Influence of concentration, temperature and humidity on the toxicity of phosphine to the strongly phosphine-resistant psocid Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae)

Sublethal phosphine fumigation induces transgenerational hormesis in a factitious host, Corcyra cephalonica

BACKGROUND

The rice moth, Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) is a pest of stored grains and widely used as a factitious host during the mass rearing of several natural enemies of crop pests. Hormesis is well-documented in pest insects, to some extent in natural enemies of pests.

RESULTS

We report transgenerational stimulatory effects of the widely used fumigant, phosphine. The study reports the consequences of sublethal, low lethal and median lethal concentrations (LC5 , LC25 and LC50 ) and untreated control for two sequential generations of the species (G1 to G2 ). In this study, we investigated the life-history traits, nutrient reserves (protein, lipid and carbohydrate) and larval gut microbiome (using 16 s rRNA V3-V4 metagenomics sequencing) of C. cephalonica. Stimulatory effects were observed for various biological traits of C. cephalonica, notably adult longevity, emergence and increased egg hatchability when exposed to LC5 of phosphine. The total protein, lipid and carbohydrate contents of C. cephalonica also were found to be significantly increased by LC5 in both generations. The microbial diversity of LC5 treated larval gut was higher and found to be different from the rest of the treatments. This is the first report showing hormesis to a fumigant insecticide.

CONCLUSION

Our findings increase knowledge on the interaction between hormesis, nutrient reserves and gut bacteria in C. cephalonica exposed to insecticides. Overall, the present study establishes phosphine-induced hormesis at LC5 in the host C. cephalonica, which might help improve the quality of mass rearing of various natural enemies. © 2023 Society of Chemical Industry.

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.

Pesticidal Toxicity of Phosphine and Its Interaction with Other Pest Control Treatments

Phosphine is the most widely used fumigant for stored grains due to a lack of better alternatives, all of which have serious shortcomings that restrict their use. The extensive use of phosphine has led to the development of resistance among insect pests of grain, which threatens its status as a reliable fumigant. Understanding the mode of action of phosphine as well as its resistance mechanisms provides insight that may lead to improved phosphine efficacy and pest control strategies. The mechanisms of action in phosphine vary from disrupting metabolism and oxidative stress to neurotoxicity. Phosphine resistance is genetically inherited and is mediated by the mitochondrial dihydrolipoamide dehydrogenase complex. In this regard, laboratory studies have revealed treatments that synergistically enhance phosphine toxicity that may be used to suppress resistance development and enhance efficacy. Here, we discuss the reported phosphine modes of action, mechanisms of resistance and interactions with other treatments.

Effects of Dehumidification on the Survivorship of Four Psocid Species

Psocids are damaging stored-product pests. In this study, eggs and early-instar nymphs, adults, and all life stages of Liposcelis entomophila, L. decolor, L. bostrychophila, and L. paeta were subjected to 43, 50, or 75% (Control) relative humidity (RH) for 2, 4, 6, 8, 10, 12, 14, or 16 d at 30.0°C. All adults of these species died within 8 d at both 43 and 50% RH, except for L. bostrychophila, which required 12 d at 50% RH for 100% mortality to occur. For all life stages and eggs and early-instar nymphs, maximum survival times (times to 100% mortality) at 43 or 50% RH for L. entomophila, L. decolor, L. bostrychophila, and L. paeta, were 8 and 10 d, 8 and 12 d, 12 and 14 d, and 12 and 16 d, respectively. During this study, numbers of nymphs and adults of all species 14 d after the RH treatments increased within the 75% RH Control arenas. Different species and life stages responded differently to 43 and 50% RH, as time to kill all stages of the four psocid species was 8-12 and 10-16 d, respectively. Results indicate that using a specific RH environment may be effective in psocid management.

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.

RNA-seq Analysis Reveals Mitochondrial and Cuticular Protein Genes Are Associated with Phosphine Resistance in the Rusty Grain Beetle (Coleoptera:Laemophloeidae)

The rusty grain beetle, Cryptolestes ferrugineus (Stephens), is a serious pest of stored grain, which has developed high levels of resistance to phosphine. In this study, five geographically distant populations of C. ferrugineus had been collected in China, specifically in granaries where phosphine fumigant is used for pest control, and they showed a high resistance ratio up to 1,907 (LC50 = 21.0 mg/liter). Then, a reference transcriptome was constructed to use as a basis for investigating the molecular mechanisms of phosphine resistance in this species, which consisted of 47,006 unigenes with a mean length of 1,090. Subsequently, the RNA-Seq analysis of individuals from the most susceptible and resistant populations led to the identification of 54 genes that are differentially expressed. GO and KEGG analysis demonstrated that genes associated with mitochondrial and respiration functions were significantly enriched. Also, the 'structural constituent of cuticle' term was annotated in the GO enrichment analysis and further qRT-PCR confirmed that the expression levels of nine cuticular protein genes were significantly increased in the resistant population. In conclusion, we present here a transcriptome-wide overview of gene expression changes between resistant and susceptible populations of C. ferrugineus, and this in turn documents that mitochondria and cuticular protein genes may play together a crucial role in phosphine resistance. Further gene function analysis should enable the provision of advice to expedite resistance management decisions.

High-dose strategies for managing phosphine-resistant populations of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

BACKGROUND

Rhyzopertha dominica is a serious pest of stored grains and many populations have resistance to the fumigant phosphine. Some populations contain beetles with a 'strong resistance' phenotype. Recent work found the LC₅₀ values for two strong-resistant populations recently studied in North America, Belle Glade and Minneapolis were 100- and 595-fold higher, respectively, compared to LC₅₀ of a lab-susceptible strain. Populations with 'weak-resistant' phenotypes had LC₅₀ values 5- to 10-fold that of a susceptible strain. The work reported below aimed to determine the minimum phosphine concentrations and number of days of exposure needed to effectively control all life stages of representative weak- and strong-resistant strains, and then to recommend the treatment conditions needed to control strongly phosphine-resistant R. dominica in pest populations.

RESULTS

A dose-mortality assay estimated that phosphine fumigation over 48 h using 730-870 ppm at 25° C would control adults of both strongly resistant R. dominica populations. Fumigations with mixed life stage cultures found 200 ppm killed all susceptible and weak-resistant beetles in 2 days, but the strong-resistant Minneapolis and Belle Glade strains had substantial survivors at 200 ppm. Furthermore, the Belle Glade strain had beetles that survived 1000 ppm in 2-day fumigations. The strong-resistant Belle Glade strain needed nearly 10 days at over 400 ppm to have acceptable levels of control.

CONCLUSION

This study recommends protocols to manage strongly resistant R. dominica populations provided that a minimum phosphine concentration of 400 ppm be maintained at 25° C or higher for up to 10 days. © 2019 Society of Chemical Industry.

Contact toxicity and repellent efficacy of Valerianaceae spp. to three stored-product insects and synergistic interactions between two major compounds camphene and bornyl acetate

In this work, the essential oil (EO) and supercritical CO₂ fluid extract (SF extract) of four Valerianaceae plants (Valeriana officinalis L., Valeriana officinalis L. var. latifolia Miq., Valeriana jatamansi Jones and Nardostachys chinensis Bat.) were chemically characterized. GC-MS analysis identified 74 compounds, representing 35.2%-82.4% of the total EOs and SF extracts. The EO was dominated by low-molecular-weight components while the SF extract was rich in fatty acids. Bornyl acetate and camphene were the characteristic compounds in EO and SF extracts. The efficacy of six extracts against three stored-product insects was investigated. In contact assays, V. officinalis exhibited strongest toxicity to red flour beetle (LD₅₀ = 10.0 μg/adult), and V. jatamansi EO was the most active one against the cigarette beetle (LD₅₀ = 17.6 μg/adult), while V. officinalis var. latifolia EO showed outstanding efficacy against the booklouse (LD₅₀ = 40.2 μg/cm²). Binary mixtures of two major compounds (camphene and bornyl acetate) were assessed for the contact toxicity to the red flour beetle. Additive effect existed in the natural proportion of V. officinalis, and synergism was observed in that of V. officinalis var. latifolia. This work confirmed the insecticidal efficacy of the species of the Valerianaceae family, and it would offer some information for the development of botanical insecticide.

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.

Efficacy of bornyl acetate and camphene from Valeriana officinalis essential oil against two storage insects

The essential oil was extracted from the roots of Valeriana officinalis L. by hydrodistillation. The qualitative and quantitative analysis of its chemical constituents was conducted on GC-MS and GC-FID in this study. Seventeen compounds were detected and the major constituents included bornyl acetate (48.2%) and camphene (13.8%). The toxic and repellent effects of the essential oil and its two major constituents were evaluated on Liposcelis bostrychophila and Tribolium castaneum. The results of bioassays indicated that the essential oil showed the promising fumigant and contact toxicity against L. bostrychophila (LC₅₀ = 2.8 mg/L air and LD₅₀ = 50.9 μg/cm², respectively) and the notable contact effect on T. castaneum (LD₅₀ = 10.0 μg/adult). Meanwhile, the essential oil showed comparable repellent effect on T. castaneum at all testing concentrations. Bornyl acetate and camphene also exhibited strong fumigant and contact toxicity against both species of pests (LC₅₀ = 1.1, 10.1 mg/L air and LD₅₀ = 32.9, 701.3 μg/cm² for L. bostrychophila; > 126.3, 4.1 mg/L air, and 66.0, 21.6 μg/adult for T. castaneum). Bornyl acetate and camphene showed moderate repellent effect on T. castaneum and conversely showed attractant effect on L. bostrychophila. This work highlights the insecticidal potential of V. officinalis, which has been noted as a traditional medicinal plant.

Efficacy and Phytotoxicity of Phosphine as Fumigants for Frankliniella occidentalis (Thysanoptera: Thripidae) on Asparagus

The insecticidal activity of phosphine (PH3) and ethyl formate (EF) toward Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) and their phytotoxicity to asparagus were evaluated. Both the PH3 and EF fumigants showed higher lethal concentration and time (LCT) values at lower temperatures. The LCT99 values of PH3 and EF at 5°C in a 12 liters desiccator for 4 h showed the following ranking: eggs (64.69 mg·h/liter for PH3 and EF indicating phytotoxicity to asparagus), nymphs (5.54 and 17.48 mg·h/liter, respectively), and adults (3.83 and 14.67 mg·h/liter, respectively). The adsorption of PH3 was approximately 11% at 2°C and 13% at 5°C, whereas the adsorption of EF increased sharply to 88% at 2°C and 97% at 5°C. The hatching rate of F. occidentalis eggs was approximately 95% at all locations (top, middle, and bottom) in the presence of 4 mg/liter PH3 at 5°C in a 0.65-m3 fumigation chamber for 24 h. However, extension of the treatment to 48 h resulted in 100% inhibition of egg hatching. The atmospheric level of PH3 decreased below the threshold limit value after 80 min, and phytotoxicity was not observed. The results revealed that EF is highly absorbed by asparagus and is not suitable as a fumigant, but PH3 is a suitable alternative to the fumigant methyl bromide for the control of western flower thrips in asparagus.

Proteomic Evaluation of Insecticidal Action of Phosphine on Green Peach Aphids, Myzus persicae

Phosphine (PH3) fumigation is one of the best alternatives to methyl bromide for regulating insect pests during storage and shipping. Recently, this treatment has been applied to other agricultural insect pests, including Myzus persicae. To understand the mode of PH3 toxicity in M. persicae, proteomic analyses using liquid-chromatography tandem mass spectrometry were conducted to measure comparative protein expression levels between PH3-treated samples and controls. PH3 treatment increased NADH dehydrogenase (ubiquinone) flavoprotein 1, mitochondrial-like (complex I) expression, but decreased complex II and ATPases in the mitochondrial electron transport chain (ETC) of M. persicae. Glucosidase and antimicrobial proteins such as lysozymes showed enhanced expression in PH3-treated M. persicae. Some regulatory proteins related to apoptosis were more abundant in PH3-treated M. persicae. Biochemical activities of acetylcholinesterase (AChE) and cytochrome c oxidase (COX) were also measured because these enzymes are known to be targeted by PH3. Only COX activity decreased in relation to increasing PH3 concentrations in adult M. persicae. The expression of six selected genes were determined in relation to PH3 treatments. No two-fold changes in the expression of the six genes was observed. Thus, PH3 toxicity caused disruption in the ETC and glucose supply, as well as dis-regulation of apoptosis in M. persicae.

Toxicity of Chlorine Dioxide Gas to Phosphine-Susceptible and -Resistant Adults of Five Stored-Product Insect Species: Influence of Temperature and Food During Gas Exposure

Adults of phosphine-susceptible and -resistant strains of the red flour beetle, Tribolium castaneum (Herbst); lesser grain borer, Rhyzopertha dominica (F.); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); maize weevil, Sitophilus zeamais Motschulsky; and rice weevil, Sitophilus oryzae (L.), were exposed for 2-12 h to a chlorine dioxide gas concentration of 1.40 g/m3 (520 ppm) in an outdoor trailer during July and October of 2015. The mean ± SE temperatures in July and October were 32.8 ± 0.5°C and 24.8 ± 0.6°C, respectively. In July, complete mortality after 5 d was achieved for all species and strains in vials with wheat after a 4- or 8-h exposure; in October, a longer exposure time was needed for complete mortality of insects in vials with wheat. Chlorine dioxide was more toxic to all insect species and strains at warmer than cooler temperature and in vials without wheat than those with wheat. Both phosphine-resistant and -susceptible strains were equally susceptible to chlorine dioxide. The presence of wheat resulted in delayed mortality of insects because of reaction of chlorine dioxide with active sites on kernels. Progeny production 8 wk after chlorine dioxide exposure showed a significant reduction (72-100%), compared with that in control vials for strains of R. dominica, S. zeamais, and S. oryzae. There was no progeny production in control and treatment vials for T. castaneum and O. surinamensis, as these species require dockage. Chlorine dioxide is a potential fumigant to control phosphine-resistant strains of the five stored-product insect species.

Evaluation of Low-Temperature Phosphine Fumigation for Control of Oriental Fruit Fly in Loquat Fruit

Oriental fruit fly, Bactrocera dorsalis (Hendel; Diptera: Tephritidae), is recognized as a quarantine pest and a threat to Chinese loquat (Eriobotrya japonica Lindl.) fruit exports. Since loquat fruit is very sensitive to methyl bromide (MB) fumigation and cold treatment, in this study, low-temperature phosphine (PH3) fumigation was investigated to develop an alternative phytosanitary treatment method. Tolerance tests showed that the third instar was the most tolerant of all life stages of B dorsalis to PH3 gas at 8°C. Toxicity assay with 500-3000 ppm PH3 and subsequent probit analysis showed that 2000 ppm PH3 was optimal for fumigation and 152.75 h of treatment duration were required to achieve 99.9968% mortality. In the verification test, 144 and 168 h of treatment duration with 2000 ppm PH3 completely killed 35,277 and 35,134 B. dorsalis third instars, respectively. However, 13 live larvae were found after 120 h of treatment. Furthermore, these treatments reduced fruit respiration rates while causing no adverse effects on other fruit quality parameters, including firmness, soluble solid content, and titratable acidity over 192 h storage at 8°C. The results strongly suggest that low-temperature PH3 fumigation could be used for the postharvest control of B. dorsalis in loquat fruit.

Reference gene selection to determine differences in mitochondrial gene expressions in phosphine-susceptible and phosphine-resistant strains of Cryptolestes ferrugineus, using qRT-PCR

Cryptolestes ferrugineus is a serious pest of stored grain and has developed high levels of resistance to phosphine fumigants in many countries. Measuring differences in expression levels of certain 'resistant' genes by quantitative real-time PCR (qRT-PCR) may provide insights into molecular mechanisms underlying resistance to phosphine in C. ferrugineus, but reliable qRT-PCR results depend on suitable reference genes (RGs). We evaluated the stability of nine candidate RGs across different developmental stages and phosphine strains of C. ferrugineus, using four softwares. The results showed that RPS13 and EF1α were the most stable RGs, whereas α-TUB was the least under developmental stages. Across the different strains, RPS13 and γ-TUB were the most stable RGs, whereas CycA and GAPDH were the least. We confirmed the reliability of the selected RGs by qRT-PCR analyses of the mitochondrial cox1 gene. Expression of cox1 was not significantly different in the phosphine-resistant strain compared with the phosphine-susceptible strain, but three mitochondrial genes (nad3, atp6 and cob) were significantly down-regulated. These results suggest that alterations in the expressions of these three genes may be associated with phosphine resistance in C. ferrugineus. The findings will facilitate future functional genomics studies on the development and phosphine resistance in C. ferrugineus.

Phosphine Resistance in Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) Collected From Grain Storage Facilities in Oklahoma, USA

Phosphine gas (PH3) is one of the most commonly used fumigants for controlling stored-grain pests worldwide. We estimated the discriminating dose for Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) adult insects using a laboratory susceptible strain. This discriminating dose was then used to determine presence or absence of PH3 resistance (resistance frequencies) in 19 field-collected populations of C. ferrugineus from Oklahoma, United States. The discriminating dose was estimated as 56.2 ppm of PH3 over a 20-h exposure period at 25 °C. Discriminating dose bioassay results showed that PH3 resistance was present in all 19 populations of C. ferrugineus tested. However, five populations-Stillwater (Stil), Enid Terminal 1 (ET-1), Enid Terminal 2 (ET-2), Johnson-Enid population (JE), and DK Farm 20 population (DK Farm 20) had ≥90% resistance frequencies. LC99 values estimated by probit analyses of dose-response mortality data for the laboratory susceptible strain (Lab-S), JE, and DK Farm 20 were 7.3, 636.4, and 968.6 ppm, respectively, over a 3-d exposure period. The level of resistance in DK Farm 20, the most resistant population, was 133.5 times that of the susceptible laboratory strain. This study shows that PH3 resistance in C. ferrugineus may be widespread in Oklahoma. Based on this study, there is a need for a wider PH3 resistance survey in grain-growing regions of Oklahoma and United States. Furthermore, results show there is a need to develop PH3 resistance management strategies for C. ferrugineus and other stored-product insect pest species to combat resistance and ensure continued effective future use of PH3.

Comparative transcriptome profiling of a thermal resistant vs. sensitive silkworm strain in response to high temperature under stressful humidity condition

Thermotolerance is important particularly for poikilotherms such as insects. Understanding the mechanisms by which insects respond to high temperatures can provide insights into their adaptation to the environment. Therefore, in this study, we performed a transcriptome analysis of two silkworm strains with significantly different resistance to heat as well as humidity; the thermo-resistant strain 7532 and the thermos-sensitive strain Knobbed. We identified in total 4,944 differentially expressed genes (DEGs) using RNA-Seq. Among these, 4,390 were annotated and 554 were novel. Gene Ontology (GO) analysis of 747 DEGs identified between RT_48h (Resistant strain with high-temperature Treatment for 48 hours) and ST_48h (Sensitive strain with high-temperature Treatment for 48 hours) showed significant enrichment of 12 GO terms including metabolic process, extracellular region and serine-type peptidase activity. Moreover, we discovered 12 DEGs that may contribute to the heat-humidity stress response in the silkworm. Our data clearly showed that 48h post-exposure may be a critical time point for silkworm to respond to high temperature and humidity. These results provide insights into the genes and biological processes involved in high temperature and humidity tolerance in the silkworm, and advance our understanding of thermal tolerance in insects.

Quarantine Treatments of Imported Nursery Plants and Exported Cut Flowers by Phosphine Gas (PH3) as Methyl Bromide Alternative

Quarantine treatments by phosphine (PH₃) gas have been performed to replace methyl bromide (MeBr) for export cut flowers and imported nursery plant in Korea. In this preliminary study, two dominant insect pests of cut flowers, Tetranychus urticae Koch and Frankliniella occidentalis Pergande, and the dominant insect pest of nursery plants, Planococcus citri Risso, were used to certify optimum concentration and fumigation time, along with evaluation of phytotoxic damages. To validate the results of preliminary tests, quarantine treatments for export cut flowers was performed in a 58-m³ reefer container. When 14 species of cut flowers were fumigated with 2 g m^-3 PH₃ for 24 h (Ct product was 30.9 g h m^-3) at 5 °C, all pests were effectively controlled and no phytotoxic damage were observed on roses and chrysanthemums. On quarantine trials for imported nursery trees, which was performed at 10 m³ scale covered with a PVC-tarpaulin tent, 2 g m^-3 of PH₃ for 24 h (Ct product was 30.0 g h m^-3) at 15 °C was enough to kill all pests and no damage was observed on seven species of nursery plants. Phosphine gas shows the promise as MeBr alternative to perishable commodities in terms of efficacy to certain quarantine pest and maintenance of its quality as well as being a more environmentally safe fumigant.

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.

Effectiveness of Sulfuryl Fluoride Fumigation for the Control of Phosphine-Resistant Grain Insects Infesting Stored Wheat

A field experiment was conducted in eight 13.6-MT steel bins containing 6.8 MT each of wheat to assess efficacy of sulfuryl fluoride or SF fumigant to control phosphine-resistant and susceptible Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst). Approximately 400 adults of each type of beetle were added to each bin. Additionally, muslin bags containing immature stages and adults, with their respective diets, were also placed in bins. Four bins were fumigated with SF and others were untreated control bins. The SF dosages in treated bins ranged from 1,196–1,467 mg-h/liter. Mortality of adults in each bag was assessed 5 d postfumigation; diet minus adults was incubated in a jar, and number of adults counted after 8 wk. No significant change occurred in number of insect-damaged kernels in SF-treated bins. In trier samples from SF-treated bins, R. dominica numbers declined from 24 prefumigation to 0 at 3- and 6-wk postfumigation; T. castaneum numbers were unchanged. In WBII traps from SF-treated bins, numbers R. dominica and T. castaneum declined from 25 and 33, respectively, prefumigation to 0 or near 0 at 3- and 6-wk postfumigation. Mortalities of resistant and susceptible adult R. dominica, and adult and large larvae of T. castaneum in SF-treated bags was 100%. For all four types of beetles, adult numbers in jars associated with SF-treated bins were 0 or near 0. Results show SF is effective against all life stages of phosphine-resistant R. dominica and T. castaneum, and can be used for phosphine resistance management.

Insecticide Resistance and Management Strategies in Urban Ecosystems

The increased urbanization of a growing global population makes imperative the development of sustainable integrated pest management (IPM) strategies for urban pest control. This emphasizes pests that are closely associated with the health and wellbeing of humans and domesticated animals. Concurrently there are regulatory requirements enforced to minimize inadvertent exposures to insecticides in the urban environment. Development of insecticide resistance management (IRM) strategies in urban ecosystems involves understanding the status and mechanisms of insecticide resistance and reducing insecticide selection pressure by combining multiple chemical and non-chemical approaches. In this review, we will focus on the commonly used insecticides and molecular and physiological mechanisms underlying insecticide resistance in six major urban insect pests: house fly, German cockroach, mosquitoes, red flour beetle, bed bugs and head louse. We will also discuss several strategies that may prove promising for future urban IPM programs.

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.

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.

Developing effective fumigation protocols to manage strongly phosphine-resistant Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae)

BACKGROUND

The emergence of high levels of resistance in Cryptolestes ferrugineus (Stephens) in recent years threatens the sustainability of phosphine, a key fumigant used worldwide to disinfest stored grain. We aimed at developing robust fumigation protocols that could be used in a range of practical situations to control this resistant pest.

RESULTS

Values of the lethal time to kill 99.9% (LT99 .9 , in days) of mixed-age populations, containing all life stages, of a susceptible and a strongly resistant C. ferrugineus population were established at three phosphine concentrations (1.0, 1.5 and 2.0 mg L(-1) ) and three temperatures (25, 30 and 35 °C). Multiple linear regression analysis revealed that phosphine concentration and temperature both contributed significantly to the LT99 .9 of a population (P < 0.003, R2 = 0.92), with concentration being the dominant variable, accounting for 75.9% of the variation. Across all concentrations, LT99.9 of the strongly resistant C. ferrugineus population was longest at the lowest temperature and shortest at the highest temperature. For example, 1.0 mg L(-1) of phosphine is required for 20, 15 and 15 days, 1.5 mg L(-1) for 12, 11 and 9 days and 2.0 mg L(-1) for 10, 7 and 6 days at 25, 30 and 35 °C, respectively, to achieve 99.9% mortality of the strongly resistant C. ferrugineus population. We also observed that phosphine concentration is inversely proportional to fumigation period in regard to the population extinction of this pest.

CONCLUSION

The fumigation protocols developed in this study will be used in recommending changes to the currently registered rates of phosphine in Australia towards management of strongly resistant C. ferrugineus populations, and can be repeated in any country where this type of resistance appears.

Array of Synthetic Oligonucleotides to Generate Unique Multi-Target Artificial Positive Controls and Molecular Probe-Based Discrimination of Liposcelis Species

Several species of the genus Liposcelis are common insect pests that cause serious qualitative and quantitative losses to various stored grains and processed grain products. They also can contaminate foods, transmit pathogenic microorganisms and cause allergies in humans. The common occurrence of multi-species infestations and the fact that it is difficult to identify and discriminate Liposcelis spp. make accurate, rapid detection and discriminatory tools absolutely necessary for confirmation of their identity. In this study, PCR primers and probes specific to different Liposcelis spp. were designed based on nucleotide sequences of the cytochrome oxidase 1 (CO1) gene. Primer sets ObsCo13F/13R, PeaCo15F/14R, BosCO7F/7R, BruCo5F/5R, and DecCo11F/11R were used to specifically detect Liposcelis obscura Broadhead, Liposcelis pearmani Lienhard, Liposcelis bostrychophila Badonnel, Liposcelis brunnea Motschulsky and Liposcelis decolor (Pearman) in multiplex endpoint PCRs, which amplified products of 438-, 351-, 191-, 140-, and 87-bp, respectively. In multiplex TaqMan qPCR assays, orange, yellow, red, crimson and green channels corresponding to reporter dyes 6-ROXN, HEX, Cy5, Quasar705 and 6-FAM specifically detected L. obscura, L. brunnea, L. bostrychophila, L. pearmani and L. decolor, respectively. All developed primer and probe sets allowed specific amplification of corresponding targeted Liposcelis species. The development of multiplex endpoint PCR and multiplex TaqMan qPCR will greatly facilitate psocid identification and their management. The use of APCs will streamline and standardize PCR assays. APC will also provide the opportunity to have all positive controls in a single tube, which reduces maintenance cost and labor, but increases the accuracy and reliability of the assays. These novel methods from our study will have applications in pest management, biosecurity, quarantine, food safety, and routine diagnostics.

Efficacy of Methyl Bromide for Control of Different Life Stages of Stored-Product Psocids

The psocid species Liposcelis paeta Pearman, Liposcelis entomophila (Enderlein), Liposcelis decolor (Pearman), Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae), and Lepinotus reticulatus Enderlein (Psocoptera: Trogiidae) were evaluated in laboratory bioassays to determine their susceptibility to six concentrations of methyl bromide (0.027, 0.113, 0.280, 0.393, 0.452, and 0.616 g/m3) after 48 h of exposure at 27.5°C. The life stages that were evaluated were adults (for all species), nymphs (for all species except Lep. reticulatus), and eggs (for L. entomophila, L. decolor, and L. bostrychophila). Adults and nymphs were very susceptible, and complete mortality was recorded at concentrations between 0.027 and 0.280 g/m3. In contrast, eggs were by far more tolerant than adults and nymphs for all species tested. At 0.027 g/m3, mortality did not exceed 53%, while survival was high even at 0.113 g/m3. Complete (100%) egg mortality was recorded at 0.393 g/m3 for L. decolor and at 0.452 g/m3 for L. entomophila and L. bostrychophila; concentrations estimated to give 99% mortality for eggs of these three species were 0.710, 1.044, and 0.891 g/m3, respectively. These results show that stored-product psocids are susceptible to methyl bromide, but concentrations of ≥0.452 g/m3 should be used to control all life stages.

Evaluation of Potential Attractants for Six Species of Stored-Product Psocids (Psocoptera: Liposcelididae, Trogiidae)

Psocids have emerged as worldwide pests of stored commodities during the past two decades, and are difficult to control with conventional management tactics such as chemical insecticides. Therefore, it is necessary to investigate alternative management strategies, such as the use of attractants for monitoring and controlling psocids, which can be incorporated into integrated pest management programs for psocids. Using a two-choice pitfall test, we studied the response of adults of different ages and sexes of Liposcelis entomophila (Enderlein) (Psocoptera: Liposcelididae), Liposcelis paeta Pearman, Liposcelis decolor (Pearman), Liposcelis brunnea Motschulsky, Liposcelis corrodens (Heymons), and Lepinotus reticulatus Enderlein (Psocoptera: Trogiidae) to volatiles from different potential attractants including grains, grain-based oils, brewer's yeast, wheat germ, and commercially available kairomone lures. For all species tested, sex and age did not have a major influence on response to the different potential attractants. Brewer's yeast most consistently elicited the strongest response for psocids, but this response frequently was not different from that to wheat germ and wheat germ oil. The percentage response to brewer's yeast varied among the psocid species tested: L. decolor (73-78%), L. entomophila (62-73%), L. brunnea (64-68%), L. paeta (42-57%), Lep. reticulatus (40%), and L. corrodens (15-19%). Two psocids species (L. corrodens and Lep. reticulatus) had low responses to all the potential attractants evaluated compared with the other four species. These results show there is high potential for using these attractants in a psocid-monitoring program.

Mining genes involved in insecticide resistance of Liposcelis bostrychophila Badonnel by transcriptome and expression profile analysis

BACKGROUND

Recent studies indicate that infestations of psocids pose a new risk for global food security. Among the psocids species, Liposcelis bostrychophila Badonnel has gained recognition in importance because of its parthenogenic reproduction, rapid adaptation, and increased worldwide distribution. To date, the molecular data available for L. bostrychophila is largely limited to genes identified through homology. Also, no transcriptome data relevant to psocids infection is available.

METHODOLOGY AND PRINCIPAL FINDINGS

In this study, we generated de novo assembly of L. bostrychophila transcriptome performed through the short read sequencing technology (Illumina). In a single run, we obtained more than 51 million sequencing reads that were assembled into 60,012 unigenes (mean size = 711 bp) by Trinity. The transcriptome sequences from different developmental stages of L. bostrychophila including egg, nymph and adult were annotated with non-redundant (Nr) protein database, gene ontology (GO), cluster of orthologous groups of proteins (COG), and KEGG orthology (KO). The analysis revealed three major enzyme families involved in insecticide metabolism as differentially expressed in the L. bostrychophila transcriptome. A total of 49 P450-, 31 GST- and 21 CES-specific genes representing the three enzyme families were identified. Besides, 16 transcripts were identified to contain target site sequences of resistance genes. Furthermore, we profiled gene expression patterns upon insecticide (malathion and deltamethrin) exposure using the tag-based digital gene expression (DGE) method.

CONCLUSION

The L. bostrychophila transcriptome and DGE data provide gene expression data that would further our understanding of molecular mechanisms in psocids. In particular, the findings of this investigation will facilitate identification of genes involved in insecticide resistance and designing of new compounds for control of psocids.

Biology and management of psocids infesting stored products

Previously regarded as minor nuisance pests, psocids belonging to the genus Liposcelis now pose a major problem for the effective protection of stored products worldwide. Here we examine the apparent biological and operational reasons behind this phenomenon and why conventional pest management seems to be failing. We investigate what is known about the biology, behavior, and population dynamics of major pest species to ascertain their strengths, and perhaps find weaknesses, as a basis for a rational pest management strategy. We outline the contribution of molecular techniques to clarifying species identification and understanding genetic diversity. We discuss progress in sampling and trapping and our comprehension of spatial distribution of these pests as a foundation for developing management strategies. The effectiveness of various chemical treatments and the availability and potential of nonchemical control methods are critically examined. Finally, we identify research gaps and suggest future directions for research.

Strong resistance to phosphine in the rusty grain beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae): its characterisation, a rapid assay for diagnosis and its distribution in Australia

BACKGROUND

The recent development of very high resistance to phosphine in rusty grain beetle, Cryptolestes ferrugineus (Stephens), seriously threatens stored-grain biosecurity. The aim was to characterise this resistance, to develop a rapid bioassay for its diagnosis to support pest management and to document the distribution of resistance in Australia in 2007-2011.

RESULTS

Bioassays of purified laboratory reference strains and field-collected samples revealed three phenotypes: susceptible, weakly resistant and strongly resistant. With resistance factors of > 1000 × , resistance to phosphine expressed by the strong resistance phenotype was higher than reported for any stored-product insect species. The new time-to-knockdown assay rapidly and accurately diagnosed each resistance phenotype within 6 h. Although less frequent in western Australia, weak resistance was detected throughout all grain production regions. Strong resistance occurred predominantly in central storages in eastern Australia.

CONCLUSION

Resistance to phosphine in the rusty grain beetle is expressed through two identifiable phenotypes: weak and strong. Strong resistance requires urgent changes to current fumigation dosages. The development of a rapid assay for diagnosis of resistance enables the provision of same-day advice to expedite resistance management decisions.

Phosphine resistance in Tribolium castaneum and Rhyzopertha dominica from stored wheat in Oklahoma

Phosphine gas, or hydrogen phosphide (PH3), is the most common insecticide applied to durable stored products worldwide and is routinely used in the United States for treatment of bulk-stored cereal grains and other durable stored products. Research from the late 1980s revealed low frequencies of resistance to various residual grain protectant insecticides and to phosphine in grain insect species collected in Oklahoma. The present work, which used the same previously established discriminating dose bioassays for phosphine toxicity as in the earlier study, evaluated adults of nine different populations of red flour beetle, Tribolium castaneum (Herbst), and five populations of lesser grain borer, Rhyzopertha dominica (F.) collected from different geographic locations in Oklahoma. One additional population for each species was a laboratory susceptible strain. Discriminating dose assays determined eight out of the nine T. castaneum populations, and all five populations of R. dominica, contained phosphine-resistant individuals, and highest resistance frequencies were 94 and 98%, respectively. Dose-response bioassays and logit analyses determined that LC99 values were approximately 3 ppm for susceptible and 377 ppm for resistant T. castaneum, and approximately 2 ppm for susceptible and 3,430 ppm for resistant R. dominica. The most resistant T. castaneum population was 119-fold more resistant than the susceptible strain and the most resistant R. dominica population was over 1,500-fold more resistant. Results suggest a substantial increase in phosphine resistance in these major stored-wheat pests in the past 21 yr, and these levels of resistance to phosphine approach those reported for other stored-grain pest species in other countries.

Effectiveness of sulfuryl fluoride for control of different life stages of stored-product psocids (Psocoptera)

With the phase-out and impending ban of methyl bromide, sulfuryl fluoride is among the most promising alternative fumigant insecticides for control of stored-product insect pests. It has been evaluated for control of several stored-product insect pests, but there are few data available on its efficacy for control of stored-product psocids (Psocoptera). We evaluated sulfuryl fluoride for control of different life stages of the psocids Liposcelis paeta Pearman, L. entomophila (Enderlein), L. bostrychophila Badonnel, L. decolor Pearman, and Lepinotus reticulatus Enderlein (Trogiidae) in 48-hr trials at 27.5 degrees C. Adults and nymphs were susceptible to sulfuryl fluoride. Complete (100%) adult and nymphal mortality was recorded at concentrations between 4 and 8 g/m3, except for L. decolor for which all adults were only killed at 24 g/m3. Eggs were tolerant to sulfuryl fluoride. Complete egg mortality was achieved at 24 and 72 g/m3 for L. reticulatus and L. decolor, respectively. Survival of L. paeta eggs was recorded even after exposure to 96 g/m3. Given that the highest United States label concentration for sulfuryl fluoride for a 48-h exposure interval is 31.25 g/m3, our study indicates that high doses and/or longer exposures are needed for complete mortality of eggs of L. decolor and L. paeta. Moreover, the present work suggests that there is considerable variation in efficacy of sulfuryl fluoride for control of different psocid species.

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 heat treatment for disinfestation of concrete grain silos

Field experiments were conducted in 2007 and 2008 to evaluate heat treatment for disinfestations of empty concrete elevator silos. A Mobile Heat Treatment Unit was used to introduce heat into silos to attain target conditions of 50 degrees C for at least 6 h. Ventilated plastic containers with a capacity of 100 g of wheat, Triticum aestivum L., held Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Polyvinyl chloride containers with a capacity of 300 g of wheat held adults of Liposcelis corrodens (Heymons) (Psocoptera: Liposcelididae) and Liposcelis decolor (Pearman), which were contained in 35-mm Petri dishes within the grain. Containers were fastened to a rope suspended from the top of the silo at depths of 0 m (just under the top manhole), 10 m, 20 m, and 30 m (silo floor). When the highest temperature achieved was approximately 50 degrees C for 6 h, parental mortality ofR. dominica and T. castaneum, and both psocid species was 98-100%. Progeny production of R. dominica occurred when there was parental survival, but in general R. dominica seemed less impacted by the heat treatment than T. castaneum. There was 100% mortality of L. corrodens at all depths in the heat treatments but only 92.5% mortality for L. decolor, with most survivors located in the bioassay containers at the top of the silo. Results show wheat kernels may have an insulating effect and heat treatment might be more effective when used in conjunction with sanitation and cleaning procedures.

Mechanisms of phosphine toxicity

Fumigation with phosphine gas is by far the most widely used treatment for the protection of stored grain against insect pests. The development of high-level resistance in insects now threatens its continued use. As there is no suitable chemical to replace phosphine, it is essential to understand the mechanisms of phosphine toxicity to increase the effectiveness of resistance management. Because phosphine is such a simple molecule (PH₃), the chemistry of phosphorus is central to its toxicity. The elements above and below phosphorus in the periodic table are nitrogen (N) and arsenic (As), which also produce toxic hydrides, namely, NH₃ and AsH₃. The three hydrides cause related symptoms and similar changes to cellular and organismal physiology, including disruption of the sympathetic nervous system, suppressed energy metabolism and toxic changes to the redox state of the cell. We propose that these three effects are interdependent contributors to phosphine toxicity.

Efficacy of ozone fumigation against the major grain pests in stored wheat

Field experiments were conducted in steel bins containing 13,600 kg of hard red winter wheat, Triiticum aestivum L. One bin was treated with ozone and the second bin served as a control. Stored grain insects were placed in bins for 1-, 2-, 3-, and 4-d exposure periods in sampling tubes to test ozone concentrations of 0, 25, 50, and 70 parts per million by volume (ppmv). Ozone treatments on eggs and larvae of Plodia interpunctella (Hübner) were not effective, but pupae were more susceptible. Sitophilus oryzae (L.) adults were the most susceptible species with 100% mortality reached after 2 d in all ozone treatments. However, some progeny were produced at all concentrations and exposure periods. Tribolium castaneum (Herbst) adults had 100% mortality only after 4 d at 50 or 70 ppmv. No T. castaneum progeny were produced after 2-4 d at 70 ppmv. For Rhyzopertha dominica (F.), Cryptolestes ferrugineus (Stephens), and Oryzaephilus surinamensis (L.), 100% mortality was never achieved and progeny were produced at all ozone concentrations. Laboratory experiments, testing the effectiveness of ozone in controlling psocids, were conducted in two polyvinyl chloride cylinders each containing 55 kg of hard red winter wheat. Ozone treatment at a concentration of 70 ppmv was highly effective against adult female Liposcelis bostrychophila Badonnel and Liposcelis paeta Pearman after only 1 d of exposure. However, it was not effective against eggs of both species at all exposure periods. Ozonation has potential for the control of some stored grain insect pests on wheat.

Reproductive parameters of the parthenogenetic psocid Lepinotus reticulatus (Psocoptera: Trogiidae) at constant temperatures

We investigated effects of temperature, at 70% RH, on the reproductive parameters of the parthenogenetic psocid Lepinotus reticulatus Enderlein (Psocoptera: Trogiidae). The lowest fecundity (21) was at 35 degrees C and the highest (41) at 27.5 degrees C. At 22.5, 25, and 27.5 degrees C, peak oviposition rates (eggs/female/week) occurred in week 3 and were 4.7, 6.6, and 7.8, respectively; also 51, 57, and 62%, respectively, of all eggs were laid in the first 4 wk. At 30, 32.5, and 35 degrees C, peak oviposition rates occurred in week 2 and were 8.2, 9.0, and 7.4, respectively; 80, 85, and 98%, respectively, of all eggs were laid in the first 4 wk. The longest preoviposition period (4.4 d) was at 22.5 and 25 degrees C, and the longest postoviposition period (13.1 d) was at 22.5 degrees C. Oviposition period and longevity decreased with increasing temperature; at 22.5 degrees C, these parameters were 66 and 83 d, respectively, and at 35 degrees C, they were 18 and 24 d, respectively. Mean weekly oviposition rate increased with temperature and was highest at 32.5 degrees C (5.8 eggs/female/week). At 22.5, 25, 27.5, 30, 32.5, and 35 degrees C, it took 29, 20, 12, 11, 8, and 6 wk, respectively, for all females to die. Intrinsic rate of population increase increased with temperature until 32.5 degrees C (0.128) and then declined. We have developed temperature-dependent equations for preoviposition period, postoviposition period, oviposition period, oviposition rate, and longevity. Reproductive parameters affect population dynamics, and information on these parameters can be used in simulation models to predict L. reticulatus population dynamics to aid in developing effective management strategies.

Efficacy of vaporised ethyl formate/carbon dioxide formulation against stored-grain insects: effect of fumigant concentration, exposure time and two grain temperatures

BACKGROUND

The ethyl formate/carbon dioxide (CO(2)) formulation Vapormate is a rapid-acting fumigant being developed for the control of stored-grain insects. The effects have been investigated of concentration, exposure times of 1, 3, 24 and 72 h and two grain temperatures, 15 and 25 degrees C, on its efficacy against mixed-stage cultures of Sitophilus oryzae (L.) Tribolium castaneum (Herbst) and strongly phosphine-resistant Rhyzopertha dominica (F.) strain QRD569.

RESULTS

High mortalities (> or = 92%) of mixed-stage cultures of all three species were obtained when grain was fumigated with the formulation (193 g m(-3) ethyl formate) for 1 h. Complete control of R. dominica QRD569 and T. castaneum was achieved with 63 and 76 g m(-3) ethyl formate respectively, with exposure for 24 h, whereas mean mortality of S. oryzae was 86% under the same conditions. Mortalities of S. oryzae juvenile stages were significantly lower than adults under the conditions tested, which was due to pronounced tolerance of mid-stage pupae to the fumigant. Reducing grain temperature from 25 to 15 degrees C had no effect on insect mortality.

CONCLUSION

Ethyl formate/CO(2) formulation is highly effective against stored-grain insects over a range of concentrations and exposure times. Efficacious fumigations were conducted in as little as 1 h, and a strongly phosphine-resistant R. dominica strain was readily controlled with the fumigant.

Biorational approaches to managing stored-product insects

Stored-product insects can cause postharvest losses, estimated from up to 9% in developed countries to 20% or more in developing countries. There is much interest in alternatives to conventional insecticides for controlling stored-product insects because of insecticide loss due to regulatory action and insect resistance, and because of increasing consumer demand for product that is free of insects and insecticide residues. Sanitation is perhaps the first line of defense for grain stored at farms or elevators and for food-processing and warehouse facilities. Some of the most promising biorational management tools for farm-stored grain are temperature management and use of natural enemies. New tools for computer-assisted decision-making and insect sampling at grain elevators appear most promising. Processing facilities and warehouses usually rely on trap captures for decision-making, a process that needs further research to optimize.

Changes in phosphine sorption in wheat after storage at two temperatures

BACKGROUND

Wheat can be stored for many months before being fumigated with phosphine to kill insects, so a study was undertaken to investigate whether the sorptive capacity of wheat changes as it ages. Wheat was stored at 15 or 25 degrees C and 55% RH for up to 5.5 months, and samples were fumigated at intervals to determine sorption. Sealed glass flasks (95% full) were injected with 1.5 mg L(-1) of phosphine based on flask volume. Concentrations were monitored for 11 days beginning 2 h after injection. Some wheat samples were refumigated after a period of ventilation. Several fumigations of wheat were conducted to determine the pattern of sorption during the first 24 h.

RESULTS

Phosphine concentration declined exponentially with time from 2 h after injection. Rate of sorption decreased with time spent in storage at either 15 or 25 degrees C and 55% RH. Rate of sorption tended to be lower when wheat was refumigated, but this could be explained by time in storage rather than by refumigation per se. The data from the 24 h fumigations did not fit a simple exponential decay equation. Instead, there was a rapid decline in the first hour, with phosphine concentration falling much more slowly thereafter.

CONCLUSIONS

The results have implications for phosphine fumigation of insects in stored wheat. Both the time wheat has spent in storage and the temperature at which it has been stored are factors that must be considered when trying to understand the impact of sorption on phosphine concentrations in commercial fumigations.

Efficacy of grain protectants against four psocid species on maize, rice and wheat

BACKGROUND

Psocids are emerging pests in stored products, particularly in amylaceous commodities such as grains. Currently, their control is based on the use of fumigants and contact insecticides; however, newer data indicate that psocids are tolerant to insecticides used to control other stored-grain species. This study evaluated the insecticides registered in the USA for use on stored maize, rice and wheat for control of the psocid species Lepinotus reticulatus, Liposcelis entomophila, L. bostrychophila and L. paeta. Mortality of exposed adult females was recorded after 7 and 14 days of exposure, while progeny production was assessed after 30 days of exposure.

RESULTS

On wheat and rice, chlorpyriphos-methyl + deltamethrin was generally more effective against exposed parental adults than spinosad or pyrethrin, while pirimiphos-methyl was more effective on maize than spinosad or pyrethrin. In most cases, progeny production was suppressed in the treated grains. Progeny production was consistently lowest on wheat and rice treated with chlorpyriphos-methyl + deltamethrin and maize treated with pirimiphos-methyl.

CONCLUSIONS

Chlorpyriphos-methyl + deltamethrin and pirimiphos-methyl were the most effective insecticides for all species and commodities. Conversely, efficacy of spinosad or pyrethrum was highly dependent on the psocid species and commodity.