Stored-product Pests Research Articles

Ruta chalepensis L. (Rutaceae) uçucu yağının beş coleopteran depo ürün zararlısına karşı fumigant ve kontak toksisitesi ile kolinesterazlar üzerine etkileri

The essential oil composition of aerial parts of Ruta chalepensis L. was analyzed with GC-MS. Seventy-nine compounds were detected representing 85.93 ± 1.08% (n = 3) of the essential oil. The major components of the essential oil were 2-undecanone 21.52 ± 0.21%, 2-nonanone 18.31 ± 0.27%, and 2-nonyl acetate 13.22%. The highest insecticidal contact toxicity of the oil was observed against Rhyzopertha dominica F. with 0.018 μl/insect LD50 and 0.039 μl/insect LD90 after 24h. Essential oil also produced considerably low 0.50 and 0.59 μl/insect LD50 values after 24h against Sitophilus oryzae L. and Sitophilus granarius L. respectively. The lowest contact toxicity was observed against Tribolium castaneum Herbst. and Tribolium confusum Jacquelin du Val. 0.138 and 0.078 μl/insect LD50 after 24h respectively. The highest fumigant toxicity was observed against S. granarius for the application concentration of 10 μl, 10% oil/acetone (v:v) in a 10 ml chamber which afforded 100.00 ± 0.00% mortality after 48h. The essential oil also produced high fumigant toxicity against S. oryzae, T. castaneum and R. dominica which were 95.47 ± 3.41%, 93.30 ± 5.54%, and 85.47 ± 3.41% mortality at 20 μl application concentration of the oil solution after 48h. The R. chalepensis essential oil produced low acetylcholinesterase enzyme 5.29 ± 1.20% (n=3) inhibition and mediocre butyrylcholinesterase enzyme inhibition 42.6 ± 0.71% (n=3). According to the insecticidal activity assays performed, the essential oil R. chalepensis seems to be a promising source that could yield natural compounds that could be employed in stored product pest management.

Importance of Sanitation for Stored-Product Pest Management.

Sanitation is essential for the cost-effective pest management of stored-product insects. The Food, Drug and Cosmetic Act of 1938 led to the Food and Drug Administration (FDA) tightening regulatory standards, and many local surveys, courses and conferences were organized to prepare the industry for these new regulations. Sanitation removes insects and residual food, which may also provide shelter for insects, with heat treatments and insecticide applications. The number of insects removed by cleaning may be reduced as the number of available hiding places increases. Decreased sanitation negatively affects the efficacy of most other pest management practices, with means of 1.3- to 17-fold decreases in efficacy. The majority of studies quantifying the efficacy of sanitation have been performed on the farm storage of grain, but some studies have been conducted for grain elevators, food processing, and the marketing system. Results ranged from no effect of sanitation alone to very effective alone or with other methods. Sanitation can also reduce insect infestation prior to harvest. Some cost-benefit analyses have been conducted for sanitation.

Low concentrations of selenium nanoparticles enhance the performance of a generalist parasitoid and its host, with no net effect on host suppression.

The environmental and economic costs of conventional insecticides have stirred an interest in alternative management tactics, including the use of nanotechnologies. Selenium nanoparticles (SeNPs) have many applications in agriculture but may not be compatible with biological control; however, low concentrations of SeNPs may benefit natural enemies via hormesis. This study investigates the concentration-dependent effects of SeNPs (0-1000 mg L-1 ) on Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae), a generalist parasitoid of stored product pests. The LC50 of SeNPs was 1540 mg L-1 for female parasitoids and 1164 mg L-1 for males. SeNPs had a significant hormetic effect; average lifespan increased by 10% at a concentration of 4.03 mg L-1 for females and by 35% at 13.83 mg L-1 for males. In a bioassay including hosts [the azuki bean beetle, Callosobruchus chinensis (L.) (Coleoptera: Chrysomelidae: Bruchinae)], a low concentration of SeNPs (25 mg L-1 ) enhanced the performance of female parasitoids; lifespan increased by 23% and the number of offspring increased by 88%. However, the number of emerging hosts did not significantly decrease; in the absence of parasitism, SeNPs actually improved host emergence by 17%. Because higher concentrations of SeNPs reduced parasitoid lifespan, whereas low concentrations enhanced not only parasitoid performance but also host emergence, practitioners should exercise caution when considering SeNPs for use in integrated pest management. © 2023 Society of Chemical Industry.

Infestation and storages in Balochistan during 2019-2020

The present study was aimed to inspect the stored product insect pests from different godowns (Governmental and Private) of four districts namely Quetta, Pishin, Loralai and Sibi (two from cold and two from hot climatic regions). Insect pests damaging cereals were collected from godowns of these localities. The collections were made on a monthly basis from five (Private/Govt./Plinth) godowns of each district. All insect pests were collected during January -December 2019-2020. These samples were identified by using the standard identification keys [1–3]. Tribolium castaneum showed the highest increase, from 10.28% in 2019 to 13.54% in 2020. Trogoderma granarium also had a significant increase from 9.28% to 12.25%, followed by Rhizopertha dominica with an increase from 7.18% to 9.83%. Sitophylus oryzae showed a smaller increase from 7.18% to 8.40%, while Angoumois grain moths had the smallest increase from 1.06% to 1.59% in Sibi while least population was noticed in Quetta as Tribolium castaneum were found with 5.03% and increased to 7.25% in 2020. Trogoderma granarium from 3.80% to 5.56%, Rhizopertha dominica were from 2.67% to 3.48%, Sitophylus oryzae from 1.75% to 1.49% and Angoumois grain moths were collected from 0.51% to 0.41%. The collected data also reveal that in governmental godowns the population of stored product insect pests were found higher than the private godowns due to their basic facilities. The values in Sibi showed an increase from 11.74% to 16.42% in 2020 for government godowns and an increase from 6.95% to 12.30% in open areas. Private godowns had 15.34% in 2019 and increased to 16.89% in 2020. Similarly, Loralai and Pishin government godowns also showed an increase in insect pests in 2020. In contrast, Quetta government godowns had a relatively stable percentage of insect pests in 2019 and 2020, while private godowns showed an increase from 2.88% to 4.04%. The present study is the first of its kind and is helped full for the identification and prevalence of different stored product pests in different storages of Balochistan during 2019-2020 in Covid condition.

Aerosolized Insecticide Spray Distributions and Relationships to Efficacy against Stored Product Pests.

Aerosol insecticides are widely used in stored product insect management programs in food facilities. Previous research has shown spatial variation in aerosol efficacy within facilities, but information on how spatial patterns of aerosol droplet concentration, size distribution, dispersal, and deposition contribute to this variation in efficacy is limited. This study involved two aerosol application systems: a high-pressure cylinder containing TurboCide Py-75® with pyriproxyfen IGR (ChemTech Ltd., Des Moines, IA, USA) and a hand-held fogger containing Pyrocide 100® (MGK, Minneapolis, MN, USA) with Diacon II which contains methoprene IGR (Wellmark, Schaumburg, IL, USA). These systems were used at single or multiple application locations. The spray trials were conducted in a small-scale flour mill, Hall Ross Flour Mill (Kansas State University, Manhattan, KS, USA). The droplet size distributions were monitored at multiple positions within the room using nine aerodynamic particle sizing (APS, TSI Incorp, Shoreview, MN, USA) instruments. The APS data collected over the treatment period were summarized into a mass concentration index (MCI), which ranged from 155 to 2549 mg/m3 for Turbocide and 235-5658 mg/m3 for Pyrocide. A second parameter called the Deposition Index (Dep.Idx) was derived to estimate potential insecticide depositions on the floor and has units of g/m2. The Dep.Idx was below 5.3 g/m2 for most Turbocide applications, while the Dep.Idx was below 8.4 g/m2 for most Pyrocide applications. The MCI and Dep.Idx values varied with APS position and spray application location, with proximity to the aerosol application location and degree of obstruction between the release point and APS position contributing to this variation. We assessed the relationship between aerosol droplet parameters and insect efficacy using Tribolium confusum Jacqueline DuVal, the confused flour beetle. The adults were treated directly, while the larvae were treated two weeks later during the residual test (previously published). For Turbocide, efficacy against adults increased with MCI and Dep.Idx values, but for residual efficacy of the IGR, efficacy was high at all aerosol droplet values, so no relationship was apparent. In contrast, the relationship between Pyrocide deposition and adult insect efficacy was highly variable. But with larval insect efficacy, residual larvae control was directly related to increases in Pyrocide MCI and Dep.Idx. Contour plots of Dep.Idx values were developed, which could be used to predict areas of the mill that are not receiving an adequate application rate, and this could be used to develop more effective application strategies for aerosol insecticides in food facilities.

Dispersal and parasitic ability of Anisopteromalus calandrae (Hymenoptera: Pteromalidae) against Lasioderma serricorne (Coleoptera: Anobiidae) larvae in an experimental warehouse

Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae) is a solitary ectoparasitoid parasitizing most stored-product insects. The ability of A. calandrae to locate and parasitize late-instar larvae of Lasioderma serricorne (F.) (Coleoptera: Anobiidae) was investigated in an experimental warehouse. Three residence times (the time between wasps release and removing from the experimental room, i.e., 1, 2, and 3 d) were tested. The number of A. calandrae progeny increased with increasing residence times, and the progeny were male biased. After releasing A. calandrae for 1, 2, and 3 d, the percentages of female offspring of A. calandrae were 12.77, 27.57, and 30.89% respectively. Mortality of the late-instar larvae of L. serricorne also significantly increased with increasing residence times, reaching the highest mortality 64.30% after wasps release for 3 d, followed by 40.45% (2 d), and 18.71% (1 d). The control ability and disperse range of the A. calandrae also significantly increased over time. About 261.91, 566.34, and 900.32 late-instar larvae of L. serricorne were paralyzed and oviposited by A. calandrae after 1, 2, and 3 d of wasps release, respectively. All L. serricorne larvae 0.85, 2.14, and 4.28 m away from the release site of A. calandrae were parasitized after wasps release for 1, 2, and 3 d, respectively. The present study results are helpful to the rational use of A. calandrae for controlling stored product pests.

Cellophane packaging treated with nano silica is superior to polyethylene in reducing stored irradiated flour from Tribolium confusum infestation

Most packaged food products are attacked and penetrated by insects. Causing reducing food quality. Since, different ways are investigated for controlling stored-product pests without application of chemical methods. So, the present study included laboratory methods to evaluate the effectiveness of two packaging materials, polyethylene and cellophane with silica nano particles to prevent or minimize the insect infestation and grain wastage resulting by the attack of wheat grain by confused flour beetle, Tribolium confusum. Studies made to determine the protecting capacity of the two packaging materials through assessing some parameters, number of adults infested poly ethelene and cellophane bags, percentage weight loss of grains, the results revealed that cellophane was the better packaging material than polyethelene, so polyethylene was the susceptible packaging material because it had maximum number of holes as a result penetrations by insects into them. Also, treatment the two types with packaging materials with different concentrations of nano silica protect the treated packaging materials from insect infestation and the protection increase with the increase of the concentration of silica nano particles

The lethal and sterile doses of gamma radiation on the museums pest, varied carpet beetle, Anthrenus verbasci (Coleoptera: Dermestidae)

Museums preserve historical cultural artifacts and serve as an essential resource for current and future generations seeking first-hand knowledge about the diversity of life on Earth. However, significant changes in climate from temperature and humidity cause serious biotic degradation. Despite ongoing insect control treatments, insect pests are still a major problem for museums due to the lack of suitable and unsafe environments that are provided for the storage and display of the collection. The varied carpet beetle, Anthrenus verbasci (Coleoptera: Dermestidae) is one of the major stored product pests whose larvae cause serious damage to household items and museum specimens. Therefore, this research aims to study the effect of gamma radiation on the larval, pupal and adult stages. The effects of gamma radiation have been studied on 3rd instar larvae (100, 200, 300, 400 and 500 Gy). The results showed that mortality in the larval stage significantly increased with increasing gamma radiation dose, which was reflected in the eclosion of the adult stage. The exposure of one-day-old pupae to 200, 400, 600, 800 and 1000 Gy of gamma radiation showed that the higher the dose, the lower the percentage of adult emergence. Additionally, there was a significant increase in the percentage of mortality in A. verbasci adults with increasing radiation doses when the newly emerged adults were irradiated with 200, 400, 600, 800 and 1000 Gy. The LD50 and LD90 of gamma radiation doses on larvae, pupae and adults were calculated, and the malformations in all stages were photographed. The fecundity and fertility of A. verbasci adults that were exposed to radiation as one-day-old pupae decreased gradually with increasing doses of gamma radiation and reached 100% sterility when exposed to a dose of 150 Gy. Among all the treatments, the sterile dose (150 Gy) or lethal dose (1000 Gy) showed superior performance over other treatments and was adjudged as the best treatments, which prevented the subsequent development and complete mortality of the pest.

Optimizing phosphine fumigation efficiency in hazelnut industry: Determining optimal exposure time for stored product pest control

Hazelnut, as with many other stored products, are susceptible to infestation by a variety of stored insect pests. Phosphine fumigation is a widely used method to control pests in stored products, including hazelnut kernels. This study aimed to determine the optimal exposure time for phosphine fumigation for management of stored product pests in hazelnuts. Four treatments with different exposure times (3, 4, 5, and 6 days) were conducted using various development stages of Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae), Tribolium confusum Jaqcquelin du Val, (Coleoptera: Tenebrionidae), Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) together with the control group. The trials were conducted in a commercial chamber of a hazelnut processing facility. The insects were placed in plastic containers within jute sacks filled with hazelnuts, fumigations were done under gas-proof sheet and the survival rate was assessed after treatments. The results showed that a 3-day exposure period was sufficient to fully eradicate the pupal and adult stages of O. surinamensis. For T. castaneum, 100% mortality was achieved in both larvae and adults from 3 days of exposure, but the pupal stage required at least 5 days. For T. confusum, all larvae and adults died in all exposure periods, but the pupal stage required at least 4 days. In the case of the moth species, a 100% mortality rate was achieved in the larval and pupal stages of both E. kuehniella and P. interpunctella at all exposure periods. The mortality rate of E. kuehniella eggs was 99% after 3 and 4 days of exposure, and a fumigation period of 5 days was required to control the entire population. However, only 67% of P. interpunctella eggs were controlled after 3 days of exposure. The time and stage factors were found to be significant in the egg stage of P. interpunctella. The results suggest that a 5-day exposure period is the most effective for controlling tested stored product pests in hazelnuts.

The behavioral response to the putative necromones from dead Tribolium castaneum (Coleoptera: Tenebrionidae) in traps by conspecifics as a function of density and time since capture.

Long-term trapping programs of stored product pests provide information for timely and accurate pest management. Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is a highly successful external-infesting grain pest and is frequently monitored using a commercial pitfall trap that combines pheromonal and kairomonal stimuli. However, an often overlooked component of lure-based traps is the potential for the volatile plume to change over time as individuals are captured. These now-dead insects may then release necromones altering the captures of conspecifics. In this study, we evaluated changes in (i) the behavior of T. castaneum and (ii) the relative change in volatiles over time since dead insects were added and among different densities of dead conspecifics in a commercially available kairomone oil. We used multiple behavior assays, including wind tunnel, release-recapture, and 2-way olfactometer, and performed chemical analyses via headspace collection and gas chromatography coupled with mass spectrometry. Tribolium castaneum response to the kairomone lure was not consistent among assays of density of conspecifics between 4 and 40 adults after 24 or 96 h, or time of seeding over 1-96 h or 8-11 days prior. Tested strains collected in 2012 and 2019 ruled out strain-specific differences. Oil batch effects were also ruled out as a factor contributing to the response of T. castaneum. The relative volatile composition was generally stable among the treatments despite using different seeding densities and seeding times. Given that attraction and relative volatile composition were generally unaffected by prior captures, long-term monitoring programs may be robust in their interpretability over time.

Purification and characterization of acetylcholinesterase from Hide Beetle (Dermestes maculatus, De gee) larvae

Adult and larvae of Hide Beetle (Dermestes maculatus) are pests of stored animal materials or products rendering them unsuitable both in quantity and quality for consumption. Some chemical insecticides have been known to irreversibly inhibit Acetylcholinesterase (AChE) activities, an enzyme that catalyzes the breakdown of acetylcholine to choline and acetic acid at cholinergic synaptic sites. The aim of this study was to purify and characterize AChE from D. maculatus larvae with a view to evaluate some its biochemical properties. Acetylcholinesterase, purified to apparent homogeneity from the larvae of D. maculatus, was confirmed by SDS-PAGE, its physicochemical and kinetics properties were evaluated. Some chemicals and plant-based inhibitors were used for inhibition studies. Purified AChE from D. maculatus larvae accounted for 4.5% activity remaining with a specific activity of 4.19 mmol/min/mg and has a molecular weight of 42.65 kDa. Its stability at pH range of 8–10 and temperature range of 40–55 °C as well as kinetic values favored breakdown of acetylcholine iodide. From the inhibition patterns, anisaldehyde and α-terpineol inhibited the purified enzyme in similar way to chlorpyrifos and cypermethrin. The inhibition of the purified AChE by chemical and plant-base insecticides in similar manners suggests probable use of plant chemicals as an effective bio-insecticide for the control of Hide Beetle larvae and hence, can be used for an overall improvement of the duration of stored products in terms of quality and quantity.

Population development ofRhyzopertha dominica(F.) (Coleoptera: Bostrichidae) on different stored products

AbstractThe lesser grain borer,Rhyzopertha dominica, is an important pest of various stored products around the world. In this study, the development, survival, reproduction, and life table parameters ofR. dominicawere investigated on six stored products (angelica, jujube, maize, rice, soybean, and wheat). The developmental time of the immature stage ofR. dominicawas shortest on wheat (40.20 days) and longest on angelica (67.04 days). The survival rate of the immature stage was highest on wheat (76.33%) and lowest on angelica (41.00%). The fecundity level ofR. dominicawas highest on wheat (246.05 eggs/female) and lowest on angelica (69.38 eggs/female). The net reproductive rate (R0) and intrinsic rate of increase (rm) ofR. dominicadiffered significantly among the six stored products. The highestR0ofR. dominicawas on wheat (68.50), followed by rice (41.28), maize (32.32), soybean (27.17), jujube (23.16), and angelica (20.18); thermvalues showed a similar trend, with values of 0.059, 0.046, 0.042, 0.039, 0.036, and 0.033, respectively. Our results indicate that wheat was the most suitable stored product, whereas angelica was the least suitable, for the feeding, development, and population increase ofR. dominica. These findings provide basic information about the occurrence trends and characteristics ofR. dominicathat will be useful for the control of this pest on different stored products. The physicochemical properties of angelica should be further explored for potential application in the control or integrated management ofR. dominica.

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

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. 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. 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.

First Record, Distribution and Occurrence of A Protistan Entomopathogen, Adelina mesnili Perez (Coccidia: Adeleidae) in the Indian Meal Moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) Populations in Türkiye.

Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) originating from South America is one of the important insect pests that damages storage products and is found on every continent. There is a new interest in using enthomopathogens for microbial control of P. interpunctella as well as other stored product pests. Coccidia as a group of protistan entomopathogens are host specific and their pathogenic effects on the hosts are more pronounced. Although this pathogenic effect results in increased host mortality or higher susceptibility to insecticides, the suppressive potential of coccidia in natural populations has not been adequately studied. In this study, characterization, distribution and occurrence of a coccidian entomopathogen was aim to show its natural suppressing potential in P. interpunctella populations. During the three years (from 2019 to 2021), a total of 3.432 P. interpunctella samples (2.047 dead and 413 living larvae, 932 adults and 40 pupae) were collected from fourteen populations. After macroscopic examination, suspected samples were dissected in Ringer's solution and then prepared wet smears including host fat body were examined for presence of coccidian pathogens under a light microscope at a magnification of 400-1000X. The oocysts of the coccidian were measured and photographed using a microscope with a digital camera and soft imaging system. The pathogen was observed in the fat bodies of the larvae, pupae and adults. Oocysts measured as 29.52±3.32 (25.27- 35.08) μm in diameter and they include 8 sporocysts. Sporocysts measured as 9.11±0.61 (8.90-9.85) μm. Forty-five of 3.432 P. interpunctella larvae, pupae and adults were found to be infected. Coccidian infections have also reached to the levels that can be considered high in some populations, as significant as 29.2%. The infection was observed in the three (21.4%) of the examined fourteen populations. The coccidian entomopathogen presented in this study is the first Adeleid coccidian record from P. interpunctella populations in Türkiye. The detection of Adelina mesnili Perez (Coccidia: Adeleidae) in at least three populations and the infection rate reaching 29.2 percent, confirms that this pathogen has a considerable effect P. interpunctella populations that cannot be underestimated. Our results confirm that the coccidian pathogen is very effective in the larval stage.

Identification and characterization of a novel Iflavirus in a stored-product psocid, Liposcelis bostrychophila (Psocodea: Liposcelididae)

Liposcelis bostrychophila (Badonnel) is a worldwide stored-product pest that tends to develop resistance to commonly used insecticides rapidly. To control insect pest biologically, insect-specific viruses (ISVs) are considered to be a promising agent, but few ISVs have been reported in stored-product psocids. In this study, a novel iflavirus named Liposcelis bostrychophila iflavirus (LbIFV) was identified. This virus has a genome length of 9,263 nucleotides and was isolated from L. bostrychophila using RNA-Seq technology. The polyprotein of LbIFV contains two picornavirus capsid protein-like domains, an RNA-dependent RNA polymerase (RdRp) domain, an RNA helicase, and a 3C-protease. The virus replicates in its host, and triggers the activation of the host's antiviral immunity, specifically through the small interfering RNA (siRNA)-based mechanism. Phylogenetic analysis showed that LbIFV clustered with Bundaberg bee virus 4, Sacbrood virus, and Darwin bee virus 4, which suggested that LbIFV was presumed to belong to Iflaviridae. LbIFV was transmitted vertically from parent to offspring, and the viral infection rate reached 100%. LbIFV was present at all developmental stages of L. bostrychophila, and it successfully co-existed in this psocid for a long period. The abundance of LbIFV in L. bostrychophila decreased significantly under high temperatures and insecticide exposures. In summary, LbIFV is the first characterized RNA virus in Liposcelis species, and it established stable symbiotic relationships with L. bostrychophila.

Persistence and efficacy of diatomaceous earth against stored product insects in semi-field trials

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.

New species based on the biological species concept within the complex of Lariophagus distinguendus (Hymenoptera, Chalcidoidea, Pteromalidae), a parasitoid of household pests.

The pteromalid parasitoid Lariophagus distinguendus (Foerster) belongs to the Hymenoptera, a megadiverse insect order with high cryptic diversity. It attacks stored product pest beetles in human storage facilities. Recently, it has been shown to consist of two separate species. To further study its cryptic diversity, strains were collected to compare their relatedness using barcoding and nuclear genes. Nuclear genes identified two clusters which agree with the known two species, whereas the barcode fragment determined an additional third Clade. Total reproductive isolation (RI) according to the biological species concept (BSC) was investigated in crossing experiments within and between clusters using representative strains. Sexual isolation exists between all studied pairs, increasing from slight to strong with genetic distance. Postzygotic barriers mostly affected hybrid males, pointing to Haldane's rule. Hybrid females were only affected by unidirectional Spiroplasma-induced cytoplasmic incompatibility and behavioural sterility, each in one specific strain combination. RI was virtually absent between strains separated by up to 2.8% COI difference, but strong or complete in three pairs from one Clade each, separated by at least 7.2%. Apparently, each of these clusters represents one separate species according to the BSC, highlighting cryptic diversity in direct vicinity to humans. In addition, these results challenge the recent 'turbo-taxonomy' practice of using 2% COI differences to delimitate species, especially within parasitic Hymenoptera. The gradual increase in number and strength of reproductive barriers between strains with increasing genetic distance also sheds light on the emergence of barriers during the speciation process in L. distinguendus.

Individual and combined effects of α-Pinene and a native diatomaceous earth product on control of stored product beetle pests

The development of alternatives to chemical insecticides has been an attractive topic in stored product pest management due to the limited number of options. This study examined the individual and combined activities of two promising eco-friendly alternatives, the diatomaceous earth product Detech® and the plant-based essential oil α-pinene, against Sitophilus granarius (L.), S. zeamais Motschulsky, 1855 (Coleoptera: Curculionidae), Tribolium confusum Jaquelin Du Val, 1868 (Coleoptera: Tenebrionidae) and Rhyzopertha dominica (Fabricius, 1792) (Coleoptera: Bostrichidae) under laboratory conditions. Individual and combined insecticidal effects of Detech® and α-pinene were evaluated by their direct application to wheat or maize. Complete mortality against S. granarius, R. dominica, and T. confusum occurred at 2 days with 10 and 15 ppm of α-pinene, while 15 ppm of α-pinene produced 100% mortality after 3 days of exposure for S. zeamais. The highest mortality with Detech® was 38.6% at 21 days using 500 ppm for S. zeamais, while it was 51.7 % against S. granarius, and 72.7 % against R. dominica. Detech® did not show any significant activity against T. confusum at any application level. Combined applications of Detech®+α-pinene demonstrated the highest mortality on R. dominica (40.4% mortality), S. zeamais (27.9%), and S. granarius (18.5%), while no significant effect was found on T. confusum (1.1%). Overall, α-pinene was more effective than Detech® against all four tested beetles species. Combined applications led to reduced mortality.

The serine/threonine kinase Akt gene affects fecundity by reducing Juvenile hormone synthesis in Liposcelis entomophila (Enderlein)

The serine/threonine kinase Akt is an important component of the insulin signalling pathway (ISP) in regulating insect metabolism, growth, and reproduction. The psocid Liposcelis entomophila (Enderlein) is a distasteful stored products pest for its fecundity. However, the molecular mechanism of Akt that controls vitellogenesis and oviposition in L. entomophila remains obscure. In this study, the function of the Akt gene in the female reproduction of L. entomophila (designated as LeAkt) was characterized and investigated. LeAkt contains a 1587 bp open reading frame encoding a 529 amino acid protein that possesses a conserved Pleckstrin Homology domain (PH) and a Ser/Thr-type protein kinase (S_TKc) domain. The mRNA expression of LeAkt was the highest in female adult stages and peaked for 7-day female adults. In female adult tissues, LeAkt was highly expressed in the head and the ovary, indicating that LeAkt was closely correlated with female ovarian development. LeAkt transcription level was significantly suppressed by oral feeding on artificial diets mixed with dsRNA-LeAkt. RNAi-mediated silencing of LeAkt led to a severe inhibition of vitellogenein (Vg) expression and ovarian development, together with lower fecundity and hatchability compared to that of the normal feeding group, suggesting a critical role for LeAkt in L. entomophila reproduction. Further studies revealed that LeAkt silencing significantly decreased the mRNA levels of several signalling and biosynthetic genes in the juvenile hormone (JH) signalling pathway, such as methoprene-tolerant (LeMet), krüppel homolog 1 (LeKr-h1) and JH methyltransferase (LeJHAMT), leading to a severe inhibition of JH biosynthesis in L. entomophila female adults. These results suggested that LeAkt was affecting JH synthesis, thereby influencing Vg synthesis and ultimately L. entomophila reproduction.

Cold tolerance of Acanthoscelides obtectus, the bean weevil: Effects of cold acclimation, life stage and strain

The bean weevil, Acanthoscelides obtectus, is one of the most destructive insect pests of stored pulses globally. Cold treatment is a method used for controlling many insect species that are pests of stored-products. To understand if cold treatment can be used to control A. obtectus, we evaluated its cold tolerance at −5 °C and its supercooling point. Firstly, we measured the survival time of eggs, early instars, late instars, pupae, and adults at −5 °C using non-cold-acclimated insects, originally collected in Florida, USA. Secondly, we measured the survival time of late instars and adults at −5 °C using the strain from Florida and a strain from Ontario, Canada, and compared the effect of cold acclimation. To acclimate insects to cold, they were placed for 2 weeks at 15 °C followed by 2 weeks at 10 °C. The Florida strain had a slightly greater survival than the Ontario strain at −5 °C. Results show that at −5 °C, for non-cold-acclimated insects from the Florida strain, the most cold-sensitive stages were the eggs (LT50 of 2.3 d and LT95 of 5.3 d) and the pupae (LT50 of 1.6 d and LT95 of 6.0 d), whereas the late instars (LT50 of 4.0–4.8 d and LT95 of 8.2–8.7 d) were the most cold hardy stage. Cold acclimation increased insect survival time at −5 °C by several days. The egg was the stage with the lowest freezing point, with an average SCP of −27.7 °C. Therefore, all stages of A. obtectus would die instantaneously when exposed to this temperature. These results show that cold treatment can be used to control A. obtectus, particularly in Canada and other northernly regions where winter temperatures can be sustained below −5 °C for months and aeration fans can be used to blow cold ambient air into bins of stored pulses.