Toxicological and physiological effects of allyl isothiocyanate upon Callosobruchus maculatus

This study aimed at evaluating the toxicity of allyl isothiocyanate (AITC) to adults of Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae) and its effects upon oviposition rate, population development, respiration rate, and dry mass loss in cowpea beans. The toxicity of AITC was determined by applying lethal concentrations (LC) of the compound, whereas the mortality curves were drawn by utilizing increasing concentrations of AITC (from 5.0 to 13.33 mL m⁻³ of grains). Population development was assessed through oviposition, progeny and both daily and accumulated emergence at sublethal concentrations (LC₁ = 3.81 mL m⁻³, LC ₁₀ = 5.71 mL m⁻³, LC ₃₀ = 7.67 mL m⁻³, and LC ₅₀ = 9.41 mL m⁻³). Furthermore, the loss of dry mass in grains and the respiration rate of adults when exposed to AITC (LC₁, LC₁₀, LC₃₀, and LC₅₀) were withal appraised. The values of LC ₅₀ and LC ₉₅ to adults of C. maculatus were of 9.41 and 17.85 mL m⁻³ of grains, respectively. At sublethal concentrations of AITC, the respiration oviposition, and emergence rates declined. The fumigant agent also prevented mass loss in cowpea beans. On account of that, it is safe to say that the compound has significant potential for controlling C. maculatus, inhibiting its development in storage conditions.     

Fumigant toxicity of allyl isothiocyanate to populations of the red flour beetle Tribolium castaneum

The phasing out of methyl bromide as a fumigant, the phosphine resistance problems in stored product insect-pests, and the ever-growing concerns with human health and environmental safety have been guiding the search of alternative fumigants. Allyl isothiocyanate (AITC) is the main component of mustard oil with reported pesticide activity and potential as a fumigant of stored foodstuffs. The fumigant toxicity of AITC was assessed in adults of 18 populations of the red flour beetle Tribolium castaneum (Coleoptera: Tenebronidae). These populations were all susceptible to AITC with negligible variation among them. Two of these populations were further used to test the AITC susceptibility of eggs, larvae (early and late instars), and pupae of T. castaneum. All of the developmental stages of both populations were similarly susceptible to AITC. No cross-resistance between phosphine and AITC was observed. Despite the significant variation in body mass, respiration rate, and fitness among the populations of T. castaneum, they were not correlated with AITC susceptibility. Larvae and adult malformations were observed when larvae and pupae were exposed to AITC. These results show the potential of AICT as an alternative fumigant against stored product insects.     

Phosphine resistance in Brazilian populations of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Phosphine resistance was assessed in adults of 22 Brazilian populations of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). The concentration-mortality bioassays for the detection of phosphine resistance followed the FAO standard method. Twenty populations of S. zeamais were resistant to phosphine and the resistance ratios at the LC₅₀ ranged from 1.1- to 86.6-fold. This is the first report of phosphine resistance in populations of S. zeamais in Brazil, where previous surveys did not detect resistance in this species. There was significant variation in respiration rate (CO₂ production) among the populations (P < 0.05). Respiration rate was significantly inversely correlated with phosphine resistance for this species (P < 0.05). The populations with lower respiration rates showed higher levels of phosphine resistance, suggesting that the lower respiration rate is associated with the physiological basis of phosphine resistance due to reduced fumigant uptake.     

Control failure and insecticides resistance in populations of Rhyzopertha dominica (Coleoptera: Bostrichidae) from Colombia

The lesser grain borer Rhyzopertha dominica is a serious pest that causes significant economic damages in stored grains. The presence of this pest is mainly controlled using a small number of insecticides increasing risks of compromising the control efficacy due to the selection of resistant populations. Here, the control failure and potential resistance to pyrethroid and organophosphate insecticides frequently used for the control of R. dominica in Colombia were assessed. Concentration–mortality bioassays with synergized and unsynergized insecticides were used to assess potential metabolic-based pyrethroids resistance mechanisms. Based on the field recommended doses, the results revealed that while the pirimiphos-methyl is still efficient against R. dominica, both type I (i.e., bifenthrin) and type II (i.e., deltamethrin) pyrethroids presented control failure and their insecticidal activity was compromised. Although no differences in susceptibilities between the populations were found for the bifenthrin insecticide, the LC₅₀s of Ibagué (1.83 μl/gr of grains) and El Espinal (1.67 μl/gr of grains) populations were higher than the recommended rate. Furthermore, significant differences in susceptibility to deltamethrin resulted in resistance ratios RR₅₀ > 32-fold and RR₉₅ > 188-fold between the least (El Espinal) and the most (Ibagué) susceptible populations. Moreover, when synergized, the toxicity of deltamethrin was enhanced but resistance ratios kept at high levels (RR₅₀ > 11-fold and RR₉₅ > 40-fold) indicating possible existence of simultaneous metabolic and altered action-site mechanisms of resistance to pyrethroids in Colombian populations. Our results highlight the urgent need for nationwide monitoring of insecticides control failure and resistance in stored pests for better management schemes.     

Base-line susceptibility of field populations of Rhyzopertha dominica (F.) to spinosad in Australia

Spinosad has recently been registered in several countries for long-term protection against a range of stored grain insects including the lesser grain borer, Rhyzopertha dominica (F.). The potential for development of resistance to spinosad is demonstrated by the existence of resistance in many insect pests of agriculture. The aim of this study was to determine the base-line susceptibility of R. dominica to spinosad, to provide a basis for future resistance monitoring. Eighteen insect populations of R. dominica were collected from field storage sites across four States within Australia, and exposed to a range of spinosad rates, including its current registered rate of 1 mg kg⁻¹ (1 ppm). Base-line susceptibility was assessed based on adult mortality and production of F₁ adults. Comparison of LC₅₀ and LC_99.9 indicated the existence of low level of variation among the tested R. dominica populations, in their susceptibility to spinosad. For adults, there was a narrow range of LC₅₀ values with the highest (0.027 ppm) being 2.5 × the lowest (0.011 mg kg⁻¹). Similarly, LC_99.9 values showed a narrow range with the highest (0.36 mg kg⁻¹) being 3.6 × the lowest (0.10 mg kg⁻¹). For adult progeny produced in spinosad treated grain, there was a narrow range of LC₅₀ values with the highest (0.025 mg kg⁻¹) being 5 × the lowest (0.004 mg kg⁻¹) and the highest LC_99.9 values (0.67 mg kg⁻¹) being 5 × the lowest LC_99.9 (0.13 mg kg⁻¹). Based on the data generated from this study, we recommend a dose of 1 mg kg⁻¹(1 ppm) to be used to discriminate between susceptible and resistant populations for future resistance monitoring programs.     

Ozone as a management alternative against phosphine-resistant insect pests of stored products

This study was carried out to assess ozone toxicity to 16 populations of Tribolium castaneum (Herbst), 11 populations of Rhyzopertha dominica (F.) and nine populations of Oryzaephilus surinamensis (L.) collected from six regions of Brazil. These populations were also used to test if there is cross-resistance to ozone and phosphine. The relationship between susceptibility to ozone and respiration rate, and associated fitness costs were also evaluated. The instantaneous population growth rate (r_i), CO₂ production and mean insect body mass of each population were measured. Ozone toxicity was determined using time-response bioassays at the dosage rate of 150 ppm ozone in a continuous flow of 2 L min⁻¹. All of the populations were susceptible to ozone and there was no cross-resistance to ozone and phosphine. The populations of each species differed in respiration rate and body mass, but there was no significant association between respiration rate or body mass and susceptibility to ozone, as was also the case for the instantaneous rate of population increase (r_i). As none of the populations showed resistance to ozone, regardless of their susceptibility to phosphine, ozone is a potential alternative for phosphine resistance management in the insect species evaluated in this study.     

Mobility parameters of Tribolium castaneum and Rhyzopertha dominica populations with different susceptibility to phosphine

Phosphine (PH₃) is the most commonly used fumigant to protect stored products from arthropod infestations worldwide. Our knowledge about the behavioral differences between phosphine-resistant and -susceptible stored product pest populations is limited. This study evaluated differences in mobility and behavior of populations of two major stored product insects, Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.), which have different susceptibility to phosphine. In this regard, laboratory bioassays in Petri dish arenas were designed to determine if phosphine resistance has an impact on the walking and mobility behavior of adult beetles of both species. Results indicated that there were significant differences between resistant and susceptible populations for both species. Regarding velocity, R. dominica susceptible individuals moved faster than resistant ones. However, the resistant population showed reduced activity for several parameters tested compared to the susceptible population. Similar trends were also noted for T. castaneum. Knowledge of these parameters should be further utilized in management tactics, as resistant populations may behave in a different way in key management indicators such as trapping and sampling, as compared with susceptible ones.     

Field validation of phosphine efficacy on the first recorded resistant strains of Sitophilus granarius and Tribolium castaneum from the Czech Republic

This study first estimated the current state of phosphine sensitivity (using a knock-down/KT₁₀₀/Degesch kit) in Sitophilus granarius (23 strains) and Tribolium castaneum (8 strains) in Czech Republic grain stores. The resistance of S. granarius (21.7% resistant strains; coefficient of resistance KT₁₀₀ ranged from 0.5 to 2.3 among strains) was substantially lower and less frequent than that of T. castaneum (87.5% resistant strains; coefficient of resistance KT₁₀₀ ranged from 0.9 to 52.5 among strains). The phosphine efficacy of the laboratory and field (i.e., resistant) pest strains was validated during commercial fumigation when suboptimal tarpaulin sealing resulted in low-concentration phosphine exposure (Ct products ranged from 5.9 to 7.4 g*hr/m³). Although even low-dose fumigation led to 100% adult mortality of both laboratory and field strains of S. granarius and laboratory strains of T. castaneum, the mortality of the field strain of T. castaneum ranged from 47% to 95%. Larval emergence from the fumigated commodity samples with pest eggs was zero or near zero for laboratory strains, while 1.3–6.0 (S. granarius) and 63.7–80.00 (T. castaneum) field-strain larvae emerged per sample (100 g). This study shows that although a high proportion of the tested pest populations were still sensitive, several T. castaneum populations showed an elevated level of resistance that may decrease field fumigation efficacy, especially under suboptimal phosphine dosage conditions.     

Efficacy of ozone against adults and immature stages of phosphine susceptible and resistant strains of Rhyzopertha dominica

Ozone was investigated as a potential alternative to control phosphine resistant strains of the lesser grain borer, Rhyzopertha dominica (F.). The efficacy of 0.21 and 0.42 g/m³ concentrations of ozone against one phosphine-susceptible laboratory and two phosphine-resistant field strains of R. dominica was evaluated. Vials holding 20 adults with 0 and 10 g of wheat were exposed to each ozone concentration for up to 24 h to estimate lethal doses required for 50 (LD₅₀) and 99% (LD₉₉) mortality. After ozone exposure, mortality was assessed 5 d later. There were no significant differences between LD₅₀ values of the samples exposed to 0.21 and 0.42 g/m³, regardless of strains and presence or absence of wheat. The small amount of wheat (10 g) affected efficacy at 0.21 g/m³, but showed a non-significant effect at 0.42 g/m³. Ozone tends to react with active sites on the surface of wheat kernels prior to reaching an effective lethal concentration for insects. High ozone concentration in the supply air reduced the time to saturate all active sites and ensured that lethal levels of free ozone were available to kill insects.Ozone successfully suppressed the adult progeny production for all tested strains. Emergence of adults from eggs of all three strains was reduced by 96.3–100% only after 72 h exposure to an ozone concentration of 0.42 g/m³. At the same ozone concentration, emergence of adults from young and old larvae was reduced by 97.1–99.7% after a 24 to 34 h exposure. However, reduction in emergence of adults from ozone exposed pupae at 10 h varied among the strains and ranged from 32.8 to 96.6%. After 2 and 6 h of exposure the reduction in emergence of adults from pupae ranged from 19.6 to 76.5%.     

Processing and protein-fractionation characteristics of different polymeric membranes during filtration of skim milk at refrigeration temperatures

Serum protein concentrates (SPCs) were generated from reconstituted skim milk (3.2% protein) using lab-scale tangential-flow filtration at 3–4 °C. The influence of membrane type on process performance (e.g., permeate flux) and protein-enrichment (e.g., protein profile) was assessed with polyvinylidene-difluoride membranes (0.1 μm and 0.45 μm pore-size), and a polyethersulfone membrane (1000 kDa cut-off). The 1000 kDa membrane exhibited the highest starting flux (6.7 L m⁻² h⁻¹), followed by the 0.1 μm (5.4 L m⁻² h⁻¹) and 0.45 μm (4.8 L m⁻² h⁻¹) membranes. Flux decreased by >40% during filtration with the 1000 kDa and 0.1 μm membranes, while the decrease was lower (<20%) with the 0.45 μm membrane. β-Casein comprised >97% of casein in SPCs from the 0.1 μm and 1000 kDa membranes. SPCs from the 0.45 μm membrane had higher β-casein:α_s-casein ratios than the feed and higher levels of minor whey proteins (e.g., lactoferrin) relative to the other SPCs.     

A rapid assay for the detection of resistance to phosphine in the lesser grain borer,Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Resistance to the fumigant phosphine in stored product insect pests is a global problem. Diagnosis of resistance relies on a bioassay developed by the FAO that involves a mortality assessment after 20-h fumigation of a pest population at a discriminating concentration of gas, followed by a 14-day post fumigation assessment. This bioassay is impractical for monitoring and early detection of phosphine resistance in routine pest management. We utilized the procedure of a commercial resistance detection test kit for rapid detection in field populations of lesser grain borer, Rhyzopertha dominica (F.). We established a knockdown effect of either susceptible or resistant insects by exposing them to a high concentration of phosphine. We assessed the relationship between adult knockdown times and the FAO method for 18 beetle populations utilizing knockdown criteria for a single beetle in a chamber, or for 50% or 100% knockdown times for groups of beetles, exposed to 3000 ppm of phosphine. We also determined the most effective concentrations that would elicit the quickest knockdown while estimating the recovery times from exposure. Results suggest that a KT₁₀₀ test was better than the KT₅₀ and the KT_single tests. Based on the responses of susceptible populations, we established that a KT₁₀₀ of approximately 18 min can be used as a viable knockdown time to distinguish a susceptible from a resistant populations. Higher concentrations of phosphine significantly elicited a quicker recovery in strongly resistant populations compared to susceptible populations. These findings have potential for developing a robust commercial kit for practical phosphine resistance detection in populations of R. dominica by commercial fumigators, and could be incorporated in a resistance management program.     

Toxicity of Schizonpeta multifida essential oil and its constituent compounds towards two grain storage insects

BACKGROUND: The essential oil derived from the flowering aerial parts of Schizonpeta multifida was investigated for insecticidal activity against two grain storage insects, maize weevil (Sitophilus zeamais) and red flour beetle (Tribolium castaneum). RESULTS: The main constituents of the essential oil were menthone (40.34%) and pulegone (26.87%), followed by D ‐limonene (5.81%) and isomenthone (5.14%). Bioactivity‐directed chromatographic separation on repeated silica gel columns led to the isolation of menthone and pulegone. Pulegone showed pronounced contact toxicity against S. zeamais and T. castaneum adults (7 day LD₅₀ = 14.46 and 1.55 µg per adult respectively) and was more toxic than menthone (7 day LD₅₀ = 33.47 and 2.67 µg per adult respectively), while the crude essential oil had 7 day LD₅₀ values of 30.17 and 2.75 µg per adult respectively. Pulegone also displayed strong fumigant toxicity against S. zeamais and T. castaneum adults (7 day LC₅₀ = 3.47 and 11.56 mg cm^?3 respectively) and was again more toxic than menthone (7 day LC₅₀ = 10.32 and 31.25 mg cm^?3 respectively), while the crude essential oil had 7 day LC₅₀ values of 8.33 and 26.41 mg cm^?3 respectively. CONCLUSION: The essential oil of S. multifida and its two main components may have potential to be developed as new natural fumigants/insecticides for the control of stored product insects. Copyright © 2011 Society of Chemical Industry     

Enhanced antimicrobial activity of nisin in combination with allyl isothiocyanate against Listeria monocytogenes,Staphylococcus aureus,Salmonella Typhimurium and Shigella boydii

This study was designed to evaluate the synergistic antimicrobial effect of nisin and allyl isothiocyanate (AITC) against Listeria monocytogenes, Staphylococcus aureus, Salmonella Typhimurium and Shigella boydii. The synergistic interactions between nisin and AITC were observed against all foodborne pathogens, showing the fractional inhibitory concentrations <1. The populations of L. monocytogenes and S. aureus at the combined treatment of nisin and AITC were decreased to below 1 log CFU mL^?1 after 10‐h incubation at 37 °C. The changes in fatty acid profiles of all strains were substantially influenced by nisin alone and the combined treatment of nisin and AITC. A good agreement was observed among cell viability, membrane permeability and depolarisation activity in response to nisin and AITC. The results suggest that nisin and AITC as synergistic inhibitors could be an effective approach to achieve satisfactory antimicrobial activity against a wide range of foodborne pathogens.     

Ozone toxicity to Sitophilus zeamais (Coleoptera: Curculionidae) populations under selection pressure from ozone

Two populations of Sitophilus zeamais (Coleoptera: Curculionidae) were subjected to selection pressure with ozone (O₃), and the possibility of acquiring resistance to O₃ was investigated. The pattern of locomotion and the rate of respiration were evaluated following each selection cycle. Two source populations were used in the study: one was a mixture composed of 30 populations (MP), and the other was composed of the population that was the least susceptible to O₃ among these 30 populations (LSP). The beetles from each source population experienced selection cycles with O₃ using the lethal time for 80% (LT₈₀) of the insect population from each generation. The O₃ toxicity (50 ppm at a continuous flow rate of 2 L min⁻¹) to each generation was calculated using time-response bioassays. The locomotor pattern (distance traveled, resting period, and walking speed) and the respiratory rate (CO₂ production) were also evaluated. The S. zeamais populations that were subjected to successive cycles of selection with O₃ did not acquire resistance to O₃, and the pattern of locomotion and the rate of respiration did not change following the selection cycles with O₃.     

Individual and combined effects of insecticides,inert dusts and high temperatures on Callosobruchus maculatus (coleoptera: Chrysomelidae)

In this study individual and combined effects of some chemical and physical factors including cypermethrin, dichlorvos, ash, kaolin and high temperatures were assessed on adults of cowpea seed beetle Callosobruchus maculatus (F.) at laboratory conditions. The adults were exposed to the studied factors on concrete arenas prepared in plastic Petri dishes. Twenty up to 24 h old adults were released in each Petri dish, and their mortality was recorded 72 h after treatment. The LC₂₅ values of the insecticides, LD₂₅ values of the inert dusts and LTi₂₅ values of high temperatures were estimated and used for determining combination effects of the two factors. To determine combination effects of three factors, LC₁₅ values of insecticides, LD₁₅ values of inert dusts and LTi₁₅ values of high temperatures were estimated and used in the bioassays. The LC₅₀ and LD₅₀ values for cypermethrin, dichlorvos, ash and kaolin were 1286.96 mg a. i./L, 1350.55 mg a. i./L, 36.64 g/m² and 45.18 g/m², respectively. The LTi₅₀ values at 45, 48, 50, 52 and 55 °C were 34, 29, 18, 11 and 8 min, respectively. The results indicated that the effect of simultaneous exposure to cypermethrin, high temperatures and ash or kaolin was significantly more than sum of individual effects of these factors. It means the effects of cypermethrin, high temperatures and inert dusts were synergized by each other. If similar treatments performed at larger scales give comparable results, it may be concluded that reduced dosage of cypermethrin, high temperatures and ash or kaolin combinations would be effective alternative control methods and can be used in cowpea seed beetle management programs.     

Face or flee? Fenitrothion resistance and behavioral response in populations of the maize weevil, Sitophilus zeamais

Insect survival in the presence of contact insecticides may be through physiological mechanisms or avoidance of contact with the compound. Curiously, although the first alternative is the object of frequent attention, the second is often neglected, but both may lead to insecticide resistance. Preliminary evidence for both physiological and behavioral resistance to pyrethroids has been obtained for a few strains of the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). Here we carried out a more comprehensive survey using 15 populations of S. zeamais, by examining a long-used but relatively little studied organophosphate - fenitrothion, recording not only physiological resistance, but also the behavioral responses to exposure. Physiological resistance to fenitrothion among populations of S. zeamais reached low to moderate levels (ranging from 0.9 to 14.1× at the LC₅₀), an increase in resistance levels compared with previous studies. Fenitrothion-induced behavioral avoidance varied among populations, particularly regarding insecticide irritability (i.e., avoidance after contact with fenitrothion), but the behavioral responses observed were mainly stimulus-independent. However, there was no correlation between physiological and behavioral resistance to fenitrothion in S. zeamais populations. Both survival strategies to fenitrothion - facing or fleeing the insecticide exposure, were observed and may co-occur in a single population, emphasizing the need of assessing both responses and their relative importance in designing management programs against stored-product insects.     

Deleterious effects of Myracrodruon urundeuva leaf extract and lectin on the maize weevil,Sitophilus zeamais (Coleoptera,Curculionidae)

Deterioration and degradation of grains by storage insect pests lead to economic losses of several billion dollars and affect food security. Sitophilus zeamais is responsible for pre- and post-harvest damages to maize. The high toxicity of synthetic insecticides and the development of resistance by insects to the chemicals currently used stimulate the investigation of plant-derived insecticides as new alternatives for pest control. In this study, we report the effects of diets containing Myracrodruon urundeuva leaf extract (10–150 mg/g) and lectin (MuLL; 3–150 mg/g) on the survival, feeding, and nutrition of the storage pest S. zeamais. The digestive enzyme activity in gut extracts from the insects reared on the leaf extract (25 mg/g) or MuLL (15 mg/g) diets was also evaluated. The leaf extract induced mortality (LC₅₀: 72.4 mg/g), while MuLL (30–150 mg/g) exerted strong feeding deterrence. The leaf extract and MuLL promoted the loss of biomass, as reflected in the negative values for relative biomass gain rates and efficiencies in converting ingested food. Protease, trypsin-like, acid phosphatase, and amylase activities in the insects reared on leaf extract or MuLL diets were significantly (P < 0.05) lower than those in the control insects. MuLL ingestion also significantly reduced (P < 0.05) endoglucanase and alkaline phosphatase activities. In conclusion, the leaf extract and MuLL have the potential for S. zeamais control by killing adults and preventing the use of a food source, respectively. The deleterious effects of the extract and lectin on S. zeamais may be linked to enzyme inhibition and consequent suppression of digestive processes.     

Chemical composition and bioactivity of peel oils from Citrus aurantiifolia and Citrus reticulata and enantiomers of their major constituent against Sitophilus zeamais (Coleoptera: Curculionidae)

Peel oils from Citrus aurantiifolia and C. reticulata cultivated in northeastern Brazil were analyzed using gas chromatography with flame ionization detection and gas chromatography-mass spectrometry. The insecticidal activity of the oils and both enantiomeric forms of the main constituent – limonene [(R)-(+)-limonene and (S)-(−)-limonene] – was evaluated against Sitophylus zeamais under laboratory condition. The results were compared with deltamethrin as the positive control. Chromatographic analysis of the Citrus oils demonstrated limonene to be main constituent, accounting for 38.9% of the C. aurantiifolia oil and 80.2% of the C. reticulata oil. Peel oil from C. reticulata proved to be more toxic to S. zeamais adults in the contact, ingestion and fumigant tests (LC₅₀ = 71.18 μL mL⁻¹, 1.52 μL g⁻¹ and 41.92 μL L⁻¹ of air, respectively) than the C. reticulata oil. A non-significant different was found between (R) and (S)-limonene in the contact and fumigant tests. However, (R)-limonene exhibited greater toxicity against S. zeamais than the (S)-limonene during the ingestion assay. Deltamethrin was much more toxic in the contact and ingestion bioassays than the Citrus oils and the two enantiomeric forms of limonene. The C. reticulata oil was more repellent than C. aurantiifolia. In the repellency test, S zeamais adults were more susceptible to (S)-limonene than (R)-limonene. The results of the present study suggest that these Citrus oils and the two enantiomeric forms of limonene have toxic effects on S. zeamais in different ways (i.e., via the cuticle, digestive system and respiratory system) as well as a behavioral effect (repellency).     

TcYellow-h基因过表达参与介导赤拟谷盗对磷化氢的抗性形成

以赤拟谷盗为研究对象,旨在明确表皮相关基因TcYellow-h在害虫磷化氢抗性形成过程中的作用。序列分析结果表明TcYellow-h编码468个氨基酸,其拥有一段保守的MRJP(major royal jelly protein)特征序列;RT-qPCR结果显示,TcYellow-h在赤拟谷盗外周组织器官(头、胸、腹的表皮、翅和足)中表达水平较高,在内部器官(脂肪体、肠道、马氏管)中的表达量相对较低;此外,在不同地理种群中,TcYellow-h的表达量随磷化氢抗性水平的增加呈上升趋势;注射dsRNA能有效抑制TcYellow-h基因的表达,沉默效率为73.0%;干扰抗性种群(GD)TcYellow-h基因的表达后再用LC₃₀的磷化氢处理试虫,赤拟谷盗的死亡率显著上升至64.4%。本研究显示赤拟谷盗表皮相关基因Yellow-h的过表达与磷化氢的抗性形成相关。     

Development of resistance in stored grain pest,Trogoderma granarium (Everts) against deltamethrin and its effective control by synergistic toxicity of bifenthrin and chlorpyrifos

The current investigation was conducted to estimate the resistance level against deltamethrin in fourth and sixth instar larvae of Trogoderma granarium collected from wheat storage warehouses of Dera Ghazi Khan (DGK), Okara (OKR) and Gujranwala (GUW). Results showed that the fourth and sixth instar larvae of collected strains warehouses moderately resistant to deltamethrin compared with the same developmental stages of insecticide susceptible laboratory strain (LAB-S). Efficacies of bifenthrin, chlorpyrifos and their various combinations were analyzed against fourth and sixth instar larvae of different strains of pest populations to minimize the development of resistance against deltamethrin. LC_50s of bifenthrin against fourth and sixth instar larvae of all the four populations were recorded at low concentrations compared to deltamethrin. The LC₅₀ values of bifenthrin against fourth instar larvae of LAB-S, DGK, OKR and GUW populations were 359.32, 416.58, 524.01 and 598.91 ppm, respectively, while these values were 204.30, 262.98, 301.89 and 355.22 ppm against sixth instar larvae of those populations, respectively. Chlorpyrifos was found to be the most effective insecticide compared to bifenthrin and deltamethrin. The LC₅₀ values of chlorpyrifos were 189.33, 305.37, 376.30 and 459.15 ppm against fourth instar larvae of LAB-S, DGK, OKR and GUW populations, respectively, whereas for sixth instar larvae those values were 98.24, 129.61, 163.43 and 230.74 ppm, respectively. Various combinations of bifenthrin and chlorpyrifos viz., 1:1, 2:1, 3:1, 1:2 and 1:3 were also tested. Based on the values of LC₅₀ and relative toxic unit, 1:3 combination was observed as the most effective among all combinations. The LC₅₀ values of fourth instar larvae of all the four populations against each insecticide and their combinations were recorded at high concentration compared to that of sixth instar larvae. Results of current investigation need to be considered in present stored grain insect pest control program of warehouses in Punjab¹.