South Carolina State University researchers have found that ozone treatment could be an alternative for managing all life stages of select stored-product insect pests. Hence, there could be a reduction in the use of other chemicals and, therefore, a reduction in the environmental and health issues associated with these chemicals.
Stored-product insects cause millions of dollars of losses annually to stored-durable commodities such as grain, grain-based products, legumes, dried fruits, nuts and spices. In general, insect infestations in bulk grain are managed using fumigants and contact insecticides.
Methyl Bromide Ban Triggers Search for Alternatives
The search for alternative control options has become necessary because of the ban of methyl bromide, the most effective fumigant once used to control stored-product insect pests. Phosphine fumigation is another method to control stored-product insects, but its continuous and indiscriminate use has resulted in the evolution of resistant populations and control failures. Therefore, the food and feed industries are constantly looking for effective pest management alternatives, especially those that are environmentally benign.
Ozone application is currently attracting the attention of scientists because of its inherent advantages in controlling insects and molds associated with grain. Ozone is a toxic gas that has proven to kill insects effectively and degrade rapidly to molecular oxygen in atmospheric conditions. Therefore, ozone can be safely and effectively used in food processing industries to disinfest insect infestations.
For the reporting period, the NIFA-funded project led by Dr. Rizana Mahroof, who now is the National Program Leader with NIFA’s Division of Community and Education, focused on the effects of ozone on two stored-product insect pests of economic importance. These are the red flour beetle and the Indian meal moth.
Previously, the study evaluated the dose-time-response requirements for the most tolerant life stage of these insects. Various ozone concentrations and different exposure times were tested on eggs, larvae, pupae and adults of these two species. Based on these data, further, the experiments were built on testing the most tolerant life stage. For both species, results showed eggs were hard to kill.
As a follow-up study, five construction surface materials were selected to expose the eggs of the red flour beetle and the Indian meal moth on such surface materials to test the effectiveness of ozone on various surfaces on the most tolerant life stage.
This project, which was supported by NIFA’s 1890 Capacity Grants Program, indicated that ozone might be required in high concentrations, and insects may have to be exposed to the gas for a significant amount of time to cause a substantial mortality rate in the insects. Studies also showed that susceptibility to ozone varies based on the life stage of a particular insect. Some stages are relatively easy to kill while others are not.
Variability in Egg Susceptibility to Ozone Gas Depends on Several Factors
Overall, the study has shown that variability in egg susceptibility to ozone gas depends on the dose, exposure time, species and presence or absence of food during the treatment. The study also showed common construction materials used in grain bins, mill equipment and processing and storage plants absorb insignificant proposition of the ozone gas, allowing ozone to be used in these facilities.
It is essential to identify tolerance levels for all species of stored-product insects to establish industry guidelines for treatment. The efficacy of ozone gas may vary depending on the packaging materials where the value-added products are packaged. Therefore, further studies are needed to evaluate the susceptibility of insects to gaseous ozone, those that were not studied previously and the characteristic flow and penetration of ozone through various packaging materials.
Whether the food was present or absent in the testing arena, eggs exposed to ozone failed to hatch compared to corresponding controls. Treated surfaces did not influence ozone toxicity, and the percentage of mortality remained high and above 95% for all surfaces. This study showed construction materials made of aluminum, wood, concrete, vinyl, or glass behave similarly in reacting to ozone. These surfaces do not absorb a significant proportion of the gas, leaving the ozone to react with the insects.
This story originally appeared in ARD Updates and is reprinted with permission.
Photo: Dr. Rizana Mahroof, left, demonstrates how to sort male and female pupae of the red flour beetle. Photo courtesy of ARD Updates and South Carolina State University.