Effect of exposure period on degree of dominance of phosphine resistance in adults of Rhyzopertha dominica (Coleoptera: Bostrychidae) and Sitophilus oryzae (Coleoptera: Curculionidae)

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.

The Correlation between Volatile Compounds Emitted from Sitophilus granarius (L.) and Its Electrophysiological and Behavioral Responses

Simple Summary

Postharvest loss has become a crucial issue for the grain supply chain. Storage of grain without losses in quality is a critically important aspect of global food security. The monitoring and detection of insect infestations in stored grain is essential to inform pest management decisions. Insect olfaction is a principal sensory modality for sensing semiochemicals from their external environment and regulates their behaviors. Some semiochemicals function as attractants or repellents, which could be used for insect surveillance and pest control. In this study, the granary weevil Sitophilus granarius (L.), was used as an example to evaluate volatile compounds released from the weevils’ and their initiated electrophysiological and behavioral responses. An improved understanding of S.granarius chemical ecology will lead to developing more efficient and environmentally friendly pest control strategies and technologies.

Abstract

The granary weevil Sitophilus granarius (L.) is one of the most serious primary insect pests of stored products. When S. granarius present in grains, various volatile organic compounds are released as chemical signals which can be used to detect the insects. In this study, volatile chemical compounds released from S. granarius were analyzed using the headspace solid phase micro-extraction (HS-SPME) coupled with gas chromatography (GC)–mass spectrometry (MS) techniques. Two key compounds, 3-hydroxy-2-butanone and 1-pentadecene, were identified from mixed gender of S. granarius adults at high density. Moreover, both male and female adults showed dose-dependent electroantennography (EAG) responses to 3-hydroxy-2-butanone. In behavioral assays, S. granarius was attracted to 3-hydroxy-2-butanone at 0.001 µg/10 µL but repelled at 10 µg/10 µL or higher. S. granarius was consistently repelled by 1-pentadecene at concentrations at 0.001 and 1000 µg/10 µL. 3-hydroxy-2-butanone and 1-pentadecene have considerable potential to offer in the development of new approaches for the monitoring and management of this destructive stored grain insect pest.

Scaling recovery of susceptible and resistant stored product insects after short exposures to phosphine by using automated video-tracking software

BACKGROUND

Phosphine-susceptible or resistant populations of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) adults were exposed to 0 (control), 1000 and 3000 ppm of phosphine for 15 or 90 min, to estimate behavioral and mobility responses after exposure to phosphine. Knockdown of the exposed individuals after exposure was recorded visually. The total distance moved and velocity of movement were assessed immediately after exposure to phosphine, 2 or 24 h later using a camera coupled with automated video tracking software (i.e. Ethovision®).

RESULTS

For both species tested, the highest percentage of dead adults was noted at the highest concentration (3000 ppm) for both exposure times. For T. castaneum, total distance moved and velocity decreased as the concentration increased for the susceptible population, whereas there was significant variation among individuals in the resistant population. For R. dominica, the distance moved was reduced at the highest concentrations. Individuals of R. dominica moved less than those of T. castaneum and there were significant differences in mobility between susceptible and resistant populations for both species tested. Recovery was much faster in the case of the resistant populations.

CONCLUSIONS

Changes in movement parameters can be further exploited in assessing the efficacy of different management tactics, such as trapping and sampling. Automated video tracking systems such as Ethovision® can be used to track and record insect behavioral response, providing a more objective measure of insecticide efficacy than visual categorizations. These data shed light on insect mobility and behavioral responses to fumigation treatments in relation to resistance. © 2020 Society of Chemical Industry.

Delayed mortality, resistance and the sweet spot, as the good, the bad and the ugly in phosphine use

Phosphine is the most commonly used gas for fumigation for durable commodities globally, but there is still inadequate information regarding its efficacy in conjunction with proper concentration monitoring. In a series of bioassays, insect mortality after specific exposure intervals to phosphine in selected species was examined, as well as the appearance of the so called "sweet spot". The species that were tested were: Oryzaephilus surinamensis (L.), Tribolium castaneum (Herbst), Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) with populations that had different levels of phosphine resistance. Evaluation was conducted by using the Phosphine Tolerance Test (PTT), with exposure of the adult stage for 15, 30, 60, 90, 150 and 300 min at 3000 ppm. At the end of these intervals (separate bioassays for each time interval), the insects were transferred to Petri dishes, in which recovery was recorded at different time intervals (2 h, 1, 2 and 7 days). The majority of susceptible populations of all species were instantly immobilized even in the shortest exposure period (15 min), in contrast with resistant populations that were active even after 300 min. After exposure to phosphine, populations and exposure time affected mortality of susceptible populations, whereas resistant populations recovered regardless of species and exposure time. Additional bioassays at the concentrations of 500, 1000, 2000 and 3000 ppm for 1, 3, 5, 20, 30 and 40 h showed the presence of the "sweet spot", i.e., decrease of mortality with the increase of concentration. In fact, for most of the tested species, the "sweet spot" appeared in 1000 and 2000 ppm at a 5-h exposure time, regardless of the level of resistance to phosphine. This observation is particularly important both in terms of the assessment of resistance and in the context of non-linear recovery at elevated concentrations, indicating the occurrence of strong hormetic reversals in phosphine efficacy.

Fumigation Activity against Phosphine-Resistant Tribolium castaneum (Coleoptera: Tenebrionidae) Using Carbonyl Sulfide

Simple Summary

Phosphine is one of the most widely used fumigants for the control of stored grain pests in quarantine. However, PH₃ resistance to many stored pests has been reported. In this study, the fumigation activity of carbonyl sulfide was researched as an alternative fumigant to control PH₃-resistant pests. In PH₃ treatment, there was a clear difference in the fumigation activity of domestic strain Tribolium castaneum and resistance strain T. castaneum, but both the d- and r-strains of T. castaneum showed similar results in the carbonyl sulfide (COS) treatment. Furthermore, both PH₃ and COS showed no significant difference in fumigation activity in Oryzaephilus surinamensis.

Abstract

Phosphine resistance is occurring among stored-grain pests worldwide. This study investigated the fumigation activity of phosphine (PH₃) and carbonyl sulfide (COS) against domestic strain (d-strain) Tribolium castaneum, resistance strain (r-strain) T. castaneum and Oryzaephilus surinamensis. All developmental stages of the pests were exposed to two fumigants (PH₃ and COS), and the fumigation activity according to the dose and exposure time was evaluated in a 12-L desiccator and 0.5 m³ fumigation chamber. The rice sorption rate and quality following exposure to thetwofumigants were evaluated. The mortality was 2.9% in r-strain T. castaneum, 49.5% in d-strain T. castaneum and 99.2% in O. surinamensis when 2 mg/L PH₃ was used in a 12-L desiccator for 4 h. However, all pest developmental stages showed 100% mortality after 24 h of exposure in the 0.5 m³ fumigation chamber, except for the r-strain T. castaneum. A mortalityof 100% was observed in all of the r-strain T. castaneum developmental stages at an exposure time of 192 h. For COS applied at 40.23 mg/L and 50 g/m³ in the 12-L desiccator and the 0.5 m³ fumigation chamber, respectively, 100% mortality was observed across all developmental stages regardless of species and strain. The sorption of COS was 10% higher than that of PH₃, but there was no significant difference in rice quality compared to that in the control. Therefore, this study suggests that COS can be used for controlling T. castaneum resistant to PH₃.

Resistance to the Fumigant Phosphine and Its Management in Insect Pests of Stored Products: A Global Perspective

Development of resistance in major grain insect pest species to the key fumigant phosphine (hydrogen phosphide) across the globe has put the viability and sustainability of phosphine in jeopardy. The resistance problem has been aggravated over the past two decades, due mostly to the lack of suitable alternatives matching the major attributes of phosphine, including its low price, ease of application, proven effectiveness against a broad pest spectrum, compatibility with most storage conditions, and international acceptance as a residue-free treatment. In this review, we critically analyze the published literature in the area of phosphine resistance with special emphasis on the methods available for detection of resistance, the genetic basis of resistance development, key management strategies, and research gaps that need to be addressed.

Response of Suidasia pontifica (Acaridida: Suidasiidae) to phosphine fumigation

The present study evaluated the level of phosphine toxicity of various strains of Suidasia pontifica, infesting stored agricultural products in the Philippines. The bioassays for the efficacy of phosphine fumigation followed the FAO standard method. A full assay comprised eight concentrations ranging from 0.005 to 1.00 mg/L with 20, 72 and 144-h exposure periods. A total of 15 strains were collected, representing 15 provinces in the country. Results revealed that the most susceptible strain (MR12gsn) was recorded from a private owned warehouse in General Santos City-LC₅₀ and LC₉₉ were 0.009 and 0.025 mg/L, respectively. On the other hand, the most resistant strain (LR3tar) was collected from a private owned warehouse in Tarlac City-LC₅₀ and LC₉₉ were 1.501 and 2.407 mg/L, based on discrimination dose tests. Eggs were more tolerant than the adults; complete mortality of eggs was achieved at 0.50 mg/L for 72 h and 0.35 mg/L for 144 h, whereas complete mortality of adults was obtained with 0.10 and 0.20 mg/L for 144 and 72 h exposure, respectively. The estimated minimum effective concentration (MEC) of phosphine to give complete kill of S. pontifica at various exposure periods must exceed 0.50 mg/L for 72 and 144 h. These results simply illustrate the increased efficiency (i.e., increased mortality) of phosphine fumigation of longer exposure of S. pontifica to lower concentrations.

Efficacy of Modified Atmospheres on Trogoderma granarium (Coleoptera: Dermestidae) and Sitophilus zeamais (Coleoptera: Curculionidae)

We investigated the efficacy of two types of modified atmospheres (MA) against adults of the khapra beetle, Trogoderma granarium Everts, and the maize weevil, Sitophilus zeamais Motschulsky, under laboratory conditions. Adults of the above species on wheat were exposed to a carbon dioxide (CO2) concentration of 70% or a low oxygen (O2) concentration of 0.1% for durations of 0.67 (16 h), 1, 2, 4, and 6 d and stored in an environmental chamber set at 28 ± 2°C, 70 ± 5% RH, and a photoperiod of 16:8 (L:D) h. After each exposure interval, immediate mortality and knockdown were recorded, and the surviving or knocked down individuals were transferred to normal atmospheres and returned to the environmental chamber, where survival was recorded 7 d later. In addition, after the immediate and delayed mortality counts, all adults were removed from the substrate, and the number of progeny produced was recorded 60 d later. Both MA conditions totally controlled (100% mortality) the adults of T. granarium and S. zeamais immediately after a 6-d exposure or after a 4-d exposure when delayed mortality was taken into account, showing the postexposure effect of the MA. Moreover, high CO2 was more effective than low O2 for S. zeamais, whereas the reverse was true for T. granarium. The 4-d exposure period was crucial for the production of progeny of both species because after that period surviving insects did not produce offspring. Our results show that both MA conditions can be used with success to control these species.

Comparing six mathematical link function models of the antifeedant activity of lesser grain borer exposed to sub-lethal concentrations of some extracts from calotropis procera

In the present study, Probit, Cauchy Fractional and three types of Log methods, i.e., Logit, Log-log, and Complementary log-log were employed to model the feeding deterrence of the lesser grain borer, Rhyzopertha dominica (F) (Coleoptera: Bostrichidae), when fed latex protein, crude flavonoid fraction, 3-O-rutinosides of quercetin, kaempferol and isorhamnetin, isolated from Calotropis procera (Ait.) (Gentianales: Asclepiadaceae). A nutritional study with treated flour discs at sub-lethal concentrations indicated that the tested natural products negatively affected the feeding behavior of the lesser grain borer, causing high feeding deterrent indices. Our results assure that Probit, Logit and Clog-log model the feeding deterrent indices with high goodness of fit. The models aim to support the management of the test insect when fed grains treated with sub-lethal doses of the tested phytochemicals in order to develop a viable, precise and long-term strategy to minimize the excessive reliance on the chemical pesticides currently in use.

Ancient origin and recent range expansion of the maize weevil Sitophilus zeamais, and its genealogical relationship to the rice weevil S. oryzae

Archeological records attest the early association of Sitophilus with stored cereals from the beginning of agriculture on Asia. The maize weevil (Sitophilus zeamais) became particularly damaging to maize, a cereal crop domesticated on Mesoamerica. We investigated the late evolutionary history of the maize weevil to gain insights on its origin, timing of association with maize, and genealogical relationship to the almost morphologically indistinguishable rice weevil (Sitophilus oryzae). Two mitochondrial genes (cytochrome oxidase subunit I and cytochrome oxidase subunit II) and the nuclear ribosomal gene region were partially sequenced. Analyses showed that the maize weevil shared no haplotypes with the rice weevil; instead, each species exhibited distinct mitogroups and ribogroups. The two weevil species likely split about 8.7 million years ago (95% highest posterior density: 4.0-15.0). Microsatellite data analyses sorted the 309 specimens from 15 populations of the maize weevil into three genotypic groups, which displayed low genetic differentiation and widespread occurrence worldwide. The maize weevil and the rice weevil are each a distinct species; both of which emerged prior to the onset of agriculture. The maize-maize weevil association took place after maize became widespread as a global crop. The maize weevil populations lack spatial genetic structure at the regional, continental, and intercontinental scales.

Phosphine resistance in Australian Cryptolestes species (Coleoptera: Laemophloeidae): perspectives from mitochondrial DNA cytochrome oxidase I analysis

BACKGROUND

The flat grain beetle (FGB) species Cryptolestes ferrugineus, C. pusillus, C. pusilloides and C. turcicus are major stored-product pests worldwide, of which the first three are present in Australia. C. ferrugineus is also a species with high phosphine resistance status in various countries. Morphological identification of Cryptolestes species is difficult and represents an additional barrier to effective management of phosphine resistance in FGBs.

RESULT

Mitochondrial DNA cytochrome oxidase I (mtDNA COI) gene characterisation enabled differentiation of the four major FGB pest species through direct sequence comparison, and enabled the development of a PCR-RFLP method for rapid species differentiation. We detected two mtDNA haplotypes (Cunk-01, 02) present at low frequencies with an average nucleotide divergence rate of 0.079 ± 0.011 (SE) from C. pusillus. This nucleotide divergence rate is similar to that between C. ferrugineus and C. pusilloides (0.088 ± 0.012). Male and female genitalia morphologies of the Cunk-02 individuals indicated they were consistent with C. pusillus, yet DNA sequence analyses suggested species-level divergence. The mtDNA COI gene of phosphine-bioassayed, lab-reared F1 generation survivors supported the presence of strong phosphine resistance in C. ferrugineus, but unexpectedly also in C. pusilloides and C. pusillus F1 survivors.

CONCLUSION

We demonstrated the utility of molecular DNA techniques for differentiating closely related insect species, and its usefulness in assisting the management of pest insect species. The likely presence of a cryptic C. pusillus species in Australia and the possible development of strong phosphine resistance in Australian FGB pest species require further investigation. © 2014 Society of Chemical Industry.

Genetic characterization of field-evolved resistance to phosphine in the rusty grain beetle, Cryptolestes ferrugineus (Laemophloeidae: Coleoptera)

Inheritance of resistance to phosphine fumigant was investigated in three field-collected strains of rusty grain beetle, Cryptolestes ferrugineus, Susceptible (S-strain), Weakly Resistant (Weak-R) and Strongly Resistant (Strong-R). The strains were purified for susceptibility, weak resistance and strong resistance to phosphine, respectively, to ensure homozygosity of resistance genotype. Crosses were established between S-strain×Weak-R, S-strain×Strong-R and Weak-R×Strong-R, and the dose mortality responses to phosphine of these strains and their F1, F2 and F1-backcross progeny were obtained. The fumigations were undertaken at 25°C and 55% RH for 72h. Weak-R and Strong-R showed resistance factors of 6.3× and 505× compared with S-strain at the LC50. Both weak and strong resistances were expressed as incompletely recessive with degrees of dominance of -0.48 and -0.43 at the LC50, respectively. Responses of F2 and F1-backcross progeny indicated the existence of one major gene in Weak-R, and at least two major genes in Strong-R, one of which was allelic with the major factor in Weak-R. Phenotypic variance analyses also estimated that the number of independently segregating genes conferring weak resistance was 1 (nE=0.89) whereas there were two genes controlling strong resistance (nE=1.2). The second gene, unique to Strong-R, interacted synergistically with the first gene to confer a very high level of resistance (~80×). Neither of the two major resistance genes was sex linked. Despite the similarity of the genetics of resistance to that previously observed in other pest species, a significant proportion (~15 to 30%) of F1 individuals survived at phosphine concentrations higher than predicted. Thus it is likely that additional dominant heritable factors, present in some individuals in the population, also influenced the resistance phenotype. Our results will help in understanding the process of selection for phosphine resistance in the field which will inform resistance management strategies. In addition, this information will provide a basis for the identification of the resistance genes.

Phosphine gas generated from an aluminium phosphide tablet exhibits early knock down effects on tamarind pod borer

The tamarind pod borer, Sitophilus linearis (Herbst), is highly susceptible to phosphine fumigation compared to its congener, Sitophilus oryzae.

Ecological Networks in Stored Grain: Key Postharvest Nodes for Emerging Pests, Pathogens, and Mycotoxins

Wheat is at peak quality soon after harvest. Subsequently, diverse biota use wheat as a resource in storage, including insects and mycotoxin-producing fungi. Transportation networks for stored grain are crucial to food security and provide a model system for an analysis of the population structure, evolution, and dispersal of biota in networks. We evaluated the structure of rail networks for grain transport in the United States and Eastern Australia to identify the shortest paths for the anthropogenic dispersal of pests and mycotoxins, as well as the major sources, sinks, and bridges for movement. We found important differences in the risk profile in these two countries and identified priority control points for sampling, detection, and management. An understanding of these key locations and roles within the network is a new type of basic research result in postharvest science and will provide insights for the integrated pest management of high-risk subpopulations, such as pesticide-resistant insect pests.

Dosage consistency is the key factor in avoiding evolution of resistance to phosphine and population increase in stored-grain pests

BACKGROUND

Control of pests in stored grain and the evolution of resistance to pesticides are serious problems worldwide. A stochastic individual-based two-locus model was used to investigate the impact of two important issues, the consistency of pesticide dosage through the storage facility and the immigration rate of the adult pest, on overall population control and avoidance of evolution of resistance to the fumigant phosphine in an important pest of stored grain, the lesser grain borer.

RESULTS

A very consistent dosage maintained good control for all immigration rates, while an inconsistent dosage failed to maintain control in all cases. At intermediate dosage consistency, immigration rate became a critical factor in whether control was maintained or resistance emerged.

CONCLUSION

Achieving a consistent fumigant dosage is a key factor in avoiding evolution of resistance to phosphine and maintaining control of populations of stored-grain pests; when the dosage achieved is very inconsistent, there is likely to be a problem regardless of immigration rate.

Bioactivity of short-chain aliphatic ketones against adults of the granary weevil, Sitophilus granarius (L.)

BACKGROUND

The granary weevil, Sitophilus granarius (L.), is one of the most damaging pests of stored grains, causing severe quantitative and qualitative losses. Sustainable control means, alternative to the commonly used fumigants and broad-spectrum contact insecticides, are urgently needed owing to legislative limits, the development of resistant insect strains and increasing consumer demand for safe food. Short-chain aliphatic ketones, known to be emitted by cereal grains and previously identified as repellents to adult granary weevils, were evaluated for their ability to disrupt insect orientation towards wheat grains and as possible natural fumigants.

RESULTS

In behavioural bioassays, 2-pentanone, 2-hexanone, 2-heptanone and 2,3-butanedione significantly reduced insect orientation towards odours of wheat grains, with 2-hexanone and 2-heptanone being the most active. In fumigation tests, all compounds were effective in killing weevil adults, but they performed differently according to chemical structure, speed of action and presence of wheat grains. In the presence of grains, the highest fumigant toxicity was shown by 2-pentanone (LC(50) = 8.4 ± 1.0 mg L(-1)) after 24 h exposure, and by 2-pentanone (LC(50) = 4.5 ± 0.3 mg L(-1)), 2-heptanone (LC(50) = 7.1 ± 0.3 mg L(-1) ) and 2-hexanone (LC(50) = 8.1 ± 0.6 mg L(-1)) 1 week after the treatment end.

CONCLUSION

Short-chain aliphatic ketones have potential for applications in IPM programmes for the granary weevil because of their behaviour-altering activity and fumigant toxicity.

Improved fumigation process for stored foodstuffs by using phosphine in sealed chambers

In this paper we present an innovative device designed and constructed to improve the fumigation process for stored foodstuffs with the use of phosphine gas in sealed chambers. The device allowed a considerable reduction in phosphine production time (from about 5 to 7 days for traditional systems to 2 days for the equipment considered), maintaining the system below the inflammability threshold, and at the same time achieving the total exhaustion of aluminum (or magnesium) phosphide so as to avoid toxic residues at the end of the process. With the standard device currently available on the market, after the normal 5-7 day fumigating period, the powder residue contains as much as 1-2% (w/w) of phosphide. Thus the residues, according to current legislation, have to be considered toxic and harmful. To overcome this disadvantage, appropriate modifications were made to the cylindrical tray used for the fumigation process: a nebulizer was installed, which has the function of increasing the moisture of the air spreading around the phosphide pellets and allowing a more rapid reaction with phosphide. Moreover, the cylindrical tray was also heated by means of an electrical resistance, and temperature was checked by a thermostat, so as to always obtain the same efficiency, independently of outside temperature, for both hot and cold periods, since reaction speed depends on the system temperature considered. In addition, a control device for air saturation allows condensation processes to be avoided. Using the modified cylindrical tray we performed tests to determine the best values of humidity and temperature for the process concerned, avoiding phosphine concentrations that might result in a fire hazard, and the remixing of phosphide pellets inside the cylindrical tray. Our experimental data allowed us to obtain a mathematical model used to gain an insight into the process in question.

Efficacy of layer treatment with methoprene for control of Rhyzopertha dominica (Coleoptera: Bostrychidae) on wheat, rice and maize

BACKGROUND

Insect growth regulators are promising alternatives to traditional pesticides in stored grain. The efficacy of the juvenile hormone analogue methoprene was evaluated as a layer treatment in a laboratory experiment for control of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) in wheat, rice and maize.

RESULTS

Adults of R. dominica were placed in vials containing 33, 26 and 29 g (to a depth of 6.5 cm) of wheat, rice and maize, respectively, that was entirely or partially treated with 1, 5 or 10 mg kg(-1) methoprene. In wheat and rice, the layer treatments were not as effective as the whole-grain treatment, but there was decreased progeny production as the application rate increased. However, on maize the partial treatments were as effective as the whole-grain treatment at 5 and 10 mg kg(-1) .

CONCLUSIONS

The results suggest that partial layer treatments with methoprene can be used to control R. dominica on maize but may not be effective for control of this species on wheat and rice.