Interaction of treatment of both adult and immature Coleoptera with a chitin synthesis inhibitor affects mortality and development time of their progeny

Chitin synthesis inhibitors, like many other insect growth regulating insecticides, do not kill adult insects but cause mortality of the immature stages. Pre-exposure of adult stored grain Coleoptera, Rhyzopertha dominica (F.) (Bostrichidae) and Sitophilus oryzae (L.) (Curculionidae) and development of their progeny in grain treated with the chitin synthesis inhibitor, chlorfluazuron, influenced the mortality and development rate of the progeny. Hatch rate of eggs from R. dominica adults that had both developed and laid on wheat treated with 0.75 mg kg–1 chlorfluazuron was reduced by almost 50% compared with untreated eggs, with an LC50 of 0.84 mg kg–1 . Eggs laid on treated wheat by R. dominica adults that had been exposed only to treated wheat for 2 weeks before oviposition showed greater reduction in hatch: 75% reduction of normal hatch rate at 0.25 mg kg–1 and almost 100% reduction at 2 mg kg–1 chlorfluazuron, with an LC50 of 0.19 mg kg–1 chlorfluazuron. X-rays were used to monitor the development and mortality of the immature stages of S. oryzae that developed within the wheat grains. Numbers of eggs laid were not affected by chlorfluazuron treatment. The combination of pre-exposure of adults and chlorfluazuron concentration had an additive effect on mortality of immature S. oryzae. Pre-exposure of adults caused most mortality in the first three weeks of development (eggs and larvae), whereas development in treated wheat caused mortality from weeks 3 to 8 (pupae and adults); higher concentrations of chlorfluazuron caused higher mortality. Development in wheat treated with 1 mg kg–1 chlorfluazuron caused 12% corrected overall mortality of progeny while pre-exposure to the same concentration and development in untreated wheat caused 29% corrected mortality. Pre-exposure combined with development in wheat treated with 1 mg kg–1 caused 30% corrected mortality. Thus, pre-exposure of adults appears to have a greater effect on mortality of S. oryzae progeny than development of immature stages in treated grain. Development on treated grain had no effect on development rate. Pre-exposure of adults did not appear to affect the rate of immature development, as assessed by X-rays, but did slow the emergence of adults, lengthening development time by about 2 days. This significant, additive effect of pre-exposure of adults on the mortality of their progeny will enhance the toxicity of chitin synthesis inhibitors such as chlorfluazuron, since most adults receive treatment when the immature stages are treated in crops either before they are harvested or in storage. Assessing the proportion of eggs that hatch from pre-exposed adults would be a simpler bioassay for CSIs.     

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.     

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.     

Effect of acrolein vapors on stored-product insects and wheat seed viability

In laboratory experiments, toxicity of acrolein vapors was investigated against four species of stored-product insects. In empty-space trials, estimates of the median lethal doses of acrolein against adults of Oryzaephilus surinamensis (L.), Sitophilus oryzae (L.), Rhyzopertha dominica (F.), and Tribolium castaneum (Herbst), were 1.87, 2.35, 3.12, and 6.65 mg/liter, respectively. Penetration tests revealed that acrolein vapors could penetrate into the wheat mass and kill concealed insects in interkernel spaces. Comparison of LD50 values between empty-space tests and penetration experiments after 24-h exposure indicated that the increase in penetration toxicity was 6.34-, 6.31-, 7.17-, and 4.54-fold for O. surinamensis, S. oryzae, R. dominica, and T. castaneum, respectively. In the hidden infestation trials, the acrolein vapors destroyed all the developmental stages of S. oryzae and R. dominica concealed inside the wheat kernels, resulted in a complete control with dose of 80 mg/liter for 24 h, and subsequently observed during 8 wk after the exposure. Wheat germination rate was diminished by fumigation with acrolein. The plumule length was reduced after exposure to all doses of acrolein. Together, the data suggest acrolein could be a potential compound for empty-space fumigations.     

Effect of short exposures to spinetoram against three stored-product beetle species

Laboratory bioassays were carried out to evaluate the effectiveness of two formulations of spinetoram, water dispersible granules (WG), and suspension concentrate (SC-NC), against three major stored-grain beetle species, the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae); the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae); and the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae). Adults of the above species were exposed on wheat treated with spinetoram at 1 ppm (1 mg/kg of wheat) for 0, 2, 4, 6, 8, 16, 40, and 72 h. After this interval, mortality was recorded (immediate mortality) and the surviving individuals were transferred in untreated wheat, where mortality was recorded again 7 d later (delayed mortality). Then, all adults were removed, and the number of progeny production in the untreated substrate was measured 65 d later. From the species tested, R. dominica was by far the most susceptible, given that immediate and delayed mortality for the 72-h exposure interval reached 44 and 97%, respectively. At the same time, progeny production was low, in most of the exposure intervals tested. In contrast, for S. oryzae, delayed mortality was negligible, with the exception of 72 h at the SC-NC formulation. However, in most of the cases examined, progeny production for S. oryzae was high. Finally, adult mortality for T. confusum was extremely low, regardless of the exposure interval and the type of the formulation. Nevertheless, offspring emergence of this species was low. By combining the results of the current study and the data that are available from the literature for short exposures to spinosad, we can conclude that the two ingredients were equally effective against these three stored-grain beetle species.     

Effectiveness of spinosad on four classes of wheat against five stored-product insects

Spinosad is a commercial reduced-risk pesticide that is naturally derived. Spinosad's performance was evaluated on four classes of wheat (hard red winter, hard red spring, soft red winter, and durum wheats) against adults of the lesser grain borer, Rhyzopertha dominica (F.); rice weevil, Sitophilus oryzae (L.); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); red flour beetle, Tribolium castaneum (Herbst); and larvae of the Indianmeal moth, Plodia interpunctella (Hübner). Beetle adults (25) or P. interpunctella eggs (50) were exposed to untreated wheat and wheat treated with spinosad at 0.1 and 1 mg (AI)/kg of grain. On all untreated wheat classes, adult beetle mortality ranged from 0 to 6%, and P. interpunctella larval mortality ranged from 10 to 19%. The effects of spinosad on R. dominica and P. interpunctella were consistent across all wheat classes. Spinosad killed all exposed R. dominica adults and significantly suppressed progeny production (84-100%) and kernel damage (66-100%) at both rates compared with untreated wheat. Spinosad was extremely effective against P. interpunctella on all wheat classes at 1 mg/kg, based on larval mortality (97.6-99.6%), suppression of egg-to-adult emergence (93-100%), and kernel damage (95-100%), relative to similar effects on untreated wheats. The effects of spinosad on S. oryzae varied among wheat classes and between spinosad rates. Spinosad was effective against S. oryzae, O. surinamensis and T. castaneun only on durum wheat at 1 mg/kg. Our results suggest spinosad to be a potential grain protectant for R. dominica and P. interpunctella management in stored wheat.     

Factors affecting laboratory bioassays with diatomaceous earth on stored wheat: effect of insect density, grain quantity, and cracked kernel containment

Laboratory bioassays were carried out to evaluate the effect of insect density (10, 30, 60, and 100 adults), wheat quantity (10, 30, 60, and 100 g), and cracked kernel containment (5, 15, 30, and 50%) on the efficacy of diatomaceous earth (DE). Three beetle species, Sitophilus oryzae (L.), Rhyzopertha dominica (F.), and Tribolium confusum Jacquelin du Val, as well as two DE formulations, Insecto and SilicoSec, and one DE enhanced with pyrethrum, PyriSec (all commercially available) were tested. In the first two series of bioassays, the three DE formulations were applied at three dose rates, 500, 1000 and 1,500 ppm. In the third series, the dose rates used were 500 and 1,000 ppm. Dead adults were counted 14 d later. For insect density, wheat quantity, and cracked kernel containment, significant differences were noted in mortality levels of the tested species among the three DE formulations and among doses. No significant differences were noted in the mortality levels among the four adult densities of any of the insects tested. The increase of wheat quantity used in the bioassays increased significantly adult mortality of T. confusum. The increase of cracked wheat containment decreased significantly adult mortality of S. oryzae.     

Transmission of Salmonella montevideo in Wheat by Stored-Product Insects

Sitophilus oryzae (L.), S. granarius (L.), Tribolium castaneum (Hbst.), Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.), Tenebroides mauritanicus (L.), and Cryptolestes pusillus (Schon.) transmitted Salmonella montevideo from wheat contaminated with 10(6) organisms/g to clean wheat. The insects were fed on the contaminated grain for 21 days and were then transferred to clean grain and allowed to feed for 21 days. They were subsequently transferred to two more samples of clean wheat. All species carried S. montevideo into the initial sample of clean wheat but not into a second or third sample. Progeny of the original insects that developed in the contaminated wheat exhibited less ability than the original adults to contaminate clean wheat. Data indicated that few S. montevideo could be carried by the stored-product insects in large masses of grain.     

Cytochrome c oxidase inhibition in the rice weevil Sitophilus oryzae (L.) by formate, the toxic metabolite of volatile alkyl formates

Volatile alkyl formates are potential replacements for the ozone-depleting fumigant, methyl bromide, as postharvest insecticides and here we have investigated their mode of insecticidal action. Firstly, a range of alkyl esters, ethanol and formic acid were tested in mortality bioassays with adults of the rice weevil, Sitophilus oryzae (L.) and the grain borer, Rhyzopertha dominica (F.) to determine whether the intact ester or one of its components was the toxic moiety. Volatile alkyl formates and formic acid caused similar levels of mortality (LC(50) 131-165 micromol l(-1)) to S. oryzae and were more potent than non-formate containing alkyl esters and ethanol (LC(50)>275 micromol l(-1)). The order of potency was the same in R. dominica. Ethyl formate was rapidly metabolised in vitro to formic acid when incubated with insect homogenates, presumably through the action of esterases. S. oryzae and R. dominica fumigated with a lethal dose of ethyl formate had eight and 17-fold higher concentrations of formic acid, respectively, in their bodies than untreated controls. When tested against isolated mitochondria from S. oryzae, alkyl esters, alcohols, acetate and propionate salts were not inhibitory towards cytochrome c oxidase (EC 1.9.3.1), but sodium cyanide and sodium formate were inhibitory with IC(50) values of 0.0015 mM and 59 mM, respectively. Volatile formate esters were more toxic than other alkyl esters, and this was found to be due, at least in part, to their hydrolysis to formic acid and its inhibition of cytochrome c oxidase.     

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.     

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.     

Effect of temperature, exposure interval, and depth of diatomaceous earth treatment on distribution, mortality, and progeny production of lesser grain borer (Coleoptera: Bostrichidae) in stored wheat

Diatomaceous earth (DE) can be used as a surface treatment in stored wheat Triticum aestivum (L.) to control pest infestations. However, it is not known how the thickness of the DE-treated wheat layer or grain temperature impact effectiveness. Therefore, we conducted an experiment in growth chambers to assess the effect of different surface layers of hard winter wheat combined with DE on spatial distribution, adult survival, and progeny production of lesser grain borer, Rhyzopertha dominica (F.), and to determine whether temperature and exposure interval modified this effect. When adult lesser grain borers were released in experimental towers containing untreated wheat or wheat admixed with DE to a surface layer depth of 15.2, 22.9, or 30.5 cm, they were able to penetrate all DE layers and oviposit in the untreated wheat below. However, survival was significantly reduced in adults exposed to DE. Survival decreased both with increasing depth of the DE-treated wheat and with exposure interval. Temperature had no effect on adult survival, but significantly more progeny were produced at 32 than at 27 degrees C. Progeny production was inversely correlated with the depth of the DE-treated layer. Vertical distribution patterns of parental beetles were not significantly different among treatments or exposure intervals; however, more insects were found at greater depths at 32 than at 27 degrees C. The F1 production was reduced by 22% at the thickest DE-treated layer. However, we conclude that this level of survival could leave a residual population of lesser grain borers that would probably be above an allowable threshold for insect damage.     

Persistence and efficacy of spinosad residues in farm stored wheat

Degradation and insecticidal effectiveness of spinosad residues were evaluated in Kansas during November 2000 to November 2001 in farm bins holding wheat (34-metric ton capacity). About 50 kg of hard red winter wheat from each of three bins were brought to the laboratory and treated separately with 1-ml aqueous suspensions of spinosad to provide rates of 0.1, 0.5,1, 3, 6 mg (AI)/kg of wheat. Wheat treated with distilled water served as the control treatment. Untreated and spinosad-treated wheat samples (250 g each) were placed in three plastic pouches of two different mesh sizes, and buried 2.5 cm below the grain surface. Pouches with large mesh openings were used to monitor insect infestations and kernel damage in untreated and spinosad-treated samples. Pouches with small mesh were used for extracting spinosad residues and for conducting laboratory bioassays with adults of the lesser grain borer, Rhyzopertha dominica (F.) and red flour beetle, Tribolium castaneum (Herbst) at 28 degrees C and 65% RH. Wheat temperature and relative humidity near the pouches during the 1 yr of storage ranged from -10 to 32 degrees C and 50 to 70%, respectively. Moisture of wheat samples varied from 12.4 to 13%. Observed spinosad residues on wheat samples were 25% less than the calculated rates of 0.1 to 6 mg/kg. However, these residues were stable during the 1 yr of storage, and killed all R. dominica adults exposed for 14 d in the laboratory. Mortality of T. castaneum adults increased with an increase in spinosad rate. The linear regression slope of LD50s (0.3-2.7 mg/kg) against storage time was not significantly different from zero, indicating no loss in spinosad toxicity to T. castaneum adults. Insect species, insect numbers, and kernel damage over time in wheat samples inside pouches with large mesh openings were highly inconsistent, and failed to accurately characterize spinosad performance. Laboratory bioassays with R. dominica and T castaneum adults using grain from pouches with small mesh openings accurately gauged spinosad persistence and insecticidal activity under the field conditions.     

Effectiveness of spinosad against seven major stored-grain insects on corn

In January 2005, the United States Environmental Protection Agency registered spinosad as a stored grain protectant. No referenced data on the efficacy of spinosad on corn in suppressing major stored-grain insects have been published. In this paper, we evaluated the efficacy of spinosad against seven major stored-grain insects on shelled corn in the laboratory. Insect species tested were the red flour beetle, Tribolium castaneum （Jacquelin duVal）; rusty grain beetle, Cryptolestesferrugineus （Stephens）; lesser grain borer, Rhyzopertha dominica （F.）; sawtoothed grain beetle, Oryzaephilus surinamensis （L.）; rice weevil, Sitophilus oryzae （L.）; maize weevil, Sitophilus zeamais （Motschulsky）; and Indian meal moth, Plodia interpunctella （Htibner）. Corn kernels were treated with spinosad at 0, 0. 1, 0.5, 1, and 2 active ingredient （a.i.） mg/kg for controlling the seven species. Beetle adults or P. interpunctella eggs were introduced into each container holding 100 g of untreated or insecticide-treated corn. The seven insect species survived well on the control treatment, produced 28 to 336 progeny, and caused significant kernel damage after 49 days. On spinosad-treated corn, adult mortality of C. ferrugineus, R. dominica, 0. surinamensis, S. oryzae, and S. zeamais was 〉 98% at 1 and 2 mg/kg after 12 days. Spinosad at≥ 0.5 mg/kg completely suppressed egg-to-larval survival after 21 days and egg-to-adult emergence of P. interpunctella after 49 days, whereas 16% T. castaneum adults survived at 1 mg/kg after 12 days. Spinosad at 1 or 2 mg/kg provided complete or near complete suppression of progeny production and kernel damage of all species after 49 days. Our results indicate that spinosad at the current labeled rate of 1 mg/kg is effective against the seven stored-grain insect pests on corn.     

Bioactivities of the leaf essential oil of Curcuma longa (var. ch-66) on three species of stored-product beetles (Coleoptera)

Essential oil extracted from the leaves of turmeric, Curcuma longa L., was investigated for contact and fumigant toxicity and its effect on progeny production in three stored-product beetles, Rhyzopertha dominica F. (lesser grain borer), Sitophilus oryzae L. (rice weevil), and Tribolium castaneum Herbst (red flour beetle). Oviposition-deterrent and ovicidal actions of C. longa leaf oil were also evaluated against T. castaneum. The oil was insecticidal in both contact and fumigant toxicity assays. The adults of R. dominica were highly susceptible to contact action of C. longa leaf oil, with LD50 value of 36.71 microg/mg weight of insect, whereas in the fumigant assay, adults of S. oryzae were highly susceptible with LC50 value of 11.36 mg/liter air. Further, in T. castaneum, the C. longa oil reduced oviposition and egg hatching by 72 and 80%, respectively at the concentration of 5.2 mg/cm2. At the concentration of 40.5 mg/g food, the oil totally suppressed progeny production of all the three test insects. Nutritional indices indicate >81% antifeedant action of the oil against R. dominica, S. oryzae and T castaneum at the highest concentration tested.     

Efficacy of ozone fumigation against the major grain pests in stored wheat

Field experiments were conducted in steel bins containing 13,600 kg of hard red winter wheat, Triiticum aestivum L. One bin was treated with ozone and the second bin served as a control. Stored grain insects were placed in bins for 1-, 2-, 3-, and 4-d exposure periods in sampling tubes to test ozone concentrations of 0, 25, 50, and 70 parts per million by volume (ppmv). Ozone treatments on eggs and larvae of Plodia interpunctella (Hübner) were not effective, but pupae were more susceptible. Sitophilus oryzae (L.) adults were the most susceptible species with 100% mortality reached after 2 d in all ozone treatments. However, some progeny were produced at all concentrations and exposure periods. Tribolium castaneum (Herbst) adults had 100% mortality only after 4 d at 50 or 70 ppmv. No T. castaneum progeny were produced after 2-4 d at 70 ppmv. For Rhyzopertha dominica (F.), Cryptolestes ferrugineus (Stephens), and Oryzaephilus surinamensis (L.), 100% mortality was never achieved and progeny were produced at all ozone concentrations. Laboratory experiments, testing the effectiveness of ozone in controlling psocids, were conducted in two polyvinyl chloride cylinders each containing 55 kg of hard red winter wheat. Ozone treatment at a concentration of 70 ppmv was highly effective against adult female Liposcelis bostrychophila Badonnel and Liposcelis paeta Pearman after only 1 d of exposure. However, it was not effective against eggs of both species at all exposure periods. Ozonation has potential for the control of some stored grain insect pests on wheat.     

Bioactivities of l-carvone, d-carvone, and dihydrocarvone toward three stored product beetles

The rice weevil, Sitophilus oryzae L., adults were highly susceptible by contact to l-carvone, d-carvone, and dihydrocarvone when compared with the lesser grain borer, Rhyzopertha dominica F., adults and red flour beetle, Tribolium castaneum (Herbst.). Adults of R. dominica were more susceptible than the other species to fumigant vapors of l-carvone, d-carvone, and dihydrocarvone. The three larval stages (14-, 16-, and 18-d-old) of T. castaneum progressively became more susceptible with age toward contact toxicity of three test compounds but in fumigant toxicity, 16-d-old larvae of T. castaneum were more susceptible to the three compounds. Comparison of contact and fumigant toxicity of the test compounds indicates that l-carvone and d-carvone possess 24 times more fumigant toxicity toward adults of R. dominica than its contact toxicity. Overall order of toxicity was l-carvone > d-carvone > dihydrocarvone. Egg hatching and subsequent larval and adult survival of T. castaneum were significantly reduced when the eggs of T. castaneum were treated with l-carvone, d-carvone, and dihydrocarvone. l-Carvone completely suppressed egg hatching at the concentration of 7.72 mg/cm2. Data on feeding-deterrent indices indicate the high potency of l-carvone as feeding-deterrent in order of S. oryzae adults > T. castaneum adults > R. dominica adults > T. castaneum larvae.     

Field evaluation of spinosad as a grain protectant for stored wheat in Australia: efficacy against Rhyzopertha dominica (F.) and fate of residues in whole wheat and milling fractions

Abstract  The potential of spinosad as a grain protectant for the lesser grain borer, Rhyzopertha dominica , was investigated in a silo-scale trial on wheat stored in Victoria, Australia. Rhyzopertha dominica is a serious pest of stored grain, and its resistance to protectants and the fumigant phosphine is becoming more common. This trial follows earlier laboratory research showing that spinosad may be a useful pest management option for this species. Wheat (300 t) from the 2005 harvest was treated with spinosad 0.96 mg/kg plus chlorpyrifos-methyl 10 mg/kg in March 2006, and samples were collected at intervals during 7.5 month storage to determine efficacy and residues in wheat and milling fractions. Chlorpyrifos-methyl is already registered in Australia for control of several other pest species, and its low potency against R. dominica was confirmed in laboratory-treated wheat. Grain moisture content was stable at about 10%, but grain temperature ranged from 29.3°C in March to 14.0°C in August. Bioassays of all treated wheat samples over 7.5 months resulted in 100% adult mortality after 2 weeks exposure and no live progeny were produced. In addition, no live grain insects were detected during outload sampling after a 9 month storage. Spinosad and chlorpyrifos-methyl residues tended to decline during storage, and residues were higher in the bran layer than in either wholemeal or white flour. This field trial confirmed that spinosad was effective as a grain protectant targeting R. dominica .     

Insecticidal effect of NeemAzal against three stored-product beetle species on rye and oats

The insecticidal effect of the azadirachtin-based insecticide, NeemAzal, was examined against adults of Rhyzopertha dominica (F.), Sitophilus oryzae (L.), and Tribolium confusum Jacquelin du Val in rye, whole oats, and peeled oats. The insecticide was applied at three dose rates, which were equivalent to 50, 100, and 200 ppm of azadirachtin A. Adults of the above-mentioned species were exposed to the treated grains at 25 degrees C and 65% RH, and mortality was assessed after 24 h, 48 h, 7 d, and 14 d of exposure. Then, all adults were removed, and the treated substrate remained at the same conditions for an additional 45 d. After this interval, the grains were checked for progeny production. In all species and commodities tested, mortality increased with the increase of dose and exposure interval, except for T. confusum on whole and peeled oats. For R. dominica, NeemAzal was more effective on oats than on rye and peeled oats. In contrast, at rates > or = 100 ppm, azadirachtin was equally effective against S. oryzae on whole rye and oats, where mortality was 100% after 7 and 14 d of exposure, respectively. NeemAzal was not very effective against T. confusum where adult mortality was low, even after 14 d of exposure at the highest rate. For all species, significantly less progeny were recorded in the treated grains than in the untreated grains, with the exception of T. confusum on oats where offspring was significantly reduced only at the highest rate.     

Locomotor Behaviour of Blattella germanica Modified by DEET

N,N-diethyl-3-methylbenzamide (DEET) is the active principle of most insect repellents used worldwide. However, its toxicity on insects has not been widely studied. The aim of this work is to study the effects of DEET on the locomotor activity of Blattella germanica. DEET has a dose-dependent repellent activity on B. germanica. Locomotor activity was significantly lower when insects were pre-exposed to 700 µg/cm² of DEET for 20 or 30 minutes, but it did not change when pre-exposure was shorter. Locomotor activity of insects that were pre-exposed to 2.000 µg/cm² of DEET for 10 minutes was significantly lower than the movement registered in controls. No differences were observed when insects were pre-exposed to lower concentrations of DEET. A 30-minute pre-exposure to 700 µg/cm² of DEET caused a significant decrease in locomotor activity. Movement was totally recovered 24 h later. The locomotor activity measured during the exposure to different concentrations of DEET remained unchanged. Insects with decreased locomotor activity were repelled to the same extent than control insects by the same concentration of DEET. We demonstrated that the repellency and modification of locomotor activity elicited by DEET are non-associated phenomena. We also suggested that the reduction in locomotor activity indicates toxicity of DEET, probably to insect nervous system.