Dominica Adults Research Articles

Mortality of Four Stored Product Pests in Stored Wheat When Exposed to Doses of Three Entomopathogenic Nematodes

The insecticidal effect of Heterorhabditis bacteriophora Poinar (Nematoda: Heterorhabditidae), Steinernema carpocapsae (Weiser) (Nematoda: Steinernematidae), and Steinernema feltiae (Filipjev) (Nematoda: Steinernematidae) against Mediterranean flour moth, Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) (larvae), lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) (adults), rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) (adults), and confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) (adults and larvae) was examined under laboratory conditions in wheat, Triticum aestivum L. The nematodes were applied at the following doses: 0 (control), 100, 500, 1,000, 1,500, 5,000, 10,000, and 20,000 infective juveniles (IJs) per ml, corresponding to 10, 50, 100, 150, 500, 1,000, and 2,000 IJs per insect, and their infectivity was tested at 20 and 30 degrees C after 4 and 8 d of exposure. For E. kuehniella larvae wheat treatments with S. feltiae provided mortality that ranged from 36.7 to 78.3% whereas no mortality was noted in the treatment with S. carpocapsae at 100 IJs per ml at 20 or at 30 degrees C. Also, at 20 degrees C, in wheat treated with H. bacteriophora at 100 IJs per ml, very few larvae were dead. For R. dominica adults, at 20 degrees C, the mortality of adults in wheat treated with S. feltiae and S. carpocapsae did not exceed 23.3 and 41.7%, respectively, at 20,000 IJs per ml, with no significant differences among doses. In the case of S. oryzae adults, the mortality was very low at all doses, and temperatures and did not exceed 9%. Mortality of T. confusum adults did not exceed 17% regardless of the entomopathogenic nematode species tested. In contrast, mortality of T. confusum larvae was notably higher and exceeded 56% in wheat treated with 10,000 or 20,000 IJs per ml of S. feltiae at 20 degrees C. Unlike S. feltiae and S. carpocapsae, the application of H. bacteriophora resulted in lower mortality levels. Generally, the increase of temperature reduced the mortality levels of the T. confusum larvae. In most cases, the efficacy level of the tested entomopathogenic nematode species increased with the dose and decreased with the increase of 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°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.

Immediate and Delayed Mortality of <I>Rhyzopertha dominica</I> (Coleoptera: Bostrichidae) and <I>Sitophilus oryzae</I> (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.

Survival and reproduction of lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) on flora associated with native habitats in Kansas

Capture of Rhyzopertha dominica in pheromone-baited traps located many kilometers away from grain storage suggests that this species may be exploiting non-grain food sources. To investigate the potential for survival of this species on alternative hosts in the absence of grain, we conducted no-choice feeding assays with twigs and seeds of trees, and seeds of grasses, forbs, and shrubs, commonly encountered on Kansas prairie landscapes where R. dominica has been captured. In addition, R. dominica development and progeny production were assessed on seeds that adults were able to survive on for at least two weeks. Adult survival was poor on grass and forb seeds, although 13.4% of individuals survived on Elymus canadensis, Canada wildrye, seeds after two weeks, compared with 80.3% on Triticum aestivum, wheat, and 0.0% survival in the absence of food. Beetles readily tunneled into twigs from a wide range of tree species, but survival was generally low. A few individuals survived up to four weeks on Gleditsia triacanthos, honey locust. In contrast, bioassays showed that R. dominica could survive and reproduce on damaged seeds (acorns) of six species of oak, but not on undamaged seeds. For example, survival was 95.8% on damaged Quercus muehlenbergii, chinquapin oak. A survey of acorns at the original field collection site showed that the majority of the acorns on the ground had been cracked or bored into by insects and small mammals. Furthermore, we recovered three R. dominica adults from acorns collected in the field and held in sealed containers in the laboratory. These findings suggest that R. dominica populations in Kansas can persist on wild acorns when grain is not available.

Evaluation of a new, enhanced diatomaceous earth formulation for use against the stored products pest, Rhyzopertha dominica (Coleoptera: Bostrychidae)

Laboratory bioassays were carried out with DEBBM, a new enhanced diatomaceous earth (DE) formulation that contains the plant extract bitterbarkomycin, against adults of Rhyzopertha dominica (F.). Three series of tests were conducted. In the first, R. dominica adults were exposed on wheat treated with DEBBM at three dose rates, 50, 100 and 150 ppm, and mortality was measured after 7 and 14 days of exposure, at three temperatures (20, 25 and 30°C) and 65% R.H. Mortality increased with increasing temperature; at temperatures ≥25°C, after 14 days of exposure, mortality exceeded 98% even at 50 ppm. In the second series of tests, the same doses were assessed at 25°C and at two levels of R.H. (55 and 75%). In this case, relative humidity did not seriously affect the insecticidal effect of DEBBM, at the doses tested. All adults were dead after 14 days of exposure at 55% R.H. at doses ≥100 ppm. In the third test series, 50 and 150 ppm of DEBBM were added to wheat, barley, maize and rice, in order to evaluate the impact of grain type on the effect of this DE. No significant differences were noted in mortality levels among different grains. With the exception of maize, after 14 days of exposure, all adults were dead. This new enhanced DE formulation is shown to be effective at dose rates that are considerably lower in comparison with older DE formulations.

Evaluation of spinosad as a grain protectant on three Kansas farms

The persistence and insecticidal activity of a commercial insecticide, spinosad, based on the fermentation products of the actinomycete bacterium Saccharopolyspora spinosa Mertz and Yao (Actinomycetales: Actinomycetaceae), was evaluated on three Kansas farms between July 2002 and January 2003. Spinosad was applied to newly harvested hard red winter wheat at 1 mg (a.i.)/kg of grain at the time of storage in round, steel bins with capacity of 60–125 metric tons. Insect populations in grain samples collected monthly from bins receiving spinosad treatment were compared with populations in bins receiving no treatment (control), bins receiving 3 mg (a.i.)/kg of chlorpyrifos-methyl, and bins receiving 1 mg (a.i.)/kg spinosad+3 mg (a.i.)/kg chlorpyrifos-methyl treatment. The actual spinosad residue on wheat immediately after treatment was 30% less than the application rate of 1 mg (a.i.)/kg, but there was no significant degradation of these residues during the 6-month test period. None of the July samples from any of the four treatments had live adults of stored-product insects. No live adults of the lesser grain borer, Rhyzopertha dominica (F.), and very low densities (⩽3 live adults/kg of sample) of the red flour beetle, Tribolium castaneum (Herbst); rusty grain beetle, Cryptolestes ferrugineus (Stephens); and sawtoothed grain beetle, Oryzaephilus surinamensis (L.), were found in grain samples collected between August and January from bins treated with spinosad or spinosad+chlorpyrifos-methyl. The density of all four insect species combined in untreated grain samples steadily increased from 0.5 adults/kg in August 2002 to a high of 22.1 adults/kg in January 2003. In grain samples from bins treated with chlorpyrifos-methyl, the density of R. dominica adults increased from 0.4 adults/kg in September 2002 to a maximum of 10.2 adults/kg in January 2003, whereas densities of the other three species were ⩽1 adult/kg. Laboratory bioassays with monthly grain samples collected from the field applications showed that spinosad, alone or in combination with chlorpyrifos-methyl, was effective in killing adults of R. dominica and C. ferrugineus, but not T. castaneum. Progeny production of these three species was suppressed on spinosad-treated grain, irrespective of the sampling month. Results show that a single application of spinosad at 1 mg (a.i.)/kg is effective for managing common stored-grain insects, including R. dominica, for at least 6 months.

Efficacy of surface applications with diatomaceous earth to control Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in stored wheat

Commercial formulations of diatomaceous earth (DE) products labeled for use as grain protectants usually specify on the label the depth for using them as a surface treatment, which is often 30.5 cm. An experiment was conducted at two temperatures (27 and 32 °C) and three exposure intervals (7, 10 and 14 d), at a relative humidity of 57–60% to determine if Rhyzopertha dominica (F.), the lesser grain borer, could penetrate a 30.5-cm layer of wheat treated with the labeled rates of three commercial formulations of DE, and, if so, to measure rates of adult survival and progeny production. When R. dominica adults were introduced to this surface layer of 30.5-cm wheat admixed with DE, they were able to penetrate the DE-treated layer and oviposit in the untreated wheat below. Both adult survival and progeny production were significantly lower in wheat with a surface-layer treatment of Dryacide ® (1000 ppm) as compared to Insecto™ (500 ppm), Protect-It ® (400 ppm) or the untreated control. Temperature and exposure interval had no effect on adult survival or progeny production. The vertical displacement patterns of adults were significantly different among DE treatments, but not for temperature or exposure intervals. More R. dominica traveled a greater distance in the untreated control, followed by Insecto™, Protect-It ®, and then Dryacide ®. Results indicate that R. dominica can penetrate a surface layer of DE-treated wheat and reproduce within and below it, but it is possible that pest suppression is dose dependent, or it may depend on a combination of application rate and specific DE formulation.

Effect of the combined use of Metarhizium anisopliae (Metschinkoff) Sorokin and diatomaceous earth for the control of three stored-product beetle species

Laboratory bioassays were conducted in order to evaluate the use of the entomopathogenic fungus, Metarhizium anisopliae (Metschinkoff) Sorokin (Deuteromycotina: Hyphomycetes), against adults of three stored-grain beetle species, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae). Two fungal preparations were compared, a conidial suspension and a conidial powder. These were applied to wheat, at three dosages, 8×10 6, 8×10 8 and 8×10 10 conidia/kg of wheat, alone, or in combination with the diatomaceous earth (DE) formulation SilicoSec ® (Biofa Gbmh, Germany), applied at 0.5 g/kg of wheat. Adult insects were exposed to treated wheat for 24 h, 48 h, 7 d and 14 d. The mortality of R. dominica adults after 14 d of exposure to the treated substrate was 100% and 96% at the dosages in combination, for the suspension and the powder, respectively. The respective figures without DE were 94.4% and 74.6%. In contrast, against S. oryzae adults, the application of conidial suspension combined with DE was not as effective as the application of DE alone. Adult mortality of S. oryzae increased notably on wheat treated with the conidial powder. Similarly, the conidial suspension, with or without DE, was not as effective against T. confusum as the conidial powder. The progeny production of R. dominica on wheat treated with the highest suspension dosage, with or without DE, was significantly lower than that for the other aqueous fungal dosages. Moreover, significantly less progeny were produced on wheat treated with the highest dosage of powder conidia combined with DE, in comparison with the other treatments. In contrast, S. oryzae progeny production was notably reduced only in wheat treated with the highest dosage of fungal spore powder mixed with DE. No T. confusum progeny were found on wheat treated with the highest dosage of both fungal preparations combined with DE.

Mortality and F1 production of Rhyzopertha dominica (F.) on wheat treated with diatomaceous earth: impact of biological and environmental parameters on efficacy

A series of experiments were conducted in which label rate (0.3 g per kg of wheat) with diatomaceous earth (DE) formulation Protect-It. Exposure studies were carried out at two levels of relative humiditiy (40% and 55%), two levels of insect density (10 or 20 adults per vial), and three levels of exposure periods. Test insects were placed in vials containing 40 g of soft white winter wheat mixed with either 0 or 0.3 g Protect-It per kg of wheat. After relating exposure periods for both insect density and relative humidity levels, highest mortality was only 16%. Mortality, regardless of the dose rate applied (0 and 0.3 g) were not significantly increased as the exposure period increased. Regardless of relative humidity (r.h.) (40% and 55%r.h.), mortality in control were not significantly increased as the exposure period increased for the same insect density. However, significant differences among the three exposure periods in 10 adults’ density in 0.3 g DE application. Mortality was significantly increased in 10 adults’ density. In this case mortality of R. dominica adults increased with the increasing of the exposure intervals. As for 20 adults’ density, mortality in 0.3 g DE application was not significantly changed along with the exposure intervals. After insects were exposed for 1, 2, or 3 week, dead and live insects were removed, and the wheat in the vial were returned to relating humidity box and kept for 8 week until F1 adults emerged. Then, the number of F1 adult was counted. The mean numbers of F1 adults on untreated wheat at all density and r.h. combinations, regardless of exposure periods were significantly higher than that of 0.3 g DE- treated wheat (Fig. 3). At each density and treatment, the mean number of F1 adults at 55% r.h. were higher that that of 40%r.h. The comparison between adult densities at each r.h. and treatment showed that adult densities influenced the F1 production of R. dominica and F1 adults were always higher at 20 adults’ density. The mean number of F1 adults at each density, regardless of treatment progressively increased as the exposure period increased. Fewer progeny were produced at 10 adults’ density compared to 20 adults’ density for same exposure periods. The highest reproduction occurred in 3 week of exposure period for both insect densities. Regardless of adult densities, the mean number of F1 adults was significantly increased as the exposure period increased (Fig. 5) for both control and 0.3 g DE treatment. Reduction of F1 adults at 0.3 g DE application compared to control were found to be 76.88, 74.78 and 67.63% for 1, 2 and 3 week of exposure period, respectively.

Influence of grain type on the insecticidal efficacy of two diatomaceous earth formulations against Rhyzopertha dominica (F) (Coleoptera: Bostrychidae)

Laboratory bioassays were carried out in order to evaluate the effectiveness of two diatomaceous earth (DE) formulations, Insecto and SilicoSec, against adults of Rhyzopertha dominica (F) in eight different grain commodities. The adherence of the two DEs to each grain was also measured. The eight grains tested were wheat, whole barley, peeled barley, oats, rye, triticale, rice and maize. These commodities were treated with the DEs at three rates, 0.75, 1.0 and 1.5 g DE kg(-1) grain. The mortality of R dominica adults was measured after 24 h, 48 h, 7 days and 14 days of exposure in the treated grains at 26 degrees C and 55% RH. After the 14-day mortality count, all adults were removed and the treated grains retained under the same conditions for a further 60 days. The treated grains were subsequently examined for F1 progeny. Significant differences were recorded among the eight grain types as well as between the DE formulations tested. After 14 days of exposure, even at the lowest DE rate for both formulations, adult mortality was high (>90%) in wheat and triticale. In contrast, adult mortality was significantly lower in peeled barley. Increasing the rate improved the efficacy of the DEs significantly in only some of the grains tested. Reproductive capacity in all the treated grains was significantly suppressed when compared with untreated grains. Generally, more F1 individuals of R dominica were noted in the treated peeled barley than in the other commodities. Significant differences in the percentage of DE retention were noted among the eight grains. The highest retention level was noted in rice (>87%) and the lowest in maize (<6%). However, the degree of DE adherence to a given grain was not always indicative of the effectiveness of DE against R dominica.

Insecticidal effect and adherence of PyriSec ® in different grain commodities

Exposure studies were carried out in the laboratory to assess the insecticidal effect of the formulation PyriSec ®, which contains diatomaceous earth with natural pyrethrum and piperonyl butoxide, against Rhyzopertha dominica (F.). PyriSec ® was applied to eight grain commodities: wheat, whole barley, peeled barley, oats, rye, triticale, rice and maize, at three doses 0.75, 1 and 1.5 g/kg of grain. Dead R. dominica adults were counted after exposure to treated grain for 24 h, 48 h, 7 d and 14 d at 26 °C and 55% r.h. After the termination of the 14-d-interval count, the treated quantities remained in the same conditions for an additional 60-d incubation period, and the progeny production was recorded. Mortality of R. dominica adults notably varied according to the commodity, but, in most cases more than 50% of the exposed adults were dead after only 24 h of exposure. After 14 d of exposure, adult mortality was ⩾95% in all grains treated with the highest PyriSec ® dose, with the exception of peeled barley, where the respective figure was 84.2%. No progeny was found in the grains treated with the highest PyriSec ® rate, but the number of F 1 individuals was low even in the case of the lowest PyriSec ® rate. Significant differences in the degree of PyriSec ® retention in kernels were noted among the eight grains tested. The highest retention level was noted for rice (91.4%) and the lowest for maize (10.1%). However, the degree of retention to a given grain was not indicative of the effectiveness of PyriSec ® against R. dominica.

Management of five stored‐product insects in wheat with pirimiphos‐methyl and pirimiphos‐methyl plus synergized pyrethrins

Hard red winter wheat was treated with pirimiphos-methyl at 4, 6 and 8 mg kg(-1), synergized pyrethrins at 0.38, 0.75, 1.13 and 1.5 mg kg(-1), and combinations of the two insecticides, to conduct laboratory bioassays against four beetle pests of stored grain, red flour beetle Tribolium castaneum (Herbst), rusty grain beetle Cryptolestes ferrugineus (Stephens), lesser grain borer Rhyzopertha dominica (F), and rice weevil Sitophilus oryzae (L), and one moth pest, Indianmeal moth Plodia interpunctella (Hubner). Beetle adults and P interpunctella larvae survived well on control wheat, producing a large number of progeny (65-1037 insects per container). Kernel damage in control wheat among the insect species ranged from 9 to 99%. On pirimiphos-methyl-treated wheat, mortality of R dominica adults was > or =72%, but that of the other beetle species and P interpunctella larvae was 100%. Progeny were not produced on pirimiphos-methyl-treated wheat, and the kernel damage was negligible (< or =1%). Synergized pyrethrins were ineffective against the five insect pests. Pirimiphos-methyl combined with synergized pyrethrins was not superior to pirimiphos-methyl alone against the five insect pests. Pirimiphos-methyl is not registered in the USA for use on wheat, but our results suggest that it could be a viable grain protectant at rates of 4-8 mg kg(-1).

Efficacy of diflubenzuron plus methoprene against Sitophilus oryzae and Rhyzopertha dominica in stored sorghum

The efficacy of diflubenzuron (1 mg kg −1)+methoprene (1 mg kg −1) against Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) in sorghum was evaluated in a silo-scale trial in southeast Queensland, Australia. Sorghum is normally protected from a wide range of insects by mixtures of grain protectants. The chitin synthesis inhibitor diflubenzuron was evaluated as a potential new protectant for S. oryzae in combination with the juvenile hormone analogue methoprene, which is already registered for control of R. dominica. Sorghum (ca 200 t) was treated after harvest in 2000 and assessed for treatment efficacy and residue decline during 6.5 months storage. The reproductive capacity of S. oryzae and R. dominica was greatly reduced in bioassays of treated sorghum throughout the trial, and efficacy remained relatively stable during the trial. An initial exposure of S. oryzae adults to treated sorghum for 2 weeks reduced F 1 progeny production of all strains by 80.8–98.8%, but a second exposure of 4 weeks reduced F 1 progeny production by 98.5–100%. In addition, the reproductive capacity of any S. oryzae progeny produced was greatly reduced. Exposure of R. dominica adults to treated sorghum for 2 weeks reduced F 1 progeny production of all strains by 99.6–100%, including a methoprene-resistant strain. The results indicate that S. oryzae or R. dominica adults invading sorghum treated with diflubenzuron (1 mg kg −1)+methoprene (1 mg kg −1) would be incapable of producing sustainable populations.

Control of the lesser grain borer ( Rhyzopertha dominica (F.), Coleoptera: Bostrichidae) by treatments with residual formulations of Metarhizium anisopliae (Metschnikoff) Sorokin (Deuteromycotina: Hyphomycetes)

Treatments with conidia of the entomopathogenic fungus Metarhizium anisopliae formulated in invert emulsion (water-in-oil formulation) or in wheat flour were applied to Rhyzopertha dominica adults infesting Cicer arietinum grains. The application rates were 4.1×10 5 conidia/cm 2 of treated area using a concentration of 1.8×10 7 conidia/ml of the invert emulsion and 8.2×10 6 conidia/cm 2 of treated area using a concentration of 6.5×10 8 conidia/g of the wheat flour formulation. Results have indicated significant mortality ( P<0.05) when newly emerged R. dominica adults were introduced and then treated with the invert emulsion and wheat flour formulations (86.7–93.3%, control treatment 10.0–26.7% mortality). When treated grains were left until the emergence of F 1 adults, there was also significant mortality ( P<0.05) in both treatments (28.3–60.0%, control treatment 1.7–8.3% mortality). This indicates a residual effectiveness of the treatment with the two formulations against R. dominica adults which extended to >2 months (equivalent to the duration of the insect life-cycle at 23±2°C and 75±5% r.h.). Infestation rate of C. arietinum grains by R. dominica at 23±2°C and 75±5% r.h. was significantly reduced in the treatments with the fungal conidia formulated in invert emulsion (0.7%) or in wheat flour (1.0%) when compared with the control treatment (19.0–23.3%). The preventive treatments significantly retarded R. dominica development ( P<0.05) by 8–12 days compared with the control treatment. The infection with the fungus thus delayed adult emergence of R. dominica by 8–12 days. Overall results give promise for control of R. dominica with M. anisopliae mixed with wheat flour or introduced into invert emulsion.

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.

Contribution of contact toxicity and wheat condition to mortality of stored-product insects exposed to spinosad.

Spinosad, a reduced-risk commercial insecticide derived from a bacterial fermentation product, possesses both contact and oral toxicities against insects. Contact toxicity of spinosad to adults of Rhyzopertha dominica (F), Sitophilus oryzae (L), and Tribolium castaneum (Herbst) was evaluated by exposure for 24 or 48 h to treated glass Petri dishes. Adults were exposed to different deposits (0.001-0.79 mg cm(-2)) of spinosad in 24-h tests and to deposits of 0, 0.0016 and 0.016mg cm(-2) in 48-h tests. Rhyzopertha dominica was most susceptible to spinosad in 24- and 48-h tests, followed by S. oryzae, and T. castaneum. The 24-h LD50 values were 0.0004, 0.077 and 0.189mg cm(-2) for R. dominica, S. oryzae, and T. castaneum, respectively. All R. dominica adults were dead following 48 h exposure to both spinosad deposits, whereas mortality of S. oryzae and T. castaneum ranged from 10 to 85% and 12 to 48%, respectively. Rhyzopertha dominica, T. castaneum, and O. surinamensis adults were exposed for 14 days to whole wheat, cracked wheat and wheat flour treated with 0, 0.1 and 1.0 mg kg(-1) of spinosad. Rhyzopertha dominica adults were highly susceptible to spinosad, followed by O. surinamensis and T. castaneum. Immatures (eggs and larvae) of T. castaneum and O. surinamensis exposed for 14 days were more susceptible on spinosad-treated whole wheat than on treated cracked wheat and wheat flour. This is the first report documenting contact activity of spinosad, and the effect of grain condition on spinosad toxicity, to stored-product insects.

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 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.

A simple technique to assess compounds that are repellent or attractive to stored-product insects

We have developed a simple and rapid technique that mimics storage conditions, and determines if products are repellent or attractive to stored-product insects. The technique determines the response of insects to potential repellents and attractants by measuring their movement from grain. The technique used a device consisting of a perforated cup (2 mm perforations) that holds 200 g of wheat. A Petri dish and cup collected the insects as they left the wheat. Several natural products were tested for repellency: diatomaceous earth (DE), ground peas ( Pisum sativum), protein-rich pea flour, pea starch, and pea fibre. Adult insects of three species were tested: the rice weevil, Sitophilus oryzae, the red flour beetle, Tribolium castaneum, and the rusty grain beetle, Cryptolestes ferrugineus. DE at 0.01% was repellent to all insects tested. Pea fibre, pea protein, and ground pea at 1% caused increased emigration of C. ferrugineus from the wheat. Pea starch did not affect movement out of the grain for all three insects. Only pea fibre and ground pea increased the movement of T. castaneum out of the grain. For S. oryzae, there were no differences after 1 h, but after 24 h both pea protein and ground pea increased movement out of the grain. Several potential attractants were placed outside the grain and the emigration out of the grain noted. For R. dominica, the commercial R. dominica pheromone increased the emigration of insects from the grain; R. dominica adults on broken grain enclosed in a ventilated vial in the collection jar also increased emigration, but not as much as the synthetic pheromone. The commercial Tribolium pheromone did increase movement out of the grain for T. castaneum, but the other treatments were no different from the control. None of the potential attractants increased the movement of S. oryzae from the grain. The implications of this work are discussed with reference to controlling and sampling stored-product insect pests.

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

AbstractChitin 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.