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Insect growth regulators (IGRs) have been playing a major role in the effective management of a range of stored product insect pests including species that have developed resistance to major groups of insecticides, such as organophosphates (OPs) and synthetic pyrethroids (SPs). In the present study, we evaluated the efficacy of S-methoprene alone and in combination with piperonyl butoxide (PBO), an adjuvant component of insecticides for synergy, against two strains, Lab-S (susceptible) and Met-R (Methoprene resistant) of an economically important pest species, the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae). Adults of both Lab-S and Met-R strains were exposed to wheat treated with multiple concentrations of S-methoprene ranging from 0.001 to 0.01 and 10 to 60 mg/kg, respectively, alone and in combination with PBO. A variety of concentrations, including 0.27, 0.53, 0.80, and 1.07 g/kg, were evaluated for PBO. Mortality of adults and percent reduction in progeny were assessed after 14 and 65 days of treatment, respectively. As anticipated, the adult mortality rates of both strains were not significantly affected by S-methoprene alone. However, the number of progeny produced confirmed that the Met-R strain exhibited a high level of resistance to S-methoprene alone, with over 50 F1 progeny adults surviving in wheat treated with the maximal rate, 10 mg/kg. In contrast, the toxicity of S-methoprene was increased against the same resistant strain (Met-R), by 0.80 or 1.07 g/kg of PBO in combination treatment, resulting in a significant reduction in progeny numbers (25 adults per container). Although the tested concentrations of S-methoprene and PBO were well above the currently registered rate globally, our results highlight the fact that PBO enhances the toxicity of S-methoprene to some extent, reaffirming that the mode of action of the latter involves the inhibition of mixed-function oxidases (MFOs) and highlights the need for further research into developing potential binary or triplet formulations containing these two active ingredients (AIs). [ABSTRACT FROM AUTHOR]

Simple Summary: Natural insecticides are currently given high priority in Integrated Pest Management (IPM) protocols. To this end, diatomaceous earth (DE) has gained a lot of attention as an environmentally friendly alternative to conventional insecticides that can successfully repel and control a diverse variety of the most important stored-product insect pests, such as the species Sitophilus, Rhyzopertha, Tribolium, and others. However, most published research about the DEs' insecticidal efficacy has been conducted in simplistic short-term laboratory experiments, excluding the evaluation of the persistence of such ingredients in grain applications. In this study, we evaluated two different DE formulations derived from a single deposit from Greece, when applied in wheat and maize against two primary stored-product insect pests, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae). Based on the results, the DE application was effective and persistent as a grain protectant against major stored-product insects for a storage period of six months. This study provides more evidence for the successful utilization of these natural insecticides for long-term protection of stored products from insect infestations, as an alternative to residual insecticides and fumigants that are commonly used in stored-grain protection systems or as part of integrated pest management (IPM) strategies. We evaluated the persistence and efficacy of two different, in granulometry and content of diatoms, diatomaceous earth (DE) formulations (i.e., DE5 and DE6), against two major beetle species of stored products, i.e., Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae). The formulations were applied as powders in soft wheat and maize in two doses of 500 and 1000 mg kg−1 (ppm). Samples of the treated grains were taken on the day of application and every 30 days until completion of the six-month period of storage. Adults of S. oryzae and R. dominica were exposed to the treated grains at 25 °C and 55% relative humidity, and the mortality was measured after 7, 14, and 21 days of exposure. Rhyzopertha dominica survival was not affected by any combination of DE formulation, dose, and commodity. Contrariwise, the DEs caused significant adult mortality of S. oryzae, in most of the cases tested. We observed that DE6 was equally effective in both wheat and maize, and no considerable variations were observed in S. oryzae mortality during the 6-month experimental period. Furthermore, DE6 was more effective against S. oryzae than DE5, a difference that could have potentially contributed to the variations in the diatom granulometry between these two DEs. Thus, a DE treatment of 1000 ppm was shown to provide long-term protection of wheat and maize against S. oryzae, but this is strongly dependent on the DE formulation, commodity, and insect species. Overall, such natural resource-based inert silicaceous deposits could be used with success in stored-product protection with only some minor modifications, such as sieving and drying of the raw deposit. [ABSTRACT FROM AUTHOR]

Simple Summary: Inert dusts including diatomaceous earths and zeolites have been proved very effective as grain protectants against stored product insects. However, little progress has been made towards the evaluation of their insecticidal activity when applied directly to different types of surfaces. In this study, we evaluated two diatomaceous earth formulations and one zeolite deposit from Greece when applied to concrete and steel against three major stored product insect pests. Based on the results, both dusts achieved complete control of all insect species within a week. The type of surface was found to not be a factor of significance for the effectiveness of the dusts. These data further encourage the exploitation of these natural insecticides for structural treatments in storage facilities, either as alternatives to residual insecticides and fumigants that have been used as essential components for stored-grain protection systems, or for integrated pest management (IPM) approaches. We evaluated formulations of diatomaceous earth and zeolite originated from natural deposits from Greece as insecticides in concrete and steel surfaces for the control of three major beetle species of stored products: Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae). The formulations were tested as dusts at 0.5 or 1 g/m2. Our results indicated that, in most of the cases tested, the inert materials caused 100% adult mortality for all three species, even at the lowest dose, after 7 days of exposure. At the same time, there were no considerable differences in the insecticidal effect of the formulations between concrete and steel surfaces. Among the species tested, R. dominica was the most susceptible, followed by S. oryzae and T. confusum. Our results indicate that natural resource-based inert silicaceous deposits could be used with success in stored product protection against insects at dose rates that are comparable with other commercially available inert material-based formulations. [ABSTRACT FROM AUTHOR]

Simple Summary: Insecticides are currently the most effective method to control stored product insect pests worldwide. However, insecticide resistance poses a continuous threat to the viability of these management tools and thus, on food availability. Since there is very limited information available on the existence of resistant/tolerant insect populations in Greece, the objective of our study was to investigate the tolerance status of insect populations sampled from Greek warehouses and silos to a wide range of insecticides. According to our data, all field-collected insect populations indicated different patterns of tolerance, suggesting the occurrence of possible resistance to widely used insecticides. Our findings can be used for the reduction of the cases of control failures by revising the current pest management practices followed by Greek farmers and operators in stored product protection. The protection of stored products from insect pests is mainly based on suppressive methods by using contact and gaseous insecticides, globally. Following their continuous and improper use, insecticide resistance has been observed in several major insect species and pose a continuous threat to the sustainability of a wide range of active ingredients that are currently in use in stored product protection. In the present work, on-site samplings of insect populations were carried out in local warehouses containing different types of cereals. The collected insects, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) and Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), were reared under laboratory conditions to determine tolerance/resistance to widely used insecticides, using different diagnostic protocols. Laboratory populations of the same species were also examined for comparative purposes. Adult knock down and mortality of all populations indicated different patterns of tolerance to phosphine, deltamethrin, cypermethrin, and pirimiphos-methyl. In many cases, the recommended label doses were not able to completely control some of these populations, regardless of their origin, i.e., field-collected or laboratory. The results of the present work underline the importance of population on the efficacy of insecticides that are currently in use in stored product protection. [ABSTRACT FROM AUTHOR]

Laboratory bioassays were conducted to evaluate the insecticidal efficacy of a diatomaceous earth deposit from Greece, for a wide range of stored product insects. In this context, populations of five different insect species, Tribolium confusum Jacquelin DuVal, the confused flour beetle; Sitophilus oryzae (L.), the rice weevil; Rhyzopertha dominica (F.), the lesser grain borer; Oryzaephilus surinamensis (L.), the sawtoothed grain beetle; Cryptolestes ferrugineus (Stephens), the rusty grain beetle, which cover a major spectrum of insects species of stored products worldwide, were used in the bioassays. The different treatment of diatomaceous earth (DE) rocks (grinding, diatomaceous enrichment, powder granulometry) led to the creation of five types of formulations (namely DE1, DE2, DE3, DE5 and DE6) that exhibited significant fluctuations in their insecticidal efficacy when applied on wheat. In general, some of the modified formulations were found to be very effective against species such as R. dominica and T. confusum that may be difficult to control at the current labeled doses of commercial DE formulations. Overall, our data clearly indicate that this specific Greek deposit has considerable insecticidal properties, which can be further utilized in designing commercial formulations for insect control at the postharvest stages of durable agricultural commodities, provided that the deposit will be modified at specific enrichment and granulometry levels. [ABSTRACT FROM AUTHOR]

The utilization of inert dusts, such as diatomaceous earths (DEs), has been successfully evaluated against a wide range of major stored-product pest species, as an environmentally friendly alternative to conventional insecticides, emphasizing further their prominent position in Integrated Pest Management (IPM) protocols. However, the majority of the published research about the DEs' insecticidal efficacy has been conducted under laboratory conditions in small-scale samples (usually in small vials containing few grams of grains) and against specific insect species, while field and semi-field applications for the same purpose are disproportionally few. The objective of this work was to evaluate the insecticidal activity of a commercial DE formulation against stored product species that either artificially or naturally infested hard wheat, under "real-world" storage conditions. For this purpose, DE doses of 0 (control), 500 and 1000 ppm were applied in a series of lots of 20 kg of hard wheat stored in polypropylene woven bags and kept from August to December in a storage facility in Central Greece. According to our results, even the lower DE dose significantly suppressed the insect populations of Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Trogoderma granarium Everts (Coleoptera: Dermestidae) that were artificially added in the wheat bags but also of five other insect pest species that were found in the commodity, based on weekly monitoring via probe traps or grain samples. Rhyzopertha dominica , T. granarium and S. zeamais were the most numerous species found, while T. granarium was the most frequently sampled species. In general, the probe traps were more sensitive to captures, as compared to the grain samples. The evaluation of the grain quality (bulk density, insect damaged kernels) throughout the trials indicated higher insect infestations in the untreated wheat as compared to the treated one. At the same time, grain bulk density was lower in the treated than in the untreated wheat. We conclude that DE applications can effectively suppress the populations of a wide range of stored insect species, offering a prolonged protection under a wide range of environmental conditions. • Diatomaceous earth suppressed several stored product insect pests for four months. • The effectiveness of diatomaceous earth was stable under fluctuating environmental conditions. • Grain damage by insects was considerably reduced by applying diatomaceous earth. • Probe traps were more sensitive than grain samples for the early insect detection. [ABSTRACT FROM AUTHOR]