High concentrations of piperonyl butoxide (PBO) enhance toxicity of S-methoprene against the lesser grain borer, Rhyzopertha dominica.

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).

Exploring the efficacy of pyrethroid incorporated nets for the control of stored product moth species: immediate and delayed effects on Ephestia kuehniella and Plodia interpunctella (Lepidoptera: Pyralidae).

Insect pests pose a significant threat to stored commodities, necessitating the exploration of alternative pest management strategies. Long-lasting insecticide-incorporated nets (LLINs) have emerged as a promising tool, offering selectivity and reduced ecological impact compared to conventional chemical approaches. However, their efficacy against Ephestia kuehniella Zeller and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), cosmopolitan stored product moth species, has remained underexplored. This study investigated the immediate and delayed effects of 2 commercial pyrethroid-incorporated nets, Carifend (0.34% α-cypermethrin) and D-Terrence (0.4% deltamethrin), on the adult and larval stages. Both LLINs demonstrated high efficacy in controlling E. kuehniella and P. interpunctella, with mortality rates reaching up to 100% depending on exposure and post-exposure durations. Particularly, rapid knockdown was observed with D-Terrence net inducing 100% of adults in P. interpunctella after 30 min exposure. LLINs achieved almost 100% immediate mortality rate against adults after just 1 day of exposure. In addition, immediate rates of affected individuals reached as high as 81% and 91% in E. kuehniella and P. interpunctella larvae, respectively, following just 5 h of exposure to the D-Terrence. Different responses were observed between the adult and larval stages, with larvae exhibiting higher tolerance and potential for recovery from the affected phase after short exposures. There were increasing mortality rates after greater exposure to LLIN. Findings highlight the potential of LLINs as a pest management tool in storage facilities against these important stored product moths. Understanding the responses between life stages and the significance of delayed effects is crucial for optimizing LLIN deployment strategies.

Development, application and evaluation of three novel TaqMan qPCR assays for phosphine resistance monitoring in major stored product pests Tribolium castaneum and Rhyzopertha dominica.

BACKROUND: Stored product protection from insect pests relies heavily on the use of phosphine. The most serious drawback of phosphine is the development of resistance in major stored product insects worldwide, including the red flour beetle, Tribolium castaneum (Herbst) and the lesser grain borer, Rhyzopertha dominica (F.). Two genetic loci are responsible for phosphine resistance: the rph1 (S349G mutation in the cyt-b5-r homolog) in T. castaneum and the rph2 (P45/49S mutation in the dihydrolipoamide dehydrogenase (dld) gene) in T. castaneum and R. dominica. RESULTS: In this study, we have developed and applied high-throughput, practical and specific molecular diagnostics (TaqMan qPCR) for monitoring mutations S349G, P45S and P49S. In our pilot monitoring application, we have included phosphine-resistant and susceptible populations from different parts of the world (USA, Australia, Brazil) and European strains from Greece and Serbia. Our results for the resistant T. castaneum showed a P45S mutant allele frequency (MAF) of 100% and 75.0% in the populations from Serbia and Brazil, respectively. Regarding the susceptible T. castaneum, P45S was detected in Greece (MAF = 62.5%) and was absent in Australia (MAF = 0.0%). Additionally, the S349G mutation was found to be fixed in all resistant populations, while it was also detected in susceptible ones (frequencies: 65.0% and 100.0%). The only case where both mutations were fixed (100%) was a resistant population from Serbia. In R. dominica, the P49S mutation was found only in the two resistant R. dominica populations from Serbia and Greece (50.0% and 100%) and was absent from the susceptible one from Greece; thus, P49S seems to be a satisfactory indicator for monitoring phosphine resistance. CONCLUSIONS: Our P49S detection assay in R. dominica seems to be a viable option in this direction, yet its utilization needs additional large-scale confirmatory work. The identification of additional resistance markers also should be prioritized. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Comparison of different traps and attractants in 3 food processing facilities in Greece on the capture of stored product insects.

Certain lures are marketed toward particular pests or classes of pests, while others might be multi-species lures. Investigative aims for this study included both which trap was most sensitive and whether different combinations of traps and attractants were delivering novel information about the stored product insect community. Comparisons were made for all combinations of 3 commercial traps and 4 different attractants plus an untreated control on the capture of stored-product insects for 2 consecutive years in 3 food processing facilities in Central Greece. The traps used in the experiments were Dome Trap (Trécé Inc., USA), Wall Trap (Trécé) and Box Trap (Insects Limited, Ltd., USA). The attractants that were evaluated were 0.13 g of (i) PantryPatrol gel (Insects Limited), (ii) Storgard kairomone food attractant oil (Trécé), (iii) wheat germ (Honeyville, USA), and (iv) Dermestid tablet attractant (Insects Limited). The traps were inspected approximately every 15 days and rotated. A total of 34,000+ individuals were captured belonging to 26 families and at least 48 species. The results indicated that Indian meal moth, Plodia interpunctella (Hübner), red flour beetle, Tribolium castaneum (Herbst), and cigarette beetle, Lasioderma serricorne (F.) were the most abundant. Although there were noticeable differences among the different traps and attractants for specific species, all combinations provided similar information on population dynamics. Generally, Dome traps baited with either the oil or the gel, were found to be the most sensitive. The results of the present study demonstrate the importance of long-term trapping protocols, as a keystone in IPM-based control strategies in food processing facilities.

Quick knockdown results in high mortality: is this theory correct? A case study with phosphine and the red flour beetle.

BACKGROUND: The fumigant phosphine is used all over the world for disinfestation of stored grains and commodities. Adults of 23 different populations of Tribolium castaneum from 10 different countries were evaluated for phosphine resistance using a modification of the Detia Degesch Phosphine Tolerance Test Kit (DDPTTK). Adults were exposed to 3000 ppm and recorded for 5-270 min for their mobility. RESULTS: Among the tested populations, high levels of phosphine resistance were recorded in populations from Brazil, Serbia, and Spain. No survivals were recorded after 7 days post exposure for eight of 23 in a tested population. CONCLUSIONS: Our work revealed four scenarios: 1, quick knockdown-low (or no) recovery; 2, Slow knockdown-high recovery; 3, Quick knockdown-high recovery; and 4, Slow knockdown-low recovery. Our data indicate that post exposure period is critical for the evaluation and characterization of phosphine resistance. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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

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

Population growth of phosphine resistant and susceptible populations of Lasioderma serricorne (F.) (Coleoptera:Anobiidae) exposed to different temperatures and commodities.

The aim of this work was to investigate the population growth of Lasioderma serricorne (F.) with two populations with different susceptibility to phosphine (one resistant and one susceptible). Population growth was recorded on different days (35 days, 50 days, 65 days, 80 days, 95 days, and 110 days) in two different commodities: (a) mixed food consisted of wheat flour (10 parts) + cornmeal (10 parts) + brewers' yeast (1.5 parts) and (b) wheat flour. Our results clearly indicate that both populations preferred mixed food compared to wheat flour for all combinations tested. Moreover, the increase in temperature from 25 to 30 °C showed a positive effect in some combinations in the population growth of both populations. In general, we found some differences in the production of offspring between the susceptible and the resistant population. Based on the results of the present study, population growth may provide critical information for the fitness advantages or disadvantages of each population.

Residual efficacy of selected larvicides against Culex pipiens pipiens (Diptera: Culicidae) under laboratory and semi-field conditions.

Mosquitoes are a threat worldwide since they are vectors of important pathogens and parasites such as malaria, dengue, yellow fever, and West Nile. The residual toxicity of several commercial mosquito larvicides was evaluated for the control of Culex pipiens pipiens under controlled laboratory and semi-field conditions during late spring and summer of 2013. The evaluation included six different active ingredient formulations, i.e., diflubenzuron Du-Dim), Bacillus thuringiensis var. israelensis (Bti) (Vectobac), spinosad (Mozkill), S-methoprene (Biopren), temephos (Abate), and polydimethylsiloxane (PDMS) (Aquatain), that are currently registered of and had been registered in the past for mosquito control. Under controlled laboratory conditions, the residual activity ranged from 1 week (S-methoprene) up to 2 months (spinosad, PDMS). Exposure of larvicides under semi-field conditions resulted in noticeable differences regarding their efficacy as compared to the laboratory bioassays. Exposure of S-methoprene, Bti, and spinosad, for up to 3 days, resulted in similar adult emergence to the controls. On the other hand, the residual efficacy of diflubenzuron, temephos, and PDMS ranged from 14 to 28 days, depending on the season of exposure. Longevity and fecundity of adults that had emerged from surviving larvae, in most of the cases tested, did not differ significantly from that of the controls. The results of the present study demonstrate the necessity of both field and laboratory studies to draw safe conclusions regarding the efficacy of larvicides against mosquitoes and the selection of the proper formulation for each application scenario. In addition, defining the seasonal variation in the residual toxicity of the tested formulations could be useful for improving mosquitos' management programs.

Efficacy of Spinetoram for the Control of Bean Weevil, Acanthoscelides obtectus (Say.) (Coleoptera: Chrysomelidae) on Different Surfaces.

In this study, the contact toxicity of spinetoram on three different surfaces, concrete, ceramic floor tile and laminate flooring, against Acanthocelides obtectus (Say.) (Coleoptera: Chrysomelidae) was evaluated in laboratory bioassays. Different concentrations were evaluated ranging from 0.0025 to 0.05 mg AI/cm2, against adults of A. obtectus. Adult mortality was measured after 1-, 3-, 5- and 7-day exposure. After 1-day exposure, the mortality was low on all surfaces, ranging from 0 to 27.2%. After 5- and 7-day exposure, spinetoram at concentrations of 0.01 mg/cm2 and above achieved 100% or close mortality on concrete and laminate flooring surface, whereas low concentrations (0.0025, 0.005 and 0.0075 mg AI/cm2) resulted in significantly lower mortality levels, ranging from 1.6 to 30.8%, than high concentrations. In the case of ceramic floor tile surface, spinetoram treatments at all tested concentrations did not result in 100% mortality. Significant differences were recorded among the surfaces, depending on concentrations and exposure intervals. After 3-, 5- and 7-day exposure, mortality levels on ceramic floor tile surface were generally higher at low concentrations than those on the concrete and laminate flooring surfaces, whereas those on concrete and laminate flooring surfaces were significantly higher at high concentrations than ceramic floor tile surface. These results indicate that spinetoram at 0.025 and 0.05 mg AI/cm2 achieve satisfactory control at relatively short exposures on common types of surfaces and thus can be used as an effective insecticide against A. obtectus.

Insecticidal effect of diatomaceous earth and pirimiphos-methyl against phosphine-susceptible and phosphine-resistant populations of two stored product beetle species.

In the present study, we evaluated the insecticidal efficacy of diatomaceous earth (DE) and pirimiphos-methyl for the control of phosphine-susceptible and phosphine-resistant populations of Tribolium castaneum (Herbst) and Sitophilus oryzae (L.). Insecticides were applied on wheat or rice at two doses: DE was applied at 1000 and 2000 ppm and pirimiphos-methyl at 1 and 5 ppm. Adult mortality was measured after 7, 14, and 21 days of exposure, and progeny production capacity on the treated substrates was evaluated 65 days later. For T. castaneum, we found that DE, at 2000 ppm, was able to provide 100% control of two of the three populations tested, while for the third population mortality reached only 84%. Similarly, there were differences in mortality levels after exposure to DE-treated grains between the two S. oryzae populations tested. At 1 ppm, pirimiphos-methyl was not effective for any of the T. castaneum populations tested, but complete mortality was recorded for all populations at 5 ppm. In general, populations of S. oryzae were more susceptible than those of T. castaneum, for both commodities. Our data indicate that both insecticides can be used with success in phosphine resistance management programs, but there are populations of a given species that may be less susceptible, which constitutes a preliminary screening essential.

Transcriptomic analysis of s-methoprene resistance in the lesser grain borer, Rhyzopertha dominica, and evaluation of piperonyl butoxide as a resistance breaker.

BACKGROUND: The lesser grain borer, Rhyzopertha dominica is a serious pest of stored grains. Fumigation and contact insecticides play a major role in managing this pest globally. While insects are developing genetic resistance to chemicals, hormonal analogues such as s-methoprene play a key role in reducing general pest pressure as well as managing pest populations that are resistant to fumigants and neurotoxic contact insecticides. However, resistance to s-methoprene has been reported in R. dominica with some reports showing a remarkable high resistance, questioning the use of this compound and other related analogues in grain protection. The current study attempts to identify possible molecular mechanisms that contribute in resistance to s-methoprene in R. dominica. RESULTS: Transcriptome analysis of resistant and susceptible strains of this pest species identified a set of differentially expressed genes related to cytochrome P450s, indicating their potential role in resistance to s-methoprene. Laboratory bioassays were performed with s-methoprene treated wheat grains in presence and absence of piperonyl butoxide (PBO), a cytochrome P450 inhibitor. The results indicate that PBO, when applied alone, at least at the concentration tested here, had no effect on R. dominica adult emergence, but has a clear synergistic effect to s-methoprene. The number of produced progeny decreased in presence of the inhibitor, especially in the resistant strain. In addition, we also identified CYP complement (CYPome) of R. dominica, annotated and analysed phylogenetically, to understand the evolutionary relationships with other species. CONCLUSIONS: The information generated in current study suggest that PBO can effectively be used to break resistance to s-methoprene in R. dominica.

Population-Mediated Responses of Lasioderma serricorne (Coleoptera: Anobiidae) to Different Diagnostic Protocols for Phosphine Efficacy.

We evaluated different monitoring protocols for phosphine resistance in adults of three populations of the cigarette beetle, Lasioderma serricorne (F.), termed LB, 2KT, and E1. The protocols evaluated were as follows: 1) the Food and Agriculture Organization (FAO) bioassay, i.e., the exposure at 30 ppm of phosphine for 20 h, 2) the dose response, based on the exposure at 50-1,000 ppm of phosphine for 3 d, 3) the Cooperation Center for Scientific Research Relative to Tobacco (CORESTA) bioassay, which is based on exposures of 4 d at 200 ppm, and, if there are surviving individuals, of 10 d at 700 ppm, and 4) Detia Degesch Phosphine Tolerance Test Kit (DDPTTK), based on the evaluation of the exposed insects for short intervals of exposure (in our case 90 min) at 3,000 ppm. From the populations tested, E1 indicated the highest survival in the FAO bioassay. Moreover, adults of this population were able to survive at 200 ppm, in the dose response, in contrast with the other populations. However, both 2KT and E1 gave similar results in DDPTTK, but only E1 had survivors after 7 d postexposure. Finally, only adults of E1 survived the CORESTA bioassay for 200 ppm and 4 d, but not for 700 ppm and 10 d. Our results show that, at least in the range of the populations tested here, there are some trends that are comparable among the different diagnostics for L. serricorne, which can be utilized further in designing a widely adopted standardized protocol.

Effect of Nitrogen on Phosphine-Susceptible and -Resistant Populations of Stored Product Insects.

In this study, we evaluated nitrogen treatment on phosphine-resistant field and -susceptible laboratory populations of different stored product beetles. Nine trials were conducted in commercial nitrogen chambers with the O2 level set at 1.0%. Two different temperatures-i.e., 28 and 40 °C-and three exposure intervals-i.e., 2.5, 3 and 9 d-were used in our tests. Adults of the sawtoothed grain beetle, Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae); the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae); and the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) were used in the trials. The insects were placed in vials with different commodities per species and population, and their mortality was measured after the termination of each trial. Then, the vials were kept in incubator chambers at 25 °C and 65% relative humidity for 65 d to measure progeny production. Complete parental mortality was observed in all cases for O. surinamensis and S. oryzae, but there was some survival for T. castaneum at 28 °C and 3 d of exposure. In general, progeny production was completely (100%) suppressed, with some exceptions for all species and populations. The results indicate that low oxygen is effective for all species tested, regardless of their resistance status to phosphine, and can be further adopted as an alternative method to mitigate resistance in stored product beetles.

Delivering Beauveria bassiana with electrostatic powder for the control of stored-product beetles.

BACKGROUND: The efficacy of a Beauveria bassiana-based formulation (Bb38) with Entostat, an electrostatically charged powder, was investigated as a surface treatment against Cryptolestes ferrugineus, Oryzaephilus surinamensis and Sitophilus granarius adults. In lab bioassays, the efficacy of Bb38 against the aforementioned species was examined on concrete, plywood, steel and ceramic, whereas its residual efficacy against the same species was assessed on concrete and steel in the presence or absence of illumination. Finally, the efficacy of Bb38 against O. surinamensis and S. granarius adults was assessed in a commercial grain storage facility under realistic field conditions. RESULTS: In the lab trials, O. surinamensis and C. ferrugineus were much more susceptible to Bb38 than S. granarius on all types of surfaces. Moreover, Bb38 was, at least for O. surinamensis and C. ferrugineus, as effective as the chemical standard (deltamethrin) for at least 2 months after the application, regardless of the presence or absence of illumination. Finally, in the field trial Bb38 provided a satisfactory level of control against O. surinamensis. CONCLUSION: Bb38 is an effective surface treatment, but its efficacy varies according to the target species, the type of surface and the time post-application. This is the first published report that examines the efficacy of Bb38 as a surface treatment for wider uses in empty warehouses and related storage facilities. © 2017 Society of Chemical Industry.