Efficacy of methoprene for multi-year protection of stored wheat,brown rice,rough rice and corn

Hard red winter wheat, brown rice, rough rice, and corn were treated with the insect growth regulator (IGR) methoprene at rates of 1.25 and 2.5 ppm, held for 24 months at ambient conditions in buckets on the floor of a grain bin, and sampled every two months. Bioassays were done by exposing 10 mixed-sex adults of Rhyzopertha dominica (F.), the lesser grain borer, and Tribolium castaneum (Herbst), the red flour beetle, on wheat, R. dominica and Sitotroga cerealella (Oliver), the Angoumois grain moth, on brown rice and rough rice, and T. castaneum and S. cerealella on corn. Sample size for all commodities was about 80 g, and these samples were held for 3 months at 27°C-60% r.h. Both rates of the IGR completely suppressed adult progeny development of R. dominica with little resulting feeding damage, sample weight loss, or insect damaged kernels (IDK). Some adult progeny production of S. cerealella and resulting IDK occurred at both rates on rough rice, brown rice, and corn, but was far less than in untreated controls. There was little adult progeny production but some feeding damage caused by larval T. castaneum in the treated wheat and corn but again far less than in untreated control. Allowing continual exposure of parental adults on grains treated with an IGR, rather than exposing those parental adults for a short time period, may give more accurate evaluations of residual efficacy. Results show that methoprene used as a grain protectant will give residual control of stored product beetles for 24 months, but complete control of S. cerealella may require inclusion of a contact insecticide.     

Susceptibility of varieties of stored rough rice to losses caused by storage insects

Losses caused by Sitophilus oryzae (L.), Rhyzopertha dominica (F.), and Sitotroga cerealella (Olivier) in 6 commercial varieties of rough rice from the Southern United States were assessed as weight loss of rough rice, loss of milling yield, and loss of monetary value. Over 3 insect generations, S. oryzae caused the least damage, probably because this species requires grains with gross hull defects and the proportion of such grains was relatively small. Damage attributable to S. cerealella or R. dominica was approximately equal. The varieties Vista and Lebonnet were the most susceptible and the variety Dawn the most resistant after 3 generations.     

Insecticidal effect of spinetoram against six major stored grain insect species

Spinetoram is a novel insecticide that belongs to the spinosyn class of insecticidal chemicals. The efficacy of spinetoram against numerous insect pest species in a variety of field crops has been well demonstrated. However, there are no data available for the effectiveness of spinetoram against stored grain insects. In the present study, we evaluated spinetoram as a grain protectant, against six stored-product Coleoptera. The species tested were: the rice weevil, Sitophilus oryzae, the lesser grain borer, Rhyzopertha dominica, the larger grain borer, Prostephanus truncatus, the confused flour beetle, Tribolium confusum, the granary weevil, Sitophilus granarius and the sawtoothed grain beetle, Oryzaephilus surinamensis. All species were tested at the adult stage, on wheat (or maize in the case of P. truncatus) treated to achieve spinetoram concentrations of 0.01, 0.1, 0.5, 1, 2, 5 and 10 ppm. Mortality was recorded after 1, 2, 7, 14 and 21 d of exposure, and 65 d later the wheat and maize were examined for offspring emergence. Among the species examined, P. truncatus and R. dominica were by far the most susceptible, given that mortality was close to 100% after 7 d on wheat treated or maize with 0.1 ppm of spinetoram. At this concentration, progeny production of P. truncatus and R. dominica was negligible. On the other hand, T. confusum was the least susceptible; mortality reached 95% only at 10 ppm, and only after 14 d of exposure. Similarly, O. surinamensis was of limited susceptibility to spinetoram; mortality reached 95% only after 14 d of exposure on wheat treated with 5 ppm. Nevertheless, offspring emergence of these species was extremely low. For S. granarius and S. oryzae, complete (100%) mortality was recorded after 14 d of exposure, at 0.5 and 1 ppm, respectively. At these concentrations or higher, progeny production was notably reduced. The results of the present study demonstrate that spinetoram is effective as a grain protectant, but its efficacy varies according to the target species, concentration and exposure interval.     

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 diflubenzuron plus methoprene against Sitophilus oryzae and Rhyzopertha dominica in stored sorghum

The efficacy of diflubenzuron (1 mg kg⁻¹)+methoprene (1 mg kg⁻¹) against Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) in sorghum was evaluated in a silo-scale trial in southeast Queensland, Australia. Sorghum is normally protected from a wide range of insects by mixtures of grain protectants. The chitin synthesis inhibitor diflubenzuron was evaluated as a potential new protectant for S. oryzae in combination with the juvenile hormone analogue methoprene, which is already registered for control of R. dominica. Sorghum (ca 200 t) was treated after harvest in 2000 and assessed for treatment efficacy and residue decline during 6.5 months storage. The reproductive capacity of S. oryzae and R. dominica was greatly reduced in bioassays of treated sorghum throughout the trial, and efficacy remained relatively stable during the trial. An initial exposure of S. oryzae adults to treated sorghum for 2 weeks reduced F₁ progeny production of all strains by 80.8-98.8%, but a second exposure of 4 weeks reduced F₁ progeny production by 98.5-100%. In addition, the reproductive capacity of any S. oryzae progeny produced was greatly reduced. Exposure of R. dominica adults to treated sorghum for 2 weeks reduced F₁ progeny production of all strains by 99.6-100%, including a methoprene-resistant strain. The results indicate that S. oryzae or R. dominica adults invading sorghum treated with diflubenzuron (1 mg kg⁻¹)+methoprene (1 mg kg⁻¹) would be incapable of producing sustainable populations.     

Persistence and efficacy of indoxacarb against three stored product insect species on wheat and maize

In the present study, we investigated the insecticidal efficacy of indoxacarb on wheat and maize, against adults of three major stored-grain species, the rice weevil, Sitophilius oryzae (L.) (Coleoptera: Curculionidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and the confused flour beetle, Tribollium confusum Jacquelin Du Val (Coleoptera). For this purpose, bioassays were carried out with indoxacarb at the doses 0.1, 1 and 10 ppm. Moreover, the treated grains were left at the laboratory for a period of six months, in order to examine the residual effect of indoxacarb, by conducting bioassays at monthly intervals. For S. oryzae and R. dominica, adults were exposed in the treated grains for 7 and 14 d, while for T. confusum adults were exposed for 14 and 21 d, in order to estimate the mortality level. After the termination of this interval, the treated samples were left for an additional period of 65 days, on which progeny production was recorded. R. dominica was by far more susceptible than S. oryzae, given that mortality, in many cases, reached 100% even after 7 d of exposure, even at the lowest dose rate of 0.1 ppm. At the same time, for this species, progeny production was low. For S. oryzae, mortality was low at 0.1 ppm, with high levels of progeny production. T. confusum was the least susceptible of the species tested. Generally, during the experimental period, the efficacy of indoxacarb was decreased, but mortality was higher on wheat than on maize. Indoxacarb residues determination by GC-ECD indicated that after 6 months 33% of the insecticide remains in grains at 0.1 ppm dose, about 40–50% at 1 ppm and about 40–60% at 10 ppm dose. Based on the results of the present work, indoxacarb is an effective grain protectant, at least in the case of R. dominica and S. oryzae.     

Efficacy of layer grain treatment with thiamethoxam against adults of Rhyzopertha dominica (F.) and Sitophilus oryzae (L.)

The insecticidal effect of the neonicotinoid insecticide thiamethoxam, applied in layers of wheat, was studied in laboratory experiments, for the control of the lesser grain borer, Rhyzopertha dominica (F.) and the rice weevil Sitophilus oryzae (L.). In general, the increase of the size of the treated layer of wheat increased parental morality and decreased progeny production for both species. However, progeny production could not be totally avoided, even when the entire grain quantity was treated. Parental morality was lower for R. dominica than for S. oryzae, but the reverse was observed for progeny production for all treatments. Insect placement drastically affected thiamethoxam efficacy, since morality was generally higher when insects were forced to move downwards from the upper layer, as compared with insects that had been placed in the bottom part of the wheat column. Our study shows that thiamethoxam can reduce insect populations in partially treated wheat, at concentrations that are comparable with other, currently registered grain protectants.     

Effect of paddy variety,milling status and aeration on the progeny emergence of Sitophilus oryzae L. (Coleoptera: Curculionidae)

In Sri Lanka, insects cause enormous losses in stored paddy; the rice weevil Sitophilus oryzae is a devastating insect. The magnitude of losses in stored paddy caused by insects varies with characteristics of paddy but has not yet been fully investigated. Due to the increased concerns on the use of synthetic chemicals, safer alternative pest management strategies for stored paddy are needed. Objectives of this study were to determine the effect of paddy variety, milling status and nature of aeration on the progeny emergence of S. oryzae. The experimental design was a three-factor factorial, completely randomized design (CRD).Freshly emerged S. oryzae adults were introduced to un-milled paddy or milled/polished rice belonging to traditional and improved varieties. The samples were maintained either open or airtight, and the progeny adults emerged was determined at monthly intervals. Progeny emergence was lower in the traditional varieties, un-milled paddy and under air-tight condition compared to improved varieties, milled/polished rice and aerated samples, respectively. Overall, the improved variety Bg 300 exhibited the maximum resistance to infestation by S. oryzae. Furthermore, white-colour and long-grain varieties produced lower progeny of S. oryzae than red-colour and short-grain varieties, respectively. It is concluded that the maximum protection in paddy/rice from insect infestation during storage can be achieved by using traditional varieties, stored as un-milled paddy (without dehusked) under airtight condition.     

Gone with the weed: Population growth of Sitophilus oryzae and Rhyzopertha dominica in wheat and barley containing seeds of Silybum marianum

In the present study we examined the effect of seeds of the weed Silybum marianum (L.) Gaertn. (Asterales: Asteraceae) in different combinations with wheat or barley in the population growth of two major stored product insects, Rhyzopertha dominica (F.) (Coleoptera: Bostryhidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae). The evaluation took place on 7 different quantitative combinations of the weed, i.e. 0, 1, 5, 10, 20, 50 and 100% of the total amount of the grain mass. All combinations were kept under constant conditions of 25 ^οC and 65% relative humidity (r.h.) for 65 days. After this interval, adult progeny production was counted, and classified as dead or alive. In general, progeny production was higher on wheat than on barley for R. dominica, but the reverse was recorded for S. oryzae. No progeny production was recorded for either species when S. marianum containment was 100%. Moreover, for both species, the decrease of the percentage of S. marianum caused an increase in progeny production, but this decrease was not linear. The study concludes that R. dominica and S. oryzae cannot develop on S. marianum seeds, but they can develop in mixtures of these seeds with grains.     

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.     

Laboratory evaluation of natural embelin as a grain protectant against some insect pests of wheat in storage

The effectiveness of natural embelin isolated from berries of Embelia ribes is discussed as a grain protectant for wheat in storage. More than 50% mortality of Sitophilus oryzae (L.) adults was observed in wheat grains when treated at 0.025% concentration. The F1 progeny was reduced in treatments. However, productivity (progeny/21 adult-days) in treatments was not significantly different from controls. In the case of Rhyzopertha dominica (F.), there was 50% adult mortality at 0.025% concentration after 1 day and 3 months of storage, and both progeny and productivity were reduced significantly at all the concentrations. After 8 months of storage, only the highest concentration of 0.1% exhibited appreciable adult mortality, yet the F1 progeny and productivity were significantly low in all the concentrations of embelin. Against larvae of Corcyra cephalonica (Stainton) and Ephestia cautella (Walker), 0.0125% concentration retained its effectiveness after 8 months, while higher concentrations of 0.05 and 0.1% offered good protection against Trogoderma granarium Everts larvae. Embelin in the present study did not show any contact toxicity to adults of S. oryzae or R. dominica. The treatment did not have any adverse effect on germination of wheat seeds. In general, the effectiveness of embelin tested against five insect species was C. cephalonica > E. cautella > R. dominica > T. granarium > S. oryzae.     

Comparative toxicity of nanostructured alumina and a commercial inert dust for Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) at varying ambient humidity levels

The widespread concern for environmental and human health has raised the need for new reduced-risk control strategies and the search for new chemical classes of pesticides. Recently, a novel type of particulate material, nanostructured alumina (NSA) has been found to induce mortality in insects exposed to wheat treated with NSA dust. Preliminary studies have shown insecticidal activity of NSA particles on two insect species, Sitophilus oryzae (L.), and Rhyzopertha dominica, (F.), major pests of stored grain. We investigated the toxicity of NSA and Protect-It^® diatomaceous earth (DE) using dry dust applications at three different relative ambient humidity levels. Results showed that NSA was more effective in killing S. oryzae than Protect-It^® and was equally toxic to R. dominica. Treatment with both products also reduced progeny production. In addition, R. dominica was less susceptible to inert dusts than S. oryzae. Our results suggest that NSA might prove a good alternative or complement to DE based products, and encourage further testing with other insect pests and systems, plus experiments on delivery options to further enhance NSA products.     

Residual toxicity of a commercial cypermethrin formulation on grains against four major storage beetles

In the present study, we investigated the residual insecticidal efficacy of a commercial cypermethrin formulation applied on grains (wheat, maize) against adults of Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.) and Prostephanus truncatus (Horn) in laboratory bioassays. The insecticide was applied in its label dose on the grains and a bioassay was initiated at the day of application and every month for four consecutive months (5 bioassays in total). In each bioassay, adult mortality levels were determined after exposure for 7, 14 and 21 d. After the final evaluation, all beetles (dead and alive) were removed and the number of offspring was assessed after an additional interval of 65 d. Based on our results, the application of the tested cypermethrin formulation as a grain protectant provided long-term protection against R. dominica and P. truncatus adults, as in most cases complete control was achieved for these two species, even after four months of storage of the treated commodities. In the case of S. oryzae and O. surinamensis, adult mortality did not reach 100% in any of the cases, moreover, a gradual decline of mortality levels was recorded over the 4-month period of storage. Finally, for S. oryzae and P. truncatus progeny production was notably suppressed by cypermethrin. Results show that the cypermethrin formulation tested could be a valuable tool for stored grain protection, however, factors such as the target species and the storage interval should be taken into consideration.     

Assessment of Rhyzopertha dominica (F.) progeny and feeding damage on rice dried with infrared radiation

Infrared radiation (IR) is a method of drying grains that eliminates insect and microbial pests. It is unknown if IR could cause grains to be more susceptible to insects. Thus, the effects of IR on Rhyzopertha dominica development and feeding damage using long-grain rice varieties, Clearfield XL745 (hybrid) and CL152 (pureline), were examined. Rough rice was dried with three IR intensities: 2.15, 2.83, and 10.84 kW/m². The number of progeny developed, feeding damage, and frass weight after IR-drying were compared with air-drying methods for rough rice and rice milled to brown rice after drying. Since R. dominica develop internally, X-ray technology was used to examine internal progeny and feeding damage. Progeny development and kernel damage appeared to be more affected by fraction (brown rice) than the cultivar of rice or intensity of IR used, with more progeny produced on brown rice than rough rice. An IR intensity of 10.84 kW/m² increased the number of overall progeny, the amount of adults, and frass produced on CL152 brown rice. An intensity of 10.84 kW/m² also increased the amount of larvae observed for both varieties and fractions. The intensity of 10.84 kW/m², under the conditions of this study, is not recommended for drying rice.     

Evaluation of a new insecticide formulation (F2) as a protectant of stored wheat, maize, and rice

A new commercial formulation, F2, was evaluated as a protectant of stored wheat, stored maize, and stored rough (paddy) rice. This formulation comprises the technical active ingredients 0.03% deltamethrin, 0.37% piperonyl butoxide, and 0.95% chlorpyriphos-methyl, plus 10% mineral oil and 88.0% of the diatomaceous earth Protect-It^®. Tests were conducted with dust and slurry formulations at 50 and 100 ppm, 57% and 75% relative humidity, and 22°C, 27°C, and 32°C. On wheat, survival of the lesser grain borer, Rhyzopertha dominica (F.), ranged from 0% to 30.0%, survival of the rice weevil, Sitophilus oryzae (L.), was 0-6.2%, and survival of the red flour beetle, Tribolium castaneum (Herbst), was 0-97.5%. Few F₁ adults of any of the three species were found in the treated samples. Survival of the maize weevil, Sitophilus zeamais (Motschulsky), on treated corn was 0-32.5%, while survival of T. castaneum was 0-88.7% in the 50-ppm dust and slurry treatments, and 0-51.4% in the 100-ppm treatments. Again, few F₁ adults of either species were found in treated maize. Survival of R. dominica on treated rough rice averaged 0-4.1% and survival of S. oryzae on treated rice was 0-48.8%, but the majority of weevils that survived were in one replicate. F₁ adults in the treatments ranged from 0 to 24.4. Results show that the combination insecticidal product F2 was extremely effective on all three commodities at the rate of 100 ppm, as either a dust or slurry, and could be used as a commodity protectant.     

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.     

Effectiveness of spinosad as a grain protectant against resistant beetle and psocid pests of stored grain in Australia

Effectiveness of the bacterium-derived insecticide, spinosad, was determined against eight storage pests of Australia. Laboratory experiments were carried out on relevant resistant strains of four beetle and four psocid species, with the aim of determining the potential of spinosad as a new grain protectant. To explore the possibility that spinosad could have delayed effects, we exposed all insects for 14 d initially and then a further 14 and 28 d for psocids and beetles, respectively. Adult insects of each strain were exposed to untreated wheat (control) and wheat treated with spinosad at 0.1, 0.5 and 1 mg [a.i.]/kg of grain, and adult mortality and reduction of progeny were determined. Among beetles, spinosad was most effective against Rhyzopertha dominica (F.), with 100% adult mortality and progeny reduction after 14 d exposure at 1 mg [a.i.]/kg. Efficacy of spinosad was less with Sitophilus oryzae (L.), and least with Tribolium castaneum (Herbst) and Oryzaephilus surinamensis (L.). Against the psocids, spinosad was most effective against Liposcelis entomophila (Enderlein), with 100% adult mortality after 28 d exposure at 1 mg [a.i.]/kg and 92% progeny reduction after 14 d exposure and 100% subsequently. Spinosad was only moderately effective against Liposcelis bostrychophila Badonnel, L. decolor (Pearman) and L. paeta Pearman. Our findings suggest spinosad to be a potential protectant against R. dominica and L. entomophila in stored grain in Australia. This potential use would be in combination with another protectant capable of controlling other members of the pest complex.     

An evaluation of fluidized-bed heating as a means of disinfesting wheat

Wheat of 14% m.c. containing all immature stages of Sitophilus oryzae (L.), Rhyzopertha dominica (F.) and Sitotroga cerealella (Oliv.) was exposed to air temperatures of 60, 70 or 80°C in a 10 kg capacity fluidized-bed operated with an airflow of 14.51 ls^?1 kg^?1 at 1.6 m s^?1. Exposures of 12, 6 and 4 min respectively produced grain surface temperatures of 59, 62 and 65°C and gave almost complete disinfestation. The required minimum exposure was determined by the heat tolerance of R. dominica which exceeded that of the other species. The moisture content of treated wheat was not changed appreciably and its baking quality was not impaired. Experiments with S. oryzae and R. dominica showed that the adults were also controlled by such exposures. The cost of fluidized-bed heating is discussed and appears to be comparable to that of recirculatory fumigation with methyl bromide.     

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.     

Survival and reproduction of Tribolium castaneum (Herbst), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) following periods of starvation

This study determined the starvation tolerance of Tribolium castaneum (Herbst), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) in terms of both adult survival and reproduction, the impact of starvation on reproduction not having been studied before. Experiments were conducted at 30 °C and 55% or 70% r.h. using a laboratory strain and a field strain of each species. The number of progeny was a better indicator of the impact of starvation on a species than adult survival. Tribolium castaneum was the most tolerant species, requiring up to 35 d starvation before no progeny were produced. Rhyzopertha dominica and S. oryzae required up to 8 d starvation before no progeny were produced. The results suggest that hygiene will have a greater impact on populations of S. oryzae and R. dominica than T. castaneum.