Species Of Stored-product Insects Research Articles

Assessment of Phosphine Resistance in Major Stored-Product Insects in Greece Using Two Diagnostic Protocols.

Post-harvest losses due to insect infestation and spoilage by bacteria and molds pose significant challenges to global cereal production. This study investigates the prevalence of resistance to phosphine, a commonly used grain protection agent, in stored-grain insects. The research, conducted in various storage facilities across Greece, examined 53 populations of key stored-product insect species. Two assessment protocols, namely, dose-response (at 50-1000 ppm for 3 days exposure) and CORESTA (at 300 ppm for 6 days), were used herein to estimate phosphine resistance. The results showed that 13.3% of field populations were resistant, and mortality rates increased with higher phosphine concentrations. Specifically, according to the dose-response protocol, among the 53 field populations, 37.7% were found to be resistant to phosphine, namely, two populations of O. surinamensis, one of S. oryzae, seven of T. confusum, one of C. ferrugineus, one of T. castaneum, and all populations of R. dominica, whereas, according to the CORESTA protocol, all populations were found to be susceptible to phosphine. The observed resistance patterns differ from those reported in other regions of the world. The study highlights the importance of tailored fumigation strategies, considering insect species varying susceptibility to phosphine. It recommends the use of best management practices and rotational strategies, such as combining phosphine with other methods, to develop effective resistance management plans. The results provide valuable insights into the dynamic landscape of phosphine resistance in stored-product insects and suggest potential avenues for further research and control measures.

Efficacy of thiamethoxam against Sitophilus oryzae, Tribolium confusum and Rhyzopertha dominica: The effect of commodity and dose rate

Laboratory bioassays were conducted to evaluate the efficacy of thiamethoxam as a grain protectant against Sitophilus oryzae, Tribolium confusum and Rhyzopertha dominica adults. Five concentrations (0.1, 0.5, 1, 2, and 4 ppm) and four commodities (wheat, maize, rice, and barley) were evaluated. Mortality rates were recorded after 7, 14, and 21 d and progeny production was assessed 65 d after exposure. Thiamethoxam was more effective at higher concentrations and S. oryzae was the most susceptible species. Surprisingly, the highest progeny production was recorded for S. oryzae with 154.3 adults/vial, while no progeny production was observed for T. confusum at 2 and 4 ppm in most of the commodities tested. To conclude, thiamethoxam can provide an adequate level of control against major stored-product insect species in wheat, maize, rice and barley.

Population growth of different stored product species on wheat, barley, and tritordeum

Stored product species can be developed in a variety of stored product grains. In this study, were compare three different grains for their suitability for population growth of primary and secondary stored product insects. In the first series, we evaluated the population growth and damage of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), Sitophilus granarius (L.) (Coleoptera: Curculionidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on whole wheat, barley and tritordeum kernels after 65 days. In the second series, three different percentages of whole and cracked kernels were tested: 100% cracked kernels, 100% whole kernels and 50% cracked +50% whole kernels, for Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). The results showed that tritordeum was suitable for the population growth of all species tested. In most of the cases, R. dominica showed higher frass production but S. granarius showed a higher number of damaged kernels. Cracked kernels were preferred by secondary pests than whole kernels and wheat showed the highest progeny production than tritordeum and barley. Overall, commodity, and grain type and percentage of cracked kernels can affect the population growth of stored product insect species. Results of this study showed that stored product insect species can develop in tritordeum and thus should be taken into consideration for further results as may be damaged during storage.

Use of irradiation against stored product insect species that infest edible insect rearing

Hermetia illucens (Linnaeus, 1758) and Tenebrio molitor (Linnaeus, 1758) larvae are considered the most important edible insects almost of the world. Infestation of these insect meals with stored-product pests may pose a significant threat to their production process or storage. This study investigated the efficacy of phytosanitary irradiation in protecting H. illucens and T. molitor meals from the three major stored-product pests, Necrobia rufipes (De Geer, 1775), Tribolium castaneum (Hrebst, 1797) and Oryzaephlius surinamensis (Linnaeus, 1758). The obtained data revealed that the longevity periods of N. rufipes, T. castaneum and O. surinamensis were higher (16.8, 30.7 and 19.7 day), respectively when fed on T. molitor compared to BSF diet (7.4, 18.6, and 18.35 days, respectively). Results indicated that O. surinamensis was highly susceptible to irradiation followed by N. rufipes and T. castaneum in response to different doses when reared on both H. illucens and T. molitor meals. The data demonstrated that exposure of the three tested insect pests reared on the both diets to gamma radiation has reduced their population growth and next offspring. The present findings provide a new set of valuable insights towards a comprehensive pest management approach that can be utilized to optimize the farming facility and maximize the utilization of H. illucens and T. molitor products.

Eucalyptus and spearmint oils inhibit the biological activity of lesser grain borer and red flour beetles

The objective of this investigation was to assess the insecticidal efficacy of essential oils derived from eucalyptus (Eucalyptus camaldulensis) and spearmint (Mentha spicata) against two species of stored-product insects. The process of Clevenger-type water distillation was employed to extract essential oils from two distinct plant species. Subsequently, the insecticidal properties of these oils were evaluated against specimens of the American wheat weevil (Rhyzopertha dominica) and the red flour beetle (Tribolium castaneum), belonging to the Coleoptera: Bostrichidae and Tenebrionidae families, respectively. Eucalyptus oil exhibited the highest level of inhibition of insects’ reproduction. Still, when tested on adults of both types of insects, eucalyptus and spearmint oils were more effective than the control treatment. A complete inhibition of egg-laying activity (100%) was achieved using a 7% concentration of eucalyptus oil. The trials were done within controlled laboratory settings, with a notable absence of tests conducted under authentic operational conditions. Researchers who want to learn more about using essential oils as insecticides in the future should focus on making pesticide formulations that work well in a wide range of production settings.

Efficacy of Four Insecticides Applied to Fortified Rice with Basil against Major Stored-Product Insect Species

Rice is one of the most important foods since it is grown in many countries and consumed by the majority of the population. Ensuring food security through the protection of stored-product commodities has become one of the most important priorities worldwide. In this study, the effects of three insecticidal formulations and an available diatomaceous earth formulation on basil-fortified rice against the major stored-product insects were evaluated. The label dose of each insecticidal formulation was used. Insect mortality was determined after 1, 3, 7, 14 and 21 days for each species. The entire experiment was repeated three times by preparing different lots of treated and untreated rice for each treatment. The results of the diatomaceous earth treatments showed that the most susceptible individuals were Sitophilus oryzae adults and Oryzaephilus surinamensis larvae, while the least susceptible individuals were Rhyzopertha dominica and Tribolium castaneum adults. The tested insecticides were effective against S. oryzae, as mortality was 100%. Between the two pyrethroids, deltamethrin was more effective than cypermethrin in the tested insecticides. Our findings indicate that there are available insecticides on the market which can be obtained successfully for the durable protection of agricultural commodities after the harvest stage.

The essential oil of Kochia scoparia (L.) Schrad. as a potential repellent against stored-product insects.

Chemical composition of the essential oil from Kochia scoparia (L.) Schrad. (syn. Bassia scoparia (L.) A. J. Scott) was analyzed in quality and quantity by GC-MS and GC-FID. Repellent activities of the essential oil from K. scoparia (KSEO) were evaluated against two common species of stored-product insects Tribolium castaneum Herbst and Liposcelis bostrychophila Badonnel. Results indicated that KSEO mainly consisted of eugenol, β-caryophyllene, and α-humulene, accounting for 75.6%, 8.2%, and 1.4% of the total oil, respectively. KSEO and the three major components were repellent to T. castaneum and L. bostrychophila adults. Notably, KSEO exerted significant effects, comparable to the positive control DEET at 2 and 4h post-exposure. Eugenol at 63.17-2.53 nL/cm2 exhibited high percentage repellency ranging from 96 to 70% against L. bostrychophila during 4-h exposure. To gain further insights into the repellent activity, molecular docking simulation was performed with eugenol as the ligand and an odorant binding protein TcOBPC12 (gene: TcOBP10B) from the model insect T. castaneum as the receptor. Docking calculation results revealed that TcOBPC12 had binding affinity to eugenol (△G = - 4.52kcal/mol) along with a hydrogen bond of 0.18nm (1.8Å) long forming between them, which could be an important target protein associated with identifying volatile repellent molecules. This work highlights the promising potential of KSEO as a botanical repellent for controlling stored-product insects.

Real-time stored product insect detection and identification using deep learning: System integration and extensibility to mobile platforms

Existing stored product insect monitoring methods are time-consuming, costly, and often require specialized equipment or training. This study proposed an integrated insect monitoring system that employs a simple RGB camera and data-driven deep-learning models to detect and identify stored product insect species in warehouses, food facilities, and retail environments. Top-down images of six common insect species were acquired with a setup simulating a conceptualized probe-type monitor under varying lighting and background conditions. These images were preprocessed and manually annotated, resulting in an insect dataset of 2630 images with 14,509 labeled insects. A state-of-the-art computer vision model from YOLO family was selected, and six YOLO variants (YOLOv5s/m/l and YOLOv5s/m/l) were trained and evaluated on the insect dataset. All trained YOLO models delivered an impressive performance in terms of high detection accuracy (above 76% for mAP@[0.50:0.95]) and fast inference time (12–36 ms range). Subsequently, the best-performing YOLOv8l model was integrated and deployed on a mobile device, achieving a good detection performance with average detection speeds of 16 and 29 fps on a desktop computer and smartphone, respectively. The study provided an end-to-end framework for automatic and real-time insect detection and identification in a stored product environment. The lightweight variant of YOLO can be deployed on low-cost edge hardware, mobile devices, or cloud computing. The proposed system is relatively fast, accurate, and inexpensive for insect monitoring and may prove an alternate solution to existing methods. The system would serve as a decision-making tool for stored product facilities managers and can be easily scaled and adapted in a variety of stored product environments.

Identifying common stored product insects using automated deep learning methods

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

Efficacy of Contact Insecticides for the Control of the Larger Grain Borer, Prostephanus truncatus (Horn), on Stored Maize

One of the most destructive insect species for stored maize is the larger grain borer, Prostephanus truncatus. Its control is challenging, as it seems to have a natural tolerance to active ingredients that are effective for other stored-product insect species that cause infestations in maize. The objective of the present study was to comparatively evaluate a wide range of insecticides that are currently in use in stored product protection for the control of P. truncatus. Specifically, three inert dusts—namely, a kaolin, a zeolite and a diatomaceous earth formulation—and three residual insecticides—i.e., the pyrethroid deltamethrin, the bacterial insecticide spinosad and the juvenile hormone analogue S-Methoprene—were evaluated against adults of P. truncatus. Adult mortality was assessed after 7, 14, 21 and 28 d of exposure, whereas progeny production was measured after an additional interval of 28 d for inert dusts and 65 d for the contact insecticides. Moreover, the number and weight of infested and uninfested kernels per vial was measured. Low mortality levels were recorded for the three inert dusts even for the highest application rate and after 28 d of exposure. Moreover, the inert dusts tested failed to suppress the progeny production of P. truncatus. In contrast, high mortality levels were recorded for deltamethrin and spinosad that exceeded 95% already after 7 d of exposure at the lowest application rate (0.5 ppm). The application of S-Methoprene did not result in high adult mortality rates, irrespective of the application rate and the evaluation interval. Deltamethrin, spinosad and S-Methoprene significantly suppressed progeny production of the species at the doses tested.

Insecticidal Effect of Diatomaceous Earth Formulations for the Control of a Wide Range of Stored-Product Beetle Species.

Diatomaceous earth (DE) formulations are promising alternatives over the use of traditional insecticides. In the present study, a series of laboratory bioassays was carried out to assess the efficacy of three diatomaceous earth formulations, i.e., Silicid, Celatom® MN-23, and SilicoSec®, for the control of a wide range of stored-product insect species in soft wheat. The species tested were Tribolium confusum, Tribolium castaneum, Sitophilus oryzae, Sitophilus granarius, Rhyzopertha dominica, Oryzaephilus surinamensis, and Alphitobious diaperinus. Different dose rates, i.e., 0 (control), 100, 300, 500, and 1000 ppm, were used for each of the aforementioned dust formulations. Mortality levels of the exposed individuals were assessed after 3, 7, 14, and 21 days of exposure. Moreover, progeny were counted 65 days later. Based on our results, dust formulations were effective for the control of most of the stored-product beetle species tested. Among the DE formulations tested, Silicid could adequately control the stored-product insect species. Complete suppression of offspring was observed only for secondary species (T. confusum, T. castaneum, O. surinamensis, and A. diaperinus). For primary species (S. oryzae, S. granarius, and R. dominica), the lowest number of progeny was observed in wheat treated with Silicid. For instance, in the case of R. dominica, significantly fewer individuals were produced in Silicid-treated wheat at the highest dose rate. The results of the present study aim to encourage the utilization of DE in stored-product protection as an integrated pest management tool. Additional experimentation is required to apply the tested DE formulations in the field and on different surfaces.

Effect of Nitrogen on Stored-Product Insect Control at Industrial Scale.

In this study, we evaluated the insecticidal effect of nitrogen against Sitophilus granarius (L.), Sitophilus oryzae (L.), Rhyzopertha dominica (F.), Prostephanus truncatus (Horn), Tribolium confusum Jacquelin du Val, and Oryzaephilus surinamensis (L.). Four trials were conducted in chambers containing flour in bags or sacks with >99% nitrogen level. Adults of all the above species, as well as immature life stages (eggs, larvae, and pupae) of T. confusum were used in the trials. Our results showed that nitrogen caused high mortality for all species and life stages tested. Some survival was recorded for R. dominica and T. confusum pupae. Low progeny production was recorded for S. granarius, S. oryzae, and R. dominica. In conclusion, our trials indicated that a high nitrogen environment can provide satisfactory control of various primary and secondary stored-product insect species.

Delayed responses of major stored-product beetle species after exposure to an alpha-cypermethrin-coated net

Carifend® is an alpha-cypermethrin-coated net that has been evaluated with success for the control of insects that infest stored tobacco. More recent data indicate that nets that contain insecticides can be further utilized against a wide range of stored-product insect species in different application scenarios. The aim of the current study was to evaluate Carifend® against adults of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), the granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae), the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), the saw-toothed grain beetle, Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae), the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae), and the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae). Adults of these species were exposed to dishes containing Carifend® for 2, 8 and 24 h, and then they were transferred to untreated dishes, where mortality was recorded 7 d later. In most of the cases, the duration of the initial exposure increased mortality, but, in general, mortality was further increased after the termination of the post-exposure interval. Among the species tested, T. confusum was found to be the least susceptible to Carifend®. For instance, the mortality level was 5.5% for T. confusum even 7 d after exposure, while for P. truncatus it was 100%. The results of the present study clearly demonstrate that Carifend® can be an effective tool against a wide range of major stored-product beetle species, even at exposures that last for <24 h.

Population growth of stored product insects on wheat containing wheat bugs

In the present study we examined the effect of the presence of wheat bugs (Eurygaster spp. and Aelia spp.) on wheat on the mortality, progeny production and infestation patterns of three stored product insects, Trogoderma granarium Everts, Sitophilus oryzae (L.) and Rhyzopertha dominica (F.). The bioassays were carried out under laboratory conditions (25 ± 1 °C, 60 ± 5% relative humidity (r.h.) and continuous darkness), and 20 adults of each stored product insect species were placed in plastic vials (3 cm in diameter, 8 cm in height) with wheat that contained different numbers of wheat bugs (1, 2, 3 or 5 adults). In general, stored product insect mortality was not affected by the presence of wheat bugs, in most of the combinations examined. In most of the cases, mortality of T. granarium was higher on wheat which contained Eurygaster that wheat containing Aelia, while progeny production of S. oryzae was also affected by the presence of wheat bugs. Frass production for all combinations was similar, but greater frass production occurred by all combinations of R. dominica with Aelia. Overall, the presence of wheat bugs could affect the survival and the progeny production of both S. oryzae and R. dominica. In general, our results showed that beetle longevity and fecundity can be affected by the presence of wheat bugs that are likely to be present in stored grains after harvest.Graphical abstract

Population Growth Changes in Major Stored Product Insects on Rice Fortified with Spearmint and Basil

Rice is the most important durable food product for more than half of the world’s population, as it is very nutritious food in terms of carbohydrate containment and can meet a large part of human caloric needs on a daily basis. The sensitivity of a rice product fortified with spearmint or basil was evaluated for three stored product insect species: Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). Five different containments of fortified rice were used (0, 25, 50, 75 and 100% of the total rice quantity), and the population growth of the above species was examined after 65 days. We found that fortification generally reduced the infestation level of the species tested and reduced their population growth, as compared with the control rice. In some of the treatments, there were some differences between the application of spearmint and basil. There was higher frass production in the rice that had been fortified with basil than that with spearmint, indicating different infestation patterns. For S. oryzae, with the gradual increase in fortification, the number of insect-damaged kernels and weight of damaged kernels reduced, and significant differences were recorded between the fortification with spearmint and that with basil. The results of the present study are certainly encouraging for further utilization of the characteristics of fortified rice for stored product insect control.

A Biomass Pyrolysis Oil as a Novel Insect Growth Regulator Mimic for a Variety of Stored Product Beetles.

As fumigants face increasing regulatory restrictions, resistance, and consumer pushback, it is vital to expand the integrated pest management (IPM) chemical toolkit for stored products. The production of biomass derived insecticides (e.g., bio-oil fraction) from byproducts of biofuel production may be a promising alternative source of chemistries for controlling stored product insects. These potential insecticidal bio-oils were fractionated based on boiling points (ranging from 115 to 230°C in one series and 245-250°C in another). Fractions were analyzed using GC-MS, and were found to be unique in composition. The lethality of these fractions was tested on Tribolium castaneum, Tribolium confusum, and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). Fractions were tested at concentrations ranging from 5-260 mg/ml to screen for efficacy against adults for durations of 2-8 hr sprayed on concrete arenas. In addition, a separate assay evaluated adult emergence of larvae after 6 wk with supplemental food in arenas, while repellency was evaluated against four stored product insect species in a laminar wind tunnel. A greenhouse gas (GHG) emissions life cycle assessment was also performed, which found the use of the bio-oil fraction could reduce GHG emissions associated with the insecticide supply chain by 25-61% relative to a fossil-fuel based insecticide or pyrethroid. While adults were largely unaffected, we found that larval emergence was significantly suppressed compared to controls by roughly half or more. We also determined that there was minimal repellency to most fractions by most species. We conclude that the use of bio-oil fractions is a climate-friendly choice that may support IPM programs.

Comparative Population Growth of the Khapra Beetle (Coleoptera: Dermestidae) and the Warehouse Beetle (Coleoptera: Dermestidae) on Wheat and Rice.

We evaluated the relative population growth of two stored-product insect species in the genus Trogoderma, the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), and the warehouse beetle, Trogoderma variabile Ballion (Coleoptera: Dermestidae). Ten adults of each species were placed in vials containing wheat or paddy rice. These tests were performed at 27 and 32°C and the number of adults in the vials were counted after 35 and 70 days. For all the time intervals and temperatures of both species on wheat, the resulting larval abundances were similar, with the exception of 27°C at 70 days where more T. variabile larvae developed. At the higher temperature, both species had similar population growth on rice. However, the success was mixed at 27°C with T. granarium having a greater abundance after 35 days, while T. variabile dominated after 70 days. Frass production in both commodities was usually similar for the two species, but greater frass production occurred by T. variabile on wheat after 70 days at 27°C, while T. granarium produced more frass on rice after 35 days at 32°C. Both species nearly always caused equivalent commodity damage. Our research suggests that under ideal conditions these two closely, but very differently treated species in commerce from the genus Trogoderma have comparable population growth, and cause similar damage on wheat and rice.

Residual efficacy of spinetoram on wheat and maize against Rhyzopertha dominica and Sitophilus oryzae

In the present work, we evaluated the residual efficacy of spinetoram on grains (wheat and maize) against two stored product insect species, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae). All bioassays were conducted with spinetoram at different dose rates, 0.1, 1 and 10 ppm. The treated grains were kept in controlled conditions 25 °C and 65%, five months, in order to investigate the insecticidal effect of spinetoram. Spinetoram residues were measured at 1 ppm right after the application and during the last month. For both tested species, adult mortality was evaluated in the treated grains after 7 and 14 days of exposure. After the termination of the exposure, progeny production (65 d later) was counted. The most susceptible species was R. dominica for both tested commodities, given that mortality was reached 100% even after 7 days of exposure at the lowest dose rate of 0.1 ppm. Regarding progeny production numbers of R. dominica were suppressed, in contrast with S. oryzae, in which survival was high even at 10 ppm. Based on our results, spinetoran was quite effective on maize (86.6%) than on wheat (80.0%); however, the insecticidal efficacy remained stable for 5 months after the treatment at the tested conditions. Hence, the formulation remained stable for the whole storage period.

Tanacetum vulgare essential oil as grain protectant against adults and larvae of four major stored-product insect pests

In this study the adulticidal and larvicidal effect of tansy, Tanacetum vulgare L. (Asteraceae) essential oil (EO) was estimated against four noxious stored-product insect species; Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), Tenebrio molitor L. (Coleoptera: Tenebrionidae) and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). The EO chemical composition, as determined by GC-MS, was dominated by oxygenated monoterpenes (68.2%), with borneol (13.6%), umbellulone (11.7%), artemisia ketone (9.3%), cis-chrysanthenol (6.9%), camphor (5.9%), and terpinen-4-ol (5.5%) as the major constituents. This profile was quite different from those previously reported from other T. vulgare European accessions which are characterized by high content of the toxic trans-thujone. The T. vulgare EO was applied as wheat protectant at two concentrations of 500 and 1000 ppm. Adult and larval mortality levels were estimated after 4, 8 and 16 h and 1, 2, 3, 4, 5, 6 and 7 days. Tanacetum vulgare EO caused complete mortality (100%) to T. castaneum larvae, but only 25.6% to adults at 1000 ppm 6 and 7 days post-exposure, respectively. The mortality rates of T. confusum larvae and adults were 56.7 and 8.9% on wheat treated with 1000 ppm EO, respectively after 7 days of exposure. The ΕΟ caused moderate mortality to T. molitor adults (52.2%), and low mortality to larvae (8.9%), at 1000 ppm at the end of the experimental period. High mortality of O. surinamensis larvae (93.3%) was noticed at 1000 ppm after 7 days of exposure, while only 13.3% of the exposed adults were dead at the same concentration and exposure interval. Overall, the T. vulgare EO could be considered as a potential wheat protectant for the management of important stored-product insects. However, its efficacy depends on the species and the life stage of the target pest.

Mortality and progeny production of four stored-product insect species on three grain commodities treated with Beauveria bassiana and diatomaceous earths

Laboratory bioassays were conducted to estimate the effectiveness of the entomopathogenic fungus Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae) at 1.5 × 108 and 1.5 × 1010 conidia/kg grain alone or mixed with the diatomaceous earths (DEs) Protect-It at 150 ppm and DEBBM at 50 ppm against adults of the rusty grain beetle, Cryptolestes ferrugineus Stephens (Coleoptera: Laemophloeidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the psocid, Liposcelis paeta Pearman (Psocoptera: Liposcelididae). The adult insects were exposed to treated grains for 7, 14 and 21 days. For progeny emergence data, the treated units were remained under the same conditions for 62 days for all beetles and 30 days for psocids. The results revealed significant differences in mortalities of insect species among treatments and grains. The combined use of B. bassiana, at the highest dose, and DE increased adult mortalities of all species. In general, the treatments were least effective against T. castaneum and most effective against L. paeta. More numbers of dead insects were found on wheat than on rice or maize. The emergence of progeny was considerably reduced on grains treated with B. bassiana, at the highest dose, plus DE. The results of the present study suggest that the effectiveness of B. bassiana is fortified by the addition of DEs, but it varies among exposed insect species and commodities.