Postharvest quarantine treatments for Drosophila suzukii in fresh fruit

Authors: Walse, Spencer; Cha, Dong; LEE, B - Gyeongsang National University; Follett, Peter

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/13/2020
Publication Date: 12/6/2021
Citation: Walse, S.S., Cha, D.H., Lee, B.Y., Follett, P.A. 2021. Postharvest quarantine treatments for Drosophila suzukii in fresh fruit. In: Garcia, F.R.M, editor. Drosophila suzukii Management. Cham, Switzerland: Springer. p. 255-267. https://doi.org/10.1007/978-3-030-62692-1_13.
DOI: https://doi.org/10.1007/978-3-030-62692-1_13

Interpretive Summary: Post harvest treatment of certain fresh fruits e.g. table grapes, blueberries, strawberries, may be required before export to foreign countries (esp. Australia, New Zealand) to control the quarantine pest Drosophila suzukii, a.k.a. spotted wing drosophila, and prevent its movement to new areas. Fumigation with methyl bromide is commonly used, but other treatments such as ethyl formate and phosphine fumigation, and irradiation and cold treatment have potential. Existing and future treatment protocols for export of D. suzukii-infested fruits are described and discussed.

Technical Abstract: Certain countries have imposed restrictions on the trade of fresh fruit due to possible infestation by spotted wing drosophila, Drosophila suzukii (Diptera: Drosophilidae). A stand-alone postharvest treatment is often the simplest means to overcome an insect-related trade barrier, and several options are available that provide quarantine security against D. suzukii. With respect to stand-alone postharvest fumigation, efficacious parameters for methyl bromide, phosphine, and ethyl formate have been published. The general relationship between methyl bromide concentration (C), fumigation duration (t), and efficacy toward 2nd and 3rd instar larvae, the most methyl bromide-tolerant life stages, has been established across pulp temperature (T ) 8 to 16 'C , and in fact, exacted for numerous fruits (e.g., strawberries, blueberries, cane berries, cherries, stone fruit, oranges, and table grapes) when C < 80 g m-3 and t < 4 h. The efficacy of phosphine does not typically vary as a function of fruit or packaging type since the fumigation durations are relatively long, lasting many hours to days, thereby requiring refrigeration of fruit during treatment, at least in most cases. Maintaining phosphine C > 0.4 g m-3 (250 ppmv) and < 1.5 g m-3 (1000 ppmv) for 36 and 60 h, respectively, at T = 5 and 0.5 'C results in control of eggs, the most phosphine-tolerant life stage. Ethyl formate fumigation is a relatively new and safe postharvest fumigant that sorbs quickly into fresh fruit, hydrolyzing rapidly into formic acid and ethanol. The balance between sorption and efficacy as a function of T is currently under investigation and preliminary studies involving blueberries indicate that eggs, which are located on the periphery of the fruit, are the most ethyl formate-tolerant life stage. Cold treatments have been developed for peaches, nectarines, citrus, and table grapes from California USA with durations lasting 12 to 14 d at T of ca. < 1 'C. In irradiation studies, the late stage pupa was the most radio-tolerant stage that occurs in fruit and a radiation dose of 80 Gy applied to >33,000 late stage pupae in sweet cherries or grapes resulted in no production of F1 adults. Systems approaches combining multiple postharvest treatments have also been implemented, primarily in the context of reducing time and dosage requirements of the stand-alone treatments as well as harnessing control measure intrinsic to the commercial marketing of fruit (e.g., packing-line sorting, fungicide application, in transit cold storage, etc.). The inclusion of preharvest and/or biological factors as components of a systems approach have been directed toward establishing “conditional host” or “non-host” status of the fruit. The phytosanitary approaches cited above must be compliant with the regulations at the location of treatment and, as is the case for any phytosanitary treatment proposed for international trade, approval is the discretion of the importing country based on risk assessments and other regulatory considerations (e.g., residue tolerances, consumer exposure, environmental health).