Deliquescence‐induced release of ethyl formate and chlorine dioxide from their precursors‐loaded sachets for in‐package fumigation of spotted wing drosophila (Drosophila suzukii Matsumura)

Abstract

AbstractThe toxicity and environmental concerns of methyl bromide (MB) have been a significant impetus for research into environmentally benign fumigant alternatives. Ethyl formate (EF) and chlorine dioxide (ClO2) are FDA‐approved agents with potential as alternatives to MB. However, both are chemically unstable and pose considerable end‐use challenges. In this study, we developed moisture‐activated sachets for EF and ClO2 to facilitate their end‐use deployment for in‐package fumigation. The sachets were loaded with EF or ClO2 metastable precursors, citric acid (CA), and a deliquescent salt carrier (e.g., CaCl2 or NaCl). When placed in an elevated relative humidity environment, these combinations activate the release of EF or ClO2 gases, separately. The deliquescence lowering phenomenon and its effect on fumigants release rate were investigated when mixing CA with CaCl2 or NaCl. The mutual deliquescence relative humidity for CA–CaCl2 and CA–NaCl mixtures were 40% and 63%, respectively. CaCl2 enhanced the release rate of fumigants from their sachets, whereas NaCl resulted in a slower release rate. EF and ClO2 sachets were evaluated for fumigation of different life stages of spotted wing drosophila (SWD). Complete control of SWD adults was achieved after exposure to 10.1 mg·h/L EF, while eggs, larval, and pupal stages were more tolerant toward EF vapour and required 110.2 mg·h/L EF to achieve control. ClO2 at low concentrations was more effective than EF against all SWD life stages, excluding pupae. Complete mortality was achieved after fumigating SWD adults, eggs, and larvae with 0.73, 2.39, and 1.21 mg·h/L ClO2, respectively. These results indicated that both EF and ClO2 sachets could be employed safely for EF and ClO2 in‐packaging fumigation to control produce pests.