Loss of phosphine from unsealed bins of wheat at six combinations of grain temperature and grain moisture content

Hard red winter wheat (1.4 t) at 11.1 or 13.5% moisture content (wet basis) and 20, 25, or 30 degrees C was fumigated with tablets of an aluminum phosphide formulation in unsealed, cylindrical grain bins of corrugated metal. The fumigant leakage rate was manipulated to approximate that commonly encountered in farm and commercial-scale bins of this type. Phosphine concentration profiles were recorded and phosphine loss and sorption were characterized to determine which conditions provided the greatest probability of successful fumigation in these bins. Phosphine leakage and sorption were both positively related to grain temperature and moisture content. The fumigant concentration profiles were compared with previously-published data relating temperature to the developmental rate and fumigant susceptibility of lesser grain borer eggs, which are phosphine-resistant but become less resistant as they age. The mean phosphine concentration observed at the time corresponding to one-half of the calculated egg development time was compared to the lethal concentration (LC(99)) for a 2-day exposure at each temperature-moisture combination. In the low-moisture grain at 20 degrees C, the observed fumigant concentration was below the lethal concentration, due to the long development time under these conditions. At 25 and 30 degrees C in the low-moisture wheat, the likelihood of complete kill appeared more favorable because the fumigant concentration remained above the published LC(99) for more than half of the egg development time. In the wheat with 13.5% moisture content, rapid fumigant sorption and loss resulted in phosphine concentrations below the LC(99) at one-half of the development time at 20 or 25 degrees C. At 30 degrees C, due to the very rapid development rate, the observed phosphine concentration exceeded the LC(99) half-way through the egg development period despite the rapid rate of fumigant sorption and loss. Repeated fumigation of the same grain reduced the rate at which phosphine sorbed into the grain.     

Developing and verifying a fumigant loss model for bulk stored grain to predict phosphine concentrations by taking into account fumigant leakage and sorption

To ensure fumigation effectiveness and address phosphine resistance concerns, fumigant concentrations and movement in a grain storage silo need to be understood. A mathematically accurate fumigation model was developed that is capable of predicting fumigant concentration and movement throughout a grain storage silo that takes into account fumigant loss from leakage and sorption, and was verified with experimental fumigation data. Equations estimating fumigant leakage and sorption were developed based on literature values and added to an existing finite element model. Fumigation data was used from a fumigation conducted on an Australian made silo filled with 45.5 tonnes of maize in Manhattan, Kansas. Two verifications were conducted based on phosphine concentration release times of 24 h and 30 h, with both verifications demonstrating accurate prediction of phosphine fumigant values and trends. The two verifications resulted in concentration-time products that were within 0.9% and 4.3% of the experimental values, respectively. The fumigation model is most accurate during the times of highest phosphine concentration. However, the model under predicted phosphine concentrations during the first 12 h of fumigation and over predicted phosphine concentrations beyond the first six days of fumigation. This fumigation model was found to be sufficiently accurate to allow for future experimentation on predicting fumigant concentrations as a function of environmental conditions and operational variable.     

PERSISTENCE OF PHOSPHINE GAS IN FUMIGATED IRAQI DATES

Phosphine gas (PH₃) is a widely used fumigant for stored fruits and grains. Previous studies indicated that all residues of this gas are eliminated by normal aeration but the exact time has never been determined.
The objective of this work was to determine the time required for desorption of phosphine from fumigated dates relative to aeration time and temperature. Flame photometric detection by gas chromatography was used for the detection of sorbed phosphine.
Results indicate that the initial residue level of PH₃ falls rapidly within 24 h after fumigation but residues persist for at least nine days. Higher residue levels were found in dates stored at low temperatures (4°C) than at 28°C. It is recommend that fumigated dates be marketed after longer periods of aeration, especially those aerated at temperatures of 4°C or less.     

储粮熏蒸过程中磷化氢浓度的分布模型及验证研究

谷物在长期储存过程中会受到害虫的侵扰,通常需要使用诸如磷化氢等适量的熏蒸剂对仓储粮食进行熏蒸,从而杀死害虫,同时又要避免害虫产生耐药性和熏蒸剂的残留。本研究首先建立和验证了熏蒸剂(磷化氢)的对流扩散和吸附模型,并采用计算流体动力学方法对圆筒仓内谷物熏蒸过程中磷化氢质量浓度进行了数值预测,分析了熏蒸过程中磷化氢的质量浓度分布规律,得出熏蒸过程中磷化氢质量浓度分布是不均匀的,并且受到谷物吸附和不可逆化学反应的双重影响。     

Phosphine fumigation of silo bags

Fumigation with phosphine has the potential to disinfest grain stored in silo bags but only limited research has been conducted on whether phosphine fumigation can be undertaken effectively and safely in this form of storage. Fumigation with phosphine was tested on two (70 m) replicate silo bags each containing 240 t of wheat (9.9 and 9.2% m.c.). The target application rate of phosphine was 1.5 g m⁻³ with a fumigation period of 17 days. Aluminium phosphide tablets were inserted into each bag at ten release points spaced at 7 m intervals starting 3.5 m from either end of the bag. A total of 14 bioassay cages containing mixed age populations of strongly phosphine resistant Rhyzopertha dominica (F.) were inserted into each fumigated silo bag. Complete control of all life stages of R. dominica was achieved at all locations in the fumigated silo bags. Phosphine concentrations at release points increased rapidly and remained high for the duration of the fumigation. Concentrations at midway points were always lower than at the release points but exceeded 215 ppm for ten days. The diffusion coefficient of available phosphine averaged over the first three full days of the fumigation for both fumigated silo bags was 2.8 × 10⁻⁷. Venting the silo bag with an aeration fan reduced the phosphine concentration by 99% after 12 h. Relatively small amounts of phosphine continued to desorb after the venting period. Although grain temperature at the core of the silo bags remained stable at 29 °C for 17 days, grain at the surface of the silo bags fluctuated daily with a mean of 29 °C. The results demonstrate that silo bags can be fumigated with phosphine for complete control of infestations of strongly phosphine resistant R. dominica and potentially other species.     

Does sorption of sulfuryl fluoride by wheat reduce its efficacy against adults and eggs of Rhyzopertha dominica?

Despite its growing importance as a fumigant for grain, there is no information on the impact of sorption on the efficacy of sulfuryl fluoride (SF) against target insect pests. Eggs and adults of a major grain pest, Rhyzopertha dominica, living in wheat (12% m.c.), were fumigated with SF at 0.5, 1, and 2 mg/L for 168 h at 25 °C. Sorption of the fumigant by the grain followed an exponential decay and reduced the mortality rates of both adults and eggs. The partition ratio (K), a measure of physical sorption, had a strong impact on mortality of both adults and eggs. The quadratic model showed the best fit to the data and turning points in the relationship indicated that although mortality increased as concentration increased, physical sorption removed fumigant resulting in a decrease in the mortality rate. There was a linear relationship between mortality and the rate of sorption (k) of SF by the wheat. At each concentration, mortality rate increased as k increased despite sorption continuing, indicating that the chemical sorption rate had little impact on mortality. Sorption of SF into the commodity has the potential to reduce the biological efficacy of the fumigant resulting in potential control failures. Concentration x time protocols may need to be revised to account for this phenomenon.     

Studies on the effects of phosphine on Salmonella enterica serotype Enteritidis in culture medium and in black pepper (Piper nigrum)

The effect of phosphine on Salmonella enterica serotype Enteritidis inoculated in culture medium and in black pepper grains (Piper nigrum), as well as on the reduction of the microbial load of the dried and moisturized product, was verified. The postfumigation effect was verified in inoculated samples with 0.92 and 0.97 water activity (a(w)) exposed to 6 g/m(3) phosphine for 72 h, dried to 0.67 a(w), and stored for 24, 48, and 72 h. No decreases were observed in Salmonella Enteritidis populations in culture medium when fumigant concentrations up to 6 g/m(3) were applied for 48 h at 35°C. However, the colonies showed reductions in size and atypical coloration as the phosphine concentration increased. No reduction in Salmonella counts occurred on the inoculated dried samples after fumigation. On the other hand, when phosphine at concentrations of 6 g/m(3) was applied on moisturized black pepper for 72 h, decreases in Salmonella counts of around 80% were observed. The counts of total aerobic mesophilic bacterium populations of the dried and moisturized black pepper were not affected by the fumigant treatment. The results of the postfumigation studies indicated that Salmonella Enteritidis was absent in the fumigated grains after drying and storage for 72 h, indicating a promising application for this technique. It was concluded that for Salmonella Enteritidis control, phosphine fumigation could be applied to black pepper grains before drying and the producers should rigidly follow good agricultural practices, mainly during the drying process, in order to avoid product recontamination. Additional work is needed to confirm the findings with more Salmonella serotypes and strains.     

Performance of phosphine in fumigation of bagged paddy rice in indoor and outdoor stores

Phosphine fumigation trials were carried out on bag-stacks of paddy rice to study the differences in gas loss rates and concentration–time (Ct) products achieved during the treatment of indoor and outdoor stacks. Stacks (89–132 t) were fumigated singly under 250 μm thick polyethylene sheeting, which was sealed with a double layer of sand-snakes to the concrete floor. Phosphine was applied as an aluminium phosphide formulation and the fumigations continued for 7 days. In the first experiment, stacks of paddy rice with moisture contents ranging from 12.2 to 13.7% were held in either indoor or in outdoor storage and subjected to fumigation at the rate of 2, 3 or 4 g of phosphine/tonne. The outdoor stacks held relatively low levels of phosphine with Ct products for the indoor stacks of 135, 171 and 294 g h/m³, respectively, whilst the corresponding values for the outdoor stacks were 70, 85 and 166 g h/m³ only. The average gas loss rate was 14.5% per day for the indoor stacks and 29.5% for the outdoor stacks. In the second experiment, old stacks of paddy rice inside a godown, one each with grains at 8.8 and 9.8% moisture content, were fumigated at 3 g phosphine/tonne. Release of phosphine was delayed and fumigant sorption was less and therefore higher Ct products of 204 and 216 g h/m³ were achieved. In the stacks built outdoors, the resident infestations of Rhyzopertha dominica, Cryptolestes sp. and Oryzaephilus surinamensis were completely controlled despite lower Ct products. On the other hand, in the stacks of old paddy, R. dominica survived the treatment. Subsequent testing showed that the population had a degree of resistance to phosphine.     

Detection of Rhyzopertha dominica larvae in stored wheat using ELISA: The impact of myosin degradation following fumigation

Hard red winter wheat kernels were infested with eggs of Rhyzopertha dominica. After 20 d, when the larvae reached the fourth instar, they were killed by exposing the infested kernels to phosphine gas for 24 h. The infested kernels were then divided into four portions and treated as follows: one portion was immediately frozen at −80 °C to avoid myosin degradation; the other three portions were kept at 32 °C and 65% relative humidity, and then frozen at −80 °C after 14, 28, and 56 d post-fumigation, respectively. Each treatment was replicated five times. Myosin was measured using a commercial enzyme linked immunosorbent assay (ELISA) method that specifically detects this protein (Biotect^®, Austin, TX). Myosin degradation was most rapid in the first 2 weeks after the larvae were killed, decreasing from 1.672 to 0.695 ng/well during this period (a 58.4% reduction). There were no significant differences in myosin degradation between samples that were 14, 28, and 56 d post-fumigation. Grain is often fumigated to control insects. Frequently, this occurs many weeks before the grain is milled and may be repeated during the storage period. Therefore, estimates using the ELISA test may underestimate internal insect infestation because of myosin degradation. Insect fragment estimates for previously fumigated grain could be underestimated by as much as 58%.     

Sorption and desorption of sulfuryl fluoride by wheat,flour and semolina

Sulfuryl fluoride (SF) has been developed as a fumigant for control of insect pests in stored grain. However, there is very limited information on the sorption behaviour of this fumigant, which can be critical to its bioactivity, application and potential for residues. We undertook a comprehensive laboratory study of the sorption and desorption of SF by wheat (bread and durum), flour and semolina at 15, 25 and 35 °C, moisture contents 12% and 15%, and concentration × time combinations at CT = 1500 mgh/L (4.167 mg/L × 360 h, 8.928 mg/L × 168 h and 31.25 mg/L × 48 h).At each dosage, sorption rate increased as commodity temperature and moisture content increased. The highest rates of sorption occurred at 35 °C and 15% m.c., and lowest rates at 15 °C and 12% m.c., and the rate was independent of initial concentration. Sorption followed first order reaction kinetics described by the exponential decay equation, C_t = C₀·e^−k*t, where k is the sorption rate constant. The most important factors determining the rate of sorption were commodity particle size (exposed surfaces) and temperature. Little sorption of fumigant occurred within the first 24 h whereas longer fumigation times resulted in significant sorption. Unbound SF was rapidly lost from the commodity upon aeration with no further desorption detected under any of the test conditions.SF possesses a number of characteristics that recommend it as a commodity fumigant. It is sorbed slowly by commodities relative to methyl bromide and carbonyl sulphide although it is sorbed about 4–5 times faster than phosphine. It desorbs rapidly upon aeration, and the lack of continued desorption has practical workplace health and safety benefits. On the other hand, sorbed SF appears irreversibly bound to the commodity matrix indicating the need to be alert to the possibility of excessive residues, particularly in longer term fumigations.     

Sorption of tritiated phosphine by various stages of Tribolium castaneum (Herbst)

When various stages of Tribolium castaneum were fumigated with 0.14–1.69 mg/l of tritiated phosphine for 5 hr the uptake of the fumigant was found to be considerably greater in larvae and adults than in pupae or eggs. Mature larvae absorbed 2–3 times as much phosphine as pupae at all concentrations tested and mortality was appeciably higher. Uptake by 1-day-old adults was about two fold that of the mature pupal stage from which they had emerged and increased with age so that 14-day adults absorbed about twice as much as newly emerged adults. Uptake by pupae followed a U-shaped curve somewhat similar to the characteristic pattern of oxygen uptake by pupae of different ages. Eggs retained only a small proportion of the radioactive fumigant they absorbed. A considerable amount remained at the surface of the eggs and was converted to soluble compounds that could be washed off with water. The results suggest that the higher tolerance of both eggs and pupae to phosphine may, at least partially, be attributed to the lower uptake of fumigant as compared to larvae and adults.     

Pesticide residues in foodstuffs in Great Britain. X. Bromide residues in maize, pulses and nuts

Results are presented for the determination of bromide residues in maize, in pulses and in four types of nuts sampled on arrival in British ports mostly during the five years up to June 1968. in the maize, which had been fumigated in the ships' holds before export, 75 % of the 155 samples examined contained less than 50 ppm but some contained more than 200 ppm. the problems of fumigating bulk maize and the extent to which variations in bromide residue are evened out during grain handling operations in the port granary are discussed. the samples of pulses generally contained less than 50 ppm but some samples of haricot beans contained more than 100 ppm. Out of 164 samples of groundnuts from 11 countries only one contained more than 200 ppm. Those containing more than 100 ppm came from countries in which nuts are sometimes fumigated more than once. None of the walnuts or almonds examined contained more than 100 ppm but two samples of Brazil nuts had more than this. Results are also presented for the increase in bromide residue after the fumigation of consignments in Britain and the reasons for the wide variations observed are discussed.     

Developmental and population growth rates of phosphine-resistant and -susceptible populations of stored-product insect pests

Phosphine resistance positively contributes towards an individual's fitness under phosphine fumigation. However, phosphine resistance may place resistant individuals at a fitness disadvantage in the absence of this fumigant, which can be exploited to halt or slow down the spread of resistance. This study aimed to determine if there is a fitness cost associated with phosphine resistance in populations of the red flour beetle (Tribolium castaneum (Herbst)), the lesser grain borer (Rhyzopertha dominica (F.)) and the sawtoothed grain beetle (Oryzaephilus surinamensis (L.)). The developmental rate and population growth of phosphine-resistant and -susceptible populations of these three species of stored-product insects were therefore determined under phosphine-free environment. The majority of the phosphine-resistant populations exhibited lower developmental and population growth rates than the susceptible populations indicating that phosphine resistance is associated with fitness cost in all three species, which can potentially compromise the fixation and dispersal of the resistant genotypes. Nonetheless, some phosphine-resistant populations did not show a fitness cost. Therefore, resistance management strategies based on suppression of phosphine use aiming at eventual reestablishment of phosphine susceptibility and subsequent reintroduction of this fumigant will be useful only for insect populations exhibiting a fitness cost associated with phosphine resistance. Therefore recognition of the prevailing phosphine-resistant genotypes in a region is important to direct the management tactics to be adopted.     

谷物平衡水分研究概况

控制吸湿是谷物安全贮藏的基本原则之一,平衡水分测定可用来判断谷物水分变化的趋向.概述了谷物平衡水分测定的原理及数学模型分析,并归纳,发生纳滞后效应的可能理论、影响谷物吸着(包括吸附与解吸)等温线测定的因子,还重点介绍了近年发展起来的、利用平衡水分吸附/解吸数据分析谷物及食品的热动力学函数--水分吸着等热.这些研究进展对完善我国储粮生态区域划分、谷物主产区低温干燥、设计干燥程序和设备、谷物及加工产品的包装及货架期皆有意义.     

Effects of phosphine and methyl bromide fumigation on the volatile flavor profile and sensory quality of dry cured ham

In separate experiments, randomized complete block designs with three replications were utilized to evaluate the effects of phosphine (PH₃) (0, 200 and 1000 ppm for 48 h) and methyl bromide (MB) (0, 4, 8, 16, and 32 mg/L for 48 h) fumigation concentration on the volatile flavor compound concentrations in dry cured ham. Minimal differences existed (P > 0.05) in the presence and concentration of aroma active compounds in both PH₃ and MB fumigated hams but sulfur and oxidation compounds were more prevalent (P < 0.05) in the fumigated treatments when compared to the control. As phosphine fumigation concentration increased, the residual concentration of phosphine also increased in the hams (P < 0.05), but all samples contained levels that are lower than the legal limit of phosphine allowed in stored food products (0.01 ppm) in the United States. A triangle test (n = 56) indicated that consumers could not discriminate (P > 0.75) between the control hams and those that were fumigated with PH₃. Minimal aroma/flavor differences existed among MB, PH3 and control hams, and dry cured ham that was fumigated with PH₃ was safe for consumption based on residual phosphine concentrations in the meat tissue.     

Desorption kinetics of phenanthrene in aquifer material lacks hysteresis

Desorption experiments were carried out in flow through columns following long-term sorption batch experiments (up to 1010 days at 20 degrees C; Rügner, H.; Kleineidam, S.; Grathwohl, P. Long-term sorption kinetics of phenanthrene in aquifer materials. Environ. Sci. Technol. 1999, 33, 1645-1651) to elucidate sorption/desorption hysteresis phenomena of phenanthrene in aquifer materials. Most of the sorbents employed in this study (homogeneous lithocomponents separated from aquifer sediments or fresh rock fragments) showed highly nonlinear sorption isotherms because of coal particles embedded inside the grains. Because sorption capacities were high, sorption equilibrium was not reached in most of the sorbents during the initial sorptive uptake experiments lasting up to 1010 days. Desorption was studied up to 90 days at 20 degrees C. The temperature was raised after that stepwise from originally 20 to 30, 40, 50, and finally to 70 degrees C for selected samples to estimate activation energies of desorption. A numerical intraparticle pore diffusion model was used to fit sorptive uptake data and subsequently for pure forward prediction of the release rates in the desorption column experiments. Desorption was initially fast followed by extended tailing which in other studies is fitted by using multirate first-order models. Our results demonstrate that the retarded intraparticle pore diffusion model can predict the desorption rates with a single diffusion rate constant obtained independently from the long-term batch sorption experiment. No evidence for hysteresis was found, suggesting that many hysteresis phenomena reported earlier are experimental artifacts resulting from nonequilibrium effects and "nonphysical" models. The different temperature steps allowed one to additionally calculate activation energies of desorption (45-59 kJ mol(-1)), which were in reasonably good agreement with results from earlier studies for a retarded pore diffusion process. In addition, equilibrium sorption isotherms were determined at 20 and 40 degrees C to compare sorption and desorption enthalpies. Both were in good agreement, confirming that desorption was not significantly different from sorption.     

Pesticide sorption and desorption by lignin described by an intraparticle diffusion model

Lignin was used as a model compound for soil organic matter to gain insight into the mechanisms that control the kinetics of pesticide sorption and desorption. Hydrolytic lignin was immobilized in a matrix of alginate gel, and sorption-desorption experiments were undertaken with isoproturon. Sorption increased with time and was close to equilibrium after 14 days. Desorption was measured after sorption for different time intervals and for a number of successive desorption steps of different lengths. The results showed strong differences between the sorption and desorption isotherms. The ratio of sorbed to dissolved pesticide approached and even exceeded the equilibrium ratio, depending on the number of desorption steps and the length of each equilibration period. A numerical diffusion model was developed to describe radial diffusion into the lignin particles in combination with Freundlich sorption inside the particles. Key model parameters were adjusted to fit the sorption data, and the same parameters were then used to predict stepwise desorption. Desorption was well described by the model, which suggests that sorption and desorption were driven by the same mechanism and occurred at the same rate. The observed difference between the sorption and desorption isotherms could be fully explained by the nonattainment of equilibrium due to slow diffusion into and out of the lignin particles.     

Mathematical modelling and numerical simulation of phosphine flow during grain fumigation in leaky cylindrical silos

The phosphine distribution in a cylindrical silo containing grain is predicted. A three-dimensional mathematical model, which accounts for multicomponent gas phase transport and the sorption of phosphine into the grain kernel is developed. In addition, a simple model is presented to describe the death of insects within the grain as a function of their exposure to phosphine gas. The proposed model is solved using the commercially available computational fluid dynamics (CFD) software, FLUENT, together with our own C code to customize the solver in order to incorporate the models for sorption and insect extinction. Two types of fumigation delivery are studied, namely, fan-forced from the base of the silo and tablet from the top of the silo. An analysis of the predicted phosphine distribution shows that during fan forced fumigation, the position of the leaky area is very important to the development of the gas flow field and the phosphine distribution in the silo. If the leak is in the lower section of the silo, insects that exist near the top of the silo may not be eradicated. However, the position of a leak does not affect phosphine distribution during tablet fumigation. For such fumigation in a typical silo configuration, phosphine concentrations remain low near the base of the silo. Furthermore, we find that half-life pressure test readings are not an indicator of phosphine distribution during tablet fumigation.     

Evaluation of dosimeter tubes for monitoring phosphine fumigations

Within integrated pest management options, fumigation of stored products is one method to help control post-harvest insect infestations in our food and agricultural products. Fumigant gas concentration monitoring is important to confirm that the treatment was adequate to achieve the desired insect control, but monitoring can be relatively expensive and labor intensive. This study evaluated how accurately dosimeter tubes could monitor phosphine fumigation treatments. The dosimeter tube is designed to continuously react with phosphine gas during the fumigation period and yields a measurement in terms of concentration 1 time product or CT, which can be interpreted as cumulative exposure. Two models of dosimeter tubes were evaluated (high range and low range). The reference method for these trials were wireless phosphine monitoring sensors, which recorded gas concentrations at hourly intervals during an exposure, and from this a CT product was also calculated. Model LPG-1, high-range dosimeter tube, measured within ± 25% of the phosphine monitoring sensors for CT dosages less the 70,000 ppm1hr. Model LPG-2, low-range tube, tended to significantly over-estimate phosphine CT dosage by 50%–100% of the phosphine monitoring sensor references. Secondly, bioassays of fumigant efficacy were performed using susceptible and resistant adult Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), lesser grain borers, and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), red flour beetle, for estimating insect control at the varied fumigation CT treatments. For the susceptible strains, CT dosages ∼5000 ppm1hr controlled both species. However, the insect control varied from 60% to 100% for resistant adults at CT dosages of ∼20,000 ppm1hr. The dosimeter tubes function in these ranges of dosages where each insect species are controlled and the dosimeter tube model LPG-1 provides reasonable estimates of the fumigation dosage for a given treatment level.     

Reproduction of phosphine resistant Rhyzopertha dominica (F.) following sublethal exposure to phosphine

Phosphine fumigation is commonly used to disinfest grain of insect pests. In fumigations which allow insect survival the question of whether sublethal exposure to phosphine affects reproduction is important for predicting population recovery and the spread of resistance. Two laboratory experiments addressed this question using strongly phosphine resistant lesser grain borer, Rhyzopertha dominica (F.). Offspring production was examined in individual females which had been allowed to mate before being fumigated for 48 h at 0.25 mg L^?1. Surviving females produced offspring but at a reduced rate during a two-week period post fumigation compared to unfumigated controls. Cumulative fecundity of fumigated females from 4 weeks of oviposition post fumigation was 25% lower than the cumulative fecundity of unfumigated females. Mating potential post fumigation was examined when virgin adults (either or both sexes) were fumigated individually (48 h at 0.25 mg L^?1) and the survivors were allowed to mate and reproduce in wheat. All mating combinations produced offspring but production in the first week post fumigation was significantly suppressed compared to the unfumigated controls. Offspring suppression was greatest when both sexes were exposed to phosphine followed by the pairing of fumigated females with unfumigated males and the least suppression was observed when males only were fumigated. Cumulative fecundity from 4 weeks oviposition post fumigation of fumigated females paired with fumigated males was 17% lower than the fecundity of unfumigated adult pairings. Both of these experiments confirmed that sublethal exposure to phosphine can reduce fecundity in R. dominica.