Efficacy of ozone fumigation against the major grain pests in stored wheat

Emerging trends to replace pesticides with nanomaterials: Recent experiences and future perspectives for ecofriendly environment

Despite the widespread usage to safeguard crops and manage pests, pesticides have detrimental effects on the environment and human health. The necessity to find sustainable agricultural techniques and meet the growing demand for food production has spurred the quest for pesticide substitutes other than traditional ones. The unique qualities of nanotechnology, including its high surface area-to-volume ratio, controlled release, and better stability, have made it a promising choice for pest management. Over the past ten years, there has been a noticeable growth in the usage of nanomaterials for pest management; however, concerns about their possible effects on the environment and human health have also surfaced. The purpose of this review paper is to give a broad overview of the worldwide trends and environmental effects of using nanomaterials in place of pesticides. The various types of nanomaterials, their characteristics, and their possible application in crop protection are covered. The limits of the current regulatory frameworks for nanomaterials in agriculture are further highlighted in this review. Additionally, it describes how standard testing procedures must be followed to assess the effects of nanomaterials on the environment and human health before their commercialization. In order to establish sustainable and secure nanotechnology-based pest control techniques, the review concludes by highlighting the significance of taking into account the possible hazards and benefits of nanomaterials for pest management and the necessity of an integrated approach. It also emphasizes the importance of more investigation into the behavior and environmental fate of nanomaterials to guarantee their safe and efficient application in agriculture.

Challenges related to the application of analytical methods to control insect meals in the context of European legislation

Since their approval for use in aquaculture in 2017, processed insect proteins have been extensively studied for their nutritional quality in animal feed. This new type of meal is highly promising but requires, as for other products used in animal feed, strict sanitary control in accordance with European legislation. Within this legal framework, light microscopy and PCR remain the official methods but have some analytical limitations that other methods could overcome. This paper aims to provide an overview of the European legislation concerning use of processed insect proteins, but also to highlight the advantages and disadvantages of the official methods for their analysis. It also points out other analytical methods, which have already proved their worth for the analysis of processed animal proteins, which could be used as complementary methods.

Acaricidal action of ozone on larvae and engorged females of Rhipicephalus microplus: a dose-dependent relationship

The tick Rhipicephalus microplus is a vector of infectious agents that causes great economic loss in the productivity of cattle herds. Several studies have sought natural compounds with acaricidal activity to control ticks, without allowing the development of resistance, without causing environmental damage, and without presenting toxicity to the hosts. The activity of ozone on the natural biomolecules of living beings has been studied as an alternative to control arthropods and acaricidal effects were shown on ticks. The aim of the present study was to assess the acaricidal effect on larvae and engorged females of R. microplus according to ozone dose. Larvae (n = 377) were distributed in 10 groups and engorged females (n = 284) were distributed in 14 groups. One group was used as control (not exposed to ozone) and the other groups were exposed to ozone gas for 5-105 min. Ozone had a dose-dependent acaricidal effect on both larvae and engorged females. Dosages between 355 and 2130 mg/L min had a delayed acaricidal effect (12-180 h), leading to the death of all engorged females before laying eggs, whereas doses between 3195 and 7455 mg/L min showed immediate acaricidal effect (5 min to 4 h). Doses between 1775 and 6390 mg/L min had an immediate (up to 5 min) acaricidal effect on the larvae of this species. Further studies should consider longer follow-up times during the assessment of the acaricidal activity against ticks.

Ozone reduces lifespan and alters gene expression profiles in Rhyzopertha dominica (Fabricius)

Rhyzopertha dominica is one of the most important stored grain pests that seriously damage rice and wheat. At present, the method of controlling stored grain pests mainly relies on insecticide fumigation. However, the excessive use of pesticides not only leaves pesticide residues, with harmful effects on human health and the environment, but also induces insect resistance. Ozone is a strong oxidant with the characteristics of easy decomposition and without residue. Although ozone has been widely used in the food industry in recent years, research on the control of stored grain pests is limited. In this research, we used ozone treatment to control R. dominica adults and explore the molecular mechanisms that affect them. Here, we found that ozone treatment on R. dominica adults could decrease life span and increase malondialdehyde (MDA) content, as well as reduce activity of total superoxide dismutase (SOD) and catalase (CAT). Using RNA-seq technology, we identified 641 genes that were differentially expressed between ozone-treated and control R. dominica adults [fold-change of ≥ 2 (q-value < 5%)]. When comparing ozone treatment with control R. dominica adults, 330 genes were significantly upregulated and 311 were downregulated. RT-qPCR confirmed that 11 genes were differentially expressed in ozone-treated and control R. dominica adults. These genes were involved in insect cuticle protein and antioxidant system. This research showed that ozone treatment could reduce the lifespan of R. dominica through antioxidant system. It is an environmentally benign method for the control of stored grain pests and has great development potential.

Ozone Efficiency on Two Coleopteran Insect Pests and Its Effect on Quality and Germination of Barley

Simple Summary

Rhyzopertha dominica (Fabricius) and Tribolium castaneum (Herbst) are notorious global pests, destroying various stored grains, including barley, wheat, oats, maize, and rice. Ozone (O₃) is a promising fumigant to control pests in stored grain since it can safely and rapidly auto-decompose without leaving residues, however, relatively few studies have focused on the toxicity of O₃ on stored grain pests in stored barley. In this study we not only explored the susceptibility of all life stages of R. dominica and T. castaneum in barley seeds to different durations of gaseous O₃, but also investigated the effect of O₃ on germination ability, seedling growth, and quality of barley. O₃ was effective against all life stages of two species in barley under sufficient exposure times without negative impacts affecting the commercial quality of barley. However, the germination ability and seedling growth were adversely impacted at longer O₃ exposure times. Thus, it is imperative to select an optimal O₃ exposure time to achieve the desired functional outcome, such as malting, animal feeding, and human consumption.

Abstract

Ozone (O₃) is a potential fumigant to control pests in stored grain since it can safely and rapidly auto-decompose without leaving residues. In this study, the efficacy of O₃ on all life stages of Rhyzopertha dominica (Fabricius) and Tribolium castaneum (Herbst) in barley and the physiological effects on barley and its quality were investigated. Complete control of all life stages of pests was obtained at 700 ppm for 1440 min of ozone exposure without negatively impacting the contents of soluble protein, moisture content, seed colour, hardness, and the weight of thousand barley seeds. The eggs and pupae of these two insects were the more tolerant stages than their larvae and adults. Prolonged exposure times (40 to 1440 min) and mortality assessment intervals (1, 2, and 7 days) increased O₃ efficacy due to the reaction characteristics and delayed toxicity. Aging barley seeds appeared to be more sensitive to prolonged ozone duration than new seeds. A total of 20 and 40 min could promote germination rate, and longer O₃ exposure (1440 min) was unfavourable for germination and seedling growth. Thus, it is imperative to select an optimal O₃ exposure time to transfer ozone into quality contributors of final products and achieve the desired functional outcomes.

Ozone Treatment Increases the Release of VOC from Barley, Which Modifies Seed Germination

Ozone is widely used to control pests in grain and has an impact on seed germination. The germination process involves multiple secondary metabolites, such as volatile organic compounds (VOCs), which are altered under ozone treatment. Here, an optimized solid-phase microextraction coupled with gas chromatography-mass spectrometry was implemented to explore changes in VOCs from barley seeds under ozone treatment. The data demonstrated that barley released both a greater variety and quantity of VOCs under oxidative stress. The number of alcohols and hydrocarbons gradually decreased, whereas aldehydes and organic acids markedly increased with increasing ozone treatment time. Acetic acid was identified as a potential ozone stress-specific marker. Furthermore, the dosage-dependent function of acetic acid on the germination of barley was verified, namely, a low dosage of acetic acid increased the germination and vice versa. This study provided new insights into how barley responds to ozone treatment and highlighted the role of acetic acid in seed germination.

Application of Ozone against the Larvae of Plodia interpunctella (Hübner) and Its Impacts on the Organoleptic Properties of Walnuts

ABSTRACT

One of the most important products grown in Iran is walnut (Juglans regia L.), but it can be threatened by storage pests such as insects. Ozonation is an environmentally friendly method for killing pest insects; accordingly, ozone efficacy in the control of a pest species of walnut, Indian meal moth (Plodia interpunctella (Hübner)), was assessed in this research. The selected walnut samples were infested with larvae of Indian meal moth and then subjected to various combinations of ozone concentration (3, 4.5, and 6 ppm) and exposure time (20, 30, 40, and 50 min). After exposure to the treatment combinations, larval mortality rates and changes to the sensory properties (color, taste, smell, crispness, stiffness, and overall acceptability), indicating consumer preference, of the walnuts were evaluated. Our results revealed enhanced mortality rates of P. interpunctella with an increase in both ozone concentration and exposure time: 99% mortality was recorded at the concentration and exposure time of 6 ppm and 50 min, respectively. Sensory assessments of the samples showed that ozone treatments had no significant impacts on the color, taste, crispness, stiffness, and overall acceptability of the product. Also, few changes were recorded for its smell, which could be improved over time after being exposed to the air. We conclude that application of higher ozone concentrations might provide acceptable levels of insect pest control for stored walnuts with no associated reduced trade-off for their quality attributes.

HIGHLIGHTS

Evaluation of Microwave and Ozone Disinfections on the Color Characteristics of Iranian Export Raisins through an Image Processing Technique

Raisins are one of the most important Iranian export products but are threatened by various storage pests. Because of the disadvantages of fumigants, we evaluated alternative microwave and ozone methods for their disinfection and the side effects on raisin qualities. To perform microwave disinfection, the studied raisin samples were exposed to microwave powers of 450, 720, and 900 W for 20, 30, 40, and 50 s. Also, ozone treatments included various combinations of ozone concentrations (2, 3, and 5 ppm) and exposure times (15, 30, 45, 60, and 90 min). An image processing technique was implemented to determine the color changes of raisins in terms of lightness, redness, yellowness, total color difference, chroma, and hue angle. The results revealed that increasing the microwave power and exposure time might lead to further changes of the previously mentioned color characteristics. Compared with the microwave treatments, ozone treatments had fewer effects on those features. Generally, microwave and ozone methods could successfully disinfect Oryzaephilus surinamensis in raisins, with acceptable changes in all the color characteristics. Hence, the previously mentioned methods are proposed as alternative chemical fumigants.

Ozone Effectiveness on Wheat Weevil Suppression: Preliminary Research

Insect infestations within stored product facilities are a major concern to livestock and human food industries. Insect infestations in storage systems can result in economic losses of up to 20%. Furthermore, the presence of insects and their waste and remains in grain and stored foods may pose a health risk to humans and livestock. At present, pests in commercial storage are managed by a combination of different methods ranging from cleaning and cooling to treatment of the stored material with contact insecticides or fumigation. The availability of pesticides for the treatment of grain and other stored products is decreasing owing, in some cases, to environmental and safety concerns among consumers and society, thus emphasizing the need for alternative eco-friendly pest control methods. One of the potential methods is the use of ozone. Although the mechanism of action of ozone on insects is not completely known, the insect's respiratory system is a likely the target of this gas. The main goal of this investigation was to determine the efficacy of ozone in the suppression of adult wheat weevils Sitophilus granarius. In the experiments conducted, different durations of ozone exposure were tested. In addition to ozone toxicity, the walking response and velocity of wheat weevils were investigated. The results showed the harmful effects of ozone on these insects. In addition to mortality, ozone also had negative effects on insect speed and mobility. The efficiency of the ozone treatment increased with increasing ozone exposure of insects. The ability of ozone to reduce the walking activity and velocity of treated insects is a positive feature in pest control in storage systems, thereby reducing the possibility of insects escaping from treated objects. The results of this investigation suggest that ozone has the potential to become a realistic choice for suppressing harmful insects in storage systems for humans and livestock, either alone or as a complement to other control methods.

Ozone as a Potential Fumigant Alternative for the Management of Sitophilus oryzae (Coleoptera: Curculionidae) in Wheat

Gaseous ozone, an oxidizing agent used as a disinfectant in food processing and preservation, has potential for the control of stored product insects. In this study, we investigated ozone for the management of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), a serious stored product insect pest. We exposed eggs, immature stages within wheat kernels, and adults of the rice weevil to 200-ppm ozone for 12, 24, 36, 48, and 60 h. Insects were placed at 5, 15, or 25 cm depth within a wheat mass in PVC pipes (10 cm in diameter, 30 cm in height) and exposed to ozone. Egg eclosion was recorded 10 d after treatment (DAT), and immature stages were observed for adult emergence 28 DAT. Adults were observed for survival immediately after ozone exposure and again at 1 and 2 DAT. Egg eclosion was significantly lower at 5 cm compared with 25 cm at all exposure times, but not the 12-h exposure time. For each exposure time tested, significantly lesser adults developed from kernels and none of the adults survived at the 5 cm depth compared with the 15 and 25 cm depths. Survival rate of adults was significantly higher at 25 cm depth than at 15 cm depth at the 24-60 h. The deeper the insect in the grain mass, the higher the survival rate. The work reported suggests that ozone is effective in killing all life stages of S. oryzae; however, the efficacy of the gas is dependent on the concentration, exposure time, depth, and gas loss.

Efficacy of Ozone Against the Life Stages of Oryzaephilus mercator (Coleoptera: Silvanidae)

Ozone is a highly oxidizing gas with insecticidal activity and it is a potential alternative to conventional fumigants, such as phosphine and methyl bromide, for managing stored product insects. Susceptibility of the merchant grain beetle, Oryzaephilus mercator (Fauvel; Coleoptera: Silvanidae), an important pest of stored products, to ozone treatments is unknown. In this study, we investigated the efficacy of ozone for controlling O. mercator. We determined concentration-mortality relationships for all stages of O. mercator exposed to 100-400 ppm for 1 h (1 g/m3 = 467 ppm). We also determined time-mortality relationships for adults exposed to 100 ppm for 1-6 h. Mortality was recorded as percentages of eggs that failed to hatch 10 days after treatment (DAT), larvae or pupae that failed to develop into adults 20 or 15 DAT, respectively, and adults that died 2 DAT. Generally, mortality increased with an increase in ozone concentration. Mortality was higher when insects were treated without food. When food was not provided, a minimum of 11030 ppm for 1 h is required to kill 99% of eggs, the most tolerant stage, whereas 500 ppm for 1 h is required to kill 99% of larvae, the least tolerant. When provided with food, adults were the most tolerant and larvae the least tolerant. Adults require exposure time of 7.7 h of 100 ppm ozone to kill 99% of insects in the absence of food. The work reported suggests that ozone could be an alternative fumigant for the management of all O. mercator life stages.

Application of Ozone to Control Dried Fig Pests-Oryzaephilus surinamensis (Coleoptera: Silvanidae) and Ephestia kuehniella (Lepidoptera: Pyralidae)-and Its Organoleptic Properties

Ozone is a powerful oxidant which can be used for killing insects and microorganisms. In this study, ozone was applied in the gaseous form to control two species of pests in stored dried figs. The samples of figs (50 g each) were infested with adults of Oryzaephilus surinamensis L. and larvae of Ephestia kuehniella Zeller and were subjected to different combinations of ozone concentrations (2, 3, and 5 ppm) and exposure times (15, 30, 45, 60, and 90 min). Changes in organoleptic properties (color, sweetness, firmness, aroma, and overall acceptability) during ozonation were studied. The results showed that the mortality rate increased with an increase in ozone concentration and exposure time. The total mortality of both pests was achieved at an ozone concentration of 5 ppm and exposure time of 90 min. Sensory evaluation showed that ozone only had a negligible effect on aroma. Therefore, the usage of ozone is recommended during the postharvest process instead of other chemical fumigants, such as methyl bromide and phosphine.

Efficacy of Ozone against Phosphine Susceptible and Resistant Strains of Four Stored-Product Insect Species

The efficacy of ozone was evaluated against four economically-important stored-product insect species at 27.2 °C and 20.4% r.h. Adults of phosphine-susceptible laboratory strains and phosphine-resistant field strains of the red flour beetle, Tribolium castaneum (Herbst), saw-toothed grain beetle, Oryzaephilus surinamensis (Linnaeus), maize weevil, Sitophilus zeamais Motschulsky, and rice weevil, Sitophilus oryzae (Linnaeus), were exposed in vials to an ozone concentration of 0.42 g/m³ (200 ppm) for 1, 2, 3, 5, 6, 8, 10 and 12 h with 0 and 10 g of wheat. Initial and final mortalities were assessed 1 and 5 d after exposure to ozone, respectively. After an 8–12-h exposure to ozone, initial mortality of Sitophilus spp. and O. surinamensis was 100%, whereas the highest initial mortality of T. castaneum was 90%. A 3–4-h exposure to ozone resulted in 100% final mortality of Sitophilus spp., whereas O. surinamensis required a 6- to 10-h exposure to ozone. Adults of T. castaneum were least susceptible to ozone, and after a 10-h exposure, mortality ranged between 82 and 95%. Time for the 5 d 99% mortality (LT₉₉) for adults of laboratory and field strains of Sitophilus spp., O. surinamensis and T. castaneum were 2.00–5.56, 4.33–11.18 and 14.35–29.89 h, respectively. The LT₉₉ values for adults of T. castaneum and O. surinamensis were not significantly different between bioassays conducted with 0 and 10 g of wheat. The LT₉₉ values for the laboratory strains of Sitophilus spp. in the absence of wheat were significantly lower than those obtained in the presence of wheat. Both phosphine-susceptible and -resistant strains were equally susceptible to ozone. Ozone effectively suppressed adult progeny production of all four species. Ozone is a viable alternative fumigant to control phosphine-resistant strains of these four species.

Effectiveness of Sulfuryl Fluoride Fumigation for the Control of Phosphine-Resistant Grain Insects Infesting Stored Wheat

A field experiment was conducted in eight 13.6-MT steel bins containing 6.8 MT each of wheat to assess efficacy of sulfuryl fluoride or SF fumigant to control phosphine-resistant and susceptible Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst). Approximately 400 adults of each type of beetle were added to each bin. Additionally, muslin bags containing immature stages and adults, with their respective diets, were also placed in bins. Four bins were fumigated with SF and others were untreated control bins. The SF dosages in treated bins ranged from 1,196–1,467 mg-h/liter. Mortality of adults in each bag was assessed 5 d postfumigation; diet minus adults was incubated in a jar, and number of adults counted after 8 wk. No significant change occurred in number of insect-damaged kernels in SF-treated bins. In trier samples from SF-treated bins, R. dominica numbers declined from 24 prefumigation to 0 at 3- and 6-wk postfumigation; T. castaneum numbers were unchanged. In WBII traps from SF-treated bins, numbers R. dominica and T. castaneum declined from 25 and 33, respectively, prefumigation to 0 or near 0 at 3- and 6-wk postfumigation. Mortalities of resistant and susceptible adult R. dominica, and adult and large larvae of T. castaneum in SF-treated bags was 100%. For all four types of beetles, adult numbers in jars associated with SF-treated bins were 0 or near 0. Results show SF is effective against all life stages of phosphine-resistant R. dominica and T. castaneum, and can be used for phosphine resistance management.

Oxidative stress induced by chlorine dioxide as an insecticidal factor to the Indian meal moth, Plodia interpunctella

A novel fumigant, chlorine dioxide (ClO2) is a commercial bleaching and disinfection agent. Recent study indicates its insecticidal activity. However, its mode of action to kill insects is yet to be understood. This study set up a hypothesis that an oxidative stress induced by ClO2 is a main factor to kill insects. The Indian meal moth, Plodia interpunctella, is a lepidopteran insect pest infesting various stored grains. Larvae of P. interpunctella were highly susceptible to ClO2 gas, which exhibited an acute toxicity. Physiological damages by ClO2 were observed in hemocytes. At high doses, the larvae of P. interpunctella suffered significant reduction of total hemocytes. At low doses, ClO2 impaired hemocyte behaviors. The cytotoxicity of ClO2 was further analyzed using two insect cell lines, where Sf9 cells were more susceptible to ClO2 than High Five cells. The cells treated with ClO2 produced reactive oxygen species (ROS). The produced ROS amounts increased with an increase of the treated ClO2 amount. However, the addition of an antioxidant, vitamin E, significantly attenuated the cytotoxicity of ClO2 in a dose-dependent manner. To support the oxidative stress induced by ClO2, two antioxidant genes (superoxide dismutase (SOD) and thioredoxin-peroxidase (Tpx)) were identified from P. interpunctella EST library using ortholog sequences of Bombyx mori. Both SOD and Tpx were expressed in larvae of P. interpunctella especially under oxidative stress induced by bacterial challenge. Exposure to ClO2 gas significantly induced the gene expression of both SOD and Tpx. RNA interference of SOD or Tpx using specific double stranded RNAs significantly enhanced the lethality of P. interpunctella to ClO2 gas treatment as well as to the bacterial challenge. These results suggest that ClO2 induces the production of insecticidal ROS, which results in a fatal oxidative stress in P. interpunctella.

Comparative efficacy of CO2 and ozone gases against Ephestia cautella (Lepidoptera: Pyralidae) larvae under different temperature regimes

Comparative efficacy of three different modified atmospheres: 100% CO2, 75% CO2 + 25% N2, and 22 ppm ozone were examined against larval mortality of the almond moth, Ephestia cautella (Walker) (Lepidoptera: Pyralidae) at temperature regimes of 25°C and 35 ± 2°C and 60 ± 5% relative humidity, and 9:15 dark and light. Wandering young larval instars, which are fast growing, large enough in size and considered as more tolerant to modified atmosphere, were collected directly from the rearing culture, placed inside pitted date fruits of vars.: "Khudri," "Ruziz," and "Saqie," were treated with aforementioned gases for 24, 48, and 72 h. The immediate and delayed larval mortality was recorded after each exposure timing. Ozone possessed the strongest fumigant toxicity causing 100% mortality with all varieties, at 25 and 35°C after 24 h exposure and was more effective than 75% CO2 that caused 83 and 100% immediate mortality with variety ruziz at 25 and 35°C, respectively. Extending the treatments exposure time to 72 h, 100% mortality was recorded by exposing larvae to any of the studied gases at 25 and 35°C. These results suggest that gases and temperature used in this study can be effectively used to control E. cautella in dates and stored grains.

Efficacy of Methyl Bromide for Control of Different Life Stages of Stored-Product Psocids

The psocid species Liposcelis paeta Pearman, Liposcelis entomophila (Enderlein), Liposcelis decolor (Pearman), Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae), and Lepinotus reticulatus Enderlein (Psocoptera: Trogiidae) were evaluated in laboratory bioassays to determine their susceptibility to six concentrations of methyl bromide (0.027, 0.113, 0.280, 0.393, 0.452, and 0.616 g/m3) after 48 h of exposure at 27.5°C. The life stages that were evaluated were adults (for all species), nymphs (for all species except Lep. reticulatus), and eggs (for L. entomophila, L. decolor, and L. bostrychophila). Adults and nymphs were very susceptible, and complete mortality was recorded at concentrations between 0.027 and 0.280 g/m3. In contrast, eggs were by far more tolerant than adults and nymphs for all species tested. At 0.027 g/m3, mortality did not exceed 53%, while survival was high even at 0.113 g/m3. Complete (100%) egg mortality was recorded at 0.393 g/m3 for L. decolor and at 0.452 g/m3 for L. entomophila and L. bostrychophila; concentrations estimated to give 99% mortality for eggs of these three species were 0.710, 1.044, and 0.891 g/m3, respectively. These results show that stored-product psocids are susceptible to methyl bromide, but concentrations of ≥0.452 g/m3 should be used to control all life stages.

Biology and management of psocids infesting stored products

Previously regarded as minor nuisance pests, psocids belonging to the genus Liposcelis now pose a major problem for the effective protection of stored products worldwide. Here we examine the apparent biological and operational reasons behind this phenomenon and why conventional pest management seems to be failing. We investigate what is known about the biology, behavior, and population dynamics of major pest species to ascertain their strengths, and perhaps find weaknesses, as a basis for a rational pest management strategy. We outline the contribution of molecular techniques to clarifying species identification and understanding genetic diversity. We discuss progress in sampling and trapping and our comprehension of spatial distribution of these pests as a foundation for developing management strategies. The effectiveness of various chemical treatments and the availability and potential of nonchemical control methods are critically examined. Finally, we identify research gaps and suggest future directions for research.

Lethal doses of ozone for control of all stages of internal and external feeders in stored products

BACKGROUND

Gaseous ozone (O(3)) has potential for control of insects in stored grain. Previous studies have focused on freely exposed insects. Immatures of internal pests (e.g. Sitophilus spp. and most stages of Rhyzopertha dominica F.) are protected within kernels and probably require higher doses and/or longer treatment times for full control. A laboratory study determined the doses of ozone necessary for full control of freely exposed and internal stages of eleven stored-product pest species. Test insects were three species of Sitophilus, R. dominica, Tribolium confusum Jacquelin du Val, T. castaneum Herbst, Plodia interpunctella Hübner, Sitotroga cerealella Olivier, Oryzaephilus surinamensis L., Ephestia kuehniella Zeller and Stegobium paniceum L. Insects were exposed to continuous flows of ozone in doses of 10-135 ppm and exposure times of 5-8 days. Dose-mortality bioassays were conducted on three species of Sitophilus and P. interpunctella.

RESULTS

Freely exposed stages (with a few exceptions) were controlled with 35 ppm of ozone for 6 days. Full mortality of internal stages within kernels required exposure to 135 ppm for 8 days.

CONCLUSION

This study confirms that higher doses and/or longer treatment times are necessary for control of internal stages of stored-product pests.