Effect of Nitrogen on Stored-Product Insect Control at Industrial Scale

In this study, we evaluated the insecticidal effect of nitrogen against Sitophilus granarius (L.), Sitophilus oryzae (L.), Rhyzopertha dominica (F.), Prostephanus truncatus (Horn), Tribolium confusum Jacquelin du Val, and Oryzaephilus surinamensis (L.). Four trials were conducted in chambers containing flour in bags or sacks with >99% nitrogen level. Adults of all the above species, as well as immature life stages (eggs, larvae, and pupae) of T. confusum were used in the trials. Our results showed that nitrogen caused high mortality for all species and life stages tested. Some survival was recorded for R. dominica and T. confusum pupae. Low progeny production was recorded for S. granarius, S. oryzae, and R. dominica. In conclusion, our trials indicated that a high nitrogen environment can provide satisfactory control of various primary and secondary stored-product insect species.

Knockdown-Mortality Responses of Six Stored-Product Beetle Species on Different Surfaces Treated With Thiamethoxam, Using a Standardized Lethality Index

Bioassays were conducted to evaluate the effectiveness of thiamethoxam in different surfaces, against six stored-grain insects, Sitophilus granarius (L.) (Coleoptera: Curculionidae), Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). Six different surfaces (concrete, plywood, galvanized steel, linen, plastic, and ceramic tile) treated with thiamethoxam at 0.05 and 0.1 mg/cm2 were used as substrate for adult exposure. Knockdown was recorded after 1, 3, and 7 d of exposure to the treated surface, in order to calculate a Standardized Lethality Index (SLI). Knockdown counts were ranked from '0' to '4', with '0' representing adult insects 'moved generally' and '4' representing dead insects. Based on the results, insect knockdown seems leading to mortality than to recovery and the SLI ranking of the target species according to their susceptibility to thiamethoxam showed that S. granarius being more susceptible and decreasing susceptibility in an order of S. oryzae > T. castaneum ≥ O. surinamenis ≥ C. ferrugineus ≥ T. confusum. In general, among the surfaces, thiamethoxam efficacy was lower on linen, wooden, and concrete surfaces, as compared to metallic and plastic surfaces. Nevertheless, at the end of 7-d exposure, all surfaces equally affected thiamethoxam toxicity.

Efficacy of Modified Atmospheres on Trogoderma granarium (Coleoptera: Dermestidae) and Sitophilus zeamais (Coleoptera: Curculionidae)

We investigated the efficacy of two types of modified atmospheres (MA) against adults of the khapra beetle, Trogoderma granarium Everts, and the maize weevil, Sitophilus zeamais Motschulsky, under laboratory conditions. Adults of the above species on wheat were exposed to a carbon dioxide (CO2) concentration of 70% or a low oxygen (O2) concentration of 0.1% for durations of 0.67 (16 h), 1, 2, 4, and 6 d and stored in an environmental chamber set at 28 ± 2°C, 70 ± 5% RH, and a photoperiod of 16:8 (L:D) h. After each exposure interval, immediate mortality and knockdown were recorded, and the surviving or knocked down individuals were transferred to normal atmospheres and returned to the environmental chamber, where survival was recorded 7 d later. In addition, after the immediate and delayed mortality counts, all adults were removed from the substrate, and the number of progeny produced was recorded 60 d later. Both MA conditions totally controlled (100% mortality) the adults of T. granarium and S. zeamais immediately after a 6-d exposure or after a 4-d exposure when delayed mortality was taken into account, showing the postexposure effect of the MA. Moreover, high CO2 was more effective than low O2 for S. zeamais, whereas the reverse was true for T. granarium. The 4-d exposure period was crucial for the production of progeny of both species because after that period surviving insects did not produce offspring. Our results show that both MA conditions can be used with success to control these species.

Combining electrostatic powder with an insecticide: effect on stored-product beetles and on the commodity

BACKROUND

The opportunity to reduce the amount of pirimiphos-methyl applied to grain by formulating it in an electrostatic powder was investigated. The insecticidal efficacy of pirimiphos-methyl in EC formulation or formulated using electrostatic powder (EP) as an inert carrier was investigated against Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.) and Tribolium confusum Jacquelin du Val. Furthermore, the adhesive properties of EP to rice, corn and wheat, together with the effect on bulk density and bread- and pasta-making properties, were investigated.

RESULTS

The results showed that pirimiphos-methyl formulated with EP provided better efficacy against adults when compared with EC formulation for O. surinamensis and T. confusum, but there was no difference for R. dominica. Progeny production was consistently lower in grain treated with the EP formulation than in grain treated with the EC. Tests showed that EP adhered to the kernels for longer on hard wheat than on maize or rice. In most commodities, EP did not alter the bulk density. Finally, the addition of EP did not affect flour- and bread-making properties, nor the pasta-making properties.

CONCLUSIONS

The results of the present study suggest that an EP could be used to reduce the amount of pirimiphos-methyl applied to grain for effective pest control, with no detrimental effects on grain quality. © 2016 Society of Chemical Industry.

Using a Lethality Index to Assess Susceptibility of Tribolium confusum and Oryzaephilus surinamensis to Insecticides

We evaluated knockdown caused by four insecticides: alpha-cypermethrin, chlorfenapyr, pirimiphos-methyl and fipronil against adults of Tribolium confusum Jacquelin Duval, the confused flour beetle and Oryzaephilus surinamensis (L.), the sawtoothed grain beetle. Bioassays were conducted on concrete and metal surfaces. Adults of the tested species were exposed on both surfaces treated with the above insecticides at two doses (low and high). Knockdown assessment was done after 15, 30 and 60 min of adult exposure in the treated surfaces. Also, after 1, 3, 5, 7 and 14 d of exposure, a lethality index was calculated with an equation resulting to values from 0 to 100, where 100 indicated complete mortality and 0 complete survival. We also developed a lethality index by ranking each adult on each surface from 0 to 4, 0: adults moved normally, 1: adults were knocked down, but were able to walk for short intervals, 2: adults were knocked down and unable to walk, but with visible movement of antennae etc., 3: adults were knocked down, with very minimal movement of the tarsi and the antennae and 4: adults were dead (no movement). Knockdown of adults immediately after exposure (15-60 min) was higher for pirimiphos-methyl followed by alpha-cypermethrin, for both dose rates tested and species, but only on the metal surface. The lethality index was nearly 100 for all insecticides after 5d of exposure for O. surinamensis, while for T. confusum the adult lethality index was considerably lower for alpha-cypermethrin, suggesting that that recovery from knockdown occurred. Chlorfenapyr was the only insecticide that was more effective on concrete than on metal, while the reverse was noted for the other three insecticides. These results show that knockdown has different levels, which can be used as indicators of insect mortality or recovery.

Long-Term Residual Efficacy of Spinetoram on Concrete and Steel Surfaces for the Management of Three Stored Product Beetle Species

In this study, the residual efficacy of spinetoram on concrete and galvanized steel surfaces was evaluated under fixed laboratory conditions against the rice weevil, Sitophilus oryzae (L.), the confused flour beetle, Tribolium confusum Jacquelin du Val, and the sawtoothed grain beetle, Oryzaephilus surinamensis (L.). Spinetoram was applied at the dose rates of 0.025 and 0.1 mg (active ingredient)/cm(2), on steel surfaces that were stored in continuous darkness and on concrete surfaces that were stored either in continuous darkness or in 12:12 (L:D) photoperiod. The experimental period for the residual effect of spinetoram was 6 mo. Bioassays were conducted for all types of surfaces and storage conditions at monthly intervals starting from the initial application period (seven bioassays in total). For each bioassay, mortality of the exposed adult beetles was measured after 3 and 7 d of exposure. Among the tested species, T. confusum was the least susceptible, regardless of the surface type, storage conditions, and dose rate. Regarding the bioassays conducted in the surfaces stored in darkness, spinetoram proved very persistent and no reduction in the efficacy was noted throughout the experimental period. Moreover, there were no differences in spinetoram efficacy between the two types of surfaces. Conversely, in light [12:12 (L:D)] conditions spinetoram efficacy was notably reduced after the first month, but remained stable for the rest of the period. The results of this study indicate that spinetoram was persistent with long residual efficacy against major stored grain beetle species on the most common types of surfaces in continuous darkness, while the presence of light reduced its efficacy.

Knockdown and Mortality of Five Stored Product Beetle Species After Short Exposures of Thiamethoxam

Laboratory bioassays were conducted to evaluate the effectiveness of thiamethoxam, against five major stored-grain beetle species, the lesser grain borer, Rhyzopertha dominica (F.), the rice weevil, Sitophilus oryzae (L.), the confused flour beetle, Tribolium confusum Jacquelin du Val, the larger grain borer, Prostephanus truncatus (Horn), and the sawtoothed grain beetle, Oryzaephilus surinamensis (L.). Adults of the above species were exposed on wheat (or maize in the case of P. truncatus) treated with thiamethoxam at 0.1, 1, and 10 ppm for 0, 2, 4, 6, 8, 16, 40, 72, and 96 h. After each of these intervals, mortality was recorded (immediate mortality) and the surviving individuals were transferred in untreated wheat (or maize), where mortality was recorded again 7 d later (delayed mortality). During both immediate and delayed mortality counts, the number of adults that were knocked down was also recorded. Immediate mortality was low in all exposures, with the exception of the highest dose rate and after 72-96 h. At these conditions, during this interval, most of the surviving individuals were knocked down. Delayed mortality was further increased with the increase of dose and the initial exposure, but knockdown was extremely low, with the exception of P. truncatus. The results of the present work show that O. surinamensis was the least susceptible species, while P. truncatus was the most susceptible. These findings show that, despite the increased mortality, recovery after short exposures is likely for all species tested here. In this regard, partially treated areas on which the insects are exposed only for short intervals may reduce thiamethoxam efficacy.

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

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