Potential of some volatile oils in protecting packages of irradiated wheat flour against Ephestia kuehniella and Tribolium castaneum

Six essential oils of Citrus reticulate (mandarin peel), Pimpinella anisum (anise), Anethum graveolens (dill), Allium sativum (garlic), Ocimum basilicum (basil) and Zingiber officinale (ginger), were evaluated for fumigant toxicity against Ephestia kuehniella and Tribolium castaneum and for contact toxicity against larvae of both species. The major compounds in these volatile oils were identified using gas chromatography- mass spectrometry. Both O. basilicum and Z. officinale oils gave 100% mortality within 24 h with doses of 32 μl/l air for E. kuehniella adults, and 128 μl/l air for T. castaneum adults. The oil of A. graveolens was the most effective against larvae of both species; treated filter papers giving 100% mortality of T. castaneum and E. kuehniella larvae with exposure periods of 24 h and 96 h, respectively. The persistence of toxicity of the six tested oils varied according to their chemical components with A. graveolens and O. basilicum proving the most persistent, and C. reticulate and P. anisum the least. The possible use of the oils applied as a 30% aqueous solution for protection of wheat flour irradiated with gamma radiation (1.5 KGy) from infestation by the test insect species during a 60-day storage period in damour and gunny plastic pouches was investigated. The effect of these oils on acetylcholinesterase activity also was examined to explore their possible mode of toxic action. Dill oil was the most active against E. kuehniella larvae while ginger oil had the greatest depressive action against T. castaneum larvae.     

Insecticidal effect of Steinernema feltiae (Filipjev) (Nematoda: Steinernematidae) against Tribolium confusum du Val (Coleoptera: Tenebrionidae) and Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) in stored wheat

The confused flour beetle, Tribolium confusum, and the Mediterranean flour moth, Ephestia kuehniella, are important pests of stored grain products. The insecticidal effect of three strains (UK 76 [=Nemasys], USA/SC, and Hawaii) of the entomopathogenic nematode Steinernema feltiae was determined in the laboratory, in wheat, against these pests. The nematodes were applied at three dose rates: 100, 300 and 900 nematodes/insect individual. The Hawaii strain was most virulent against T. confusum adults and larvae, with a significant dose effect in the case of the larvae. Larval mortality of this species reached 79% and 100% after 7 and 14 d of exposure to the nematodes, respectively, at the highest dose applied. On the other hand, adult mortality of T. confusum did not exceed 66%. In the case of E. kuehniella larvae, USA/SC performed best causing 52% and 69% mortality after 7 and 14 d exposure, respectively, at the highest dose tested. Since very few data are available on the effect of entomopathogenic nematodes against these pests, it is concluded that the Hawaii and USA/SC strains of S. feltiae should be further investigated as promising biological control agents for T. confusum and E. kuehniella.     

Residual efficacy of synergized pyrethrin + methoprene aerosol against larvae of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae)

Wheat flour and different packaging surfaces (cardboard, flour bag, muslin bag, paper bag, pallet wrap, plastic overwrap, polyethylene) were exposed to aerosol formulations of either 1% active ingredient (AI) pyrethrin (synergized with piperonyl butoxide)+ 33.6% (AI) methoprene or 3% (AI) pyrethrin + 33.6% AI methoprene. The mixture was formulated as specified on the insecticide labels to give a 100 to 1 ratio of active ingredient pyrethrin to methoprene. Residual bioassays were conducted every two weeks for 16 weeks post-exposure to the aerosol by placing four-week-old larvae of the red flour beetle, Tribolium castaneum (Herbst), or the confused flour beetle, Tribolium confusum (Jacqueline duVal), on treated flour or a treated packaging surface with untreated flour added. T. castaneum was clearly the more susceptible of the two species. Less than 2% of T. castaneum larvae exposed to aerosol-treated flour or packaging surfaces emerged as normal adults, regardless of the pyrethrin concentration. Most of the T. castaneum larvae on treated flour did not advance to the pupal stage because they were either developmentally arrested or died as larvae. They were able to develop further on the treated packaging surfaces, but still could not emerge as adults. T. confusum larvae exposed to aerosol-treated flour or packaging surfaces were able to develop to the pupal or adult stage. Emergence of normal-appearing adults from T. confusum larvae exposed on the packaging surfaces treated with 1% pyrethrin + methoprene gradually increased (range of 29.7 ± 2.9 to 49.0 ± 6.7%, depending on the surface), whereas adult emergence of larvae exposed to treated flour peaked at 10 weeks post-exposure. However, when T. confusum was exposed to 3% pyrethrin + methoprene treated flour or packaging surfaces, adult emergence was reduced. Overall there were few significant differences attributable to the individual packaging surfaces.     

Effectiveness of spinosad combined with diatomaceous earth against different European strains of Tribolium confusum du Val (Coleoptera: Tenebrionidae): Influence of commodity and temperature

Laboratory bioassays were carried out to assess the effects of combining spinosad at 0.01, 0.1 and 0.5 ppm, with the diatomaceous earth (DE) formulation SilicoSec at rates of 150, 300 and 600 ppm, against larvae and adults of three different populations of Tribolium confusum du Val (Coleoptera: Tenebrionidae), originating from different European countries (Greece, Portugal and Denmark). Tests were conducted on wheat and maize at 25 and 30 °C. Survival of T. confusum larvae was assessed after 7 d exposure and survival of adults was assessed after 7 d and 14 d of exposure. At each dose of spinosad, survival of T. confusum individuals decreased as the rate of DE increased. As temperature increased, the efficacy of spinosad and Silicosec applied either alone or in combination also increased. The efficacy of spinosad alone was slightly higher on maize than wheat, while the reverse was noted for all the tested combinations of spinosad with DE as well as in the case of the application of DE alone. The strain from Portugal was always the least susceptible of the three tested. Our study indicates that it is possible to combine low doses of DE (<600 ppm) with spinosad (<1 ppm) to control adults and larvae of T. confusum, especially at temperatures >25 °C.     

Effectiveness of spinosad dust against different European populations of the confused flour beetle, Tribolium confusum Jacquelin du Val

Six populations of the confused flour beetle, Tribolium confusum, obtained from Greece, Italy, Portugal, Denmark, Germany and France were tested for their susceptibility to a spinosad dust formulation, containing 0.125% spinosad. For this purpose, adults and larvae of T. confusum were exposed on wheat treated with two dose rates of the dust formulation, 0.06 and 0.19 ppm of a.i. corresponding to 50 and 150 ppm of the formulation, at 25 °C and 65% r.h. Mortality of the exposed individuals was assessed after 7, 14 and 21 days of exposure on the treated substrate. The increase of dose and exposure interval increased mortality, while adults were more tolerant to spinosad than larvae. Significant differences were noted among populations, for both adults and larvae. The most tolerant to spinosad was the strain from Greece, while the least tolerant were the strains from Germany and Denmark. After 7 days of exposure, on wheat treated with 50 ppm, mortalities of adults of the Greek, German and Danish strains were 2%, 25% and 62% respectively, while the respective figures for 150 ppm were 1%, 31% and 81% respectively. In the case of larvae, of the same strains, mortality at 50 ppm was 6%, 27% and 28% and at 150 ppm 11%, 23% and 40%, respectively. The results of the present study suggest that different strains and stages of T. confusum differ widely in their susceptibility to spinosad-treated wheat.     

Susceptibility of stored-product insects to enhanced diatomaceous earth

Mortality of adult Rhyzopertha dominica (F.), Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) was recorded after exposure for different times to application rates of 0, 0.5, 1, 1.5 or 2 g/m² of the diatomaceous earth (DE) DEBBM-P/WP and to 0, 3, 4, 5 or 6 g/m² of the DE Protect-It^®. Mortality of all insects increased with increasing exposure interval; dry dusts were more effective than slurries, and overall mortality was greater for DEBBM-P/WP than Protect-It^®.     

Impact of physical and biological factors on susceptibility of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) to new formulations of hydroprene

Three separate experiments were conducted to: (1) evaluate two new commercial formulations (202-080 and 202-084) of the insect growth regulator hydroprene, (2) determine residual efficacy of hydroprene-treated concrete stored at different environmental conditions, and (3) assess the impact of accumulated flour on residual efficacy. In the first test, late instars of Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed on concrete treated with hydroprene. At 40% relative humidity (r.h.), there was no difference between species regarding the percentage of individuals that stopped development in the larval stage (arrested larvae), but at 75% r.h. there were more arrested T. castaneum than T. confusum in all treatments except the low rate of formulation 202-084. No adult T. castaneum lived after emergence (live adults) at either relative humidity, but the percentage of live adult T. confusum ranged from 1.0% to 41.0%, depending on treatment. In the second test, late instars of T. confusum were exposed at 6 and 12 weeks post-treatment on concrete treated with the two experimental formulations and stored under different environmental conditions. At 6 weeks there was no difference between formulations. At 12 weeks, fewer live adults and more dead emerged adults with gross morphological deformities were found on concrete treated with formulation 202-084 and stored at 32°C, 75% r.h. compared to other treatment combinations. In the final experiment, wheat flour was added to treated concrete for 5 weeks before the bioassays were conducted with late-instar T. confusum. There were few live adults produced in the initial bioassays, and dead adults with gross morphological deformities ranged from 83.1% to 97.6%. However, in bioassays conducted with late-instar larvae at 6 weeks, most adults eventually emerged with few deformities. The presence of the flour apparently compromised residual control and the hydroprene was no longer effective. In summary, the new hydroprene formulations were equivalent to the registered product Gentrol^®. Tribolium confusum was less susceptible than T. castaneum, and residual control of T. confusum on a clean surface without flour lasted about 6-12 weeks.     

Initial and delayed mortality of late-instar larvae, pupae, and adults of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) exposed at variable temperatures and time intervals

Late-instar larvae, pupae, and adults of Tribolium castaneum (Herbst), the red flour beetle, or Tribolium confusum (DuVal), the confused flour beetle, were exposed for variable durations at 36-54 °C. Beetles were placed in laboratory ovens set at a baseline of 27 °C, the temperature was increased by 0.1 °C per minute until the target temperature was achieved, and beetles were then held for specified exposure durations. There was no mortality after initial exposure or after a 1-week holding period of any life stage of T. castaneum or T. confusum exposed for 32 h to 36, 39, or 42 °C. At 45 °C, there was no initial mortality of either species exposed for different time intervals except for those exposed for 28 h. However, there was a significant increase in mortality after the 1-week holding period of those beetles exposed initially for at least 16 h to 45 °C. There was a sharp increase in mortality after the initial exposures of 4 h at 48 °C; mortality of T. confusum larvae was 90.0±5.7% but was only 10.0±10.0% for larvae of T. castaneum, and no pupae of either species were dead. All life stages of both species were killed after the initial exposure of 12 h, and 1-week mortality of beetles exposed for 4 and 8 h was generally greater than initial mortality. At 51 and 54 °C, 2- and 1-h exposures, respectively, killed all life stages of each species. Mortality in conditions of gradual temperature increase was less than previous studies with sudden temperature increases.     

Mortality of Tribolium confusum J. du Val (Coleoptera: Tenebrionidae) in controlled atmospheres at different oxygen percentages

Since the 1990s an ecologically friendly alternative to insecticide treatments for controlling stored-product insect pests has been available: the methods of modified and controlled atmospheres, which involve reducing the quantity of oxygen (O₂) in the air in order to kill insects by anoxia. This study examines the effect of treatments with controlled atmospheres, considering the time necessary to obtain total mortality of insects at percentages of O₂ higher than those normally used in controlled atmospheres and estimating the possible positive influence of a temperature increase in order to compensate for the effects of the reduced anoxia.Adult populations of Tribolium confusum J. du Val were treated at various O₂ percentages (1, 3, 5, 6, 7, 8 and 10%) and temperatures (23, 26, 29, 32, 35, 37 and 40 °C). The relative humidity was very low (<18%) in all the treatments considered.Lethal exposure times varied from less than one day to a week (longer times were not considered).A multiple regression procedure was applied to the experimental data, considering the time necessary to obtain total mortality as the dependent variable. The analysis provided a good fit to the experimental data and indicated a positive correlation with the percentage of O₂ and an inverse one with temperature.     

Predation by Blattisocius tarsalis (Berlese) (Acari: Ascidae) on eggs of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

The mean predation rate of female B. tarsalis on eggs of E. kuehniella was determined at 15°C, 21°C, and 27°C with prey densities of 3, 5, 10 and 15 eggs. Young eggs less than 24 h old were used as prey. Under all experimental conditions most eggs were only partially consumed, confirming the general theory that predatory mites leave most of the food content unutilized. A mean predation rate of 2.2-7.0 eggs destroyed in 24 h was found, reflecting that a large proportion of the available prey was destroyed. The result supports the view that the predatory mite B. tarsalis could be a relevant biological control agent against E. kuehniella in flour mills. It was further demonstrated that frozen moth eggs can be considered as an appropriate food source.     

Inherited sterility in Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae): Effect of gamma radiation on insect fecundity, fertility and developmental period

The effects of gamma radiation on the fecundity, fertility, longevity, development and level of inherited sterility in the Mediterranean flour moth Ephestia kuehniella were determined. Newly emerged virgin Mediterranean flour moth adults were irradiated with 100, 200, 400 and 600 Gy in a ⁶⁰Co irradiator with a source strength of ca. 3811 Ci and a dose rate of ca. 1 Gy/min. Laboratory studies revealed that radiation did not effect the longevity of irradiated male and female adults. Inherited deleterious effects of gamma radiation were observed in the F₁ and F₂ generations. Fecundity and the daily egg laying pattern of irradiated and unirradiated females mated to irradiated males was not significantly different from untreated controls. Adverse effects of gamma radiation were observed in the percentage egg hatch and rate of development. Levels of sterility in the P₁, F₁ and F₂ generations were higher than that of untreated controls. The doses of radiation also had a significant effect on the time from oviposition to larval eclosion or adult emergence. Mortality increased with radiation dose. The incidence of larval and pupal mortality was higher in the F₂ than in the F₁ generation.     

Spatio-temporal analysis of trap catches of Tribolium confusum du Val in a semolina-mill, with a comparison of female and male distributions

By using food-bait traps, we evaluated the presence and the spatio-temporal distribution of insect pests in an industrial semolina-mill, with particular attention to Tribolium confusum du Val in which the spatio-temporal dynamics of females and males were also studied separately. A total of 1401 insect specimens was captured in the traps, belonging to 14 taxa, mainly Coleoptera. The most abundant species were T. confusum (with 1002 adults), followed by Typhaea stercorea (L.) (with 158 adults) and T. castaneum (Herbst) (with 110 adults). Of particular interest was the presence in the food-bait traps of T. confusum and T. castaneum adults in a mixed population with equal numbers of males and females. Furthermore, analysis of the spatio-temporal dynamics suggested that the distribution of the two sexes in T. confusum was almost the same during the entire sampling period. The findings of our study can usefully be applied to the management of Tribolium infestations, but further and more detailed studies are needed to better understand the ecology and behaviour of the species in association with searching for food and production of aggregation pheromones.     

Bioactivity of five monoterpenoid vapours to Tribolium confusum (du Val) (Coleoptera: Tenebrionidae)

Five monoterpenoids (terpinen-4-ol, 1,8-cineole, linalool, R-(+)-limonene and geraniol) were tested in vapour form against different stages of Tribolium confusum. Terpinen-4-ol (with LC₅₀ values ranging between 1.1 and 109.4 μl/l air), (R)-(+)-limonene (with LC₅₀ values ranging between 4 and 278 μl/l air) and 1,8-cineole (with LC₅₀ values ranging between 3.5 and 466 μl/l air) were the most toxic to all stages tested, followed by linalool (with LC₅₀ values ranging between 8.6 and 183.5 μl/l air) while the least toxic monoterpenoid tested was geraniol with LC₅₀ values ranging between 607 and 1627 μl/l air. In all cases, except for geraniol, third-instar larvae were the most susceptible stage and 3-day-old eggs most tolerant. Apart from the observed direct toxicity, exposure of females to the vapours led in some cases to lower fecundity and egg hatchability. All monoterpenoids tested revealed insect growth regulator (IGR)-like properties when applied to 3-day-old pupae, producing adultoids and deformed adults.     

The choice of probing sites by Bracon hebetor Say (Hymenoptera: Braconidae) foraging for Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

A direct behavioral assay was conducted to investigate the preferred habitat for host searching by the parasitoid Bracon hebetor (Hymenoptera: Braconidae). The effects of mating, feeding and post-emergence experience on female parasitoid choices of searching sites were also examined. B. hebetor appears to be directed to the habitat of its host through chemical cues originating from the host larvae, frass and adults. These cues elicit a series of directed responses by the female. Generally, the data showed that flour containing 30-day-old larvae was preferred by B. hebetor females. This was followed by the flour containing the frass, then the adult host, and finally the flour containing 10-day-old larvae. It appears that cues produced by young larvae were the weakest whereas cues produced by older ones were the strongest. Feeding seemed to be important in the location of the proper searching site. Although the cues were normally learned by the immature stages of the parasitoid, and were subsequently manifested in their responses as adults, adult experience increased the ability of the parasitoid to locate the suitable habitat for searching.     

Efficacy of a volatile formulation of hydroprene (Pointsource™) to control Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae)

Three- and 4-week-old Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed at five different temperature-relative humidity (r.h.) combinations to a volatile formulation of the insect growth regulator (IGR) hydroprene (called Pointsource™). Typical effects associated with IGR exposure, such as arrested larval growth, morphological deformities in adults, twisted and deformed wings, and incomplete adult emergence were produced in both species. Tribolium castaneum and T. confusum were susceptible to Pointsource™, but T. castaneum appeared to be the more susceptible species. More 3-week-old larvae of both species were arrested in that stage compared to the 4-week-old larvae. Nearly all of the 3- and 4-week-old T. castaneum larvae that were able to complete development to the adult stage quickly died after they emerged and were grossly morphologically deformed. In contrast, some emerged adult T. confusum remained alive after they emerged and were not deformed in any manner or had only twisted and incomplete wings. A greater percentage of larvae of both species were arrested in the larval stage and more adults died after they emerged in exposure studies conducted at 32°C, 75% r.h. as compared with 32°C, 30% r.h., but the reverse was true for exposures conducted at 27°C. Pointsource™ appears to have excellent potential for use in controlling Tribolium species within indoor facilities.     

The effect of sub-zero temperatures on different lifestages of Lasioderma serricorne (F.) and Ephestia elutella (Hübner)

The effect of sub-zero temperatures on different lifestages of Lasioderma serricorne and Ephestia elutella was investigated as a means of disinfesting stored tobacco. Eggs, unacclimated cocoons and acclimated cocoons of L. serricorne were exposed to −10 °C, −15 °C and −20 °C in insulated boxes. There was no adult emergence from eggs or unacclimated cocoons following exposure to the respective temperatures for 4 h, 2 h and 1 h. With acclimated cocoons there was no adult emergence after 2 h at −15 °C and 1 h at −20 °C, but at −10 °C, there was adult emergence after 8, 12 and 24 h exposures.In field-scale experiments, cold acclimated fourth-instar larvae of L. serricorne were inserted into cases of leaf tobacco and boxes of finished product, put into commercial freezers and exposed to minimum temperatures of −10 °C, −18 °C or −25 °C. Critical temperatures were measured at the core of the commodity. No adults emerged from the commodity when exposed to at least −18 °C for periods ranging between 3.75 h and 39.25 h or when exposed to at least −25 °C for between 2.4 h and 3.7 h. At a minimum of −10 °C, 3 live adults emerged after 24 h exposure.With E. elutella, diapausing larvae were inserted into small scale tobacco bales and exposed to −10 °C, −13 °C, −15 °C or −20 °C. No emergence of adults and no larval survival was achieved after 21 d, 3 d and 2 h exposure at −10 °C, −15 °C and −20 °C respectively. At −13 °C, there was no adult emergence after 2 and 5 d exposure, but live larvae remained after 24 weeks incubation at 25 °C.Minimum conditions of −18 °C for 24 h and −25 °C for 4 h are recommended for the control of L. serricorne and −20 °C for 24 h for the control of E. elutella in stored tobacco (to fit with operational logistics).     

Effect of particle size of soft wheat flour on the development of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

The effect of soft wheat flours, characterized by different particle size, protein and starch content, on the development of Ephestia kuehniella was studied. The attractiveness of the substrata to first and third instar larvae was also considered.The different protein content of the flours did not significantly affect the development of E. kuehniella, nor did it affect the ability of the flours to attract larvae. In tests with soft wheat flours with the same nutritional value but different particle size, the highest mean number of adults and the shortest developmental period were recorded on samples with greatest particle size (250-419 μm).In order to test the attractiveness of soft wheat flour to larvae, a one-way olfactometer was used. There were no significant differences observed in the number of first and third instar larvae found on flours with different protein composition and particle size. Larvae of this species show limited mobility, in fact few individuals of either instar can reach the flour from a distance of 2 m. No larvae of either instar contacted the different substrata from a distance of 2.5 m.     

Feeding deterrent activity of terpenoid lactones with a p-menthane system against stored-product pests

Feeding deterrent activity of eight enantiomeric pairs and one optically inactive terpenoid lactone with a p-menthane system against three storage pests was determined. The lactones were tested on adults of Sitophilus granarius, adults and larvae of Tribolium confusum and larvae of Trogoderma granarium. The isomeric starting natural compounds, (+) and (−) pulegones and (+) and (−) isopulegols, were also tested. The results showed that the introduction of the lactone moiety into the p-menthane system produced antifeedant activity in the lactones obtained. The lactones with a spiro arrangement of lactone and cyclohexane rings were more active than those with condensed rings. The configuration of chiral centres present in the molecule significantly influenced the activity of the compounds studied. In most cases, lactones obtained from R-(+)-pulegone were more active antifeedants than those obtained from S-(−)-pulegone.     

Insecticidal efficacy of diatomaceous earth against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Tribolium confusum du Val (Coleoptera: Tenebrionidae) on stored wheat: influence of dose rate, temperature and exposure interval

Laboratory experiments were conducted in order to assess the insecticidal effect of a diatomaceous earth formulation (Silicosec^®, Biofa GmbH, Germany) against Sitophilus oryzae and Tribolium confusum on stored wheat. Adults of the two species were exposed on wheat treated with diatomaceous earth at four dose rates: 0.25, 0.5, 1 and 1.5 g/kg of wheat, respectively. For each dose rate, the treated wheat was placed at 22°C, 25°C, 27°C, 30°C and 32°C. Dead adults were counted after 24 and 48 h, 7 and 14 d of exposure. After the 14-d interval, the live adults were removed and placed for 7 d in untreated wheat (in the case of S. oryzae) or untreated flour (in the case of T. confusum), and the production of F₁ was recorded. For both species, dose rate, temperature and exposure interval significantly affected mortality (P<0.001). Mortality was higher at longer exposure intervals. The efficacy of SilicoSec against S. oryzae increased with temperature, but for T. confusum mortality was lower at 32°C, compared to 30°C, for 24 and 48 h exposure intervals. Tribolium confusum proved less susceptible to SilicoSec than S. oryzae. In general, the rates of 1 and 1.5 g/kg of wheat provided a satisfactory level of protection against the two species examined. For S. oryzae, F₁ emerged only at 22°C, in wheat treated with 0.25 or 0.5 g/kg. However, for T. confusum, F₁ were recorded at 22°C for 0.5 g/kg and at 22°C, 25°C, 27°C and 30°C for 0.25 g/kg.     

Susceptibility of stored product insects to high concentrations of ozone at different exposure intervals

Ozone is a highly reactive gas with insecticidal activity. Past studies have indicated that ozone technology has potential as a management tool to control insect pests in bulk grain storage facilities. The objective of this study was to determine the efficacy of short periods of exposure to high ozone concentrations to kill all life stages of red flour beetle (Tribolium castaneum (Herbst)) (Coleoptera: Tenebrionidae), and Indianmeal moth (Plodia interpunctella (Hübner)) (Lepidoptera: Pyralidae), adult maize weevil (Sitophilus zeamais (Motsch.)) (Coleoptera: Curculionidae) and adult rice weevil (S. oryzae (L)) (Coleoptera: Curculionidae). Insects were treated with six ozone concentrations between 50 and 1800 ppm. The specific objective was to determine minimal time needed to attain 100% mortality. The most ozone-tolerant stages of T. castaneum were pupae and eggs, which required a treatment of 180 min at 1800 ppm ozone to reach 100% mortality. Eggs of P. interpunctella also required 180 min at 1800 ppm ozone to reach 100% mortality. Ozone treatments of 1800 ppm for 120 min and 1800 ppm for 60 min were required to kill all adult S. zeamais and adult S. oryzae, respectively. The results indicate that high ozone concentrations reduce the treatment times significantly over previously described results. Our results also provide new baseline information about insect tolerance to ozone treatment.