The toxicity of pyrethrins and five synthetic pyrethroids,to Tribolium castaneum (Herbst), and susceptible and pyrethrin-resistant Sitophilus granarius (L.)

The toxicities of five synthetic pyrethroids, resmethrin, bioresmethrin, tetramethrin, allethrin, and bioallethrin, have been compared with that of natural pyrethrins against susceptible Tribolium castaneum and susceptible and pyrethrin-resistant Sitophilus granarius, using topical application techniques. When the synthetic toxicants were used alone against the three strains of insect, bioresmethrin was by far the most toxic compound, followed in order by resmethrin, bioallethrin, allethrin, and tetramethrin. Depending on the strain tested, bioresmethrin had up to 16 times more toxicity and tetramethrin as little as 1/100 the toxicity of pyrethrins. Piperonyl butoxide (PB) synergized all the compounds against the three strains. When synergized, bioresmethrin was again the most toxic of the synthetic compounds, followed by resmethrin, bioallethrin, and allethrin. Tetramethrin had the lowest toxicity against T. castaneum, but against both strains of S. granarius tetramethrin plus PB became the third most toxic of the six compounds tested. There was a smaller range of effectiveness among the compounds when they were synergized.Except for tetramethrin, factors of synergism were low against T. castaneum (1 to 4); higher against susceptible S. granarius (4 to 37); and very high against resistant S. granarius (31 to 209). Very high factors of synergism were obtained with tetramethrin (43 to ? 216) against all three strains. Against the weevils, toxicant: synergist ratios higher than 1:10 gave higher factors of synergism with resmethrin and bioresmethrin; but not with pyrethrins.The influence of solvents and methods of application on LD50 measurements, was studied in tests with pyrethrins. The non-insecticidal fraction of pyrethrum extract was found to be toxic, at high concentrations, to resistant S. granarius.     

Control failure and insecticides resistance in populations of Rhyzopertha dominica (Coleoptera: Bostrichidae) from Colombia

The lesser grain borer Rhyzopertha dominica is a serious pest that causes significant economic damages in stored grains. The presence of this pest is mainly controlled using a small number of insecticides increasing risks of compromising the control efficacy due to the selection of resistant populations. Here, the control failure and potential resistance to pyrethroid and organophosphate insecticides frequently used for the control of R. dominica in Colombia were assessed. Concentration–mortality bioassays with synergized and unsynergized insecticides were used to assess potential metabolic-based pyrethroids resistance mechanisms. Based on the field recommended doses, the results revealed that while the pirimiphos-methyl is still efficient against R. dominica, both type I (i.e., bifenthrin) and type II (i.e., deltamethrin) pyrethroids presented control failure and their insecticidal activity was compromised. Although no differences in susceptibilities between the populations were found for the bifenthrin insecticide, the LC₅₀s of Ibagué (1.83 μl/gr of grains) and El Espinal (1.67 μl/gr of grains) populations were higher than the recommended rate. Furthermore, significant differences in susceptibility to deltamethrin resulted in resistance ratios RR₅₀ > 32-fold and RR₉₅ > 188-fold between the least (El Espinal) and the most (Ibagué) susceptible populations. Moreover, when synergized, the toxicity of deltamethrin was enhanced but resistance ratios kept at high levels (RR₅₀ > 11-fold and RR₉₅ > 40-fold) indicating possible existence of simultaneous metabolic and altered action-site mechanisms of resistance to pyrethroids in Colombian populations. Our results highlight the urgent need for nationwide monitoring of insecticides control failure and resistance in stored pests for better management schemes.     

Comparative observations on the activity of purethroids against some susceptible and resistant stored products beetles

The activity of six synthetic pyrethroids, allethrin, bioallethrin, resmethrin, bioresmethrin, cismethrin, tetramethrin and also natural pyrethrins, fenitrothion and malathion was examined against susceptible and resistant adult beetles infesting stored products. Cismethrin applied topically was the most active material, alone or synergized, against susceptible Tribolium castaneum, Lasioderma serricorne or Stegobium paniceum.

Solutions in odourless kerosene applied as direct sprays were an average of 6·9 times more active against susceptible T. castaneum than solutions in mineral oil of pyrethrins, bioresmethrin or cismethrin with or without piperonyl butoxide. The factor of synergism was greater when using mineral oil solutions than when using kerosene solutions. It was thought that the more viscous oil slowed penetration of the insecticide giving longer for detoxification, this being inhibited when the synergist was present.

Applied as a dust on wheat, bioresmethrin plus piperonyl butoxide was more active than malathion and less active than fenitrothion against Oryzaephilus surinamensis or susceptible and malathion resistant T. castaneum. Against Sitophilus granarius and susceptible or malathion resistant S. oryzae, synergized bioresmethrin and cismethrin were more active than either malathion or fenitrothion. Malathion resistant S. oryzae was more easily killed by pyrethroids than the susceptible strain. Synergized bioresmethrin was concluded to be the most suitable pyrethroid for controlling stored products beetles, except Lasioderma serricorne and Stegobium paniceum, and was of value against organophosphorus-resistant strains.     

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.     

The effectiveness of various insecticides on some resistant beetle pests of stored products from Uganda

Laboratory tests were carried out using populations of Tribolium castaneum (Herbst), Tribolium confusum Jacquelin du Val, Sitophilus zeamais Motschulsky, Callosobruchus maculatus (F.), and Zabrotes subfasciatus Boheman, from Uganda, firstly to determine whether they were resistant to malathion and/or lindane and secondly to measure the effectiveness and stability of pirimiphos-methyl, fenitrothion, etrimfos, permethrin and deltamethrin dilute dusts in protecting cereals and pulses from these insect pests. All the insect populations tested were resistant to malathion or lindane and some were resistant to both. Of the insecticides tested, deltamethrin at 1 ppm was generally the most effective. The organophosphorus compounds were only effective against the Tribolium species and Sitophilus zeamais. Permethrin was the least effective, only controlling Callosobruchus maculatus.     

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.     

Evaluation of Carifend® for the control of stored-product beetles

In the present study, the effectiveness of Carifend® (BASF AG, Ludwigshafen, Germany), an alpha-cypermethrin-coated net, was evaluated in laboratory tests against major stored-product insects. The insecticide-treated net was adjusted at the bottom of plastic petri dishes, and adult insects were placed in each dish and exposed for different exposure intervals (1, 3, 5, 7 and 14 days), after which mortality and knockdown was measured. The tests were carried out against a wide spectrum of stored-product insects, i.e. Sitophilus oryzae, Sitophilus granarius, Sitophilus zeamais, Oryzaephilus surinamensis, Tribolium castaneum, Tribolium confusum, Prostephanus truncatus, Rhyzopertha dominica and Cryptolestes ferrugineus. The results showed that O. surinamensis, R. dominica and P. truncatus were highly susceptible to Carifend®, as complete control was achieved for all three species, after 5, 14 and 5 days, respectively. Regarding Sitophilus species, S. zeamais was the most tolerant species, as mortality levels did not exceed 46%, even after 14 days of exposure. In contrast, S. oryzae and S. granarius mortality was >98% after 14 days of exposure. So far, Carifend® has been registered in many parts of the world for the protection of stored tobacco against major tobacco pests, i.e. Lasioderma serricorne and Ephestia elutella. However, our results clearly indicate that this net can be used effectively for the control of other stored-product insects that infest durable food, such as grains and related amylaceous commodities.     

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.     

Analysis of free fatty acids in food substrates and in the dust and frass of stored-product pests: Potential for species discrimination?

The larger grain borer, Prostephanus truncatus, is a serious beetle pest that tunnels extensively to produce large quantities of dust and frass. The natural enemy Teretrius nigrescens is an important biological control beetle which is known to exploit at close-range solvent-extractable chemical cues in the dust and frass. The objective of the current study was to analyse quantitatively and qualitatively, the free fatty acid mixtures in different food-substrate materials both before and after insect attack by a range of stored-product pests in order to ascertain whether differences in these mixtures could explain the T. nigrescens selectivity to P. truncatus dust/frass over that of other species irrespective of food substrate. By TLC, GC and GC-MS we found triglyceride and five free fatty acids were the most abundant chemicals in dust/frass (palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3)). In maize flour, Sitophilus species did not significantly change free fatty acid concentrations whereas with P. truncatus, Rhyzopertha dominica and Dinoderus minutus there were 4-6-fold increases, and, for Tribolium species there were over 20-fold increases. These differences provide interesting insights to tunnelling/feeding habits and are correlated with known feeding preferences within grain. Principal component analysis (PCA) demonstrated that free fatty acid ratios in dust/frass of different species are most linked to the food substrate and confer little discriminatory information that could be used to distinguish between the different species. Although increases in free fatty acid concentrations are good indicators of pest infestation and this may contribute behaviourally in an additive or synergistic way, we conclude that other chemical(s) are present and are key to T. nigrescens recognition of P. truncatus on different substrates.     

Residual toxicities and persistence of organophosphorus insecticides mixed with carbaryl as structural treatments against three liposcelidid psocid species (Psocoptera: Liposcelididae) infesting stored grain

Four organophosphorus insecticides, azamethiphos, fenitrothion, chlorpyrifos-methyl, and pirimiphos-methyl were each mixed with carbaryl and evaluated as structural treatments on concrete and galvanized steel panels (0.3×0.3 m) against adults of three liposcelidid psocids: Liposcelis bostrychophila Badonnel, L. entomophila (Enderlein), and L. paeta Pearman. Residual toxicities and persistence of these insecticide mixtures were assessed at 30±1°C, 70±2% r.h., and a photoperiod of 12:12(L:D) h from 1 day after treatment (0 week) and at weeks 1, 2, 4, 6, and 8, and then every 4 weeks up to week 40. Mortality was recorded at exposure periods of 6 h and then every 24 h until end-point was achieved. Significant enhancement in residual toxicities was observed in azamethiphos plus carbaryl against L. entomophila, and chlorpyrifos-methyl plus carbaryl and pirimiphos-methyl plus carbaryl against all three species on steel surfaces, compared with the individual effectiveness of these insecticides reported earlier. We conclude that combining carbaryl with either azamethiphos, chlorpyrifos-methyl, or pirimiphos-methyl as a structural treatment will provide long-term protection (up to 40 weeks) against infestation by all three psocid species on steel storage structures, whilst carbaryl with fenitrothion will give shorter protection (up to 8 weeks). On concrete structures, however, only azamethiphos plus carbaryl will provide long-term protection against L. bostrychophila (up to 28 weeks) and L. paeta (up to 16 weeks). None of the four insecticide mixtures studied would provide long-term protection against an L. entomophila infestation on concrete surfaces.     

Efficacy of filter cake and Triplex powders from Ethiopia applied to wheat against Sitophilus zeamais and Sitophilus oryzae

The efficacy of filter cake and Triplex powders applied to wheat was evaluated in the laboratory against the maize weevil, Sitophilus zeamais Motschulsky and rice weevil, Sitophilus oryzae (Linnaeus)—two most common insect pests associated with stored grain in Ethiopia. Efficacy of these powders was determined by exposing 20 adults of each species to 100 g of wheat treated with 0, 100, 500, 700 and 1000 mg/kg of filter cake and Triplex. Adult mortality was determined 7 and 14 d after exposure. In addition, adult progeny production, percentage of insect damaged kernels, and percentage of grain weight loss at each species-powder-concentration-time combinations were determined after 42 d. The 7 and 14 d mortality was 100% for adults of both species exposed to 1000 mg/kg of filter cake; only the 14 d mortality of Sitophilus species was 100% for adults exposed to 700 mg/kg. Mortality of S. oryzae adults was 100% when exposed for 14 d to1000 mg/kg of Triplex. Mortality of S. zeamais never reached 100% in any Triplex treatments. Adult progeny production of S. zeamais was completely suppressed at filter cake concentrations of 700 and 1000 mg/kg, whereas 1000 mg/kg was necessary for complete suppression of S. oryzae adult progeny production. Complete suppression of adult progeny production was not observed in any Triplex treatments. Complete reduction in percentage of insect damaged kernels and percentage of grain weight loss were obtained when S. zeamais and S. oryzae adults were exposed to 1000 mg/kg of filter cake; similar reductions with S. zeamais occurred only at 1000 mg/kg of Triplex. In the case of S. oryzae, complete reduction of insect damaged kernels and grain weight loss were not achieved at any concentration of Triplex. These powders can be used as alternatives to chemical insecticides for management of Sitophilus species.     

The influence of temperature on the susceptibility to eight organophosphorus insecticides of susceptible and resistant strains of Tribolium castaneum,Oryzaephilus surinamensis and Sitophilus granarius

Susceptible strains of adult Tribolium castaneum, Oryzaephilus surinamensis and Sitophilus granarius were exposed for 24 hr to a range of deposits (from 10 to 5000 mg/m²) of eight organophosphorus insecticides (bromophos, chlorphyrifos-methyl, fenitrothion, jodfenphos, malathion, phoxim, pirimiphos-methyl and tetrachlorvinphos) at 10, 17.5 and 25°C. Based upon knockdown and kill, the effectiveness of all insecticides was greater at 25°C than at 17.5°C and was markedly lower at 10°C. At 10°C tetrachlorvinphos, bromophos and jodfenphos were virtually ineffective to S. granarius even at 5000 mg/m². By contrast at 25°C, 100 mg/m² was adequate to give complete knockdown of all species with most insecticides, the exceptions being malathion and tetrachlorvinphos. The three most effective insecticides, chlorphyrifos-methyl, pirimiphos-methyl and fenitrothion were also tested, in comparison with malathion, against a known malathion-resistant strain of each of the test species. Chlorpyrifos-methyl and pirimiphos-methyl were the most effective materials against both susceptible and resistant strains of all species. Knockdown was inevitably followed by mortality although at the lower temperatures this took several days.     

Efficacy of alpha-cypermethrin,chlorfenapyr and pirimiphos-methyl applied on polypropylene bags for the control of Prostephanus truncatus (Horn), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.)

We examined the immediate and delayed mortality of adults of the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on surfaces of polypropylene storage bags under different treatment scenarios with alpha-cypermethrin, chlorfenapyr and pirimiphos-methyl. These scenarios were: only one surface of the bag was sprayed and insects were exposed on sprayed or unsprayed surface or both surfaces were sprayed. We evaluated the immediate mortality for 1, 3 and 5 days (d) of exposure. Then, we transferred the surviving adults to untreated surfaces of the same type of storage bags and measured the delayed mortality after 7 d of exposure. We also evaluated the effect of insecticidal treatments on the numbers of holes/bites made by the activity of P. truncatus and R. dominica on storage bags. In terms of immediate mortality, chlorfenapyr and pirimiphos-methyl were very effective against all three species and alpha-cypermethrin against P. truncatus. We noticed high mortality values of all species to chlorfenapyr and pirimiphos-methyl, even after 3 d of exposure, reaching 100% in many of the cases examined. For the majority of exposure intervals, insecticides and insects, we did not find significant differences in mortality counts between exposures on sprayed surfaces of the bag. Immediate mortalities of insects exposed on the untreated surface of the bag did not differ significantly with mortalities at the surface single treated with alpha-cypermethrin and pirimiphos-methyl. Concerning delayed mortality, all S. oryzae adults were found dead 7 d after their transfer to untreated bags irrespectively of the treatment. The delayed mortality of P. truncatus and R. dominica adults was either complete (after exposure to chlorfenapyr) or almost complete (after exposure to alpha-cypermethrin). The exposure of P. truncatus and R. dominica to alpha-cypermethrin almost completely suppressed the numbers of holes/bites. Our study indicates that the application of insecticides on polypropylene storage bags can be considered as an effective method for the control of stored-product insects.     

Insecticidal activities of essential oils from leaves of Laurus nobilis L. from Tunisia,Algeria and Morocco,and comparative chemical composition

Laurus nobilis essential oils from Tunisia, Algeria and Morocco were analyzed for their chemical composition and assessed for their repellent and toxic activities against two major stored product pests: Rhyzopertha dominica and Tribolium castaneum. The three oils showed quantitative rather than qualitative differences in their chemical compositions. 1,8-cineole, linalool and isovaleraldehyde, were identified as the major common compounds whereas, α-pinene, α-terpineol, eugenylmethylether, β-pinene, spathulenol and β-myrcene were also well represented in all three oils. Results showed that L. nobilis essential oils were repellant and toxic to adults of R. dominica and T. castaneum. Repellent and fumigant toxicities were highly dependent upon insect species and oil origin.In filter paper tests, L. nobilis essential oil from Morocco was more effective compared to Tunisian and Algerian oils. RD₅₀ values were respectively 0.013 μl/cm², 0.036 μl/cm² and 0.033 μl/cm² for R. dominica versus 0.045 μl/cm², 0.139 μl/cm² and 0.096 μl/cm² for T. castaneum. Moreover, fumigant activity tests showed that both R. dominica and T. castaneum were more susceptible to L. nobilis essential oil from Morocco than that from Algeria or Tunisia. The corresponding LC₅₀ values were respectively 68, 99 and 113 μl/l air for R. dominica against 172, 194 and 217 μl/l air for T. castaneum. Our work clearly vindicates interest in the efficacy of essential oils from plants of Mediterranean origin both as insecticides and repellents against stored product pests.     

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.     

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.     

The influence of some biological and physical factors on the heat tolerance relationships for Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) (Coleoptera: Bostrychidae and Curculionidae)

The influence of several biological and physical factors on the exposure time required to obtain a given level of mortality of immature Rhyzopertha dominica and Sitophilus oryzae exposed to air at 70 or 80°C in a fluidized bed of wheat was determined.The tolerances of five Australian populations of R. dominica differed little. In this species, median tolerance and variance increased as the age span of the exposed insects widened from 0–7 to 0–35 days. Acclimation of R. dominica at 22 or 32°C and S. oryzae at 15 or 30°C before exposure had no appreciable influence on heat tolerance.Changing the initial grain temperature from 32 to 22°C did not alter LT values for R. dominica. However, the LT_99.9s for both warm and cold acclimated S. oryzae in 15°C grain were greater than those in 30°C grain. The LT_99.9s for R. dominica in wheat of 14% m.c. exceeded those in 11.3% m.c. wheat. Heating curves showed that the time taken for cold or moist grain to reach a given high temperature was extended.     

A simple technique to assess compounds that are repellent or attractive to stored-product insects

We have developed a simple and rapid technique that mimics storage conditions, and determines if products are repellent or attractive to stored-product insects. The technique determines the response of insects to potential repellents and attractants by measuring their movement from grain. The technique used a device consisting of a perforated cup (2 mm perforations) that holds 200 g of wheat. A Petri dish and cup collected the insects as they left the wheat. Several natural products were tested for repellency: diatomaceous earth (DE), ground peas (Pisum sativum), protein-rich pea flour, pea starch, and pea fibre. Adult insects of three species were tested: the rice weevil, Sitophilus oryzae, the red flour beetle, Tribolium castaneum, and the rusty grain beetle, Cryptolestes ferrugineus. DE at 0.01% was repellent to all insects tested. Pea fibre, pea protein, and ground pea at 1% caused increased emigration of C. ferrugineus from the wheat. Pea starch did not affect movement out of the grain for all three insects. Only pea fibre and ground pea increased the movement of T. castaneum out of the grain. For S. oryzae, there were no differences after 1 h, but after 24 h both pea protein and ground pea increased movement out of the grain. Several potential attractants were placed outside the grain and the emigration out of the grain noted. For R. dominica, the commercial R. dominica pheromone increased the emigration of insects from the grain; R. dominica adults on broken grain enclosed in a ventilated vial in the collection jar also increased emigration, but not as much as the synthetic pheromone. The commercial Tribolium pheromone did increase movement out of the grain for T. castaneum, but the other treatments were no different from the control. None of the potential attractants increased the movement of S. oryzae from the grain. The implications of this work are discussed with reference to controlling and sampling stored-product insect pests.     

Triple bagging hermetic technology for post-harvest preservation of paddy rice Oryza sativa L. in the Sahel of West Africa

Trials of the Purdue Improved Crop Storage (PICS) bag technology for the storage of paddy rice, Oryza sativa L., were conducted in Burkina Faso, Ghana and Niger. Paddy rice naturally infested with insects, the most abundant species being Tribolium spp. and Rhizopertha dominica, was sealed in triple layer PICS bags, or in conventional woven polypropylene sacks. At the end of 7–18 months of storage in PICS bags the number of insects did not increase, the weight of 100 seeds did not change, and the proportion of damaged seeds was not different from that present when the paddy was first put into the bags. By contrast, paddy stored in the conventional way in woven polypropylene bags exhibited weight losses ranging from 3 to 8.7%. In Bolgatanga, Ghana, where paddy was stored for 18 months, germination of paddy kept in the PICS bags was comparable to that present at the beginning of the experiment. PICS bags can be used for the safe, low-cost, insecticide free storage of paddy rice.     

Screening of some indigenous plants as repellents or antifeedants for stored grain insects

Seven plant species were tested for their repellent activity against Tribolium castaneum (Herbst) and antifeedant activity against Rhyzopertha dominica F. The best repellent activity was found in the rhizomes of Saussurea lappa (DC.) and antifeedant activity in the leaves of Chenopodium ambrosioides L. and in azadirachtin isolated from neem kernels.