Impact of resistance on the efficacy of binary combinations of spinosad, chlorpyrifos-methyl and s-methoprene against five stored-grain beetles

Laboratory experiments were conducted to determine the efficacy of spinosad (a biopesticide), chlorpyrifos-methyl (an organophosphorus compound (OP)) and s-methoprene (a juvenile hormone analogue) applied alone and in binary combinations against five stored-grain beetles in wheat. There were three strains of Rhyzopertha dominica, and one strain each of Sitophilus oryzae, Tribolium castaneum, Oryzaephilus surinamensis and Cryptolestes ferrugineus. These strains were chosen to represent a range of possible resistant genotypes, exhibiting resistance to organophosphates, pyrethroids or methoprene. Treatments were applied at rates that are registered or likely to be registered in Australia. Adults were exposed to freshly treated wheat for 2 weeks, and the effects of treatments on mortality and reproduction were determined. No single protectant or protectant combination controlled all insect strains, based on the criterion of >99% reduction in the number of live F₁ adults relative to the control. The most effective combinations were spinosad at 1 mg kg⁻¹+chlorpyrifos-methyl at 10 mg kg⁻¹ which controlled all strains except for OP-resistant O. surinamensis, and chlorpyrifos-methyl at 10 mg kg⁻¹+s-methoprene at 0.6 mg kg⁻¹ which controlled all strains except for methoprene-resistant R. dominica. The results of this study demonstrate the difficulty in Australia, and potentially other countries which use protectants, of finding protectant treatments to control a broad range of pest species in the face of resistance development.     

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.     

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.     

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.     

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.     

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.     

Laboratory studies evaluating the efficacy of diatomaceous earths, on treated surfaces, against stored-product insect and mite pests

The efficacy of dry dust and slurry applications of Silico-sec^® and Diasecticide™, applied to glass and plastic surfaces, was assessed in the laboratory against the beetles Tribolium castaneum, Sitophilus granarius and Oryzaephilus surinamensis, the mites Acarus siro and Lepidoglyphus destructor, and against larvae of the moth Ephestia kuehniella. For the insects, doses of 5, 10 and 20 g/m² were evaluated for all preparations, while for the mites 0.5, 1 and 2 g/m² of the dry dusts, and 2.5, 5 and 10 g/m² of the slurries were assessed. Mortality was evaluated after 7 days and 24 h for the insects and mites, respectively, in conditions of 15 °C and 80% r.h., chosen to represent typical UK conditions immediately after harvest. The Silico-sec^® dry dust was the most effective treatment with mean mortalities ranging from 93-100% for all the pest species at all doses. The Diasecticide™ dry dust was ineffective against T. castaneum and S. granarius with mean mortalities ranging from 86-98% for the other species at the highest dose. With both DEs the slurry applications were generally less effective than the dry dusts at equivalent doses. Oryzaephilus surinamensis was the least tolerant insect species and S. granarius and T. castaneum the most tolerant. The mite A. siro was less tolerant than L. destructor.     

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.     

Laboratory assessment of insecticidal effectiveness of natural zeolite and diatomaceous earth formulations against three stored-product beetle pests

The insecticidal effectiveness of two natural zeolite formulations (Minazel plus and Minazel), applied to wheat at selected rates of 0.25, 0.50 and 0.75 g/kg, and a diatomaceous earth formulation (DE) (Protect-It™), applied at the recommended rates of 0.15 g/kg for Sitophilus oryzae, 0.20 g/kg for Rhyzopertha dominica and 0.30 g/kg for Tribolium castaneum, were tested under laboratory conditions (24 ± 1 °C temperature and 45 ± 5% relative humidity). The highest adult mortality was observed after the longest exposure period of 21 days and 7 days of recovery, when all three zeolite dosage rates and the recommended DE dosage caused 97-100% mortality of S. oryzae and 94-100% of T. castaneum. On the other hand, 100% mortality was not achieved in any test variant involving R. dominica; the highest (about 92%) was detected for DE, while 52% and 79% mortality was achieved with the zeolites at the highest rate of 0.75 g/kg. Progeny reduction by >90% was achieved after 21 days of contact of all three beetle pests with DE-treated wheat, while the same level of reduction was achieved for S. oryzae and T. castaenum only after contact with the highest rate of the zeolite product, Minazel. Thus the two zeolite formulations are comparable to diatomaceous earth in controlling adult S. oryzae, R. dominica and T. castaneum, but only the Minazel formulation could effectively protect wheat from attack by S. oryzae or T. castaneum, and only with a higher rate of application than for the DE formulation.     

Enhanced fumigant toxicity of allyl acetate to stored-product beetles in the presence of carbon dioxide

Toxicity of allyl acetate (5-25 mg/l doses) to mixed-age cultures of stored-product beetles including Cryptolestes ferrugineus, Lasioderma serricorne, Oryzaephilus surinamensis, Rhyzopertha dominica, Sitophilus oryzae and Tribolium castaneum in the presence of carbon dioxide (CO₂) (10% and 20%) with a 48-h exposure period was studied in the laboratory at 27±2 °C. Depending on dosage and the insect species, the fumigant toxicity of allyl acetate was enhanced by CO₂. At most of the allyl acetate+CO₂ combinations, increased mortality was observed in C. ferrugineus, O. surinamensis and S. oryzae. In L. serricorne and T. castaneum, which are tolerant to allyl acetate, higher mortality due to CO₂ was achieved at selected dose combinations only (e.g. 15 mg/l allyl acetate+20% CO₂). Significant increase in mortality of R. dominica (the most susceptible species to allyl acetate) exposed to allyl acetate in the presence of CO₂ was not evident except at the lower dose of 5 mg/l allyl acetate+CO₂ that caused 31.7% mortality. The mortality data show that CO₂ could be used as an adjuvant for allyl acetate.     

Bioactivity of Jatropha curcas L. to insect pests of stored products

The objective of this research was to assess insecticidal activity of seeds and derivatives of Jatropha curcas to insect pests of stored grains. Lethal exposure times were estimated for 50 and 95% (LT₅₀ and LT₉₅) of the adults of Sitophilus zeamais and Rhyzorpertha dominica to seeds of four genotypes of J. curcas: Gonçalo, Paraguaçu, Filomena and Bento. Toxicity of powders and aqueous extracts from seeds and pericarps of J. curcas were tested on S. zeamais, R. dominica, Tribolium castaneum and Oryzaephilus surimanensis. A uniform toxic response was observed among the four genotypes for S. zeamais and R. dominica. The powders and aqueous extracts from seeds and pericarps were lethal to S. zeamais, R. dominica, T. castaneum and O. surimanensis. However, insect mortality was higher in the treatments from seeds, compared to the treatments from pericarps.     

Insect population dynamics in commercial grain elevators

Data were collected in 1998-2002 from wheat stored in commercial grain elevators in south-central Kansas. Bins at these elevators had concrete walls and were typically 6-9 m in diameter and 30-35 m tall. A vacuum-probe sampler was used to collect grain samples in the top 12 m of the wheat in each bin. The primary insect species found in the wheat samples were: Cryptolestes ferrugineus, Rhyzopertha dominica, and Tribolium castaneum. In the top 3.7 m of grain, R. dominica, C. ferrugineus, T. castaneum and Sitophilus oryzae made up 44, 36, 19 and 1% of the insects found in the samples, respectively. From 3.8 to 12.2 m, R. dominica, C. ferrugineus, T. castaneum and S. oryzae were present at 84, 8, 8, and 1%, respectively. The most prevalent species also changed over time. In June, the start of wheat harvesting and storage in Kansas, insect density was low in the bins. At this time, C. ferrugineus was the most common insect, and it was found mostly in the top grain sample (0-1.2 m). In September through November, C. ferrugineus and R. dominica were at similar densities; however, from February to March, R. dominica was more common.Generally, insect density was greatest at the top and decreased with grain depth. Very few insects were found in samples collected from greater than 12 m (most of the bins contained grain to depths of 24-36 m). Insect density for all species increased rapidly from June through October. During this period less than 20% of the bins had economically significant insect densities (>2 insects/kg). From October until February, the average insect density remained fairly constant but it was greatly reduced in April, May, and June. Bins that had insect densities >2 insects/kg tended to be located adjacent to other heavily infested bins.     

Evaluation of potential use of nootkatone against maize weevil (Sitophilus zeamais Motschulsky) and rice weevil [S. oryzae (L.)](Coleoptera: Curculionidae)

Nootkatone is a natural sesquiterpene ketone that shows insecticidal activity against insects and ticks. Its contact toxicity and repellency against two major stored-product insect pests, maize weevil (Sitophilus zeamais Motschulsky) and rice weevil [Sitophilus oryzae (L.)], were investigated in the current study. Contact toxicity was evaluated using a no-choice test with treated filter paper, while repellency was evaluated using a choice test with treated corn (for maize weevils) or wheat (for rice weevils). Nootkatone showed low contact toxicity (ranging from 0 to 51%) against the two weevil species at the tested concentrations (ranging from 11.58 μg/cm² to 1158.08 μg/cm²) on filter papers. In choice tests, corn treated with 0.10% or higher and wheat treated with 0.5% nootkatone or higher had significantly fewer maize or rice weevils compared with the solvent only treated control, indicating a repellent effect. The repellency percentage ranged between 46.3 and 93.1% against maize weevils and 39.2-67.2% for rice weevils.     

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.     

Effect of Pisum sativum fractions on the mortality and progeny production of nine stored-grain beetles

Yellow field pea (Pisum sativum L.) fractions that were mainly protein (50%), fibre (90%) or starch (85%) were obtained from a commercial pea mill and mixed with wheat kernels or wheat flour. Based on the mortality and the number of offspring produced, protein-rich pea flour was more toxic than fibre, which was more toxic than starch. For the protein-rich pea flour mixed with wheat kernels, the most sensitive insects were Sitophilus oryzae (L.), Sitophilus zeamais Motschulsky and Sitophilus granarius (L.), followed by Cryptolestes ferrugineus (Stephens) which was more sensitive than Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.). For the protein-rich pea flour mixed with wheat flour, Cryptolestes pusillus (Schönherr) was most sensitive, followed by C. turcicus (Grouvelle) and T. confusum (Jacquelin du Val), with T. castaneum being the most resistant. Although protein-rich pea flour did not kill adults to a great extent when mixed with flour, it reduced offspring production significantly. Again C. pusillus was the most sensitive, followed by T. confusum, with T. castaneum offspring being the most resistant. The insecticidal activity of pea fractions decreased after treated wheat kernels were held at 30 °C, 70% r.h. for 8 months. The potential of using pea fractions to control stored-product insects is discussed.     

Responses of phosphine susceptible and resistant strains of five stored-product insect species to chlorine dioxide

Adults of phosphine susceptible laboratory strains and phosphine resistant field strains of five stored-product insect species were exposed in vials with 0 or 10 g of wheat for different time periods to 0.54 g/m³ (200 ppm) of chlorine dioxide gas. After exposure, adult mortality was determined 5 d later at 28 °C and 65% r.h. The 5-d mortality was 100% in laboratory and field strains of the red flour beetle, Tribolium castaneum (Herbst); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); lesser grain borer, Rhyzopertha dominica (F.); maize weevil, Sitophilus zeamais Motschulsky; and rice weevil, Sitophilus oryzae (L.) that were exposed in vials with 10 g of wheat to chlorine dioxide for 26, 16, 24–34, 18–24, and 15–18 h, respectively. Corresponding exposure durations for these species and strains in vials without wheat were 15, 3, 18–20, 7–15, and 5–7 h, respectively. Dosages of chlorine dioxide producing 99% mortality (LD₉₉) of T. castaneum, O. surinamensis, R. dominica, S. zeamais, and S. oryzae strains in vials with wheat ranged from 14.79−22.57, 8.20–8.41, 15.79–21.60, 10.66–14.53, and 7.67–12.20 g-h/m³, respectively. In vials without wheat, corresponding LD₉₉ values for T. castaneum, R. dominica, and S. zeamais strains were 6.51–8.66, 11.46–23.17, and 5.79–10.26 g-h/m³, respectively. LD₉₉ values for O. surinamensis and S. oryzae could not be computed, because of 100% mortality after a 3–5 h exposure to chlorine dioxide. No adult progeny production of T. castaneum and O. surinamensis was observed after 8 weeks in control and chlorine dioxide-exposed samples. Adult progeny production of Sitophilus spp. was found only in the control samples. The dosage for 99% adult progeny reduction relative to control for R. dominica strains ranged from 10.07 to 18.11 g-h/m³. Chlorine dioxide gas is effective in killing phosphine susceptible and resistant strains of five stored-product insect species and suppressing adult progeny production of three out of the five species.     

Toxicity of ethyl formate to adult Sitophilus oryzae (L.), Tribolium castaneum (herbst) and Rhyzopertha dominica (F.)

Fumigations were conducted using a continuous flow-through laboratory process to maintain constant concentrations of ethyl formate and low levels (<0.8%) of respiratory carbon dioxide. The procedure minimised the effects of sorption by exposing test insects without media and minimised the effect of carbon dioxide by use of continuous flow. The concentration×time (Ct) products of ethyl formate for adult Sitophilus oryzae, Tribolium castaneum and Rhyzopertha dominica at 25 °C and 70% relative humidity for the 6 h exposure were, respectively: (1) LD₅₀ 107.8, 108.8 and 72.8 mg h L⁻¹ and (2) LD_99.5 207.4, 167.1 and 122.2 mg h L⁻¹. Endpoint mortality was reached within 24 h of initial exposure.     

The effect of grain stability on damage caused by Prostephanus truncatus (Horn) and three other beetle pests of stored maize

In an experiment where grain was presented to Prostephanus truncatus (Horn), Rhyzopertha dominica (F), Sitophilus zeamais Motsch, and Tribolium castaneum (Herbst) in four different ways, it was found that on simulated maize cobs P. truncatus caused much more damage than on loose maize, whereas the reverse was true for the other species. Damage was measured as percentage weight loss over a 6 week period, starting with adult beetles. It is suggested that such differences in the biology of the pests should be taken into account when investigating the inherent susceptibility to infestation of different maize varieties.     

Fumigation toxicity of monoterpenoids to several stored product insects

Twenty naturally occurring monoterpenoids were evaluated in a preliminary fumigation screening test on some important stored-product pest insects, including the rice weevil, Sitophilus oryzae, the red flour beetle, Tribolium castaneum, the sawtoothed grain beetle, Oryzaephilus surinamensis, the house fly, Musca domestica, and the German cockroach, Blattella germanica. Cineole, l-fenchone, and pulegone at 50 μg/ml air caused 100% mortality in all five species tested. Ketone compounds were generally more toxic than other monoterpenoids. Three monoterpenoids, the ketones pulegone, l-fenchone, and the aldehyde perillaldehyde, were selected for further study. They were effective against T. castaneum in the fumigation assay; however the toxicity was relatively low in comparison to dichlorvos. LC₅₀ values of these three monoterpenoids tended to decrease at longer exposure times and higher temperatures. Inclusion of either maize kernels or house fly medium (HFM) increased LC₅₀ values, HFM more so than maize kernels. Monoterpenoids may be suitable as fumigants or vapor-phase insecticides because of their high volatility, fumigation efficacy, and their safety.     

Insect development in milled rice: Effects of variety,degree of milling,parboiling and broken kernels

Parboiled milled rice was less suitable than raw milled rice for progeny production by Plodia interpunctella (Hübner), Cadra cautella (Walker), Lasiodermaserricorne (F.), Tribolium confusum Jacquelin duVal, Rhyzopertha dominica (F.), Sitophilus oryzae (L.) and Oryzaephilus surinamensis (L.). The variety ‘Dawn’ was less suitable than ‘Belle Patna’, ‘Nato’ or ‘Bluebelle’ for all species except O. surinamensis and L. serricorne. An increase in milling rendered the rice less suitable for these seven species and for Tribolium castaneum (Herbst). Broken kernels did not significantly change the number of progeny from any of the species developing during a test period.