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)

The 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.