Comparison of aeration and spinosad for suppressing insects in stored wheat

Field studies were conducted from July 2002 to January 2003 for evaluating the effects of controlled aeration and a commercial biological insecticide, spinosad, in suppressing insect populations in stored wheat. Six cylindrical steel bins were filled with newly harvested (2002 crop year) hard red winter wheat on 9 and 10 July 2002. Each bin contained 30.7 metric tons (1,100 bu) of wheat. Wheat in two bins was left untreated (control), whereas wheat in two bins was treated with spinosad, and in another two bins was subjected to aeration by using aeration controllers. Spinosad was applied to wheat at the time of bin filling to obtain a rate of 1 mg ([AI])/kg. Aeration controllers were set to run the fans when ambient air temperature fell below 23.9, 18.3, and 7.2 degrees C for the first, second, and third cooling cycles, respectively. We added 400 adults each of the rusty grain beetle, Cryptolestes ferrugineus (Stephens); lesser grain borer, Rhyzopertha dominica (F.); and red flour beetle, Tribolium castaneum (Herbst), to the grain at monthly intervals between July and October 2002. Insect density in the bins was estimated monthly by taking 3-kg grain samples from 21 locations within each bin by using a pneumatic grain sampler. No live T. castaneum or C. ferrugineus and very low densities of R. dominica (<0.008 adults per kilogram) were found in wheat treated with spinosad during the 6-mo sampling period. Density of C. ferrugineus and T. castaneum in aerated bins did not exceed two adults per kilogram (the Federal Grain Inspection Service standard for infested wheat), whereas R. dominica increased to 12 adults per kilogram in November 2002, which subsequently decreased to three adults per kilogram in January 2003. In the untreated (control) bins, R. dominica density increased faster than that of C. ferrugineus or T. castaneum. Density of R. dominica peaked at 58 adults per kilogram in October 2002 and decreased subsequently, whereas T. castaneum density was 10 adults per kilogram in October 2002 but increased to 78 adults per kilogram in January 2003. Density of C. ferrugineus increased steadily during the 6-mo study period and was highest (six adults per kilogram) in January 2003. This is the first report comparing the field efficacy of spinosad and aeration in managing insects in farm bins. Our results suggest that spinosad is very effective in suppressing R. dominica, C. ferrugineus, and T. castaneum populations in stored wheat.     

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.     

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 .     

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.     

Susceptibility of laboratory and field strains of four stored-product insect species to spinosad

Two field strains of the Indianmeal moth, Plodia interpunctella (Hübner); red flour beetle, Tribolium castaneum (Herbst); and lesser grain borer, Rhyzopertha dominica (F.), and one field strain of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), were collected from hard red winter wheat stored on farms in northeastern Kansas. Fifty eggs of P. interpunctella and 25 beetle adults of each species were exposed to 100 g of untreated wheat or wheat treated with various rates of spinosad, to determine susceptibility of the field and corresponding insecticide-susceptible laboratory strains. Mortality of beetle adults and P. interpunctella larvae was assessed after 7 and 21 d postinfestation, respectively. Field strains of P. interpunctella, C. ferrugineus, and T. castaneum were less susceptible to spinosad than the corresponding laboratory strains. The LD50 and LD95 values for P. interpunctella and C. ferrugineus field strains were 1.7-2.5 times greater than values for corresponding laboratory strains. Adults of both laboratory and field strains of T. castaneum were tolerant to spinosad, resulting in <88% mortality at 8 mg/kg. The LD50 and LD95 values for the field strains of T. castaneum were 2.0-7.5 times greater compared with similar values for the laboratory strain. The field and laboratory strains of R. dominica were highly susceptible to spinosad, and one of the field strains was relatively less susceptible to spinosad than the laboratory strain. Our results confirm a range of biological variability in field populations, which is consistent with findings for other compounds, and underscores the need to adopt resistance management programs with stored grain insect pests. The baseline data generated on the susceptibility of the four insect species to spinosad will be useful for monitoring resistance development and for setting field rates.     

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.     

Survival of stored-product insect natural enemies in spinosad-treated wheat

The survival of stored product insect natural enemies in wheat treated with spinosad was investigated in laboratory and pilot scale experiments. The predator Xylocoris flavipes (Reuter), the warehouse pirate bug, and the parasitoids Habrobracon hebetor (Say), Theocolax elegans (Westwood), and Anisopteromalus calandrae (Howard) were exposed to wheat treated with aliquots of water or spinosad at 0.05-1 mg ([AI])/kg. X. flavipes was the only species that survived (92% survival) in spinosad-treated wheat at 1 mg/kg. X. flavipes suppressed populations of immature Tribolium castaneum (Herbst), the red flour beetle, by nearly 90% compared with a water-treated control, but 100% suppression of immatures was achieved in wheat receiving spinosad or spinosad + X. flavipes treatments. A 3-mo pilot scale experiment to evaluate T. castaneum suppression in drums holding 163.3 kg of wheat showed that the pest populations increased throughout the study in the control treatment, but peaked after 1 mo in the X. flavipes-treated drums. By comparison, better T. castaneum population suppression was achieved in spinosad or spinosad + X. flavipes treatments. Although X. flavipes can survive and reproduce in spinosad-treated wheat, under our test conditions spinosad alone provided adequate suppression of T. castaneum populations in stored wheat.     

Wheat in bins and discharge spouts,and grain residues on floors of empty bins in concrete grain elevators as habitats for stored-grain beetles and their natural enemies

Wheat stored in upright concrete bins at seven grain elevators in central Kansas was sampled intermittently for insects over a 2.5-yr period by collecting samples from the upper half of the grain mass, from the discharge spout at the base of the bins, and from residue remaining in empty bins before the 2000 wheat harvest. Samples were taken from the grain mass with a power vacuum sampler (PV) and from the discharge spouts (DS) by dropping grain onto the reclaim belt beneath the bins. The density and species distribution in the residue samples were compared with those found in the DS samples and samples from the grain mass (PV). Cryptolestes spp. dominated the insect populations in all types of samples, constituting >40% of all insects in the PV samples in three of five time periods and >60% of all insects in DS samples in four of the five time periods. Cryptolestes spp. was an early colonizer, being found in the grain mass shortly after new grain was added. Rhyzopertha dominica appeared to be slower to colonize grain and grain residue, but sometimes developed large populations (i.e., 2.4 +/- 0.7 adults/kg between July and December 2000). Sitophilus spp. weevils often were present in grain masses, were often abundant in grain in the discharge spouts (i.e., 11.1 +/- 2.9 adults/kg between July and December 2000), and were abundant in grain residue in empty bins in May/June 2000 (5.3 +/- 0.7 adults/kg). Differences in density and species distribution of insects in grain in the upper part of the grain mass and those in the discharge spouts indicated that the populations were not closely related. Grain in discharge spouts usually was densely infested, and parasitic wasps, natural enemies of several of the beetles, were found when the density of the pest insects was greater than approximately 10/kg. The population of natural enemies appeared to increase when the density of pest insects increased after a lag of about one month, and decreased when the population of pest insects decreased. Grain in discharge spouts appeared to provide an incubation chamber for pest insects, and removing this grain periodically should reduce the resident populations. Residue in empty bins often was densely infested compared with samples from the grain masses. Cleaning the empty bins before refilling with newly-harvested wheat resulted in a significantly-reduced density of pest insects in discharge spouts later, and the effect lasted at least 12 wk after filling.     

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.     

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.     

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.     

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.     

Fumigation of wheat using liquid ethyl formate plus methyl isothiocyanate in 50-tonne farm bins

Australian Standard White wheat, Triticum aestivum L. (a marketing grade with mixed grain hardness),with a moisture content of 12.5% was fumigated with a new ethyl formate formulation (95% ethyl formate plus 5% methyl isothiocyanate) identified and developed by Commonwealth Scientific and Industrial Research Organization Entomology, Canberra, Australia. Wheat was fumigated with the formulation at a calculated application rate of 80 g/m3 in two 50-tonne sealed metal vertical silos located at Fisherman Islands, Queensland, Australia. Access was gained through the top of the silo where the application of the formulation was completed within a few minutes by pouring it onto the top of the wheat. After 2 h of recirculation, using a 0.5-kW fan, the in-bin concentrations of ethyl formate achieved equilibrium with a concentration variation < 7%. The ethyl formate concentration, in both silos 1 and 2, during the first day's exposure period remained above 10 g/m3. The concentration of ethyl formate by time product achieved was 790 and 650 g h/m3 in silos 1 and 2, respectively. In silo 1, the formulation was sufficient to kill all life stages of mixed age cultures of Sitophilus oryzae (L.), Rhyzopertha dominica (F.), and Tribolium castaneum (Herbst). In silo 2, control was 100% for R. dominica and T. castaneum and 99.4% for S. oryzae. After 5 d fumigation, the silo top-hatch was opened but no forced aeration was initiated. The in-bin concentration of ethyl formate was lower than the Australian experimental threshold limit value of 100 ppm. The ethyl formate and methyl isothiocyanate residues in the grain had declined to below the Australian experimental maximum residue limit of 0.2 and 0.1 mg/kg, respectively. The workspace and environmental levels of ethyl formate and methyl isothiocyanate were less than the detection limit of 0.1 ppm. The treatment with ethyl formate formulation had no affect on the wheat germination and seed color compared with untreated controls.     

Three-dimensional temporal and spatial distribution of adult Rhyzopertha dominica in stored wheat and corn under different temperatures, moisture contents, and adult densities

Three-dimensional temporal and spatial distributions of adult Rhyzopertha dominica (F.) at adult densities of 1.0, 5.0, and 10.0 adults per kg grain and at 20 +/- 1, 25 +/- 1, and 30 +/- 1 degrees C were determined in 1.5 t bins filled with wheat (Triticum aestivum L.) with 11.0 +/- 0.8, 13.0 +/- 0.6, and 15.0 +/- 0.5% moisture content (wet basis) or corn (Zea mays L.) with 13.0 +/- 0.2% moisture content (wet basis). At each of five sampled locations, grain was separated into three 15-kg vertical layers, and adult numbers in each layer were counted. Inside both corn and wheat, adults did not prefer any location in the same layer except at high introduced insect density in wheat. The adults were recovered from any layer of the corn and >12, 65, and 45% of adults were recovered in the bottom layer of the corn at 20, 25, and 30 degrees C; respectively. However, <1% of adults were recovered in the bottom layer of wheat. Numbers of adults correlated with those in adjacent locations in both vertical and horizontal directions, and the temporal continuous property existed in both wheat and corn. Adults had highly clumped distribution at any grain temperature and moisture content. This aggregation behavior decreased with the increase of adult density and redistribution speed. Grain type influenced their redistribution speed, and this resulted in the different redistribution patterns inside wheat and corn bulks. These characterized distribution patterns could be used to develop sampling plans and integrated pest management programs in stored grain bins.     

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.     

Efficacy of heat treatment for disinfestation of concrete grain silos

Field experiments were conducted in 2007 and 2008 to evaluate heat treatment for disinfestations of empty concrete elevator silos. A Mobile Heat Treatment Unit was used to introduce heat into silos to attain target conditions of 50 degrees C for at least 6 h. Ventilated plastic containers with a capacity of 100 g of wheat, Triticum aestivum L., held Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Polyvinyl chloride containers with a capacity of 300 g of wheat held adults of Liposcelis corrodens (Heymons) (Psocoptera: Liposcelididae) and Liposcelis decolor (Pearman), which were contained in 35-mm Petri dishes within the grain. Containers were fastened to a rope suspended from the top of the silo at depths of 0 m (just under the top manhole), 10 m, 20 m, and 30 m (silo floor). When the highest temperature achieved was approximately 50 degrees C for 6 h, parental mortality ofR. dominica and T. castaneum, and both psocid species was 98-100%. Progeny production of R. dominica occurred when there was parental survival, but in general R. dominica seemed less impacted by the heat treatment than T. castaneum. There was 100% mortality of L. corrodens at all depths in the heat treatments but only 92.5% mortality for L. decolor, with most survivors located in the bioassay containers at the top of the silo. Results show wheat kernels may have an insulating effect and heat treatment might be more effective when used in conjunction with sanitation and cleaning procedures.     

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.     

Knockdown and mortality of adults of eight species of stored-product beetles exposed to four surfaces treated with spinosad

Contact toxicity of a commercial bacterial fermentation insecticide, spinosad, to adults of eight stored-product beetles was evaluated on four different surfaces. Aqueous spinosad suspension was sprayed with an airbrush to 30.5-cm2 surfaces of concrete, galvanized steel, unwaxed floor tile, or waxed floor tile to obtain deposits of 0.05 or 0.1 mg (AI)/cm2. Control surfaces were sprayed with distilled water. Approximately 24 h after distilled water or spinosad application, 30 adult beetles were confined, by species, to each untreated and spinosad-treated surface. Insects on surfaces were exposed for 24 h to assess knockdown at 25 +/- 1 degree C and 50 +/- 10% RH, and then were held on food for an additional 24 h to assess mortality. Knockdown and mortality of each insect species on all four surfaces were significantly greater on spinosad-treated surfaces than on distilled water-treated surfaces. Knockdown and mortality of all species on all surfaces was similar at the two spinosad deposit levels. Except for Tribolium spp., mortality of all other species exposed to spinosad was 99-100%. Tribolium spp. were highly susceptible to spinosad on concrete (98-100% mortality); however, on unwaxed floor tile, steel, and waxed floor tile recovery on food after knockdown resulted in only 72-92% mortality. Our results suggest that spinosad has excellent contact activity against adults of stored-product insects, especially on concrete, and has potential for use as a general surface, spot, or crack/crevice spray to control insects in empty bins, warehouses, food-processing facilities, and retail stores.     

Biological activity of two juvenoids and two ecdysteroids against three stored product insects

The insecticidal activity of juvenile hormone agonists methoprene and pyriproxyfen, and the ecdysone agonists RH-5849 and tebufenozide was evaluated against susceptible and actellic-resistant strains of Tribolium castaneum and susceptible strains of Rhyzopertha dominica and Sitophilus oryzae. Concentrations ranging from 0.1 to 20 ppm of the analogues were mixed in the food medium to which the tested insects were exposed. The results showed that all these compounds could affect the development of the tested species to differing extents but had no effect on the mortality of parental adults. The two JH analogues did not prolong the life span of R. dominica and S. oryzae, but very greatly extended that of T. castaneum. The extension led to the production of giant larvae and failure to pupate. Actellic-resistant strain of T. castaneum showed some cross-resistance to methoprene and pyriproxyfen, but not to RH-5849 and tebufenozide. Pyriproxyfen was the most effective compound among the four IGRs; a concentration of 0.1 ppm could completely inhibit the F(1) adult occurrence of both S- and R-strains of T. castaneum and its LC(90)s for controlling R. dominica and S. oryzae were 0.1 and 1.2 ppm, respectively. Methoprene was highly effective against R. dominica, but less active on S. oryzae. RH-5849 could achieve almost complete control of F(1) adults of T. castaneum and R. dominica at 10 ppm, but was less potent on S. oryzae. Tebufenozide appeared to be much less active on these three species compared with the other three compounds. The percentage reductions of F(1) adults for S- and R-strains of T. castaneum at a concentration of 20 ppm were 80 and 99%, respectively.     

一种新杀虫剂对储粮害虫和作物害虫的杀虫效果

测定以植物提取物异硫氰酸酯为主要成分而复配的宏劲杀虫剂对玉米象Sitophilus zeamais(Motschulsky)、赤拟谷盗Tribolium castaneum(Herbst)和谷蠹Rhizopertha dominica(Fabricius)3种重要储粮害虫的熏蒸效果及其对菜青虫Pieris rapae(L.)、红蜘蛛Tetranychus cinnabarinus(Boisduval)的杀虫效果。结果表明,宏劲杀虫剂48h对玉米象、赤拟谷盗和谷蠹的LC50分别是0.016,0.009和0.009μL/mL,均明显低于常规熏蒸剂磷化铝的要求处理剂量;对菜青虫和红蜘蛛的LC50分别是0.0159和1.3738mg/mL,其防效均优于对照药剂3%阿菊乳油和3%新型水分散性颗粒剂。