Verification of radio frequency heating uniformity and Sitophilus oryzae control in rough,brown, and milled rice

Radio frequency (RF) heating is considered to be an alternative physical method for disinfesting postharvest agricultural products to replace chemical fumigation due to its inherent dangers on human health and environment. A pilot-scale, 27.12 MHz, 6 kW RF system was used to study the RF heating uniformity and validate the developed RF treatment protocols for disinfesting rough, brown, and milled rice. The results showed that the optimum RF heating uniformity in rough and brown rice was obtained by an appropriate electrode gap of 11 cm with a forced hot air heating at 50 °C, movement of the conveyor with a speed of 12.4 m/h, two mixings, and holding at 50 °C hot air for 5 min. Mortality of adult rice weevils, Sitophilus oryzae (L.), increased with increasing heating temperature and holding time, and reached 100% while RF heating at 50 °C holding in hot air for at least 6 min. There were no significant differences in quality parameters (moisture, protein, water activity, starch, free fatty acid, ash, and color) between RF treatments and untreated controls during storage (P > 0.05). The developed non-chemical alternative RF technology may hold potential for disinfesting rough, brown, and milled rice required by the growing organic market.     

Developing radio frequency technology for postharvest insect control in milled rice

Since methyl bromide fumigation has an adverse effect on human health and environment, it is urgently needed for developing a non-chemical method to replace chemical fumigation for disinfesting milled rice. The purpose of this research was to study possible applications of radio frequency (RF) energy for disinfesting milled rice without affecting product quality. A pilot-scale, 27.12 MHz, 6 kW RF system was used to study RF heating uniformity and develop a treatment protocol for achieving 100% insect mortality and finally evaluating quality attributes in RF treated milled rice during storage. The results showed that the heating time needed only 4.3 min to heat the 3.9 kg milled rice from 25 °C to 50 °C using RF energy, but 480 min for milled rice to reach 48 °C using hot air at 50 °C. After comparing three selected electrode gaps, an appropriate gap of 11 cm was obtained to achieve the heating rate of 5.8 °C/min for further heating uniformity tests. An RF treatment protocol was finally developed to combine 1.0 kW RF power with a forced hot air heating at 50 °C, movement of the conveyor with the speed of 12.4 m/h, two mixings, and holding at 50 °C hot air for 5 min, followed by forced room air cooling through single-layer (2 cm thick) samples. There were no significant differences in quality parameters (moisture, protein, fat, starch, hardness, and color) between RF treatments and untreated controls during storage (P > 0.05). Therefore, RF treatments may provide a practical, effective and environmentally friendly method for disinfesting milled rice.     

Industrial-scale radio frequency treatments to control Sitophilus oryzae in rough,brown, and milled rice

Many previously studies have confirmed that radio frequency (RF) treatments have the potential to be developed as non-chemical alternative disinfestation methods. However, most of them are conducted in laboratory scale RF systems, and it is necessary to scale up the treatment protocol for industry scale applications. A pilot-scale, 27.12 MHz, 6 kW RF system was used to simulate the continuous industrial processing and finally estimate the heating efficiency and throughput for controlling adult rice weevils, Sitophilus oryzae (L.), in milled, brown, and rough rice. An electrode gap (11.5 cm) was chosen based on the appropriate heating rate (6–8 °C/min). RF heating uniformity in the three types of rice samples was improved by adding 50 °C forced hot air surface heating, sample movements on the conveyor belt at a speed of 12.5 m/h, and holding in 50 °C hot air for 6 min. The final industrial RF treatment achieved a complete mortality of adult S. oryzae and provided acceptable quality attributes in moisture content, water activity, color, protein, free fatty acid, and ash. The average heating efficiency and throughput of the RF treatments were 77.7, 76.3, and 74.3%, and 268.8, 247.3, and 224.8 kg/h for milled, brown, and rough rice, respectively. The industrial scale-up studies provide alternative physical methods for disinfesting milled, brown, and rough rice to replace chemical fumigation.     

Toxicity of coumaran to stored products beetles

The fumigant activity of coumaran was tested against mixed-age cultures of the rice weevil (Sitophilus oryzae L.), the lesser grain borer (Rhyzopertha dominica F.), the rust-red flour beetle (Tribolium castaneum Herbst), saw-toothed grain beetle (Oryzaephilus surinamensis L.) and flat grain beetle (Cryptolestes ferrugineus Stephens). T. castaneum was tolerant to coumaran, for total population extinction was achieved in 72 h exposure at 50 μg/L dose only. In contrast all developmental stages of O. surinamensis, C. ferrugineus and R. dominica were quite susceptible 100% mortality was attained at < 50 μg/L doses in 24 or 72 h exposure. Further results showed that T. castaneum, generally tolerant pest to fumigants and R. dominica, a predominant stored grain pest in India, could be controlled by coumaran. The findings indicate that, coumaran is good source for alternate to methylbromide for effective control of stored grain insect pests.     

Effects of spinosad on the heat tolerance and cold tolerance of Sitophilus oryzae L. (Coleoptera: Curculionidae) and Rhyzopertha dominica F. (Coleoptera: Bostrichidae)

Sitophilus oryzae and Rhyzopertha dominica are serious insect pests of stored products in Sri Lanka. Currently pirimiphos methyl and phosphine fumigation are used as control measures but grain handlers seek for alternatives. Exposure to high or low temperature is popular in stored-product insect pest management but is expensive. Spinosad is effective against certain stored-product insects but has not yet been tested for its synergy with heat or cold. This experiment was conducted to evaluate the effect of spinosad on the heat tolerance and cold tolerance of S. oryzae and R. dominica adults. The experiment was a two-factor factorial, complete randomized design with four replicates. The spinosad concentration and exposure period were changed. Adults of S. oryzae and R. dominica were first exposed to a series of spinosad concentrations. Later they were held at higher (40 °C) or lower (6–11 °C) temperatures than room temperature for different durations.Pre exposure of S. oryzae adults to Spinosad at 18 ppm or above synergized the adult mortality at high or low temperature showing a dose response. Pre-exposure of R. dominica adults to spinosad concentrations 12.5 ppm or higher synergized the mortality at high temperature whereas the spinosad synergized the mortality of R. dominica at low temperature when exposed to 6.25 ppm or higher concentrations; the effects followed a dose response. This study shows that heat and cold tolerance of S. oryzae and R. dominica adults are reduced by pre-exposure to spinosad. Therefore, spinosad is a potential grain protectant at high or low temperatures against these two insect species.     

Impact of Rhyzopertha dominica (F.) on quality parameters of milled rice

The impact of Rhyzopertha dominica, the lesser grain borer, on milling quality of Francis and Wells cultivars of rough rice was assessed for the 2007 and 2008 crop years by infesting 200-g rough rice samples harvested at moderate and low moisture contents with 0, 10, 25, 50, and 100 parental adult insects, which were removed after one week. The samples were incubated for seven weeks at either 27 or 32 °C and 60% relative humidity to determine progeny production and feeding damage (insect frass), and subsequently the milled rice yield (MRY) and head rice yield (HRY). Progeny production from each parental density level varied with variety and temperature. The number of progeny produced by the parental adults was positively correlated with feeding damage, and the feeding damage caused by the progeny was in turn negatively correlated with MRY and HRY. For both years, more progeny production and feeding damage occurred in Francis versus Wells for each of the harvest moisture contents. Results show differential susceptibility of Francis and Wells cultivars to R. dominica, and also provide new methodologies for evaluating effects of infestation on rice milling quality.     

Radio frequency heating as a disinfestation method against Corcyra cephalonica and its effect on properties of milled rice

Radio frequency (RF) heating has the potential to be developed as an alternative non-chemical disinfestation method. In contrast to microwave (MW), RF exhibited higher penetration depth, which helps RF to be a useful technique in disinfesting packaging foods. A 3 kW, 27.12 MHz RF system was used to validate the practical of radio frequency technology for rice moth (Corcyra cephalonica) control in milled rice. Rice samples were placed in the polystyrene bag and moved at a speed of 0.8 m/min, and heated in the RF system with intermittent mixing. Four electrode gaps and five sample thicknesses were chosen to confirm the optimal conditions of RF treatment. The results showed that the sample thickness of 15 mm and electrode gap of 40 mm could provide the optimum heating rate for rice. Mortality of each stage (adult, larva, egg) of C. cephalonica increased with increasing heating temperature and reached 100% while RF heated 180 s (45.8 °C), 300 s (56.9 °C), and 420 s (70 °C), respectively. No C. cephalonica was determined in the samples during 45 days storage incubation period at RF treatment to 70 °C. There were no significant differences between control and RF treated samples in quality parameters (moisture, protein, fat, gelatinization, and sensory attributes). Therefore, RF treatment may provide a practical and effective method for disinfesting milled rice without affecting product quality.     

Hot air-assisted radio frequency heating effects on wheat and corn seeds: Quality change and fungi inhibition

Hot air-assisted radio frequency (RF) heating has been proposed and studied as an alternative disinfestation method for grain seeds. In this study, hot air-assisted RF heating effects on fungi inhibition and its influence on physiological (seed vigor, germination rate) and biochemical (color, enzyme activity) qualities of wheat and corn seeds were further investigated. Results showed that high intensity hot air-assisted RF treatment (70 °C, 10 min) reduced seed vigor and germination rate for both wheat and corn seeds, but relatively mild intensity treatment (65 °C, 10 min) showed no significant influence on color and germination rate, and even enhanced enzyme activity (Superoxide dismutase-SOD, catalase-CAT and peroxidase-POD). Moreover, hot air-assisted RF treatment (65 °C, 10 min) reduced Aspergillus flavus by 2 and 3 log-scale (CUF/g) in wheat and corn seeds with the moisture content of 12.0%, and 3 and 4 log-scale for wheat and corn seeds when moisture content increased to 15.0%, respectively. These results indicated higher moisture content (a_w) of grain seeds would benefit fungi inhibition for hot air-assisted RF treatment, and with proper control of treatment conditions, hot air-assisted RF heating has the potential to inhibit fungi and maintain physiological and biochemical quality of grain seeds.     

Storage stability of pistachios as influenced by radio frequency treatments for postharvest disinfestations

There has been an increased interest in developing alternative physical methods for disinfesting postharvest nuts under growing international pressures to replace chemical fumigation due to its adverse effects on human health and environment. The present research explored the possibility of using radio frequency (RF) heating as a non-chemical treatment for disinfestations of pistachios. A pilot-scale, 27 MHz, 6 kW RF unit was used to study RF heating uniformity, develop a treatment protocol, and evaluate quality attributes and storage stability in treated samples. Only 5.6 and 5.5 min were needed to raise the centre temperature of 1.8 kg in-shell and 2.0 kg shelled pistachios to reach 55 °C using RF energy, respectively, compared to about 82 and 117 min when using hot air heating at 55 °C. RF heating uniformity in both types of pistachios was improved by adding forced hot air, sample movements on the conveyor and a single mixing in the middle of the treatment time. The final average temperatures on the surface and in the interior of both types of pistachio kernels exceeded 52 °C, following a holding step at 55 °C for 2 min using hot air. This provided a conservative and 100% mortality of fifth-instar Indianmeal moth (Plodia interpunctella [Hübner]). RF treated samples were not significantly different from control samples in weight loss, peroxide values, fatty acid values, fatty acid composition and kernel colour. RF treatments can, therefore, potentially provide an effective and rapid protocol against stored product pests in pistachios as an alternative to chemical fumigation.Industrial relevanceA pilot-scale 6 kW RF system with conveyor belt was used to determine the heating uniformity and quality changes of pistachios. For a combination with hot air surface heating and mixing, an effective and continuous RF disinfestation method could be developed for pistachios. The RF heating technology has been successfully demonstrated for disinfesting walnuts in California, USA. We tried to expand the industrial applications of RF heating for disinfesting pistachios, to replace the chemical fumigation. This research may provide potential industrial applications of RF treatments for disinfestations based on fast and uniform heating.     

Efficacy of two Nigeria-derived diatomaceous earths against Sitophilus oryzae (Coleoptera: Curculionidae) and Rhyzopertha dominica (Coleoptera: Bostrichidae) on wheat

We investigated the effectiveness of two raw diatomaceous earths (DEs) obtained from Bularafa and Abakire districts in Yobe State, Nigeria, against the rice weevil, Sitophilus oryzae (L.) and the lesser grain borer, Rhyzopertha dominica (F.). Insecto, a commercialized DE, was also tested as standard check. Adults of the two species were exposed on wheat admixed with the respective DEs at a dose rate of 1000 ppm, at 30 °C and 55% RH. Relative to R. dominica, Insecto, Bularafa and Abakire DEs induced 14-d corrected adult mortalities of 73.6, 61.2 and 40.4%, respectively. Corrected 14-day adult mortalities against S. oryzae were 100, 100 and 81%, respectively. Mortality increased with increasing exposure duration. Bularafa and Insecto DEs were more effective than Abakire DE both in terms of adult insect mortality and F1 progeny suppression in the two species investigated. Both species avoided contact with DE-treated wheat. Bularafa and Insecto DEs contain higher levels of silica (81.0% and 87.0%, respectively) than Abakire DE (60.2%), and also have smaller particle sizes than Abakire DE. These differences in silica level and particle size probably explain why Bularafa and Insecto DEs are more effective against S. oryzae and R. dominica than Abakire DE. The decreasing order of efficacy of the three DEs against the two pest species is Insecto > Bularafa > Abakire. Bularafa DE has potential for the management of insect pests of stored grain in Nigeria.     

Validation of radio frequency treatments as alternative non-chemical methods for disinfesting chestnuts

Chemical fumigation has been widely used to control insects in postharvest chestnuts but is inherent dangers when using fumigants. The purpose of this study was to validate application of radio frequency (RF) treatments for disinfesting chestnuts as an alternative to chemical fumigation. A practical process protocol was developed to control insect pests in chestnuts using a 27.12 MHz free-running oscillator RF system. Fifth-instar yellow peach moth, Conogethes punctiferalis, more heat tolerant than chestnut weevil, Curculio elephas, under three temperature and time combinations using a heating block system, was selected as the targeted insect to validate the RF treatment protocol. Mortality of fifth-instar C. punctiferalis increased with increasing holding time at 55 °C using RF heating and reached 100% while holding in hot air for at least 5 min. Furthermore, there was no significant quality difference in color, fat, firmness, moisture content, protein, and soluble sugar content of chestnuts observed between RF treatments and controls. RF treatment methods hold potential to scale up for industrial applications of disinfesting chestnuts.     

Effect of uneven distribution of spinetoram-treated wheat and rice on mortality and progeny production of Rhyzopertha dominica (F.), Sitophilus oryzae (L.) and Tribolium confusum Jacquelin du Val

Laboratory bioassays were carried out in order to evaluate the effectiveness of spinetoram on rice and wheat in layer and mixture treatment applications against three major stored-grain beetle species, Rhyzopertha dominica, Sitophilus oryzae and Tribolium confusum. Spinetoram was applied at 1 ppm (1 mg/kg of grain). In the layer treatment the grain was placed in vials (8 cm high, 3 cm in diameter); in those vials there was five categories of grain: untreated (control), totally-treated, and with the upper 1/8, 1/4 and 1/2 treated. Also, there were two categories of insect introduction: before or after the grain placement. In the mixture treatment, the vials contained 20 g of grain divided into six categories: vials that contained untreated grain (control) and vials that contained 5, 10, 25, 50 and 100% treated grains. Mortality was assessed after 14 d for both treatments but with an intermediate 7-d assessment for the mixture treatment. After this interval, all adults were removed, and progeny production was measured 65 d later. From the species tested, R. dominica was by far the most susceptible in both treatments. Generally, in the layer treatment, mortality of R. dominica reduced with the size of the treated layer in the vials. Also, mortality was significantly lower when the exposed R. dominica adults had been placed before the introduction of the grain. For S. oryzae, mortality was lower in comparison with R. dominica and in general, mortality was lower on rice than on wheat, even in the case of totally-treated grains. Survival of T. confusum was considerably higher than both R. dominica and S. oryzae. In the mixture treatment, mortality of R. dominica was 82–100% after 14 d of exposure. Again mortality was considerably lower on rice than on wheat. For S. oryzae, mortality was higher in vials containing totally-treated or 50% treated kernels, in comparison with the other treatments. Progeny production of R. dominica in the layer treatment increased with the reduction of the treated layer for both commodities. In contrast, for S. oryzae, there were no differences in progeny production counts between treated and untreated grains, with the exception of totally-treated wheat. In the mixture treatment progeny production increased with the reduction of the percentage of the treated grains, but there were considerable differences between wheat and rice. The overall results suggest that spinetoram is very effective against R. dominica, moderately effective against S. oryzae, and not very effective against T. confusum. Uneven application of spinetoram may, under certain circumstances, provide satisfactory control of R. dominica.     

Efficacy of Beauveria bassiana in combination with an electrostatically charged dust for the control of major stored-product beetle species on concrete

Laboratory bioassays were carried out to determine the insecticidal efficacy of a Beauveria bassiana formulation (Bb38, Exosect Ltd, UK), which is based on the combined use of the fungus with the electrostatically charged dust Entostat. The efficacy of Bb38 was conducted on concrete surfaces against adults of the lesser grain borer, Rhyzopertha dominica, the rice weevil, Sitophilus oryzae, the confused flour beetle, Tribolium confusum and the rusty grain beetle, Cryptolestes ferrugineus, in two series of bioassays. In the first series, adults of the above species were exposed on concrete surfaces treated with Bb38 and mortality was recorded after 7 and 14 days of exposure (immediate mortality). These tests were carried out in all combinations of two temperatures, i.e. 25 and 30° C and two levels of relative humidity (r.h.), i.e. 55 and 75%. In the second series of bioassays, adults of the above species were exposed to Bb38 for 7 days, and after this interval, the surviving individuals were transferred in untreated concrete, where mortality was recorded again 7 and 14 days later (delayed mortality). From the species tested, R. dominica was by far the most susceptible, given that mortality reached 100% in almost all temperatures and r.h. levels. From the other species, S. oryzae and C. ferrugineus were moderately susceptible, while Bb38 was less effective for T. confusum. In the second series, immediate mortality for R. dominica was much higher than that of the other species. Moreover, delayed mortality of R. dominica reached 100% in contrast with the other species, where delayed mortality was low. Based on the results of the present work, we found that the insecticidal effect of Bb38 is not affected much by temperature and r.h., for the vast majority of the species and conditions tested. Moreover, in some cases, there was some post-exposure delayed activity of the formulation. This is one of the few studies that examine commercial formulations of fungal-based insecticides against stored product insects, which are expected to provide solutions in stored product protection, where traditional insecticides cannot be applied, as in the case of organic products.     

Mortality and movement of Cryptolestes ferrugineus and Rhyzopertha dominica in response to cooling in 300-kg grain bulks

We examined the effect of low temperatures on insect population density and mortality of adult and immature stages of Cryptolestes ferrugineus and Rhyzopertha dominica in three barrels holding 300 kg of wheat each. Barrels were infested with 2 insects/species/kg and left to develop at 30 °C for 5 months. Temperature of the grain mass before cooling was 38 °C in the centre to a low of 28 °C on the periphery. On 11 February the building door was opened to allow for cooling of the grain. During the 3 weeks of cooling, temperatures in the centre reached as low as −5 °C. Segregated (11 segments) grain trier samples were collected from three locations in each barrel, from February until March 2013 (6 dates), sieved, and the number of live and dead adults counted. Sieved grain was held for 5 weeks 30 °C and emerged adults counted to give an estimation of immature stages within the grain at the time of sampling. Rhyzopertha dominica adults were found mainly in the top 40 cm of the barrel, and there was little movement to the centre as the grain mass cooled. The initial distribution of C. ferrugineus adults was more complex; in two barrels adults were mostly in the centre of the grain mass, while in the other barrel, more adults were found on the periphery. When the grain mass cooled, C. ferrugineus adults in all barrels were found mostly in the centre. On day 0, the average number of live adults of C. ferrugineus and R. dominica were 232 ± 56 and 414 ± 48 insects/100 g, respectively. Rhyzopertha dominica adults were more susceptible to low temperatures than C. ferrugineus. The density of immatures of C. ferrugineus and R. dominica were similar at 0 d, there was a decline over the 21 d, but there was some survival at day 21.     

Dosage-mortality relationships for Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) exposed to heat in a fluidized bed

Batches of wheat containing immature Rhyzopertha dominica were heated in a fluidized bed to examine the influence of air inlet temperature, bed depth and grain temperature on the exposure time needed for a given level of mortality.With a bed depth of 160 mm, raising inlet temperature from 60 to 80°C decreased the LT_99.9 for R. dominica from 16.1 to 3.25 min: corresponding values for 20 mm beds were 1.92 and 0.54 min.For a given bed depth, $\text{1}\text{LT}{}_{99.9}$ was linearly related to inlet temperature. With inlet temperatures of 80 to 90°C, LT values were linearly related to bed depth over 40 to 160 mm. By contrast, LT value and bed depth were not linearly related at lower temperatures.With beds of 40 to 160 mm, the grain temperature asociated with 99.9% mortality ranged from 57.1 to 64.0°C and varied with inlet temperature but not, generally, with bed depth. Heating grain to 56–57°C and allowing it to soak, unfluidized, before cooling increased mortality from about 50 to > 99%.Four other species of stored product beetle suffered complete mortality when subjected to a treatment expected to yield 99.9% mortality of R. dominica.The experimental results are discussed in terms of heating strategies, heat recovery and the choice of optimal bed depth.     

Effect of thiamethoxam partial grain treatment to Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) adults

The efficacy of partial treatment of two commodities (wheat and rice) with thiamethoxam against adults of Rhyzopertha dominica (F.) and Sitophilus oryzae (F.) was tested by mixing different proportions of thiamethoxam-treated and untreated grains. Thiamethoxam was applied to these grains in two different doses 1 and 5 ppm, while the percentage of the treated grain quantity ranged between 0 and 100%. Adult mortality was recorded after time exposure intervals of 7 and 14 d. Irrespectively of the dose, adult mortality was raised with increase in the percentage of treated kernels as well as the exposure time. Applications of thiamethoxam on wheat were more effective than on rice and on R. dominica than on S. oryzae, especially at 1 ppm, for both exposure intervals. The effective “critical” percentage, causing control similar to 100% treatment, of thiamethoxam to grain mass at 5 ppm was 50% for both species. For the examined scenario of partial treatment, thiamethoxam found to be effective against the tested species which makes it a candidate for use in the stored grain protection.     

Delayed mortality responses of Rhyzopertha dominica (F.) adults subjected to short exposures on spinosad-treated wheat

Laboratory studies were conducted to characterize post-exposure (delayed) mortality responses of adults of the lesser grain borer, Rhyzopertha dominica (F.), following brief exposures to wheat treated with dry and liquid spinosad formulations at the labeled rate of 1 mg (a.i.) kg⁻¹ of grain. Exposure of R. dominica adults to a dry spinosad formulation at the labeled rate for 4 h resulted in 16–34% mortality. When these adults were placed on untreated wheat, post-exposure mortality continued to increase in a non-linear fashion, with 100% mortality observed at 60 h. Similarly, when R. dominica adults were exposed to wheat treated with a liquid spinosad formulation at the labeled rate for 0.5–48 h, 100% post-exposure mortality on untreated wheat occurred within 24–168 h. Exposure for 72 h resulted in 100% mortality on spinosad-treated wheat itself. There was an inverse relationship between exposure of adults to spinosad-treated wheat and time to 100% mortality on untreated wheat. These results suggested that short exposures (0.5–48 h) of R. dominica adults to wheat treated with the labeled rate of spinosad will ensure its complete control even after removal from treated grain. Adults of R. dominica which disperse to untreated grain after brief exposures to spinosad-treated wheat may eventually die because of delayed toxicity effects of spinosad against this economically important insect species.     

Geostatistical analysis of adult Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in wheat stored at constant temperatures

Insect monitoring and sampling programmes are used in the stored grains industry for the detection and estimation of insect pests. At the low pest densities dictated by economic and commercial requirements, the accuracy of both detection and abundance estimates can be influenced by variations in the spatial structure of pest populations over short distances. Geostatistical analysis of Rhyzopertha dominica populations in 2-dimensions showed that, in both the horizontal and vertical directions and at all temperatures examined, insect numbers were positively correlated over short (0–5 cm) distances, and negatively correlated over longer (≥10 cm) distances. Analysis in 3 dimensions showed a similar pattern, with positive correlations over short distances and negative correlations at longer distances. At 35 °C, insects were located significantly further from the grain surface than at 25 and 30 °C. Dispersion metrics showed statistically significant aggregation in all cases. This is the first research using small sample units, high sampling intensities, and a range of temperatures, to show spatial structuring of R. dominica populations over short distances. This research will have significant implications for sampling in the stored grains industry.     

Impacts of Storicide II on internal feeders of Brown rice

Protectants applied to grain can reduce damage caused by insect feeding during storage. Although these protectants are effective against many external feeders, they may also reduce damage caused by internal feeders as they often interact with the exterior surface of the grain during their larval or adult stages to feed or oviposit. For this study, we investigated impacts of Storicide® II applied to brown rice on three different internal feeders: Rhyzopertha dominica (Fauvel), Sitophilus oryzae (L.), and Sitotroga cerealella (Olivier). We also investigated the effects of this protectant at three different temperatures and when it was combined with different percentages of untreated brown rice. Time-series clustering was also performed to determine whether treatments caused disruptions to the timing of progeny emergence. Overall, R. dominica was the most susceptible as mortality and knockdown were observed in mixtures containing 10% treated brown rice. In contrast, S. cerealella was the least susceptible as mixtures containing at least 50–75% treated brown rice were required to reduce progeny production. However, lowering the temperature to 22 °C did reduce the amount of treated brown rice required to reduce progeny emergence and also reduced the number of progeny that emerged synchronously, which would likely reduce mating and reduce population levels over time. Similar effects on progeny were observed for S. oryzae and R. dominica. Overall, these findings suggest that Storicide II can reduce population levels of internal feeders and that combining this protectant with cooler temperatures can provide additional protection.     

Detection and quantification of the insect pest Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in rice by qPCR

The early detection of insects during grain storage and processing remains a major issue for the cereal industry, especially when immature stages are hidden inside the grain kernels. For this reason, we developed a qPCR method to detect and quantify one of the main pests of stored products in rice: the coleopteran internal feeder Rhyzopertha dominica. For that purpose, a specific primer set was designed to amplify artificial infestations of this pest in rice. Then, using a regression model, a standard curve was generated that correlated individuals to adult equivalent DNA quantity (inverse of the C_t value). Results revealed that the designed primer set was specific for R. dominica when tested against the other 4 common internal feeders in grain. The technique showed to be accurated (DNA was detected in more than 73% of the samples) and sensitive to insect presence (i.e. from 0.02 adults, 0.1 3rd instar to pupae or 13 egg to 2nd instar detectable per kg of rice). Moreover, the detection of R. dominica was strongly associated with a given infestation size: DNA quantity increased along with the size of the population. The use of the described qPCR protocol in grain and milling factories may enhace the critical detection and quantification of R. dominica populations in raw materials and processed food.