Lethal and sublethal effects of rice polishing process on Sitophilus oryzae (Coleoptera: Curculionidae)

The mechanical impact of rice polishingon the rice weevil, Sitophilus oryzae (L.), and the subsequent postpolishing effects associated with rice quality were studied. "Brown" rice (not polished), "White (infest then polish)" rice, and "White (polish then infest)" rice were used with different polishing process intensities and different initial weevil densities. Weevil progeny were more numerous in Brown than in White (infest then polish) or White (polish then infest) rice. Polishing corresponding to a weight loss of 11% in rice generated an immediate mortality of approximately 40%; the subsequent mortality caused by rice quality was also 40% (total >80%). A polishing process corresponding to 14 and 16% of rice weight loss generated a drastic mortality in the weevil population (>95%). The progeny per adult weevil was similar with high and low initial weevil densities. The development of weevil progeny was also delayed by about 1 wk in White (infest then polish) rice compared with Brown rice. Furthermore, weevil adults of the progeny were significantly heavier in Brown than in White (infest then polish) or White (polish then infest) rice.     

Effectiveness of monoterpenes and phenylpropenes on Sitophilus oryzae L. (Coleoptera: Curculionidae) in stored wheat

Six monoterpenes, ((?)-citronellal, p-cymene, (?)-menthone, α-pinene, α-terpinene and (?)-terpinen-4-ol) and two phenylpropenes, (trans-cinnamaldehyde and eugenol) were tested for their insecticidal activity against the rice weevil, Sitophilus oryzae under laboratory conditions. The bioassays were carried out on wheat at the concentrations of 0.5, 1.0 and 5.0?g/kg. Adult mortality was assessed after 14?days of exposure. After this interval, the treated wheat was retained for an additional period of 90?days, in order to evaluate progeny production and wheat loss. At the concentrations of 0.5 and 1.0?g/kg, trans-cinnamaldehyde and eugenol achieved highest adult mortality. At 5.0?g/kg, all compounds except for p-cymene and α-pinene caused complete (100%) adult mortality. Generally, trans-cinnamaldehyde was the most potent compound causing complete inhibition of progeny at the three concentrations. Similarly, no progeny were observed in the wheat treated with (?)-citronellal, eugenol, p-cymene, (?)-menthone, and (?)-terpinen-4-ol at 5.0?g/kg after 45 and 90?days. Similar trends were noted for wheat weight loss and damage as the treatment with monoterpenes and phenylpropenes at the highest rate preserved the wheat intact and free from damage by S. oryzae for 90?days. Our findings suggest the tested compounds except p-cymene and α-pinene could be recommended for use as part of an integrated pest management program for S. oryzae control in stored wheat.     

Imaging and automated detection of Sitophilus oryzae (Coleoptera: Curculionidae) pupae in hard red winter wheat

Computed tomography, an imaging technique commonly used for diagnosing internal human health ailments, uses multiple x-rays and sophisticated software to recreate a cross-sectional representation of a subject. The use of this technique to image hard red winter wheat, Triticum aestivm L., samples infested with pupae of Sitophilus oryzae (L.) was investigated. A software program was developed to rapidly recognize and quantify the infested kernels. Samples were imaged in a 7.6-cm (o.d.) plastic tube containing 0, 50, or 100 infested kernels per kg of wheat. Interkernel spaces were filled with corn oil so as to increase the contrast between voids inside kernels and voids among kernels. Automated image processing, using a custom C language software program, was conducted separately on each 100 g portion of the prepared samples. The average detection accuracy in the five infested kernels per 100-g samples was 94.4 +/- 7.3% (mean +/- SD, n = 10), whereas the average detection accuracy in the 10 infested kernels per 100-g sample was 87.3 +/- 7.9% (n = 10). Detection accuracy in the 10 infested kernels per 100-g samples was slightly less than the five infested kernels per 100-g samples because of some infested kernels overlapping with each other or air bubbles in the oil. A mean of 1.2 +/- 0.9 (n = 10) bubbles (per tube) was incorrectly classed as infested kernels in replicates containing no infested kernels. In light of these positive results, future studies should be conducted using additional grains, insect species, and life stages.     

Immediate and delayed mortality of Rhyzopertha dominica (Coleoptera: Bostrichidae) and Sitophilus oryzae (Coleoptera: Curculionidae) adults exposed to spinosad-treated commodities

A series of tests was conducted to characterize differences in the mortality of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), and rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), exposed to three commodities treated with a liquid and dry spinosad formulation. In laboratory bioassays, adults of the two insect species were exposed to untreated wheat, Triticum aestivum L., corn, Zea mays L., and sorghum, Sorghum bicolor (L.) Moench., and to commodities treated with 1 mg (AI)/kg of liquid and dry spinosad formulations. Mortality was assessed from independent samples examined at specific time intervals to determine immediate mortality and after 24 h of recovery on untreated grain at 28 degrees C and 65% RH to determine delayed mortality. Comparison of the time required for 50% (LT50) and 95% (LT95) mortality indicated that R. dominica adults were consistently and significantly more susceptible (died quickly) than S. oryzae adults when exposed to spinosad-treated commodities. In general, the toxicity of liquid and dry spinosad formulations was similar against R. dominica or S. oryzae. The toxicity of spinosad to each species varied slightly among the three commodities, and there were no consistent trends to suggest that spinosad was more effective on one commodity versus another. LT50 values based on immediate mortality for R. dominica on all commodities ranged from 0.45 to 0.74 d; corresponding values based on delayed mortality ranged from 0.04 to 0.23 d, suggesting delayed toxic action of spinosad in R. dominica. LT50 values based on immediate and delayed mortality for S. oryzae on all three commodities treated with the two spinosad formulations were essentially similar and ranged from 2.75 to 4.56 d. LT95 values for R. dominica based on immediate mortality on spinosad-treated commodities ranged from 1.75 to 3.36 d, and those based on delayed mortality ranged from 0.49 to 1.88 d. There were no significant differences in LT95 values based on immediate and delayed mortality for S. oryzae on spinosad-treated commodities, and the LT95 values ranged from 7.62 to 18.87 d. The toxicity of spinosad was enhanced during a 24-h holding period after removal from spinosad-treated commodities only against R. dominica adults, and possible reasons for increased postexposure mortality of R. dominica adults after brief exposures to spinosad warrant further study.     

Thermal treatments to increase acoustic detectability of Sitophilus oryzae (Coleoptera: Curculionidae) in stored grain.

Hidden infestations of stored-product insect larvae are detected most rapidly by acoustic techniques when the larvae are highly active. Larval activity is periodic, however, and it tends to decrease after the larvae are disturbed or cooled. Because of the practical need for rapid inspection of grain at commercial elevators, several heat treatments were tested as potential methods of increasing larval activity and improving the speed and reliability of acoustic detection under adverse conditions. Samples of grain infested with 4th instars of Sitophilus oryzae (L.) were exposed to different radiant and convective heat treatments after they had been conditioned at 11 degrees C, 17 degrees C, or room temperature for 12-24 h. Relative activity levels were evaluated over periods of 0-12 h based on the mean levels in a 15-min interval, 2 h after the beginning of a trial. In comparisons among treatments with precooled larvae, relative activity levels 5-10 min after brief heat pulses were 2-30 times higher than activity levels in precooled controls exposed only to ambient temperatures (25 degrees C). After 15-25 min, the relative activity levels of these heated larvae remained 2-5 times higher than those of the ambient controls. Brief movement disturbances inhibited activity for approximately 20 min at any temperature. These results suggest that, in general, larval detectability is enhanced if cool grain samples are warmed and all samples are left undisturbed for 15-20 min before inspection.     

Influence of growing location and cultivar on Rhyzopertha dominica （Coleoptera： Bostrichidae） and Sitophilus oryzae （Coleoptera： Curculionidae） infestation of rough rice

Long-grain rice cultivars Cocodrie, Wells, and XP 723 grown in three locations （Hazen, MO; Essex and Newport, AR, USA）, and medium-grain rice cultivars Bengal and XP 713 grown in two locations （Jonesboro and Lodge Corner, AR, USA）, were harvested and assayed for susceptibility to Rhyzopertha dominica （F.） （Coleoptera： Bostrichidae）, the lesser grain borer, and Sitophilus oryzae （L.） （Coleoptera： Curculionidae）, the rice weevil, on rice held at 27℃, 57% and 75% relative humidity （RH）. Separate samples from the same harvest lots were also analyzed for the physical characteristics of brown rice yield, percentage whole kernels and kernel thickness. Progeny production and feeding damage of R. dominica were significantly different among long-grain cultivars within two of the three locations （P 〈 0.05）, but not for location or RH （P ≥ 0.05）, while progeny production of S. oryzae was different among cultivars, location, and RH （P 〈 0.05）. On medium-grain rice, both cultivar and location were significant for progeny production of R. dominica, but not RH, while cultivar and RH were significant for progeny production of S. oryzae, but not location. On both rice types, feeding damage of R. dominica followed the same trends and was always strongly positively correlated with progeny production （P 〈 0.05）, but for S. oryzae there were several instances in which progeny production was not correlated with feeding damage （P ≥ 0.05）. Physical characteristics of both rice types were statistically significant （P 〈 0.01） but actual numerical differences were extremely small, and were generally not correlated with progeny production of either species. Results indicate that the location in which a particular rice cultivar is grown, along with its characteristics, could affect susceptibility of the rice to R. dominica and S. oryzae.     

Pectin methylesterase from the rice weevil,Sitophilus oryzae (L.) (Coleoptera: Curculionidae): Purification and characterization

A pectin methylesterase was purified to apparent homogeneity from the adult rice weevil, Sitophilus oryzae (L.), by Q-Sepharose and S-Sepharose chromatographies followed by high-performance anion-exchange chromatography. The resulting preparation is the first pectin methylesterase which has been purified from any animal species, although at this point we cannot rule out the possibility that the enzyme is produced by a symbiotic microorganism. The molecular mass of the enzyme was estimated as 38 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This mass is similar to those of pectin methylesterases previously isolated from bacteria, fungi, and plants. The purified enzyme had a broad pH optimum between 6 and 7, which appears consistent with the enzyme's probable site of action, the gut.     

Persistence and efficacy of three diatomaceous earth formulations against Sitophilus oryzae (Coleoptera: Curculionidae) on wheat and barley

The insecticidal and residual efficacy of three diatomaceous earth (DE) formulations, Insecto, PyriSec, and SilicoSec, against Sitophilus oryzae (L.) on barley and wheat was assessed. For this purpose, 4-kg lots of barley and wheat were treated with the above-mentioned DE formulations, in three dose rates (0.75, 1, and 1.5 g/kg grain) and stored at 26 degrees C. Samples of these lots were taken at the day of storage, and every 45 d, until the completion of a 450-d period of storage. Bioassays were conducted by exposing S. oryzae adults to these samples, at 26 degrees C and 57% RH. In these bioassays, the DE efficacy was evaluated by recording adult mortality after 24 h, 48 h, 7 d, and 14 d of exposure on the treated grains. After the 14-d count, all adults were removed, and the samples were left at the same conditions for an additional 45 d, to evaluate the capacity for progeny production in the treated grains. Adult mortality after 14 d of exposure was exponentially decreased with time. During the first 270 d of storage, mortality was > 90%, and progeny production was < 1 adult per sample, whereas after 270 d a gradual decrease in adult mortality occurred, with a resulting increase in progeny production. Generally, the three DE formulations tested were equally effective against S. onyzae adults. During the first 270 d of storage, the DE formulations were equally effective on both grains tested, but from 315 d of storage and on, S. oryzae mortality was higher on barley than on wheat. At this interval, progeny production was gradually increased, especially on grains treated with the lowest DE dose rate. However, even this rate caused a satisfactory level of mortality (> 90% after 14 d of exposure) during the first 270 d of storage.     

Effect of temperature and commodity on insecticidal efficacy of spinosad dust against Sitophilus oryzae (Coleoptera: Curculionidae) and Rhyzopertha dominica (Coleoptera: Bostrychidae)

The insecticidal effect of spinosad dust, a formulation that contains 0.125% spinosad, was evaluated against adults of Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) at three temperature levels (20, 25, and 30 degrees C) and four commodities (wheat, Triticum aestivum L.; barley, Hordeum vulgare L.; rice, Oryza sativa L.; and maize, Zea mays L.). For this purpose, quantities of the above-mentioned grains were treated with spinosad at two dose rates (20 and 50 ppm of the formulation, corresponding to 0.025 and 0.06 ppm AI, respectively), and mortality of the exposed adults in the treated grains was measured after 7 and 14 d, whereas progeny production was assessed 65 d later. Generally, for both species, mortality increased with dose, exposure interval, and temperature. For S. oryzae, adult survival and progeny production were lower on wheat than the other grains. After 14 d of exposure, mortality of S. oryzae adults on wheat treated with 50 ppm ranged between 61 and 98%, whereas in the other three commodities it did not exceed 42%. Mortality of R. dominica after 14 d on grains treated 50 ppm ranged between 91 and 100%. For this species, progeny production from exposed parental adults was low in all commodities regardless of temperature. Results indicate that spinosad dust can be used as an alternative to traditional grain protectants, but its effectiveness is highly determined by the target species, commodity, dose, and temperature.     

Influence of maternal age on the fitness of progeny in the rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae)

We studied the effects of maternal age on fitness of progeny in the rice weevil, Sitophilus oryzae L. (Coleoptera: Curculionidae). Five-, 20-, and 50-d-old female rice weevils were used to study the effects of maternal age on the lifetime fecundity and longevity of their daughters. In addition, we determined the effects of maternal age on the weight and survivorship of daughters' progeny. Daughters of 5- and 20-d-old weevils lived longer, and the numbers and weights of the progeny of these daughters were higher than for daughters of 50-d-old weevils. Survivorship of immature grand-offspring of 5-, 20-, and 50-d-old female weevils was similar. None of the fitness characteristics of the daughters and grand-offspring of 5- and 20-d-old weevils that were measured differed significantly. We believe maternal age effects on rice weevil progeny fitness may at least partly be acting through maternal age effect on egg size. Individuals that developed from younger 5- and 20-d-old weevils had a greater fitness than those produced by older 50-d-old females. Our study shows maternal age is impacting life history parameters that influence population dynamics across generations. Therefore, maternal age could significantly affect population development and have far reaching implications for pest management and simulation modeling of rice weevil populations.     

Efficacy of intercropping and harvest time modification for reducing field infestation of maize by Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Most management practices of Sitophilus zeamais Motschulsky, a field-to-post-harvest insect pest of cereals, have focused on post harvest control methods. This experiment was designed to investigate the potential of cropping system and modification of time of harvest to control S. zeamais. Intercropping and harvest time modification had significant (P < 0.05) effect on the number of S. zeamais emerging 42 days post-harvest. For the early harvest (15 weeks after planting (WAP)), the mean number of S. zeamais recorded from a maize monoculture (7.39) was significantly (P < 0.05) higher than the mean numbers of weevils emerging from a maize–soybean intercrop (2.31), but not significantly higher than the number recorded in maize–groundnut (3.87) intercrop. For the late harvest (18 WAP), the mean number of emerged adult observed in the maize–soybean intercrop (6.13) was significantly lower than the mean number of adult emerging from the monocrop maize (13.24). Maize–groundnut intercrop did not significantly reduce field infestation of S. zeamais compared with monocrop maize. Percentage weight loss observed in early harvested maize was significantly (P < 0.0001) lower than what was observed in late-harvested maize. Percentage weight loss was highest in stored maize harvested from monocrop maize plots for the early harvest, whereas intercropping maize with soybean reduced percentage weight loss when harvest was delayed.     

Efficacy of cashew kernel extracts in the control of the maize weevil,Sitophilus zeamais (Coleoptera: Curculionidae)

Six different solvents namely: methanol, ethanol, water, acetone, pet-ether or n-hexane was used to extract the essential oils from cashew kernel. The extracted oils were evaluated on Sitophilus zeamais (Motschulsky 1855) for mortality, oviposition and adult emergence effects. The long-term storage and water absorption capacity of the treated maize grains was also investigated. Results showed that the steam distillate was most lethal on S. zeamais. The least potent extracts on S. zeamais were those extracted with methanol and ethanol. The extracts drastically reduced oviposition in S. zeamais. Maize grains treated with steam distillate extract had the lowest water absorption capacity, while the highest water absorption capacity was obtained in grains treated with ethanol and methanol. Extracts of steam distillate, n-hexane, petroleum ether and acetone completely prevented infestation and subsequence damage of the treated maize grains for a period of three months. In the grains treated with the methanol and ethanol extracts, damage of 28.61% and 6.24%, respectively were obtained. The results obtained reveal that extracts of cashew kernel are effective in controlling S. zeamais and could serve as an alternative to synthetic insecticides.     

Insecticidal effect of three diatomaceous earth formulations against adults of Sitophilus oryzae (Coleoptera: Curculionidae) and Tribolium confusum (Coleoptera: Tenebrionidae) on oat, rye, and triticale

Bioassays were conducted in the laboratory to assess the effect of the diatomaceous earth (DE) formulations Insecto, SilicoSec, and PyriSec, on stored oat, rye, and triticale, against adults of the rice weevil, Sitophilus oryzae (L.), and the confused flour beetle, Tribolium confusum Jacquelin du Val. The DEs were tested at three dose rates, 0.75, 1, and 1.5 g of DE/kg of grain. Adults of the two aforementioned species were exposed to all combinations of grain-formulation-dose rate, at 26 degrees C and 60% RH. Mortality in DE-treated commodities was recorded after 24 h, 48 h, 7 d, and 14 d of exposure for S. oryzae and T. confusum and after 21 d for T. confusum. In S. oryzae, adult mortality was almost 100% after 7 d of exposure in all three grains examined. The mortality of T. confusum adults in DE-treated grains did not reach 100%, even after 21 d of exposure. Generally, the application of DE in rye caused higher adult mortality of T. confusum than in the other two products. All three dose rates tested provided the same mortality level of S. oryzae adults after 7 d of exposure. In contrast, 1.5 g of DE resulted in significant higher adult mortality of T. confusum, in comparison with the other dose rates, even after 21 d of exposure. All formulations were equally effective after 7 d of exposure against S. oryzae, but at 48 h of exposure, PyriSec caused significantly higher mortality than the other two formulations. For both species, progeny production in the treated grains was significantly reduced in comparison with the untreated grains, whereas significant differences were noted among commodities, formulations, and dose rates. No progeny were recorded in the treated rye for either species or in the treated triticale for S. oryzae.     

温度和寄主密度对雅脊金小蜂寄生和刺死米象幼虫的影响（英文）

本文通过研究雅脊金小蜂Theocolax elegans在6个不同温度梯度下对米象Sitophilus oryzae幼虫的寄生和取食能力,评价了雅脊金小蜂对米象的控制效果。雅脊金小蜂寄生米象的功能反应结果表明,在17℃～29℃的温度范围内,寄生蜂的寄主处理时间与温度成反比,从0.333天（17℃）到0.063天（29℃）。寄主搜索率也随温度变化而变化,17℃时最低（0.083头/天）,26℃时最高（1.521头/天）;当温度升高到29℃,寄主搜索率略有下降;但当温度升高到32℃,寄主搜索率明显下降。温度调节的功能反应模型表明,在26℃～29℃的温度范围内,寄生率较高。所以,在26℃～29℃时,雅脊金小蜂对米象有较好的控制效果。     

Rapid assessment of insect fragments in flour milled from wheat infested with known densities of immature and adult Sitophilus oryzae (Coleoptera: Curculionidae)

Milling wheat, Triticum aestivum L., infested with low densities of internal feeding insects can result in flour containing insect fragments. The Food and Drug Administration (FDA) enforces a standard or defect action level stating that a maximum of 75 insect fragments per 50 g of flour is allowed. However, the relationship between level of infestation and number of resulting fragments is not well documented, and a more rapid method for enumerating insect fragments is needed. We characterized the number of insect fragments produced from milling small lots of wheat spiked with known densities and life stages of Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Insect fragments were enumerated with near-infrared spectroscopy (NIRS), a quick nondestructive procedure, and with the industry standard flotation method. Results showed that an individual small larva, large larva, pupa, or adult produced 0.4, 0.7, 1.5, and 27.0 fragments, respectively. NIRS-predicted counts of < or =51 (from small larvae), < or =53 (from large larvae), < or =43 (from pupae), or 0 (from adults) indicated that there were <75 actual fragments in that sample, because the upper bound of associated 95% inverse prediction confidence intervals was less than the standard; NIRS-predicted counts of > or =98, > or =117, 108, or > or =225 fragments (same life stages as above) signaled that these flour samples contained >75 actual fragments. These data suggest that NIRS could be adopted for rapid assessment of insect fragments resulting from relatively low levels of infestation with immature life states, but that it was not accurate enough for enumerating insect fragments, relevant to FDA standards, resulting from adults.     

Grain injury models for Prostephanus truncatus (Coleoptera: Bostrichidae) and Sitophilus zeamais (Coleoptera: Curculionidae) in rural maize stores in West Africa

Prostephanus truncatus (Horn) and Sitophilus zeamais Motschulsky have been reported as the two most serious pests of stored maize in sub-Saharan Africa and smallholder farmers are in urgent need of guidelines for their proper management. In this article we investigate the injury rates attributable to these two species in terms of percentage weight loss and percentage grain damage, and we derive functional response models for the two species on maize. The models successfully described the progression of grain injury in an extensive data set compiled from previously published studies, comprising 46 time series of data relating maize injury and insect pest density. The grain injury models can be used in conjunction with predictive models of pest population dynamics to guide the development of integrated management strategies for postharvest maize pests in West Africa and comparable regions elsewhere.