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.     

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.     

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.     

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.     

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.     

Optimal Xylocoris flavipes (Reuter) (Hemiptera: Anthocoridae) density and time of introduction for suppression of bruchid progeny in stored legumes

The influences of both predator density and elapsed time between initial infestation and introduction of predators were determined for suppression of bruchids infesting stored grain legumes by Xylocoris flavipes (Reuter) (Hemiptera: Anthocoridae). Predator density treatments consisted of zero, one, two, three, or five male:female pairs of adult X. flavipes added to experimental arenas 0, 24, or 120 h after bruchid introduction. Suppression of Acanthoscelides obtectus approached eradication with all predator treatments. For all other bruchid species evaluated (Callosobruchus analis, C. chinensis, C. maculatus, and Zabrotes subfasciatus), the most effective predator density and addition time (five predator pairs at 0 h) resulted in an approximately 50% reduction of emerging F1 bruchids compared with progeny produced in arenas without predators. The predator addition time of 0 h, when predators were added to experimental arenas simultaneously with the pest species, was determined to be the universally most efficacious treatment time. Predator density above one pair but lower than five pairs was less influential overall when X. flavipes was added 24 or 120 h after initial bruchid infestation; however, maximum suppression was achieved at approximately two predator pairs and not significantly improved on with increased predator density. Our results indicate that the most effective biological control of pest bruchids would occur when X. flavipes is added as soon as possible after legumes are stored.     

Suppression of the stored-product insect Tribolium confusum by Xylocoris flavipes and Amphibolus venator

Abstract:  We evaluated the suppression of the confused flour beetle, Tribolium confusum , by the anthocorid bug Xylocoris flavipes and the reduviid bug Amphibolus venator . Four treatments were tested: X. flavipes adults, A. venator adults, X. flavipes adults and A. venator adults released, and control (no predators). After 25 days, X. flavipes alone showed 96.9% suppression of T. confusum , A. venator alone showed 76.2% suppression and both the predatory bugs together showed 95.6% suppression. The rates of loss of whole-wheat flour as an index of damage caused by T. confusum were 2.7%, 6.4%, 3.6% and 11.7% in X. flavipes adults, A. venator adults, X. flavipes adults and A. venator adults released, and control respectively. Furthermore, A. venator attacked X. flavipes adults but not X. flavipes nymphs. The possibility of using both X. flavipes and A. venator against T. confusum is discussed.     

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 insecticides and Plutella xylostella (Lepidoptera: Plutellidae) genotype on a predator and parasitoid and implications for the evolution of insecticide resistance

In the laboratory and in cages in the greenhouse, we evaluated the toxicity of two insecticides (lambda-cyhalothrin and spinosad) on the parasitoid, Diadegma insulare (Cresson), and the predator, Coleomegilla maculate (DeGeer), both natural enemies of the diamondback moth, Plutella xylostella (L.). Lambda-cyhalothrin was very toxic to both natural enemies. Spinosad was less toxic to C. maculata adults and larvae, and slightly toxic to D. insulare. Both natural enemies suppressed P. xylostella populations in cages with 80% spinosad-treated and 20% nontreated plants; such suppression was not seen when lambda-cyhalothrin was used. Using broccoli, Brassica oleracea L. variety italica, a common host for P. xylostella, we also studied direct and indirect effects of both natural enemies in the presence and absence of the two insecticides and to different P. xylostella genotypes: resistant to the insecticide, susceptible, or heterozygous. Neither natural enemy could distinguish host genotype if P. xylostella were feeding on nontreated plants. They could also not distinguish between larvae feeding on spinosad-treated plants and nontreated plants, but D. insulare could distinguish between larvae feeding on lambda-cyhalothrin treated and nontreated plants. Our studies suggest that lambda-cyhalothrin has direct toxicity to these two natural enemies, can affect their host foraging and acceptance of P. xylostella and consequently would not be compatible in conserving these natural enemies in a program for suppression of P. xylostella. In contrast, our studies suggest that treatment with spinosad has much less effect on these natural enemies and would allow them to help suppress populations of P. xylostella. These findings are discussed in relation to the evolution of insecticide resistance and suppression of the pest populations.     

Impact of varying levels of sanitation on mortality of Tribolium castaneum eggs and adults during heat treatment of a pilot flour mill

The influence of sanitation on responses of life stages of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), an economically important pest in flour mills, was investigated in a pilot flour mill subjected to two, 24-h heat treatments. One hundred eggs or 100 adults of T. castaneum were exposed inside each 20-cm diameter by 15-cm high PVC rings holding 0.1-, 0.2-, 1.0-, 3.0-, 6.0-, and 10.0-cm-deep wheat flour to simulate different sanitation levels that may exist in a flour mill. These rings were placed on the first and third floors of a pilot flour mill. On the first floor, temperatures inside rings with eggs reached 50 degrees C in 7-11 h only in 0.1- and 0.2-cm-deep flour treatments. In all other treatments the maximum temperatures attained generally were below 50 degrees C and inversely related to flour depth. Adults of T. castaneum on this floor were less susceptible than eggs. The egg mortality decreased linearly with an increase in flour depth, whereas that of adults decreased exponentially. All eggs and adults in rings on the third floor were killed irrespective of flour depth, because temperatures inside rings reached 50 degrees C in 15-17 h and were held above 50 degrees C for 6-8 h with the maximum temperatures ranging between 55.0 and 57.0 degrees C. Although the protective effects of flour on survival of T. castaneum eggs and adults were evident only if temperatures did not reach 50 degrees C, removal of flour accumulations is essential to improve heat treatment effectiveness.     

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.     

Influence of spinosad on immature and adult stages of <Emphasis Type="Italic">Chrysoperla carnea</Emphasis> (Stephens) (Neuroptera: Chrysopidae)

Toxicity of spinosad to immature stages of Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) and its effect on the reproduction and survival of adult stages after direct spray and ingestion treatments were evaluated. Spinosad was harmless to C. carnea eggs and pupae irrespective of concentrations or method of treatments. Direct spray of spinosad to first instar caused significant reduction in rate of pupation and L1-adult survival, but did not affect the rate of adult emergence. Third-instar bioassay revealed significant difference in L3-adult survival. When C. carnea first instars were fed upon spinosad-treated-Brevicoryne brassicae (L.), significant differences in investigated parameters were not observed among different treatments. The weight of third instar and pupae were comparable regardless of tested spinosad concentrations. Also, feeding on spinosad treated-B. brassicae had no negative impact on fecundity and fertility. Furthermore, ingestion of spinosad contaminated-B. brassicae significantly prolonged larval and larval + pupal periods. The larval feeding capacity of C. carnea did not differ significantly between larvae fed on spinosad-treated and untreated aphids with the exception of first instar. When C. carnea adults were allowed to oviposit on spinosad treated-substrate, total number of eggs laid, percent of eggs laid on the treated substrate and egg hatching did not differ from those of control. However, when adults were fed on spinosad-treated artificial diet, negative effects on adult survival and fecundity were observed.

Insecticidal potential of natural zeolite and diatomaceous earth formulations against rice weevil (Coleoptera: Curculionidae) and red flour beetle (Coleoptera: Tenebrionidae)

Insecticidal potential of natural zeolites and diatomaceous earths originating from Serbia against Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) was evaluated. Two natural zeolite formulations (NZ and NZ Modified) were applied to wheat at rates of 0.50, 0.75, and 1.0 g/kg, while two diatomaceous earth (DE) formulations (DE S-1 and DE S-2) were applied at rates of 0.25, 0.50, 0.75, and 1.0 g/kg. A bioassay was conducted under laboratory conditions: temperature of 24 +/- 1 degrees C, relative humidity in the range 50-55%, in tests with natural zeolites, and 60-65%, in tests with DEs, and in all combinations for progeny production. Mortality was assessed after 7, 14, and 21 d of insect contact with treated wheat, and the total mortality after an additional 7-d recovery on untreated broken wheat. Progeny production was also assessed after 8 wk for S. oryzae and 12 wk for T. castaneum. The highest mortality for S. oryzae and T. castaneum was found after the longest exposure period and 7 d of recovery, on wheat treated with NZ at the highest rate and DEs at rates of 0.50 -1.0 g/kg. Progeny reduction higher than 90% was achieved after 14 and 21 d of contact of both beetle pests with wheat treated with DE S-1 at 0.50-1.0 g/kg and DE S-2 at 0.75-1.0 g/kg, while the same level of reduction was achieved only for T. castaneum after its contact with the highest rate of NZ formulation. NZ Modified, applied even at the highest rate, revealed much lower insecticidal potential.     

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.     

Acaricidal properties of spinosad against Tetranychus urticae and Panonychus ulmi (Acari: Tetranychidae)

Laboratory bioassays were conducted to characterize the activity of the insecticide spinosad against the twospotted spider mite, Tetranychus urticae Koch, and European red mite, Panonychus ulmi (Koch) (Acari: Tetranychidae). T. urticae females and larvae were individually placed on bean, Phaseolus vulgaris L. (Fabaceae), leaf disks treated with four rates of spinosad (25, 55, 121, and 266 ppm) and a water control. Significantly fewer T. urticae completed development on any spinosad rates (<15%) compared with the control (>85%), whereas spinosad exhibited no significant effects on P. ulmi development; 72.5 and 83.1% of P. ulmi completed development on apple (Malus pumila P. Mill, Rosaceae) leaf disks treated with 75 ppm spinosad and the control, respectively. T. urticae adult females placed on spinosad-treated disks had significantly higher mortality and lower oviposition rates compared with the water control; no significant mortality effects were observed until 3 d after placing adults on leaf disks. In choice tests where half of a bean leaf was treated with 55 ppm spinosad transversally or longitudinally, T. urticae females were repelled by spinosad and largely oviposited and fed on nonspinosad treated areas. Spinosad did not affect the behavior of P. ulmi females. When T. urticae females were released on potted bean plants (two-leaf stage) in which leaves received spinosad sprays on the adaxial or abaxial leaf surfaces, or complete spinosad coverage on one or two of the leaves, mite population increase lagged significantly behind those released on control plants. These results indicate that spinosad has significant acaricidal effects against T. urticae but not P. ulmi.     

Phosphine resistance in Tribolium castaneum and Rhyzopertha dominica from stored wheat in Oklahoma

Phosphine gas, or hydrogen phosphide (PH3), is the most common insecticide applied to durable stored products worldwide and is routinely used in the United States for treatment of bulk-stored cereal grains and other durable stored products. Research from the late 1980s revealed low frequencies of resistance to various residual grain protectant insecticides and to phosphine in grain insect species collected in Oklahoma. The present work, which used the same previously established discriminating dose bioassays for phosphine toxicity as in the earlier study, evaluated adults of nine different populations of red flour beetle, Tribolium castaneum (Herbst), and five populations of lesser grain borer, Rhyzopertha dominica (F.) collected from different geographic locations in Oklahoma. One additional population for each species was a laboratory susceptible strain. Discriminating dose assays determined eight out of the nine T. castaneum populations, and all five populations of R. dominica, contained phosphine-resistant individuals, and highest resistance frequencies were 94 and 98%, respectively. Dose-response bioassays and logit analyses determined that LC99 values were approximately 3 ppm for susceptible and 377 ppm for resistant T. castaneum, and approximately 2 ppm for susceptible and 3,430 ppm for resistant R. dominica. The most resistant T. castaneum population was 119-fold more resistant than the susceptible strain and the most resistant R. dominica population was over 1,500-fold more resistant. Results suggest a substantial increase in phosphine resistance in these major stored-wheat pests in the past 21 yr, and these levels of resistance to phosphine approach those reported for other stored-grain pest species in other countries.     

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 .     

Genetic structure of Tribolium castaneum (Coleoptera: Tenebrionidae) populations in mills

The red flour beetle, Tribolium castaneum (Herbst), is primarily found associated with human structures such as wheat and rice mills. Such structures are predicted to be spatially isolated resource patches with frequent population bottlenecks that should influence their genetic structure. Genetic diversity and differentiation among nine populations of T. castaneum collected from wheat and rice mills (ranging from <1-5,700 km apart) were investigated using eight polymorphic loci (microsatellites and other insertion-deletion polymorphisms, each with 3-14 alleles). Seventy-two locus-by-population combinations were evaluated, of which 31 deviated significantly from Hardy-Weinberg equilibrium, all because of a deficiency of heterozygotes. AMOVA analysis indicated significant differences among populations, with 8.3% of the variation in allele frequency resulting from comparisons among populations, and commodity type and geographic region not significant factors. Although there were significant differences in genetic differentiation among populations (F(ST) values = 0.018-0.149), genetic distance was not significantly correlated with geographic distance. Correct assignment to the source population was successful for only 56% of individuals collected. Further analyses confirmed the occurrence of recent genetic bottlenecks in five out of nine populations. These results provide evidence that populations of T. castaneum collected from mills show spatial genetic structure, but the poor ability to assign individuals to source populations and lack of isolation by distance suggest greater levels of gene flow than predicted originally.     

Susceptibility of Tribolium castaneum life stages exposed to elevated temperatures during heat treatments of a pilot flour mill: influence of sanitation, temperatures attained among mills floors, and costs

The influence of sanitation on responses of life stages of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), was investigated in a pilot flour mill subjected to three, 24-h heat treatments by using forced-air gas heaters fueled by propane. Two sanitation levels, dusting of wheat flour and 2-cm-deep flour, were created in 25 plastic bioassay boxes, each holding eggs, young larvae, old larvae, pupae, and adults of T. castaneum plus two temperature sensors. Data loggers (48) were placed on the five mill floors to record air temperatures. The time required to reach 50 degrees C, time above 50 degrees C, and the maximum temperature among mill floors and in bioassay boxes were measured. The maximum temperature in bioassay boxes and in the mill was lower on the first floor than on other floors. This trend was apparent in time required to reach 50 degrees C and time above 50 degrees C, especially in compartments with 2-cm-deep flour. The mean +/- SE mortality of T. castaneum life stages on the first floor was 55.5 +/- 12.9-98.6 +/- 0.8%; it was 93.2 +/- 6.7-100 +/- 0.0% on other floors. Adults were the least susceptible stage. Mortality of T. castaneum stages in compartments with 2-cm-deep flour was generally lower than those with flour dust. Costs for the three heat treatments ranged from US$27,438 to $28,838. An effective heat treatment can be conducted within 24 h, provided temperatures on mill floors reach 50 degrees C in 8-12 h and are held above 50 degrees C for at least 10-14 h, with maximum temperatures held between 50 and 60 degrees C.     

Repellency and toxicity of oil from Artemisia annua to certain stored-product beetles

The essential oil of Artemisia annua L. was tested for its toxic repellent and development inhibitory activities against 2 economically important stored product insects: Tribolium castaneum (Herbst) and Callosobruchus maculatus (L.). Adult beetles of T. castaneum were repelled significantly by oil of A. annua at 1% concentration (vol:vol) and above in filter paper arena test. Dose-response relationship of A. annua oil revealed a significant negative correlation between larval survival; pupal survival and adult emergence of T. castaneum (i.e., increase in dose caused decrease in survival and adult emergence). Effective concentration (EC50) to reduce F1 progeny by 50% was calculated to be 2.6 and 4.1 microl/ml solvent against both the insect species, C. maculatus and T. castaneum, respectively. The relationship between bioactivity of oil from A. annua and responses of T. castaneum and C. maculatus is discussed. We found that oil from A. annua was largely responsible for both repellent (behavioral) and toxic (physiological) actions on 2 species of insect tested.