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.     

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.     

Combined effects of contact insecticides and 50 °C temperature on Sitophilus oryzae (L.) (Coleoptera: Curculionidae) in wheat grain

The effects of the insecticides deltamethrin, bifenthrin, thiamethoxam, spinosad and abamectin were tested in the laboratory in combination with extreme temperature of 50 °C to discover potential improvements of existing pest management programmes for Sitophilus oryzae (L.) control. Adults were released into wheat grain treated with three insecticide doses ranging 0.125–1.0 mg/kg and exposed to 50±1 °C temperature at the intervals of 0, 65, 75 and 85 min, and direct and combined effects were determined after 1, 2, 7 and 14 days of exposure/recovery at 25±1 °C and 60 ± 5% r. h., as well as impact on F₁ progeny production/reduction PR (%) after 8 weeks.The results showed that the mortality of S. oryzae adults increased with exposure/recovery duration more than under the activity of each insecticide alone and its interaction with extreme temperature. After 14 days, all three rates of deltamethrin (0.125–0.5 mg/kg), the two higher rates of bifenthrin (0.25 and 0.5 mg/kg) and the highest rates of abamectin (0.5 mg/kg) and thiamethoxam (1.0 mg/kg) caused maximum adult mortality (100%) and PR (100%) after weevil exposure to 50 °C already after the interval of 65 min, while spinosad had the same effect after 75 and 85 min, which effectiveness was 1.25–20 times higher than the activities of the insecticides and 50 °C temperature alone, considering all trial variants. The lowest rate of bifenthrin (0.125 mg/kg) was found after 65 min activity in combination with exposure to 50 °C, and especially spinosad (0.25 mg/kg) after 65 and 75 min, to have stimulated progeny production 17, 33 and 236%, respectively, while deltametrin showed 100% effectiveness against S. oryzae in all combinations of wheat grain treatment at 50 °C temperature, including the dose 0.125 mg/kg.     

Influence of temperature and relative humidity on the efficacy of thiamethoxam for the control of three stored product beetle species

Laboratory bioassays were carried out in order to evaluate the effectiveness of thiamethoxam in different levels of temperature and relative humidity (r.h.) against three major stored-grain beetle species, the lesser grain borer Rhyzopertha dominica (F.), the rice weevil, Sitophilus oryzae (L.) and the confused flour beetle, Tribolium confusum Jacquelin du Val. Adults of the three species were exposed on wheat treated with thiamethoxam at 0.1, 1 and 5 ppm and under six different combinations of temperature (20, 25 and 30 °C) and r.h. levels (55 and 75%). Our study showed that the increase in temperature increased mortality in all insect species, particularly at the lowest concentration. For some of the combinations tested, the low r.h. seemed to play a significant role in thiamethoxam efficacy in the case of R. dominica. Moreover, of the species tested, T. confusum was found to be the least susceptible, while R. dominica the most susceptible. In general, thiamethoxam was found to be effective against all three species, at concentrations that are comparable with most commercially available grain protectants.     

Performance of diatomaceous earth and imidacloprid as wheat,rice and maize protectants against four stored-grain insect pests

Laboratory experiments were conducted in Pakistan to investigate the effectiveness of the diatomaceous earth (DE) formulation, Protect-It, at 150 ppm and imidacloprid, at 1.25, 2.5 and 5.0 ppm, alone or in combination, against the rusty grain beetle, Cryptolestes ferrugineus Stephens (Coleoptera: Laemophloeidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the psocid, Liposcelis paeta Pearman (Psocoptera: Liposcelididae). The bioassays were conducted at 25 °C, 65% relative humidity (r.h.) and continuous darkness by using adults of each insect pest that were exposed on treated or untreated wheat, rice and maize. Adult mortality counts were performed 1, 2, 4 and 7 days post-exposure. Progeny production was also evaluated 62 and 30 days after the last mortality count for beetles and psocid respectively. Results showed that mortality was increased with the increase of dose and exposure interval. Imidacloprid was more effective at the highest dose than the DE alone. The combination of DE plus imidacloprid resulted to higher mortalities than DE or imidacloprid alone at almost all exposure intervals. There was higher mortality on wheat than on rice or maize. In general, T. castaneum was the most tolerant insect species to any treatment while L. paeta was the least tolerant. The highest progeny production was observed for T. castaneum (i.e., 33.1 individuals per vial) while the lowest for L. paeta (i.e., 11.1 individuals per vial) on maize treated with Protect-It alone. The findings of the current study indicate that the combined use of DE and imidacloprid, as wheat, rice and maize protectants, may provide adequate level of management to several important stored-product insects.     

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.     

Effect of radio frequency heating on the mortality of Rhizopertha dominica (F.) and its impact on grain quality

The use of radio frequency (RF) heating to reach temperatures lethal to stored product pests has significant potential. We examined the lethal effects of RF on the stored grain pest, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), under four different RFs, three types of grain, and different moisture contents of rice. The quality of two rice cultivars, after RF heating, was also tested. When heated to 58 °C by RF, R. dominica adult mortality reached 100%. The mortality of R. dominica adults reached 100%. The fastest mortality rate occurred at 50–52 °C. With an increase in RF, the time needed to attain a lethal temperature decreased. The heating time to reach 100% mortality differed among the three types of grain; for example, the heating time of wheat was faster than corn or rice. Kernel size and chemical composition was the main factor influencing the RF lethal rate in the different types of grain under the same experimental conditions. There was a significant linear relationship between moisture content (m.c.) and heating time (Y = −38.05 X + 15.501, R = 0.9803) in rice. RF heating of rice to 58 °C did not significantly affect milling quality, storage quality, or seed quality. Thus, heating time, types of grain, and the m.c. of the grains are three important factors that should be considered in RF heating to control stored product pests. These results indicate that RF heating could be an effective physical method for killing stored grain pests.     

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.     

Factors affecting the insecticidal efficacy of an enhanced diatomaceous earth formulation against three stored-product insect species

An enhanced mixture of diatomaceous earth (DE) with the plant extract bitterbarkomycin (BBM) was evaluated in the laboratory against adults of three major stored-product pest species. This mixture (DEBBM) was applied at three dose levels; 50 ppm, 100 ppm and 150 ppm and on four grain commodities; hard wheat, barley, rice and maize. The species tested were Sitophilus oryzae, Tribolium confusum and Cryptolestes ferrugineus. In order to determine the influence of temperature and r.h. on the efficacy of DEBBM the bioassays were carried out at three temperatures; 20, 25 and 30 °C and two relative humidity (r.h.) levels; 55% and 75%. Mortality and progeny production of each species were assessed after exposures of 7 and 14 d. DEBBM efficacy was increased with the increase of dose, exposure and temperature whereas it was decreased with the increase of r.h. Mortality of all species was higher in treated barley compared to the other grains, although significant differences between barley and wheat were not recorded in all cases. Also, DEBBM performance in maize and rice was lower compared to that in barley or wheat. DEBBM was very effective against C. ferrugineus as mortality of this species that was achieved with 150 ppm was always >85%. Of the remaining species the least susceptible to DEBBM was T. confusum. Although DEBBM caused significant mortality to all three species, progeny production was not totally avoided. However, progeny production was significantly lower in comparison with the untreated commodities.     

Insecticidal effect of thiamethoxam against seven stored-product beetle species

Bioassays were carried out in order to assess the insecticidal value of the neonicotinoid thiamethoxam in different concentrations against seven important beetle species that are major pests of stored grains. These species were Prostephanus truncatus (Horn), Rhyzopertha dominica (F.), Sitophilus oryzae (L.), Sitophilus granarius (L.), Oryzaephilus surinamensis (L.), Tribolium confusum Jacquelin du Val, and Cryptolestes ferrugineus (Stephens). Adults of these species were exposed to grains treated with thiamethoxam at dose rates of 0 (control), 0.01, 0.1, 0.5, 1, 2, 5 or 10 ppm. Our results indicate that with the increase of the insecticide concentration, there was also an increased adult mortality and a reduction in progeny production. To illustrate the relative sensitivity to thiamethoxam of the seven insects, starting with the most susceptible, we can classify them as P. truncatus > R. dominica = S. granarius = S. oryzae > T. confusum = O. surinamensis > C. ferrugineus. The findings of the present research show that thiamethoxam can be recommended for its efficacy at a rate of 10 ppm and duration of 14 days that could be used to control all insects and their progeny.     

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

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

Abiotic and biotic factors affect efficacy of chlorfenapyr for control of stored-product insect pests

Laboratory bioassays were conducted to assess pyrole chlorfenapyr as a potential grain protectant against adults of Rhyzopertha dominica, Sitophilus oryzae, Prostephanus truncatus, Tribolium confusum, and Liposcelis bostrychophila. Factors such as dose (0.01, 0.1, 0.5, 1, 5, and 10 ppm), exposure interval (7 and 14 days), temperature (20, 25, and 30°C), relative humidity (RH; 55 and 75%), and commodity (wheat, maize, barley, and paddy rice) were evaluated. Progeny production was assessed after 74 days of exposure. For L. bostrychophila and T. confusum the increase of dose increased mortality. After 7 or 14 days of exposure, mortality was low at doses of ≤ 1 ppm and did not exceed 23 or 36%, respectively, for L. bostrychophila or 13 or 58%, respectively, for T. confusum. After 14 days of exposure, mortality of S. oryzae at 30°C and 75% RH was 82.2%. Mortality of P. truncatus was considerably higher than that of the other species. At 0.5 ppm, mortality exceeded 81% after 7 days of exposure and 91% after 14 days of exposure. Progeny production of L. bostrychophila was extremely high. Very few progeny were found for T. confusum. For S. oryzae, offspring emergence was high, except at 20°C and 55% RH. For P. truncatus, progeny production in the treated maize was not avoided, even at 10 ppm. In the case of S. oryzae, at 0.1 ppm and after 14 days of exposure, mortality in wheat was higher than in the other three commodities. For R. dominica, mortality was low at 0.1 and 1 ppm for paddy rice but reached 74.4% in barley after 14 days of exposure. For T. confusum, mortality was low at 0.1 and 1 ppm in all commodities. For progeny production counts, for S. oryzae or R. dominica, adult emergence was higher in paddy rice than in the other three commodities. Finally, overall T. confusum progeny was low. Chlorfenapyr efficacy varied remarkably among the combinations tested, and it may be a viable grain protectant in combination with other insecticides.     

Insecticidal potential of zeolite formulations against three stored-grain insects,particle size effect,adherence to kernels and influence on test weight of grains

Laboratory studies were conducted in order to evaluate the insecticidal potential of three commercially available zeolite formulations against adults of Sitophilus oryzae, Tribolium confusum and Oryzaephilus surinamensis in wheat. For each zeolite formulation, three particle size levels were tested, i.e. 0–50, 0–150 and 0–500 μm. Zeolites were applied at three dose rates, 250, 500 and 1000 ppm, and insect mortality was assessed after 2, 7, 14 and 21 d of exposure. After the final mortality count, dead and alive insects were removed and offspring numbers were determined following an additional period of 65 d. In another series of laboratory bioassays, the effect of zeolite application on the test weight of wheat, maize and barley, as well as the adherence of zeolite particles to wheat, maize, barley and rice kernels was also measured. Oryzaephilus surinamensis was the most susceptible species to zeolite application, regardless of the zeolite formulation, dose and particle size level tested, whereas T. confusum was the most tolerant. No significant differences in efficacy were recorded among the three tested zeolite formulations. At the same time, particle size did not affect zeolite efficacy, at least for the particle size levels tested. All zeolites caused a significant reduction on the test weight of the treated grains. Moreover, zeolite particles showed different adherence among wheat, maize, barley and rice kernels. The results of the present study indicate that zeolites can be used with success as grain protectants, but there is a considerable effect on some physical properties of the grains. This information aims to encourage further evaluation of zeolites as grain protectants.     

Efficacy of alpha-cypermethrin and thiamethoxam against Trogoderma granarium Everts (Coleoptera: Dermestidae) and Tenebrio molitor L. (Coleoptera: Tenebrionidae) on concrete

Laboratory bioassays were conducted to evaluate alpha-cypermethrin and thiamethoxam for the control of adults, small larvae and large larvae of the khapra beetle Trogoderma granarium, and the yellow mealworm beetle Tenebrio molitor, on concrete. Factors such as dose (0.025 and 0.1 mg alpha-cypermethrin or thiamethoxam/cm²), exposure interval (1, 3 and 7 d), and formulation (alpha-cypermethrin SC and thiamethoxam WG) were evaluated. Apart from immediate assessment at end of exposure, an assessment of delayed mortality was performed with the survivors of the 7-d exposure by removing them from the treated substrate and keeping them on untreated surfaces for 7 more days. After the 7-d exposure, more T. granarium adults were dead on dishes treated with alpha-cypermethrin than with thiamethoxam. Small larvae were generally less susceptible than adults. After 7 d, small larval mortality reached 64.4% for alpha-cypermethrin, while for thiamethoxam it was <6%. Large T. granarium larvae were more tolerant than the small ones. Delayed mortality of T. granarium adults was generally high for both insecticides and doses, and ranged between 43.3 and 63.3% of those that were still alive immediately after the 7-d treatment. For both larval categories, delayed mortality was higher for larvae that had been previously exposed to alpha-cypermethrin, than with thiamethoxam. For T. molitor, after the 7-d exposure, significantly more adults were dead on dishes treated with alpha-cypermethrin than with thiamethoxam. For small larvae mortality was 38.9% at the lowest thiamethoxam dose, but in the other cases ranged between 88.9 and 95.6%. In the case of large larvae, the overall mortality was low in all tested combinations. Regarding delayed mortality of this species, it remained at low levels, for both adults and small larvae. Our results indicate that T. molitor was more susceptible than T. granarium in both insecticides tested, but alpha-cypermethrin was more effective than thiamethoxam.     

Mortality and progeny production of four stored-product insect species on three grain commodities treated with Beauveria bassiana and diatomaceous earths

Laboratory bioassays were conducted to estimate the effectiveness of the entomopathogenic fungus Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae) at 1.5 × 10⁸ and 1.5 × 10¹⁰ conidia/kg grain alone or mixed with the diatomaceous earths (DEs) Protect-It at 150 ppm and DEBBM at 50 ppm against adults of the rusty grain beetle, Cryptolestes ferrugineus Stephens (Coleoptera: Laemophloeidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the psocid, Liposcelis paeta Pearman (Psocoptera: Liposcelididae). The adult insects were exposed to treated grains for 7, 14 and 21 days. For progeny emergence data, the treated units were remained under the same conditions for 62 days for all beetles and 30 days for psocids. The results revealed significant differences in mortalities of insect species among treatments and grains. The combined use of B. bassiana, at the highest dose, and DE increased adult mortalities of all species. In general, the treatments were least effective against T. castaneum and most effective against L. paeta. More numbers of dead insects were found on wheat than on rice or maize. The emergence of progeny was considerably reduced on grains treated with B. bassiana, at the highest dose, plus DE. The results of the present study suggest that the effectiveness of B. bassiana is fortified by the addition of DEs, but it varies among exposed insect species and commodities.     

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.     

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 flameless catalytic infrared radiation on Sitophilus oryzae (L.) life stages

A laboratory benchtop flameless catalytic infrared emitter was evaluated against all life stages of the rice weevil, Sitophilus oryzae (L.), an insect species associated with stored wheat. The emitted infrared radiation was in the 3-7 μm range. A non-contact infrared thermometer measured grain temperatures continuously during exposures of infested wheat. Insect mortality was a function of the final grain temperature attained. In general, higher grain temperatures were attained when using 113.5 versus 227.0 g of wheat, and at 8.0 cm from the emitter versus 12.7 cm, and during a 60 s exposure versus a 45 s exposure. Complete mortality of all life stages of S. oryzae was achieved at 8.0 cm from the emitter using 113.5 g of wheat, with a 60 s exposure; the mean grain temperatures attained ranged from 108.4 to 111.8 °C. The log odds ratio tests showed that eggs (0 days old) were the least susceptible stage to infrared radiation, followed by adults within kernels (28 days old), pupae (24 days old), young larvae (7 days old), larvae that were 14-21 days old, and adults (42 days old). These data using small amounts of grain indicate infrared radiation from the flameless catalytic emitter to be a viable option for disinfesting wheat containing various life stages of S. oryzae.     

Survival of Sitophilus oryzae (L.) on wheat treated with diatomaceous earth: impact of biological and environmental parameters on product efficacy

A series of experiments was conducted to evaluate the effects of temperature, relative humidity (r.h.), population density, concentration, exposure interval, and residual aging on susceptibility of Sitophilus oryzae (L.), the rice weevil, to diatomaceous earth (DE). In the first experiment, hard red winter wheat was treated with 300 ppm of the Protect-It™ formulation of DE, and 10, 20, or 30 1-2 week-old mixed-sex adult weevils were exposed on 35 g of wheat for 1 week at combinations of 22°C, 27°C, or 32°C; 40%, 57%, or 75% r.h. No weevils survived when exposed at 40% or 57% r.h., but at 75% r.h. survival was related to both population density and temperature. A higher percentage of adults survived when 30 were exposed compared to 10 and 20, and within each density, survival decreased with increasing temperature. No F₁s were produced at any r.h. on wheat held at 22°C. At 27°C and 32°C, the maximum number of F₁s was produced on wheat held at 75% r.h. In the second experiment, wheat was treated with 25%, 50%, 75%, or 100% of the label rate of 300 ppm, and 10 mixed-sex adult S. oryzae were exposed on 35 g of wheat for either 1, 2, or 3 weeks at 27°C, 57% and 75% r.h. Survival decreased with increasing exposure interval and concentration, but within exposure interval and concentration, survival was usually greater at 75% versus 57% r.h. In the final experiment, wheat was treated with 300 ppm, held at 22°C and 27°C, 57% r.h., and bioassayed at monthly intervals for 3 months by exposing 20 adult mixed-sex S. oryzae on 35 g of wheat for 1 or 2 weeks. At each month, survival of S. oryzae was greater when exposed at 22°C compared to 27°C and when exposed for 1 week compared with 2 weeks. Survival gradually increased with each monthly bioassay, except for those conducted at 3 months. Results of these studies show that S. oryzae is susceptible to DE, but survival of exposed insects will depend in part on the temperature and r.h. humidity (or grain moisture content) at which they are exposed. Survival is directly related to temperature, and as r.h. increases either higher concentrations or longer exposure intervals will be necessary to maintain a certain level of mortality. There may also be a loss of efficacy with residual aging.