New and rapid visual detection assay for Trogoderma granarium everts based on recombinase polymerase amplification and CRISPR/Cas12a

BACKGROUND

Khapra beetle (Trogoderma granarium Everts), one of the most important quarantine pests globally, is capable of causing severe infestation and huge economic loss to stored grain, and its interception rate has increased in major global trade countries over the past few years. However, difficulties remain in distinguishing this species with similar ones. In order to assist border ports and warehouses in khapra beetle's effective rapid identification as well as pest control at the early stages of monitoring or interception, we herein developed a new and rapid visual detection assay for T. granarium based on recombinase polymerase amplification (RPA) and the CRISPR/Cas12a system.

RESULTS

We designed and selected the first khapra beetle-specific RPA primers and crRNA, and optimized the visualization reaction system (Cas12a/CrRNA = 100 nM/500 nM). With only a 37 °C-heat-source and a blue light torch, RPA and CRISPR/CAS12a-based visualization assays can be completed within 40 min to differentiate between khapra beetle and nine similar Dermestidae species. After DNA extraction using a kit (4-5 h) or a simple method (5 min), the specific amplicons were obtained after a 15 min RPA reaction at 37 °C, followed by a 15 min color reaction under 37 °C in dark conditions using a CRISPR/CAS12a system and a fluorescent probe (5'-FAM/3'-BHQ1 labeled). This method is ingenious to low levels of DNA (10-1  ng μL-1 ) and meets the sensitivity requirements for detecting a single khapra beetle's egg (≈0.7 mm).

CONCLUSION

Our specificity and sensitivity analysis inferred that the present visualization system is effective to quickly and uniquely detect khapra beetle at room temperature (37 °C), thereby preventing this species before they spread widely. Our study is suitable for being pushed forward in storage pest management, and provides value as a reference for monitoring and identification of other pests. © 2023 Society of Chemical Industry.

Evaluation of Phosphine Resistance in Populations of Sitophilus oryzae, Oryzaephilus surinamensis and Rhyzopertha dominica in the Czech Republic

Phosphine is globally the most widely adopted fumigant for the control of storage pests. Recently, an increase in the frequency of stored-product pest resistance has been observed with significant geographical and interspecific variations. In this context, there are available data for the occurrence of resistant populations from America, Asia, Africa, and Australia, but there are few data in the case of Europe. Therefore, the aim of this work was to evaluate phosphine efficacy in important beetle pests of stored products, i.e., Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.), and Rhyzopertha dominica (F.) sampled from the Czech Republic, using a rapid diagnostic test that is based on the speed to knockdown after exposure. Apart from the standard laboratory populations, which were used as the controls, we tested 56 field populations of these three species, collected in Czech farm grain stores. The survey revealed that 57.1% of the tested field populations were classified as phosphine-susceptible, based on the knockdown method used. However, profound variations among species and populations were recorded. The species with the highest percentage of resistant populations was R. dominica (71.4% of the populations; resistance coefficient 0.5-4.1), followed by S. oryzae (57.1% of the populations; resistance coefficient 0.8-6.9), and O. surinamensis (9.5% of the populations; resistance coefficient 0.5-2.9). Regarding the intra-population variability in response to phosphine (slope of the knockdown time regression), the laboratory and slightly resistant populations of all species were homogenous, whereas the most resistant populations were strongly heterogeneous. Our data show that the occurrence of resistance in the Czech Republic is relatively widespread and covers a wide range of species, necessitating the need for the adoption of an action plan for resistance mitigation.

Gel Carriers for Plant Extracts and Synthetic Pesticides in Rodent and Arthropod Pest Control: An Overview

Insecticides and rodenticides form the basis of integrated pest management systems worldwide. As pest resistance continues to increase and entire groups of chemical active ingredients are restricted or banned, manufacturers are looking for new options for more effective formulations and safer application methods for the remaining pesticide ingredients. In addition to new technological adaptations of mainstream formulations in the form of sprays, fumigants, and dusts, the use of gel formulations is becoming increasingly explored and employed. This article summarizes information on the current and potential use of gel (including hydrogel) and paste formulations against harmful arthropods or rodents in specific branches of pest management in the agricultural, food, stored product, structural wood, urban, medical, and public health areas. Due to the worldwide high interest in natural substances, part of the review was devoted to the use of gels for the formulation of pesticide substances of botanical origin, such as essential or edible oils. Gels as emerging formulation of so called “smart insecticides” based on molecular iRNA disruptors are discussed.

Synthetic and Natural Insecticides: Gas, Liquid, Gel and Solid Formulations for Stored-Product and Food-Industry Pest Control

The selective application of insecticides is one of the cornerstones of integrated pest management (IPM) and management strategies for pest resistance to insecticides. The present work provides a comprehensive overview of the traditional and new methods for the application of gas, liquid, gel, and solid physical insecticide formulations to control stored-product and food industry urban pests from the taxa Acarina, Blattodea, Coleoptera, Diptera, Hymenoptera, Lepidoptera, Psocoptera, and Zygentoma. Various definitions and concepts historically and currently used for various pesticide application formulations and methods are also described. This review demonstrates that new technological advances have sparked renewed research interest in the optimization of conventional methods such as insecticide aerosols, sprays, fumigants, and inert gases. Insect growth regulators/disruptors (IGRs/IGDs) are increasingly employed in baits, aerosols, residual treatments, and as spray-residual protectants for long-term stored-grain protection. Insecticide-impregnated hypoxic multilayer bags have been proven to be one of the most promising low-cost and safe methods for hermetic grain storage in developing countries. Insecticide-impregnated netting and food baits were originally developed for the control of urban/medical pests and have been recognized as an innovative technology for the protection of stored commodities. New biodegradable acaricide gel coatings and nets have been suggested for the protection of ham meat. Tablets and satchels represent a new approach for the application of botanicals. Many emerging technologies can be found in the form of impregnated protective packaging (insect growth regulators/disruptors (IGRs/IGDs), natural repellents), pheromone-based attracticides, electrostatic dust or sprays, nanoparticles, edible artificial sweeteners, hydrogels, inert baits with synthetic attractants, biodegradable encapsulations of active ingredients, and cyanogenic protective grain coatings. Smart pest control technologies based on RNA-based gene silencing compounds incorporated into food baits stand at the forefront of current strategic research. Inert gases and dust (diatomaceous earth) are positive examples of alternatives to synthetic pesticide products, for which methods of application and their integration with other methods have been proposed and implemented in practice. Although many promising laboratory studies have been conducted on the biological activity of natural botanical insecticides, published studies demonstrating their effective industrial field usage in grain stores and food production facilities are scarce. This review shows that the current problems associated with the application of some natural botanical insecticides (e.g., sorption, stability, field efficacy, and smell) to some extent echo problems that were frequently encountered and addressed almost 100 years ago during the transition from ancient to modern classical chemical pest control methods.

Frass produced by the primary pest Rhyzopertha dominica supports the population growth of the secondary stored product pests Oryzaephilus surinamensis, Tribolium castaneum, and T. confusum

Primary pests such as Rhyzoperta dominica may increase the contents of dockage, dust, and frass in grain mass. Although it has been suggested that frass can affect the population growth of stored product pests and ecological interactions among primary and secondary pests in stored grain, this has not been validated experimentally. Therefore, this work experimentally tested the hypothesis that R. dominica wheat frass may support population increases in secondary pests such as Tribolium confusum, T. castaneum, and Oryzaephilus surinamensis for the first time. The effect of frass on secondary pest performance was compared with the effects of various physical qualities of wheat grain (i.e., intact grain kernels, grain fragments, flour, grain + frass) and an artificially enriched control diet (milled wheat kernels, oat flakes, and yeast). The results showed that the clean intact grain kernels did not support the population growth of any tested species, and the nutrient-rich control diet provided the best support. Frass was a significantly better food medium for O. surinamensis and T. castaneum than flour or cracked grain, while T. confusum performed equally well on flour and frass. Our results showed that in terms of food quality and suitability for the tested species, frass occupied an intermediate position between the optimized breeding diet and simple uniform cereal diets such as cracked grain or flour. The results suggest that (i) the wheat frass of primary pest R. dominica is a riskier food source for the development of the tested secondary pests than intact or cracked wheat grain or flour; (ii) frass has the potential to positively influence interspecific interactions between R. dominica and the tested secondary pests; and (iii) wheat grain should be cleaned if increases in R. dominica populations and/or accumulated frass are detected.

Minimal Thermal Requirements for Development and Activity of Stored Product and Food Industry Pests (Acari, Coleoptera, Lepidoptera, Psocoptera, Diptera and Blattodea): A Review

Low temperatures play an important role in arthropods because they affect both the individual and population development of all physiological and behavioural activities. Manipulation with low temperatures is a primary nonchemical pest control method. For stored product and food industry practitioners, a knowledge of pest thermal requirements, in particular threshold temperatures at which development and other activities of a particular pest species cease, is of crucial importance. This review presents summary data regarding the lower temperature thresholds of 121 species of stored product and food industry pests from six arthropod taxa (Acari, Coleoptera, Lepidoptera, Psocoptera, Diptera, and Blattodea). In particular, this review collected and summarized information regarding the lower development thresholds, lower population thresholds, lower acoustic or respiratory thresholds, lower walking and flying thresholds and lower trap capture thresholds for flying and walking arthropods. The average lower development threshold (LDT) differed among orders: the lowest was reported for Acari (6.8 °C) and Diptera (8.1 °C), followed by Lepidoptera (11.3 °C) and Psocoptera (13.8 °C), and the highest was reported for Coleoptera (14 °C) and Blattodea (15 °C). An exclusion-function was established showing the percentage of pest species (n = 112) that were developmentally suppressed (excluded) due to temperatures reaching the LDT in the range of decreasing temperatures from 25 °C to 0 °C. We scaled various temperature thresholds from the lowest to highest temperature as follows: the walking threshold, the trap capture threshold for walking insects, the lower development threshold, lower population threshold, lower flying threshold and the lower trap capture threshold for flying pests. Important pest species were identified for which information regarding the lower temperature threshold is missing, or for which the information is too variable and should be refined in future research.

First Case of Dual Size Asymmetry in an Identical Arthropod Organ: Different Asymmetries of the Combative (Sexual) and Cutting (Non-Sexual) Parts of Mandibles in the Horned Stored-Product Beetle Gnatocerus cornutus (Fabricius, 1798)

Although it is known that separate insect body structures may be asymmetrical within one species, the different functional asymmetries within a single organ as a result of differential selective regimes have not been described. Based on microscopic measurements and SEM photography, we examined the size, shape and asymmetry of the mandibular structures of males and females of the sexually dimorphic broad-horned flour beetle, Gnatocerus cornutus (Tenebrionidae, Coleoptera). It was found that sexual dimorphism only manifests in certain outgrowth parts (horns) of male mandibles, while the remaining cutting parts of the mandibles hold identical morphologies for both sexes. A more interesting finding—since this is the first published case of dual functionally selected asymmetry in an identical arthropod organ—was that the cutting part of the male mandible exhibited directional asymmetry, whereas the outgrowth horn part of the mandible showed a high degree of symmetry. Moreover, there was no relationship between the size and asymmetry of horns. The results indicate different regulatory mechanisms of sexually selected combative horns and the food-functional, more conservative (constrained by hard food and adult long life) cutting parts of mandibles.

Microsatellite markers for Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) and other Cryptolestes species

Cryptolestes ferrugineus (Stephens, 1831) is an important insect pest of stored products. Due to its broad host range, short life cycle, and high reproductive capacity, this species has rapidly colonized temperate and tropical regions around the world. In this study, we isolated 18 novel polymorphic microsatellite loci from an enriched genomic library based on a biotin/streptavidin capture protocol. These loci will be useful tool to better understand the genetic structure and migration patterns of C. ferrugineus throughout the world. The genetic parameters were estimated based on 80 individual C. ferrugineus from two natural populations. The results revealed that 18 loci were different polymorphic levels. The numbers of alleles ranged from 3 to 12, and eleven loci demonstrated polymorphic information contents greater than 0.5. The observed (H O) and expected (H E) heterozygosities ranged from 0.051 to 0.883 and 0.173 to 0.815, respectively. Five locus/population combinations significantly deviated from Hardy-Weinberg equilibrium. We also demonstrated the potential utility of the C. ferrugineus microsatellites as population and species markers for four additional Cryptolestes species.

Differences in the Bacterial Community of Laboratory and Wild Populations of the Predatory Mite Cheyletus eruditus (Acarina: Cheyletidae) and Bacteria Transmission From Its Prey Acarus siro (Acari: Acaridae)

The parthenogenetic predatory mite Cheyletus eruditus (Schrank, 1781) is used for biological control against mite pests produced as CHEYLETIN. Although there is evidence that bacteria are mainly responsible for parthenogeny in several species of predatory mites, the description of association between C. eruditus the specific and parasitic or symbiotic bacteria is still missing. We analyzed the bacterial communities of the predator, C. eruditus , and its prey, Acarus siro L. The 16S rRNA gene was amplified, cloned, and sequenced. The selected bacterial taxa were confirmed by amplification of isolated DNA with taxon-specific primers. The 16S rRNA gene sequences from the predatory and prey mites formed a total of 20 different bacterial taxa. Of these taxa, the predator and prey shared four taxa, six taxa were specific for the predatory, and 10 taxa for the prey mites. Cardinium - and Bartonella -like bacteria were found in both mite species. The reproductive parasite Wolbachia was found only in the predatory mite, and A. siro hosted Solitalea -like (Sphingobacteriales) bacteria that were not detected in C. eruditus . We focused on Cardinium occurrence in the field samples of C. eruditus. Using Cardinium -specific primers, 128 clones were obtained. Cardinium was found in seven field samples of C. eruditus as well as in the laboratory population that was used to produce CHEYLETIN. Phylogenetic analysis of the Cardinium clones identified three separate clusters: two clusters showed high similarity to the Cardinium sequences from astigmatid mites, and one cluster contained only the clones from C. eruditus . Sequences of both Cardinium and Wolbachia were found in the both adults and eggs of C. eruditus , indicating maternal transfer of these endosymbiotic bacteria.

Susceptibility of Two Strains of the Confused Flour Beetle (Coleoptera: Tenebrionidae) Following Phosphine Structural Mill Fumigation: Effects of Concentration, Temperature, and Flour Deposits

In this study, we evaluated phosphine efficacy against two strains of the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), one laboratory strain, with no previous exposure to phosphine, and one field strain, originated from the flour mill on which we performed the fumigation. The standard Detia Degesh Phosphine Resistance Kit showed that the adults of the field strain of T. confusum required 4.4 × longer time to be knocked down than the laboratory strain. In order to assess the efficacy of phosphine in the field against these strains, aluminium phosphide (AlP) was applied in a flour mill in Czech Republic, in 2014. In this application, temperature among the six floors of the flour mill varied between 20 and 30°C, relative humidity (RH) between 44 and 78%, and phosphine concentration-time-products (CtP) between 24 and 38 g.m(-3).h(-1). Moreover, the insects were bioassayed in dishes that contained either no commodity or 1, 3, and 5 cm of flour. Nevertheless, despite these variations, all adults and larvae from both strains were dead, regardless of the floor, the quantity of the commodity, and the conditions prevailing. However, larval emergence from eggs that were used in the bioassays for both strains was recorded in some of the locations tested. In addition, larval emergence was negatively correlated with both temperature and RH. At the same time, emergence was generally similar between strains. The results of the present study illustrate that highly visible dead adults and larvae after the application of phosphine falsely imply good fumigation efficacy, given that a considerable number of eggs are very likely to survive in a wider range of conditions, and the concomitant larval emergence may result in rapid population grown right after the fumigation.

The influence of environmental temperature and humidity on temporal decomposition of cockroach allergens Bla g 1 and Bla g 2 in feces

The aim of the study was to establish a model of the environmental fate of German cockroach (Blattella germanica L.) allergens Bla g 1 and Bla g 2 in feces under controlled and field conditions. Temporal decline (3, 6, and 9 mo) of allergens Bla g 1 and Bla g 2 in the feces protected from cleaning was measured under laboratory and experimental household conditions. The influence of environmental temperature (15, 20, 25, 30, and 35 degrees C) and moisture (53, 75, 85, and 100% RH) on allergen degradation was estimated for 3, 6, and 9 mo. Bla g 1 was more stable than Bla g 2 and the proteins. The proteins and Bla g 2 contents were correlated negatively with the decomposition time; Bla g 1 was not. However, when the content of Bla g 1 in control and exposed tubes was compared, the decrease after exposure was significant at exposure in 35 degrees C, 53 and 100% RH. In laboratory, the shortest half-life (16-38 d) of Bla g 2 was at high temperature and humidity (100% RH at 35 degrees C), whereas the longest half-life (340 d) was at 25 degrees C and 85% RH. In the apartment, the half-life was 406 d. The results indicate that Bla g 1 and Bla g 2 allergens can persist in feces for several months under usual household humidity and temperature.

Brief exposure of Blattella germanica (Blattodea) to insecticides formulated in various microcapsule sizes and applied on porous and non-porous surfaces

BACKGROUND

The authors explored how microcapsule size and brief exposure affected the bioavailability of five microencapsulated insecticide formulations, chlorpyrifos 23.1 g L(-1) CS (Detmol-PRO), chlorpyrifos 20 g L(-1) CS (Empire 20), fenitrothion 20 g L(-1) CS (Detmol-Mic), cyphenothrin 10 g L(-1) CS (Detmol-CAP) and diazinon 30 g L(-1) CS (Diacap), to Blattella germanica L. on porous and non-porous surfaces. The hypothesis was tested that microencapsulated (CS) insecticides comprising larger microcapsules show higher efficacy on porous surfaces than formulations with smaller microcapsules.

RESULTS

Brief exposure was accomplished by allowing B. germanica to cross a 0.3 m insecticide barrier in 30 s (1.01 cm s(-1)). Such short exposure did not lead to 100% mortality in any formulation or surface tested. Significant differences in bioavailability on the porous and the non-porous surfaces were found: the largest difference was observed in Empire 20 and Detmol CAP, while bioavailability of Detmol MIC did not differ on porous and non-porous surfaces. Comparison of their microcapsule size spectra revealed that formulations containing larger microcapsules had higher efficacy on porous surfaces than formulations with smaller microcapsules. In order to explain the difference in efficacy, the variance of microcapsule sizes was regressed on the efficacy ratio on porous versus non-porous surfaces. Although negative correlation was evident between size of capsules and the efficacy ratio on porous and non-porous surfaces, the difference in the slope parameter was not statistically significant.

CONCLUSION

Brief contact of B. germanica with insecticide spray residues, which is common in barrier treatment, may lead to low efficacy, especially on porous surfaces. The latter should be preferably treated with CS insecticides containing a fraction with large capsules. In addition to the size of the microcapsules, the role of other factors, such as wall capsule thickness and chemical composition, on CS insecticide activity on various surfaces should be examined in future work.