels and also stabilized the moisture content of the grain providing a more suitable substrate for insecticide application and c control of S. zeamais. Malathion at 12 ppm a.i., tetrachlorvinphos (12 ppm), and jodfenphos (12 ppm), applied as dust admixtures to shelled maize in traditional mud-walled, timber and thatch storage cribs, all kept damaged grains below 10% up to 10 months after harvest. Pirimiphos-methyl (4 ppm) and fenitrothion (2 ppm) maintained these low damage levels up to 8 months after harvest, but there was evidence of continued S. cerealella infestation with these two insecticides.     

Effects of flameless catalytic infrared radiation on Sitophilus oryzae (L.) life stages

A laboratory benchtop flameless catalytic infrared emitter was evaluated against all life stages of the rice weevil, Sitophilus oryzae (L.), an insect species associated with stored wheat. The emitted infrared radiation was in the 3-7 μm range. A non-contact infrared thermometer measured grain temperatures continuously during exposures of infested wheat. Insect mortality was a function of the final grain temperature attained. In general, higher grain temperatures were attained when using 113.5 versus 227.0 g of wheat, and at 8.0 cm from the emitter versus 12.7 cm, and during a 60 s exposure versus a 45 s exposure. Complete mortality of all life stages of S. oryzae was achieved at 8.0 cm from the emitter using 113.5 g of wheat, with a 60 s exposure; the mean grain temperatures attained ranged from 108.4 to 111.8 °C. The log odds ratio tests showed that eggs (0 days old) were the least susceptible stage to infrared radiation, followed by adults within kernels (28 days old), pupae (24 days old), young larvae (7 days old), larvae that were 14-21 days old, and adults (42 days old). These data using small amounts of grain indicate infrared radiation from the flameless catalytic emitter to be a viable option for disinfesting wheat containing various life stages of S. oryzae.     

Effects of Cry1F and Cry34Ab1/35Ab1 on storage pests

Two crystalline protoxins from Bacillus thuringiensis (Bt), Cry1Fa1 and Cry34Ab1/Cry35Ab1 (Cry1F, Cry34/35Ab1), were evaluated for efficacy against lepidopteran and coleopteran storage pests. Cry1F was tested against the lepidopterans Sitotroga cerealella (Angoumois grain moth) and colonies of Plodia interpunctella (Indian mealmoth) that are susceptible or resistant to Bt Cry1Ab and Cry1Ac toxins, Bt subspecies entomocidus, and the commercial formulation Dipel^®. Cry1F was also tested against the coleopterans Cryptolestes pusillus (flat grain beetle) and Tribolium castaneum (red flour beetle). Cry34/35Ab1 was tested against S. cerealella, C. pusillus, and T. castaneum, and against additional coleopteran storage pests, including Tenebrio molitor (yellow mealworm), Trogoderma variabile (warehouse beetle), Oryzaephilus surinamensis (sawtoothed grain beetle), Rhyzopertha dominica (lesser grain borer), and Sitophilus oryzae (rice weevil). Strains of Bt-susceptible or -resistant P. interpunctella generally were more sensitive to Cry1A protoxin or toxin than either Cry1F protoxin or Dipel. Despite difficulties with the bioassay of S. cerealella larvae, the data suggest that Cry1F and Cry34/35Ab1 caused increased larval mortality, and a developmental delay was observed and no pupae emerged with 0.9% Cry1F. Neither Cry1F nor the corn rootworm-active toxin Cry34/35Ab1 significantly affected the biological parameters of the coleopteran species evaluated.     

Effect of uneven distribution of spinetoram-treated wheat and rice on mortality and progeny production of Rhyzopertha dominica (F.), Sitophilus oryzae (L.) and Tribolium confusum Jacquelin du Val

Laboratory bioassays were carried out in order to evaluate the effectiveness of spinetoram on rice and wheat in layer and mixture treatment applications against three major stored-grain beetle species, Rhyzopertha dominica, Sitophilus oryzae and Tribolium confusum. Spinetoram was applied at 1 ppm (1 mg/kg of grain). In the layer treatment the grain was placed in vials (8 cm high, 3 cm in diameter); in those vials there was five categories of grain: untreated (control), totally-treated, and with the upper 1/8, 1/4 and 1/2 treated. Also, there were two categories of insect introduction: before or after the grain placement. In the mixture treatment, the vials contained 20 g of grain divided into six categories: vials that contained untreated grain (control) and vials that contained 5, 10, 25, 50 and 100% treated grains. Mortality was assessed after 14 d for both treatments but with an intermediate 7-d assessment for the mixture treatment. After this interval, all adults were removed, and progeny production was measured 65 d later. From the species tested, R. dominica was by far the most susceptible in both treatments. Generally, in the layer treatment, mortality of R. dominica reduced with the size of the treated layer in the vials. Also, mortality was significantly lower when the exposed R. dominica adults had been placed before the introduction of the grain. For S. oryzae, mortality was lower in comparison with R. dominica and in general, mortality was lower on rice than on wheat, even in the case of totally-treated grains. Survival of T. confusum was considerably higher than both R. dominica and S. oryzae. In the mixture treatment, mortality of R. dominica was 82–100% after 14 d of exposure. Again mortality was considerably lower on rice than on wheat. For S. oryzae, mortality was higher in vials containing totally-treated or 50% treated kernels, in comparison with the other treatments. Progeny production of R. dominica in the layer treatment increased with the reduction of the treated layer for both commodities. In contrast, for S. oryzae, there were no differences in progeny production counts between treated and untreated grains, with the exception of totally-treated wheat. In the mixture treatment progeny production increased with the reduction of the percentage of the treated grains, but there were considerable differences between wheat and rice. The overall results suggest that spinetoram is very effective against R. dominica, moderately effective against S. oryzae, and not very effective against T. confusum. Uneven application of spinetoram may, under certain circumstances, provide satisfactory control of R. dominica.     

Chemical,physical, and sensory changes in rice subjected to UV-C radiation and its acceptability to rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and humans

The objective of this study was to evaluate the effect of ultraviolet C (UV–C) radiation treatment of rice on both the development of S. oryzae and changes in the quality of rice Oryza sativa (L.) (Poales: Poaceae) grains. Husked rice grains were treated with UV-C, and subsequently placed alternately with the control treatment (without UV-C) in an arena. Subsequently, 500 adult S. oryzae were placed in the center of the arena, with free access to both samples for 30 days. On the 30th day of the experiment, a greater number of adult S. oryzae were identified as consuming grains subject to the control treatment; these same S. oryzae also showed greater emergence on the 40th, 50th, and 60th day. In the group treated with UV-C, reduced acidity, protein solubility, K₂₃₂, K₂₇₀, luminosity, and damage were observed; however, increases in gravimetric and volumetric yields were also observed. The sensorial analysis of the cooked grains showed that grains treated with UV-C had less acceptance and purchase intention by human panelists, mainly due to the odor attribute. Further studies are still needed to identify metabolites formed in rice subjected to UV-C; however, it is noteworthy that some S. oryzae are able to recognize irradiated rice as distinct from control.     

Efficacy of methoprene for multi-year protection of stored wheat,brown rice,rough rice and corn

Hard red winter wheat, brown rice, rough rice, and corn were treated with the insect growth regulator (IGR) methoprene at rates of 1.25 and 2.5 ppm, held for 24 months at ambient conditions in buckets on the floor of a grain bin, and sampled every two months. Bioassays were done by exposing 10 mixed-sex adults of Rhyzopertha dominica (F.), the lesser grain borer, and Tribolium castaneum (Herbst), the red flour beetle, on wheat, R. dominica and Sitotroga cerealella (Oliver), the Angoumois grain moth, on brown rice and rough rice, and T. castaneum and S. cerealella on corn. Sample size for all commodities was about 80 g, and these samples were held for 3 months at 27°C-60% r.h. Both rates of the IGR completely suppressed adult progeny development of R. dominica with little resulting feeding damage, sample weight loss, or insect damaged kernels (IDK). Some adult progeny production of S. cerealella and resulting IDK occurred at both rates on rough rice, brown rice, and corn, but was far less than in untreated controls. There was little adult progeny production but some feeding damage caused by larval T. castaneum in the treated wheat and corn but again far less than in untreated control. Allowing continual exposure of parental adults on grains treated with an IGR, rather than exposing those parental adults for a short time period, may give more accurate evaluations of residual efficacy. Results show that methoprene used as a grain protectant will give residual control of stored product beetles for 24 months, but complete control of S. cerealella may require inclusion of a contact insecticide.     

Comparison of seven methods for stored cereal losses to insects for their application in rural conditions

There are several methods for assessing harvest losses during storage with varying degrees of accuracy, reliability and practical application, however, field conditions may limit their use among subsistence farmers and traders in developing nations. We compared seven standard grain loss methods during natural and controlled infestation by Sitophilus oryzae L. in wheat and barley to select the best procedures for use in farm storage. Methods tested were: 1) visual inspection of infested lots, 2) uncorrected weight loss, 3) modified standard volume/weight ratio, 4) grain count and weight, 5) percentage of damaged grains converted to weight loss, 6) one thousand grain mass, and 7) one thousand grain mass including dust. Previously disinfested cereal lots (wheat, barley, 500 g fresh w) were exposed to 20 newly emerged adult S. oryzae for 90 d at 28 °C and 70% r.h. Naturally- infested wheat lots were also monitored under the same conditions. Before and after this period, fresh and dry weight, number, moisture content of uninfested and damaged grains, weight of 1 L of seeds and dust produced by insect activity, fresh and dry weight of 1000 kernels, and number of adult weevils was determined and applied to appropriate equations of methods (1), (2), (3), (4), (5), (6) and (7). Grain mass loss estimations varied by wide margins (9.3 ± 1.3% to 25.8 ± 2.3% in barley, 2.2 ± 0.7% to 12.5 ± 2.5% in wheat) depending on method employed, suggesting the need for careful selection of the most appropriate procedure under field conditions and farmer/trader interests. While accurate procedures such as method 7 provided dependable results, methods 3 and 5 appear most practical for wheat and barley.     

Effectiveness of hermetic containers in controlling paddy rice (Oryza sativa L.) storage insect pests

Naturally infested paddy rice was used to compare the effectiveness of polypropylene bags and hermetic storage containers over 12 months of storage in a warehouse. Insect pest identification as well as the infestation level, percentage of damaged grain, weight loss, and moisture content were evaluated. Five insect species associated with stored rice were identified during the storage period, namely lesser grain borer (Rhyzopertha dominica), red flour beetle (Tribolium castaneum), rice/maize weevil (Sitophilus spp.), angoumois grain moth (Sitotroga cerealella) and flat grain beetle (Cryptolestes ferrugineus). The lesser grain borer was the most predominant species with an average incidence above 70% after twelve months of storage, followed by the rice/maize weevil with an incidence of 17%. When compared to hermetic storage containers, polypropylene bag showed the highest mean infestation level with 233.3 individuals/kg after six months of storage, representing about 8-fold of the number of insects recorded in hermetic containers after six months of storage. In polypropylene container, the percentage of damaged grain and weight loss increased significantly achieving a maximum of 6.98% and 5.56% respectively, whereas using hermetic containers the highest percentage of damaged grain reached was 3.24% in polyethylene drum and the weight loss was 1.62% in GrainSafe bag. The results from the study show that the use of hermetic storage containers is a green alternative for safe storage of paddy rice, for 12 months without application of pesticides, bringing multiple advantages for smallholder farmers, lever food security and income generation for smallholder farmers and rice milling companies.     

Impacts of Storicide II on internal feeders of Brown rice

Protectants applied to grain can reduce damage caused by insect feeding during storage. Although these protectants are effective against many external feeders, they may also reduce damage caused by internal feeders as they often interact with the exterior surface of the grain during their larval or adult stages to feed or oviposit. For this study, we investigated impacts of Storicide® II applied to brown rice on three different internal feeders: Rhyzopertha dominica (Fauvel), Sitophilus oryzae (L.), and Sitotroga cerealella (Olivier). We also investigated the effects of this protectant at three different temperatures and when it was combined with different percentages of untreated brown rice. Time-series clustering was also performed to determine whether treatments caused disruptions to the timing of progeny emergence. Overall, R. dominica was the most susceptible as mortality and knockdown were observed in mixtures containing 10% treated brown rice. In contrast, S. cerealella was the least susceptible as mixtures containing at least 50–75% treated brown rice were required to reduce progeny production. However, lowering the temperature to 22 °C did reduce the amount of treated brown rice required to reduce progeny emergence and also reduced the number of progeny that emerged synchronously, which would likely reduce mating and reduce population levels over time. Similar effects on progeny were observed for S. oryzae and R. dominica. Overall, these findings suggest that Storicide II can reduce population levels of internal feeders and that combining this protectant with cooler temperatures can provide additional protection.     

The effect of yellow split-peas (Pisum sativum L.) and other pulses on the productivity of certain strains of Sitophilus oryzae (L.) (Col. Curculionidae) and the ability of other strains to breed thereon

The productivity of three strains of the rice weevil, Sitophilus oryzae (L.) was markedly reduced when an equal weight of yellow split-pea (Pisum sativum L.) was admixed with wheat. Other pulses (haricot beans, cow peas, green moong, soy-beans) admixed in the same concentration did not have this effect. Results were similar when the pulses were presented intact and as a paste on the outside of the wheat grain and when the adults were given a choice of wheat or a wheat/pulse mixture or confined in sufficient numbers on one or the other.A strain of S. oryzae from Trinidad was capable of breeding on yellow split-peas. It was morphologically similar to the strain bred at P.I.C.L. Slough U.K. and was interfertile with it. When bulk crosses were carried out only the progeny of the ‘Trinidad’ × ‘Trinidad’ cross were capable of significant breeding on split-peas. Examination of 66 collections of S. oryzae from various parts of the world revealed 7 capable of breeding on this pulse (3 from Trinidad, 1 from Jamaica, 2 from Callao, Peru and 1 from Singapore). The significance of the experiments is briefly discussed.     

Laboratory assessment of toxic activity of purified peptides extracted from chickpea seeds to two strains of the rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

Several peptides with entomotoxic properties were extracted from seeds of different chickpea varieties, by either aqueous or alcoholic phase extraction. The extracts were purified by anion-exchange chromatography followed by membrane dialysis. The toxicity of the purified extracts was tested on two different strains of the rice weevil, Sitophilus oryzae: a French strain feeding only on cereal grain and sensitive to pea phytotoxins (SS strain) and a Chinese strain naturally breeding on split pea (RS strain). The toxic activity of the different fractions isolated from the purified extracts was evaluated by the ‘artificial kernel method’, incorporating the fraction into a reconstituted (‘artificial’) kernel made from whole wheat flour. The toxicity of the fractions was assessed by determining the mortality of young adults of each S. oryzae strain after 7 and 14 d feeding. With the more toxic acidic fraction incorporated into the artificial kernel, the mortality rate of SS strain weevils was 83% and 100% after 7 and 14 d feeding, respectively. With all the alcoholic fractions, mortality of the SS strain remained very low. With RS strain weevils, mortality was negligible after 7 d or 14 d feeding on any peptide fraction of the extracts.     

Stored grain pest prevalence and insecticide resistance in Egyptian populations of the red flour beetle Tribolium castaneum (Herbst) and the rice weevil Sitophilus oryzae (L.)

As a consequence of the widespread use of insecticides against insect pests in grain warehouses and in the food industry, insecticide resistance has greatly increased among these species all over the world. Nonetheless, insecticide resistance in stored grain insects in Egypt was little studied. Therefore, our study aimed to forecast infestation risks and determine the insecticide resistance level in Egyptian populations of the main insect pests of stored grains. To achieve this goal, we surveyed the populations of stored-product insects in wheat in two different sites in the Alexandria governorate (Egypt) between June and August 2017. Moreover, insecticide resistance levels in Egyptian populations of Tribolium castaneum (Herbst) and Sitophilus oryzae (L.) collected from wheat storage facilities (granaries and flour mills) in Alexandria governorate were also determined. Three contact insecticides, namely malathion, pirimiphos-methyl and cypermethrin, were tested. Tarsal contact bioassays on filter paper were carried out on adults following FAO methods and concentration-mortality lines were estimated to determine the resistance ratios for each insecticide and population. The data from the monitoring of insects revealed that T. castaneum and S. oryzae were the most common species infesting wheat in both Alexandria granaries and mills. Populations of S. oryzae were generally more resistant to malathion than the populations of T. castaneum. However, T. castaneum populations were more resistant to pirimiphos-methyl than the S. oryzae populations. Both populations of T. castaneum and S. oryzae were susceptible to cypermethrin. The detected levels of insecticide resistance indicate that this phenomenon takes place and should be a concern in Egyptian populations of T. castaneum and S. oryzae requiring monitoring and design of resistance management practices.