Efficacy Of Phosphine Research Articles

Revealing the Role of CYP346 Family Genes on Phosphine Resistance in Indian Populations of Tribolium castaneum.

Phosphine resistance in Tribolium castaneum challenges grain storage. This study investigates the impact of cytochrome P450 (CYP) enzymes and CYP346 family genes on phosphine resistance in Indian Tribolium castaneum populations. Seven field populations of T. castaneum were compared with Lab- susceptible population for their resistance to phosphine. The levels of cytochrome P450 enzyme and expression of certain CYP346 family genes were tracked in these populations. The highly resistant Patiala population showed significantly increased CYP450 activity (11.26 ± 0.14 nmol/min/mg protein, 7.41-fold higher) compared to the lab-susceptible population (1.52 ± 0.09 nmol/min/mg protein) when assayed using 8 mM p-nitroanisole as the substrate. The mRNA expression was measured relative to the standard gene RPS18 and revealed significant upregulation of CYP346B1 and CYP346B3 in highly resistant populations Moga and Patiala (CYP346B1: 12.09 ± 2.19 to 21.74 ± 3.82; CYP346B3: 59.097 ± 10.265 to 50.148 ± 8.272). Patiala's CYP346B1 exhibited an impressive 685.76-fold change, and Moga's CYP346B3 showed a 361.893-fold change compared to lab-susceptible. Linear regression confirmed robust fits for each gene (R2: 0.693 to 0.756). Principal component analysis (PCA) demonstrated a strong positive correlation between CYP346 genes expression; and cytochrome P450 activity. Patiala, Moga, and Hapur populations showed conformity, associating higher resistance with increased P450 activity and CYP346 gene expression. Cluster analysis highlighted a potential correlation between CYP346B1, CYP346B2, and CYP346B3 and P450 activity, with Patiala and Moga clustering together. Variability in CYP346B1 and CYP346B3 in strong resistance populations may contribute to adaptation and resistance mechanisms. The study provides insights into specific CYP346 family genes associated with phosphine resistance, emphasizing the intricate interaction between CYP450 detoxifying enzymes, CYP346 family genes, and resistance mechanisms. The upregulation of CYP346 genes suggests a survival advantage for T. castaneum against phosphine, diminishing phosphine's efficacy as a pest control measure.

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.

Efficacy of Phosphine on Different Life Stages of Alphitobius diaperinus and Tenebrio molitor (Coleoptera: Tenebrionidae)

The efficacy of phosphine has been established for numerous major stored product insects. However, data related to the evaluation of the effect of phosphine on Tenebrio molitor L and Alphitobius diaperinus Panzer are limited. The present study aims to evaluate the susceptibility of these species to phosphine by using the following evaluation protocols: (a) all life stages were exposed for 3 days to different concentrations of phosphine, (b) adults were exposed to 3000 ppm until all exposed individuals were immobilized, using the Phosphine Tolerance Test (PTT, Detia Degesch GmbH, Germany), and (c) adults were exposed to 3000 ppm of phosphine for 90 min by again using the PTT protocol. For all series of bioassays, delayed mortality was recorded 7 and 14 d post-exposure. According to our results, 100 ppm for three days was sufficient to kill all life stages, including the eggs, for both species. Alphitobius diaperinus adults were found to be more tolerant than those T. molitor, as noticeable survival was observed, even after 90 min of exposure to 3000 ppm. Our study provides some initial data for the efficacy of short and long exposures of A. diaperinus and T. molitor to phosphine.

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

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

Temporal dynamics of phosphine fumigation against insect pests in wheat storage

Methyl bromide (MBr) fumigant has been phased out globally honouring ‘Montreal Protocol’. However, MBr is still used in India in various commodities for controlling pests as well as international trade requirements. Reports on phosphine fumigant efficacy under different ecological zones in India are scanty. In the present study fumigation trials were conducted in warehouses on 5 Metric-Tons of wheat stacks per replication of a treatment for testing phosphine efficacy against laboratory cultured and warehouse resident population of Tribolium castaneum (Herbst), Sitophilus oryzae (Lin), and Rhyzopertha dominica (Fab). The trials were organized in triplicate including untreated control at FCI warehouses at two locations, Pithoragarh in Uttrakhand and New Delhi, with varying climates. The conventional 56% Aluminium phosphide (AlP) tablet at 2 and 3 tablet/MT, and gas derived from on-site phosphine generator using 77.5% granular formulation at 1.0 and 1.5 g phosphine/m3 was tested at these warehouses against test insects for 7 and 10-days exposure periods for each dosage. Phosphine concentration was monitored every 24 h till end of the exposure periods using gas monitors. No emergence of insects was observed until 60 days after treatment in both the exposure periods using all dosages of phosphine indicating mortality of all life stages of laboratory cultured insects and resident population at both the locations. Phosphine at 1.5 g/m3 was observed as an effective alternative to methyl bromide fumigant for controlling S. oryzae, R. dominica and T castaneum at 250–27 °C and humidity 38–45% with an exposure period of 7-days, with a terminal phosphine concentration of 500–600 ppm. Locational effect was observed for gas loss and phosphine gas concentration. During fumigation, phosphine gas loss was observed to be inversely related with grain moisture and directly related with Ct values.

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.

Locational dynamics of concentration and efficacy of phosphine against pulse beetle, Callosobruchus maculatus (Fab)

Phosphine is considered as an effective substitute to methyl bromide (MB), an ozone depleting fumigant which was phased out honouring ‘Montreal Protocol’. Limited field studies are available on phosphine toxicity against storage insects of pulses under different climatic conditions in India. In the present study phosphine efficacy was investigated against laboratory cultured and field populations of Callosobruchus maculatus by organising field fumigation trials of 5 MT pulse stacks, each in triplicate, under varied climatic conditions. The trials were conducted at three locations, Jaipur for Cicer arietinum (chickpea), Cuttack for Vigna radiata (green gram) and Mumbai for Lathyrus aphaca (yellow pea) using conventional 56% Aluminium phosphide (AlP) tablets (2 tab/MT and 3 tab/MT) application; and gas derived from on-site phosphine generator with 77.5% granular (1.0 g and 1.5 g phosphine/m3) formulations for two exposure periods (7 and 10-days) for each dosage including untreated control. Phosphine gas concentration was monitored daily until the exposure periods using gas monitoring equipment. No emergence of adults was observed until 60 days after treatment indicating 100% insect mortality of both populations (laboratory and field) for both exposure periods using all dosages. The minimum effective phosphine gas concentration for controlling C. maculatus was observed as 300–500 ppm for 7-days exposure using 1.5 g phosphine/m3 depending on climatic conditions. A significant variation was observed in gas concentration monitored during fumigation of pulses at different locations. Average concentration-time (Ct) product for green gram was higher than that of chickpea and yellowpea. The loss of gas concentration was found to be significantly low in yellowpea treated with phosphine at moderately hot and humid climate.

Efficacy of phosphine fumigation for different life stages of Trogoderma inclusum and Dermestes maculatus (Coleoptera: Dermestidae)

Despite the importance of dermestid beetles as targets for stored product protection, including the protection of museum artifacts and animal-based products, there are only a few published reports regarding their susceptibility to phosphine fumigation, in contrast with other major stored product insect species. In the current study, we evaluated phosphine against all life stages of Trogoderma inclusum LeConte, the larger cabinet beetle, and Dermestes maculatus (DeGeer), the hide beetle. There were two series of laboratory bioassays; in the first series the concentrations were 0 (control), 50, 100, 200 and 600 ppm, and in the second series the concentrations were 0 (control), 50, 150, 300, 400, 500 and 600 ppm. Both series were carried out on a 5-day insect exposure protocol. The results for both species clearly indicated that eggs were by far the least susceptible life stage, followed by pupae, while most adults and larvae were killed at the 50-ppm concentration. Concentrations between 300 and 400 ppm could be utilized to provide 100% mortality for both species and all life stages. To our knowledge, our results are the first that have provided data regarding efficacy of phosphine for the control of T. inclusum and D. maculatus. Resource managers can utilize our results to more efficiently target these dermestids with specific concentrations of phosphine, depending on the target life stage.

Efficacy of phosphine and insect penetration ability in ZeroFly® bags

The deltamethrin incorporated woven polypropylene ZeroFly® storage bag is a promising novel technology for grain storage. However, if grain stored in ZeroFly bags gets infested and has to be fumigated using phosphine (PH3), data on the effectiveness of such treatments are needed. Additionally, obtaining field data on ability of stored-product insect pests to breach ZeroFly bags would facilitate insect management. Therefore, efficacy of PH3 in immature and adult Sitophilus zeamais (Motschulsky), Prostephanus truncatus (Horn), Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst) in experimental cages in maize stored in 100-kg polypropylene (PP), jute and ZeroFly bags was investigated. Post-fumigation mortality of adults was recorded after 7 d, and after 7 wk for immatures. The ability of either S. zeamais or P. truncatus to penetrate fabric of PP, jute and ZeroFly bags was assessed. Phosphine efficacy was good in all the three types of bags and resulted in complete mortality of adults and immatures of the four species tested. Sitophilus zeamais and P. truncatus were more successful in penetrating the PP bag fabric and on average made 84 and 780 holes per bag over a 4 mo-period, respectively; this was followed by jute with 37 and 614 holes. The ZeroFly bag was harder to breach and ≤3 holes per bag were made for both species. This study shows that PH3 is highly efficacious in insects that infest maize stored in ZeroFly bags, and that these bags are not easily penetrated by stored product insect pests. Hitherto, ZeroFly bags are a good technology for storing grain that is not infested, and fumigation using PH3 can be effectively conducted if infestation occurs. Therefore, ZeroFly bags can be incorporated in integrated stored product insect management (IPM) programs for bagged grains.

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 phosphine and neem oil as fumigant against pulse beetle

A laboratory experiment was carried out to understand the toxicity of phosphine and neem oil on adults of pulse beetles Callosobruchus maculatus and C. analis. Phosphine gas at 0.0125 mg/L dosage was relatively more toxic to C. maculatus (80% mortality) than C. analis (56.67%). Among neem oil and solvents combinations, neem oil in ethanol at 135 mg a.i/L dosage, resulted in 83.33% and 73.33% mortality in C. maculatus and C. analis, respectively. Probit analysis revealed neem oil in ethanol (151.24 a.i mg/l) and water (85.04 mg a.i/l) had low LC50 values with C. maculatus, while C. analis was observed with high LC50 (176.59 mg a.i/l and 102 mg a.i/l) with neem oil in ethanol and water, respectively. Thus an organic fumigant neem oil at high dosage led to more or equal adult pulse beetle mortality compared to inorganic phosphine at low dosage.

English

The export of grain from Western Australia depends on a grain supply network that takes grain from farms to port through Cooperative Bulk Handling (CBH) receival and storage sites. The ability of the network to deliver pest free grain to port and ship depends on the quality of grain delivered by farmers and the efficacy of phosphine based fumigation in controlling stored grain pests. Unfortunately, over time, common stored grain pests have developed resistance to phosphine. There is some evidence that phosphine resistance, develops on farm due to inadequate biosecurity management. This paper considers the design of farm biosecurity contracts using a principal agent approach. An optimizing non-linear programming model with different effort levels of Cooperative Bulk Handling (principal) and farmer (agent) is developed to determine: (i) whether the farmer’s effort level affect the CBH’s profit function, and (ii) whether increasing monitoring effort by the CBH has an impact on farmer’s performance on farm. Results show that; (i) the optimal effort level of farmer is higher for perfect information assumption than moral hazard one. Meanwhile, (ii) under moral hazard assumption, when Bulk Handler is engaged in intensive monitoring level, the farmer is engaged in a higher level of effort. Price premium represents the incentive for farmers, while cost-reduction represents the incentive for Grain Bulk Handler. Key words: Principal-agent model, biosecurity contracts, asymmetric information, stored grain, effort levels, farmer, grain bulk handler.

Short communication. Efficacy of phosphine as a fumigant against Rhynchophorus ferrugineus (Coleoptera: Curculionidae) in palms

The red palm weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera, Curculionidae), the major pest of palms in the Mediterranean, has mainly spread through movement of infested plants. The aim of this work was to determine the possibility of using aluminium phosphide in palms as a safe quarantine treatment against this pest. Laboratory tests were carried out on eggs, young and old larvae, pupae and adults of R. ferrugineus with different doses of Eurofume® and mortality was assessed. Fumigations of infested canary palms were carried out in a hermetic container and subsequently palms were carefully dissected and all R. ferrugineus specimens found, either dead or alive, were counted. Results suggest that a dose of 1.14 g aluminium phosphide m–3 for 3 days is enough to kill all stages of R. ferrugineus in an infested palm tree. Provided that applied dose of aluminium phosphide is not phytotoxic for palms, this treatment could significantly reduce at low cost the enormous risks that palm imports suppose worldwide.

Maneuvering humidity to augment response of phosphine against adult and egg stages of Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelidae)

Phosphine and other fumigants have proved hazardous for treatment of stored product commodities because of their residual toxicity. In the present investigation, a comprehensive study was conducted to explore the role of different levels of humidity on efficacy of phosphine against egg and adult stages of the psocid,Liposcelis bostrychophila Badonnel. The results suggested that humidity play a significant role in enhancement of phosphine efficacy against the psocid, which has posed a new threat to food safety and security. It was concluded that use of low level of humidity with low doses of phosphine can be successful as an IPM strategy against the pest, which otherwise requires high humidity to survive and high level of phosphine to control. This technique may be helpful not only in reducing the phosphine doses but also in significant reduction of exposure time to achieve a specific level of mortality. Key words: Psocid, physical control, humidity, synergism, mortality.

EXPERIMENTS ON DIFFUSION OF PHOSPHINE IN CUT FLOWER BOXES

One of the most effective fumigants for disinfestation of cut flowers is currently methyl bromide, soon to be restricted. Toxicity of a potential alternative fumigant, phosphine (2% PH 3 + 98% N 2 ), was tested earlier on insect pests of cut flowers. Effective concentrations and durations of fumigation by phosphine have been ascertained in vitro, but the efficacy of phosphine under commercial situations needs to be examined. Numerical modelling indicates that in still conditions it may take over 700 min for phosphine to equilibrate at the center of an empty fibreboard box 1.0 m X 0.3 m X 0.21 m. For flowers such as proteas with large, tight bracts covering the flower, the time for these fumigants to penetrate will be longer. In laboratory experiments we measured the change in concentration of phosphine with time in different locations of a half-sized fibreboard flowerbox. Samples taken from various locations in the box were analyzed for phosphine using gas chromatography, and the time - concentration relationship of phosphine diffusion in a box with or without flowers in still or moving air was determined. Diffusion of phosphine into flower heads of Protea was also measured. In an empty flower box, phosphine took 240 min to attain equilibrium in still air compared with 800 min predicted if mass transfer were governed by pure diffusion. Equilibrium was reached in an empty box in 35 min; in a box packed with flowers it took 60 min, whilst diffusion into a protea flower head took 75 min with some bulk movement. The results highlighted that a box full of proteas cause resistivity to the free movement of phosphine and that the time required to attain equilibrium (130 min) inside a flower head can be as much as 50% of a standard fumigation time of 4 h.

Phosphine and its effect on some common insects in cut flowers

Abstract The most effective fumigant for insect disinfestation of cut flowers is currently methyl bromide, which will soon be unavailable in several countries. The toxicity of an alternative fumigant, phosphine (2% PH3 and 98% N2), was tested at 24 °C on adult greenhouse thrips (Heliothrips haemorrhoidalis), adult aphids (Myzus persicae) and lightbrown apple moth larvae (LBAM; Epiphyas postvittana). These are commonly found as insect pests on many cut flower crops. Thrips were exposed to phosphine concentrations ranging from 20–600 μl/l for 1 or 2 h. All thrips were killed within 18 h of exposure after a treatment of 300 μl/l phosphine for 2 h. Adult aphids and fifth instar LBAM larvae were more resistant to phosphine, and trials were therefore conducted using higher phosphine concentrations (> 500 μl/l) combined with atmospheric (0.035%) or elevated (33%) CO2. The most effective treatment for aphids was 1000 μl/l phosphine + 33% CO2 for 4 h, which killed all insects within 36 h of exposure. Under atmospheric CO2, levels, 92% of aphids were killed within 36 h after exposure to 1000 μl/l phosphine for 6 h, with 100% kill attained after exposure to 5000–8000 μl/l phosphine for 6 h. Elevated CO2 levels did not improve the efficacy of phosphine on LBAM larvae. The optimal treatment was 2000–2500 μl/l phosphine for 4 or 6 h, which killed 96 or 100% of the larvae, respectively. Under atmospheric CO2 levels, 4000 μl/l phosphine killed 74% of LBAM larvae after 4 h, and 94% after 6 h exposure.

Laboratory assessment of the efficacy of phosphine and methyl bromide fumigation against all life stages of Liposcelis entomophilus (Enderlein)

Liposcelis entomophilus is common and often very abundant in cereal stores in hot, humid areas, heavy infestations in South-East Asia being associated with phosphine fumigation. Tolerance of all life stages to phosphine fumigation was investigated under tropical storage conditions. Eggs were most tolerant and required a concentration of 1.7 mg l −1 for 5 days to kill 99% of the eggs, but this gas concentration would prove difficult to attain in a typical fumigation under gas-tight sheets. When L. entomophilus was exposed to methyl bromide over a range of concentration X time (CT) products at 27°C and 30% relative humidity, all life stages were controlled at 50 mg l −1 h −1. Higher CT products would be required to kill the most tolerant life stages of common stored-product pests, such as Tribolium castaneum but the CT products normally attained using gas-tight sheet fumigations are sufficient to kill L. entomophilus.

Efficiency of phosphine and combinations of phosphine with carbon dioxide against Khapra Beetle larvaeTrogoderma granarium everts. (Col., Dermestidae)

Investigations conducted in the laboratory for comparing the efficacy of phosphine with that of mixtures of the gas plus carbon dioxide against diapause larvae ofTrogoderma granarium showed that addition of varying concentrations of CO2 (20, 50, 75 and 100%) to fixed PH3-concentrations had a negative influence on phosphine efficacy against diapause larvae of Khapra Beetle at 30°C for short exposure periods of 18 and 24 hours. On the other hand, it was found that for longer exposure periods of 48 and 72 hours, the addition of CO2 to phosphine induced significantly higher larval mortality than that by PH3 alone, whereby an additive effect was proved for mixtures contained PH3+75% and 100% CO2. The addition of 20% and 50% CO2 to PH3 at 20°C did not show any increase in larval mortalities of the mixtures for exposure periods between 24–96 hours. The larval mortalities obtained for an atmosphere contained 20 and 50% CO2 alone at 20 and 30°C was (0–6%) and (10–40%), respectively, after 10 days exposure period.