Toxicity of Propylene Oxide Alone and Combined with Low Pressure or Carbon Dioxide on the Life Stages of Plodia interpunctella Hübner (Pyralidae: Lepidoptera)

The primary objective of this research was to explore the viability of employing propylene oxide (PO) as an alternative fumigant to methyl bromide for effectively and rapidly controlling Plodia interpunctella infestations. To this end, laboratory bioassays were carried out to determine the toxicity levels—Lethal Concentration50 (LC50) and Lethal Concentration90 (LC90)—of PO under three conditions: normal pressure (PO alone), low pressure of 100 mm Hg (PO + vacuum), and in the presence of 92% CO2 (PO + CO2) against all developmental stages of P. interpunctella (eggs, larvae, pupae, and adults) for short exposure time (4 hours). The results of the lethal concentration tests indicated that the most toxic treatment against all biological stages of P. interpunctella was the combination of PO and vacuum, followed by the PO + CO2 combination and PO alone treatment. Compared to the toxicity values with PO alone treated, there was a significant reduction in LC90 values ranging from 2.07 to 4.04 times for all biological stages of P. interpunctella when PO was treated under vacuum. In the case of the PO+CO2 combination, there was also a notable decrease in LC90 values ranging from 1.24 to 1.95 times. Toxicity data revealed a significantly higher reduction in LC90 values with the PO + vacuum compared to PO+CO2 treatment and suggests a synergistic effect of the combination of PO with 100 mm Hg vacuum and 92% CO2 on biological stages of P. interpunctella. According to the results of lethal concentration tests, it was determined that PO showed different toxicity against the life stages of P. interpunctella. As a result of the study, in general, P. interpunctella larvae and pupae were the most resistant to PO alone, PO + vacuum, and PO + CO2 treatments, while P. interpunctella adults and eggs were the most sensitive. When exposed to PO alone for 4 hours, the order of tolerance between life stages at LC90 was found to be pupa > larva > adult > egg. The results of the study revealed that PO could be a promising alternative fumigant for rapid control of insect contamination. However, further research and testing in real-storage conditions will be essential to validate the practical viability of implementing PO-based fumigation on a larger scale.