Susceptibility of different life stages of Indian meal moth Plodia interpunctella (Hübner) and almond moth Ephestia cautella (Walker) (Lepidoptera: Pyralidae) to modified atmospheres enriched with carbon dioxide

The susceptibility of the different life stages of the Indian meal moth Plodia interpunctella and almond moth Ephestia (Cadra) cautella to different modified atmospheres (MAs) containing various concentrations of carbon dioxide (CO₂) was studied as an alternative to methyl bromide fumigation at 27 °C and 60 ± 5% relative humidity (r.h.). The MAs tested were 40%, 60% and 80% CO₂ in air at different exposure times. Results showed that five days were adequate to kill all eggs and pupae of the two moths under all tested MAs. Exposure time needed to be extended to 6 and 7 days at 80% CO₂ to obtain complete mortality of larva of E. cautella and P. interpunctella, respectively. The order of sensitivity of P. interpunctella to MAs was: egg = pupa > larva, while for E. cautella it was: pupa > egg > larva. Generally, eggs and pupae of P. interpunctella were more sensitive to MAs than those of E. cautella but the larvae of the latter were more sensitive.     

Chlorine dioxide fumigation to control stored product insects in rice stored in a room

Gaseous chlorine dioxide (ClO₂) was applied to fumigate larvae and adult stages of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) and Sitophilus zeamais (Motschulsky) in rice grain bags stored in a grain storage room. It was confirmed that the fumigation efficiency varied depending on the storage position and insect life stage and species. The fumigation effect was the highest on the surface of the grain bag and lowest on the middle of the outer position on the grain storage bag. The mortality of adult P. interpunctella, 5 days after ClO₂ fumigation, reached 100% regardless of their position, whereas that of the larva P. interpunctella and adult S. zeamais varied depending on their positions. The mortalities in the outer portions of the grain bag were the highest, followed by that at the top of the grain bag. The ClO₂ residue of treated rice were lower than that accepted by international standards. To achieve fumigation effectiveness which similar with lab scale experiment, more researches which are related to infiltration or circulation of gaseous ClO₂ are needed.     

Tolerance of the diapausing stages of four species of Lepidoptera to methyl bromide

The diapausing stages exposed to methyl bromide were larvae of Ephestia elutella (Hübner) and Plodia interpunctella (Hübner), pupae of Pieris brassicae (L.) and eggs of Bombyx mori (L.). Diapausing larvae of Ephestia elutella were highly tolerant, a few surviving to the adult stage after exposure to concentration-time (CT) products of up to 150 mg hr/l at 25°C and 260 mg hr/l at 15°C. Diapausing larvae of Plodia interpunctella were tolerant at low temperatures but quite susceptible at 25°C. In both species, larvae in diapause were four to six times more tolerant than other larvae at 15°C or below, and strains recently collected from the field were more tolerant than laboratory reared stocks.In E. elutella, differences in the method of induction, maintenance or termination of diapause did not affect tolerance to fumigation. P. interpunctella larvae reared at high population density were more susceptible than those reared at low density. Among strains of these species, a correlation was observed between the duration of larval diapause and tolerance to methyl bromide. Adults emerging after fumigation of diapausing larvae were of lowered fertility but rarely sterile. The CT products required for the complete control of moths in diapause were higher than those currently recommended for the disinfestation of stored products.Diapausing pupae of an outdoor species Pieris brassicae required the very high CT product of 403 mg hr/l for complete control at 25°C and were at least six times more tolerant than non-diapausing pupae. Diapausing eggs of Bombyx mori required 179 mg hr/l for complete control, while non-diapausing eggs were all killed by 125 mg hr/l.     

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.     

The tolerance of immature stages of four stored product moths to methyl bromide

Eggs, last instar larvae, and pupae of the Pyralid moths, Ephestia elutella (Hübner). E. kuehniella Zeller, E. cautella (Walker) and Plodia interpunctella (Hübner) reared at 25°C were exposed to methyl bromide over a wide range of concentrations and times at 10–30°C. One laboratory stock, and one field stock of each species were tested, but differences between stocks of the same species were small.P. interpunctella required lower CT products than the other species for complete kill of each stage. At 10°C, larvae of the field stock of E. cautella required a CT product of 110 mg h/l. for complete control. All stages of all species succumbed to a CT product of 64 mg h/l. at 15°C. When exposed at 20°C or above, pupae aged 0–3 days were more tolerant than other stages. Eggs aged 2 days or over were more tolerant than younger ones.The fertility of survivors from fumigated eggs resembled that of controls, but that of some individuals fumigated as pupae was depressed. For fumigated eggs of E. elutella and P. interpunctella at 15°C, the CT relationship held over concentrations from 4·2 to 10·8 mg/l. and exposure periods from 1 to 16 h.     

Life history of Plodia interpunctella (Lepidoptera: Pyralidae) on dried fruits and nuts: Effects of macronutrients and secondary metabolites on immature stages

The objective of this study was to investigate the effects of nutrients and secondary metabolites content in 16 types of dried fruits and four nuts from Serbia on life history traits of Plodia interpunctella (Hübner, 1813) immature stages. The analysis of nutrients content included determination of the total moisture, ash, proteins, fats, carbohydrates, sugars, and total reducing sugars, while from secondary metabolites total phenolics, flavonoids and tannins contents were determined. Life history traits included the developmental duration of larvae (LDD), developmental duration of pupae (PDD) and total immature stages (MDD), as well as the survival of larvae and pupae. Additional analyses was conducted on time-specific survival, as well as on the age- and size-growth patterns of P. interpunctella larvae. The principal component analysis (PCA) indicated that the content of proteins and fats is in strong positive correlation with larval and total immature stages survival, while in negative correlation with LDD, PDD, and MDD. The content of secondary metabolites are in strong positive correlation with LDD and MDD, while in negative correlation with larval and total immature stages survival. Considering the fastest development and high number of survived larvae and pupae, the walnuts, hazelnuts and almonds were more suitable for the development of P. interpunctella than tested dried fruits in general, while the goji berries and figs were the most suitable among tested dried fruits. The results of the effects of tested dried fruits and nuts from Serbia on life history traits of P. interpunctella, combined with studies from different countiries using local varieties and cultivars of dried fruits and nuts, could provide the data for modeling the growth and population dynamics, important for forcasting and signaling the occurance of this pest.     

Susceptibility of different life stages of saw-toothed grain beetle Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) to modified atmospheres enriched with carbon dioxide

The susceptibility of the different life stages of the saw-toothed grain beetle Oryzaephilus surinamensis to different modified atmospheres (MAs) containing various concentrations of carbon dioxide (CO₂) was studied as an alternative to methyl bromide fumigation at 30 °C and 65 ± 5% relative humidity (r.h.). The tested MAs were 55%, 65%, 75% and 85% CO₂ gas in the air. Mortality (%) was recorded after exposure periods of 3, 6, 12, 24, 48, 72 and 96 h. Larvae and adults were more susceptible while eggs and pupae were more tolerant to CO₂. A two-day exposure period was adequate to completely kill larvae and adults under all tested MAs. All eggs and pupae were killed after four days of exposure to the high-CO₂ atmospheres (75% and 85%).     

Investigation of fumigant efficacy in flour mills under real-world fumigation conditions

Fumigation experiments under laboratory conditions are common but due to a number of factors, fumigation experiments under real-world conditions are difficult and rare. This study was aimed at providing an insight into efficacy evaluations of fumigants based on insect mortality data under real-world conditions. A total of eight sulfuryl fluoride (SF) and three methyl bromide (MB) fumigations were performed in four different flour mills in the Midwestern United States. Bioassays were undertaken with all insect life stages (i.e., eggs, larvae, pupae and adults) of Tribolium castaneum (Herbst) and Plodia interpunctella (Hübner) placed inside fumigated structures. In addition, in most of the fumigations, environmental conditions (e.g., prevailing wind, temperature, and relative humidity) and gas concentrations were monitored. Complete mortality was obtained for the adults and larvae of both insect species, and for the pupae of P. interpunctella. Some T. castaneum pupae survived in all three MB fumigations and in one SF fumigation. In addition, some exposed eggs were able to reach the adult stage in one MB and four SF fumigations. The methodology and procedures presented can be used in future field studies of fumigant efficacy.     

Surface pasteurization of fresh pomelo juice vesicles by gaseous chlorine dioxide

This study developed an in-package pasteurization method that released gaseous chlorine dioxide (ClO₂) triggered when moisture vapor from the fresh produce interacted with a ClO₂ precursor. The samples were placed in sealed containers (750 ml) containing mixtures (0.1–1.0 g) of sodium chlorite and citric acid powders (1:1) and treated for up to 15 min at 25°C. Our results showed that, production of gaseous ClO₂ was linearly correlated with the reaction time (R²>0.95) with mean concentrations in the range of 1.70 – 8.66 mg/L. The gaseous ClO₂ treatments for 15 min significantly reduced Escherichia coli and fungi populations on pomelo juice vesicles with reductions of 6 and 2 log CFU/g, respectively. Perchlorate and chlorite in samples were not detected, and chlorate was only detected when the mean ClO₂ concentration was over 4.09 mg/L. The treatments did not significantly affect total soluble solids, total acids, pectin and malondialdehyde contents, and color of pomelo juice vesicles. The contents of ascorbic acid, naringin, and limonin, and bitterness score decreased with the increase of mean ClO₂ concentrations. Overall, our results demonstrate an effective nonthermal approach for microbial inactivation while maintaining the quality of fresh pomelo juice vesicles.     

Effect of gaseous chlorine dioxide treatment on the quality of rice and wheat grain

Gaseous chlorine dioxide (ClO₂), which is a strong disinfecting agent with strong oxidation properties and penetration ability, is used to control insect pests and fungal contamination in stored grains. However, the effect of gaseous ClO₂ on stored grain has yet to be reported. In the present study, we exposed rice and wheat seeds to several concentrations of ClO₂ gas for various durations and found that the viability of rice was affected less than that of wheat. After 100 ppm of gaseous ClO₂ for 12 h, the normal rice seedling rate was not significantly different than that of the control. However, that of wheat was significantly decreased. We also measured the ClO₂ residueon stored rice and wheat after 200 ppm of gas treatment for 24 h. After 10 days of storage following the treatment, ClO₂ and chlorine were not detected on either rice or wheat. Chlorite was detected on rice at 0.22 mg/kg of grain; however, it was not detected on wheat. These results suggest that gaseous ClO₂ treatment affects the viability of rice and wheat seed but leaves minimal chemical residue.     

A simple instrument-free gaseous chlorine dioxide method for microbial decontamination of potatoes during storage

An instrument-free gaseous chlorine dioxide (ClO₂) method to control microorganisms on potatoes during storage was developed. Gaseous ClO₂ was generated by combining an equal amount of impregnated sodium chlorite and activating acids in a sachet without using any solution or equipment. After activation by mixing, the sachet was placed in the application area. The decontamination efficiency of ClO₂ on natural microbiota including total microorganisms, yeasts and molds, and inoculated Pseudomonas aeruginosa on potatoes was investigated. Different treatments using 2, 3, and 4 g of materials and various time intervals (2.5 and 5 h) to generate 16, 20, 24, 30, 32, and 40 mg/L of ClO₂ were evaluated. The results were effective for natural microbiota, showing over a 5 log CFU/potato reduction with a 4 g treatment after 5 h. For P. aeruginosa, there was almost a 6 log CFU/potato reduction after 5 h of the 4 g treatment. The lowest treatment tested (2 g at 2.5 h) showed reductions of 1.7, 1.9, and 2.3 log CFU/potato for total microorganisms, yeasts and molds, and P. aeruginosa, respectively. Gaseous ClO₂ did not affect the overall visual quality of the potato. The residue of ClO₂ decreased to <1 mg/L after 14 days for each treatment, indicating ClO₂ dissipates naturally over time.     

Effectiveness of short exposures of propylene oxide alone and in combination with low pressure or carbon dioxide against Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Toxicity of the fumigant propylene oxide (PPO) alone and in combination with low pressure (100 mm Hg) or 92% CO₂ to all life stages of Tribolium castaneum using short exposure times (4 and 8 h) at 30°C was studied. Results indicated that PPO was moderately toxic with Ct products ranging from 120 to 608 mg h/l required to obtain complete mortality of the different life stages. A marked difference in susceptibility between life stages was recorded. Eggs were the most sensitive with a LD₉₉ value of 30.1 mg/l for 4 h, whereas pupae were the most tolerant with a LD₉₉ value of 146.5 mg/l. It was shown that an increase in exposure time from 4 to 8 h resulted in 23%, 42%, 48% and 47% reductions of LD₉₉ values for eggs, larvae, pupae and adults, respectively.There was no or very limited mortality of all stages except the egg (53% to 62%), when exposed to either 100 mm Hg or 92% CO₂ for 4 h. However, when 100 mm Hg or 92% CO₂ were combined with PPO, the LD₅₀ and LD₉₉ values for PPO in all stages except the egg were significantly reduced. Combinations of PPO with 100 mm Hg or 92% CO₂ produced equal reductions in the LD₉₉ value from 146.5 to about 22 mg/l for the most tolerant pupal stage. Both combinations also produced significant reductions in the LD₉₉ values for larvae and adults (6.3- to 6.6-fold) compared with those exposed to PPO alone. These results indicated that 100 mm Hg and 92% CO₂ each had a synergistic effect on the toxicity of PPO to T. castaneum. The combination of PPO with vacuum or CO₂ can thus provide a potential alternative to methyl bromide.     

Influence of maize kernel state and type on life history of Plodia interpunctella (Lepidoptera: Pyralidae)

The objective of this study was to investigate the influence of different mechanical states (whole, broken and ground kernels) and types (dent, semi-flint and flint) of maize kernels on life history parameters of Plodia interpunctella (Hübner), the Indian meal moth. These parameters included larval development and its dynamics, adult emergence, mean development duration (MDD) and fecundity. Since the larvae are the developmental stage that causes the most damage on maize, additional data on larval development helps identify conditions that promote development. The results of our study indicate that broken maize kernels are the most suitable for P. interpunctella development, where the most successful larval development, the highest number of emerged adults, the shortest MDD and the highest total fecundity were recorded. On the contrary, whole kernels were the least suitable and the most resistant to infestation by P. interpunctella. The type of kernel also significantly affects P. interpunctella developmental parameters. Females reared on flint kernels (the hardest kernel type tested in our study) laid the largest total number of eggs, which implies that kernel hardness, i.e. the type of kernel should be an important parameter when choosing maize hybrids for cultivation and for storage. Our study warrants further investigation of maize types and their susceptibility to P. interpunctella.     

The effect of modified atmospheres,an alternative to methyl bromide,on the susceptibility of immature stages of angoumois grain moth Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae)

The angoumois grain moth, Sitotroga cerealella is recognized as a common pest of grains world-wide. This investigation aimed at determining the most effective CO₂ concentration in air against the immature stages of the pest in laboratory tests. The sensitivity of newly-laid eggs (<24 h old), 4th instar larvae and 3-day-old pupae to 4 modified atmospheres (MAs) containing 30%, 45%, 65% and 75% CO₂ in air was investigated at 27 °C and exposure periods between 2 h and 264 h. The percentage mortality of the newly-laid eggs, as well as the reduction of adult emergence from 4th instar larvae and 3-day-old pupae tended to increase with the increase of CO₂ concentrations in air and exposure period. According to LT₉₅ values, the order of sensitivity of the three developmental stages of S. cerealella to the four MAs tested was as follows: eggs > pupae > larvae.     

Effects of combined nonthermal treatment on microbial growth and the quality of minimally processed yam (Dioscorea japonica Thunb) during storage

The effects of combination treatment with aqueous chlorine dioxide (ClO₂) and ultraviolet‐C (UV‐C) on the quality of yams were examined. Yam samples were treated with distilled water, 50 ppm aqueous ClO₂, 5 kJ m^?2 UV‐C or a combination of 50 ppm aqueous ClO₂ and 5 kJ m^?2 UV‐C. The microbiological analysis of the yams after aqueous ClO₂ treatment, UV‐C irradiation or combination treatment indicated significant reductions in the populations of pre‐existing microorganisms. In particular, the combination treatment reduced the populations of total aerobic bacteria, yeast and mould, and coliform bacteria in the yams by 3.2, 3.4 and 3.8 log CFU g^?1, respectively. The combination treatment also maintained the colour of the yams during storage. Sensory evaluation results indicated that the qualities of the yams treated with the combination of aqueous ClO₂ and UV‐C were better than those of the other treatments. These results clearly indicate that combination treatment with aqueous ClO₂ and UV‐C could be useful in improving the microbial safety and extending the shelf life of the yams.     

Evaluation of diatomaceous earth formulations enhanced with natural products against stored product insects

The insecticidal effect of prepared insecticide formulations labelled as Natural P, Inert Natural P and Py EC on Sitophilus oryzae, Rhyzopertha dominica and Tribolium castaneum have been evaluated on wheat grains. Formulation Natural P contains diatomaceous earth (DE), amorphous silica gel (3%), pyrethrin, flax oil, lavandin essential oil (EO) and un-activated yeast. Formulation Inert Natural P contains DE, amorphous silica gel, lavandin EO and food grade bait whereas formulation Py EC contains pyrethrin, piperonyl butoxide (PBO), flax oil, polysorbate, methyl oleate and amorphous silica gel (5%). Celatom® MN-51 (diatomaceous earth – DE) was used as a standard insecticide. Inert Natural P and Natural P were applied as dust at four different doses and Py EC was applied as emulsions on grain by spraying. All three formulations showed higher insecticidal efficacy and higher progeny inhibition on all three tested insect species and had lower impact on wheat bulk density reduction compared with Celatom® MN-51. The LD₅₀ and LD₉₀ values of Inert Natural P were 48.7 and 163.7 ppm respectively for S. oryzae, 15.2 and 178.0 ppm for R. dominica and 115.2 and 171.3 ppm for T. castaneum. The LD₅₀ and LD₉₀ values of Natural P were 83.6 and 97.9 ppm respectively for S. oryzae, 19.5 and 97.9 ppm for R. dominica and 75.4 and 105.6 ppm for T. castaneum. Applied Py EC at concentration of 2.0 ppm a.i. pyrethrin exhibited 100% mortality after 2 d of S. oryzae and T. castaneum and after 6 d of R. dominica. In addition, all three formulations caused significant reduction of progeny (F1) population compared to control, providing promising approach of integrated pest management strategy.     

Efficacy of phosphine fumigation for different life stages of Trogoderma inclusum and Dermestes maculatus (Coleoptera: Dermestidae)

Despite the importance of dermestid beetles as targets for stored product protection, including the protection of museum artifacts and animal-based products, there are only a few published reports regarding their susceptibility to phosphine fumigation, in contrast with other major stored product insect species. In the current study, we evaluated phosphine against all life stages of Trogoderma inclusum LeConte, the larger cabinet beetle, and Dermestes maculatus (DeGeer), the hide beetle. There were two series of laboratory bioassays; in the first series the concentrations were 0 (control), 50, 100, 200 and 600 ppm, and in the second series the concentrations were 0 (control), 50, 150, 300, 400, 500 and 600 ppm. Both series were carried out on a 5-day insect exposure protocol. The results for both species clearly indicated that eggs were by far the least susceptible life stage, followed by pupae, while most adults and larvae were killed at the 50-ppm concentration. Concentrations between 300 and 400 ppm could be utilized to provide 100% mortality for both species and all life stages. To our knowledge, our results are the first that have provided data regarding efficacy of phosphine for the control of T. inclusum and D. maculatus. Resource managers can utilize our results to more efficiently target these dermestids with specific concentrations of phosphine, depending on the target life stage.     

Efficacy of filter cake and Triplex powders from Ethiopia against three externally developing stored product insect species

Efficacy of filter cake and Triplex powders was evaluated against the red flour beetle, Tribolium castaneum (Herbst); saw-toothed grain beetle, Oryzaephilus surinamensis (L.); and Indian meal moth, Plodia interpunctella (Hübner). Mortality of T. castaneum and O. surinamensis was determined 14 d after exposing 20 adults to 100 g of maize and wheat treated with 0, 0.3, 0.5, 0.7, 1, 2, and 3 g/kg of filter cake and 0, 0.5, 0.7, 1, 2, 3, 6, 8, and 10 g/kg of Triplex. Adult progeny production was determined at 42 d. Live larvae at 21 d and adults of P. interpunctella that emerged at 42 d were determined by exposing 100 eggs to 0, 0.2, 0.3, 0.5, 0.7, 1, 2, and 3 g/kg of filter cake and 0, 0.3, 0.5, 0.7, 1, 2, 3, 6, and 8 g/kg of Triplex treated maize and wheat. On both grains, 100% mortality of T. castaneum and O. surinamensis adults was observed after exposure to 2–3 and 1–3 g/kg of filter cake, respectively. On wheat, 100% mortality only of O. surinamensis was observed in 2–3 g/kg Triplex treatment. Adult progeny production of T. castaneum and O. surinamensis was completely suppressed on both grains treated with 0.7–3 g/kg of filter cake. Adult progeny production of T. castaneum was completely suppressed at 1–3 g/kg of Triplex treated grains, whereas complete suppression of O. surinamensis was achieved only on maize treated with 2–3 g/kg of Triplex. Both live larvae at 21 d and adults of P. interpunctella that emerged at 42 d were completely suppressed when eggs were exposed to 2–3 and 0.5–3 g/kg filter cake treated maize and wheat, respectively, and on 6–8 and 3 g/kg Triplex treated maize and wheat, respectively. Filter cake was more efficacious compared to Triplex on both grains.     

Laboratory toxicity and large-scale commercial validation of the efficacy of ethanedinitrile,a potential alternative fumigant to methyl bromide,to disinfest New Zealand Pinus radiata export logs

We tested the efficacy of ethanedinitrile (EDN), a new fumigant considered as a potential methyl bromide (MB) replacement for the quarantine treatment of New Zealand pine, Pinus radiata D. Don, export logs. Firstly, toxicity trials were conducted in the laboratory with pine logs infested with the larvae, pupae, or adults of pine bark beetles, Hylurgus ligniperda and Hylastes ater, at 10 and 20 °C in 28-L chambers, to identify the most tolerant species and life stages. Then, logs infested with the most tolerant species and life stage were fumigated in 500-L laboratory chambers to determine whether the increase in the volume of the fumigated space and logs that will occur when scaling up from laboratory to commercial fumigations would affect EDN efficacy. Finally, confirmatory fumigation trials using commercial or semi-commercial sized log stacks, were conducted in a deforested commercial plantation area in Tokoroa, New Zealand, to demonstrate the efficacy of EDN in the field.Our results suggest EDN could be an effective alternative fumigant to MB for the phytosanitary treatment of logs exported from New Zealand. A phytosanitary fumigation schedule with EDN for P. radiata export logs that uses a concentration of 100 g/m³ for 20 h across a range of temperatures from 10 to 20 °C is recommended. Future efforts should focus on implementing the recommended schedule, under commercial practices, to provide quarantine security for export logs using EDN as a replacement for MB.     

Development of Chlorine Dioxide Releasing Film and Its Application in Decontaminating Fresh Produce

A feasibility study was conducted to develop chlorine dioxide (ClO₂)‐releasing packaging films for decontaminating fresh produce. Sodium chlorite and citric acid powder were incorporated into polylactic acid (PLA) polymer. Films made with different amounts of PLA (100 and 300 mg), percentages of reactant (5% to 60%), and ratios of sodium chlorite to citric acid (1:2 or 2:1) were prepared using a solvent casting method. The release of ClO₂ from the resultant films was activated by moisture. Increase of reactants in the films produced more ClO₂ while higher PLA content in the films resulted in less release of ClO₂. The ratio of sodium chlorite to citric acid and activation temperature (22 °C compared with 10 °C) did not affect the ClO₂ release from the films. Antimicrobial efficacy of ClO₂ released from the films was evaluated using grape tomato as a model food. The results indicate that the films were activated by moisture from tomatoes in the package and the released ClO₂ reduced Salmonella spp. and Escherichia coli O157:H7 inoculated on the tomatoes to undetectable levels (<5 colony forming units (CFU)/tomato), achieving more than 3 log reduction. The film‐treated tomatoes did not show significant changes in color and texture as compared to controls during storage at 10 °C for 21 d. This study demonstrated the technical feasibility for development of gaseous ClO₂‐releasing packaging system to enhance microbial safety and extend shelf life of fresh produce.