Evaluating the feasibility of ethyl formate fumigation as a stand-alone phytosanitary treatment of Bactrocera dorsalis (Diptera: Tephritidae) in mandarin fruit

Abstract

Oriental fruit fly, Bactrocera dorsalis, is one of the most destructive quarantine pests of fruits and vegetables, with increasing incursions reported worldwide. During a B. dorsalis outbreak, all fruits and potential host materials within the quarantine area are destroyed to prevent further spread. As a first step toward developing an emergency treatment to allow fruit movement from a B. dorsalis quarantine area, we evaluated the feasibility of using ethyl formate (EF) fumigation as a stand-alone phytosanitary treatment against B. dorsalis. In EF efficacy trials with B. dorsalis eggs and larvae in the absence of fruit (naked conditions), eggs were the most tolerant life stage, with LCt99 values—lethal concentration × time products that cause 99 % mortality—of 716.9 and 1,271.0 g h/m3 at 20 and 4 °C, respectively, followed by first and third instar larvae. When B. dorsalis were artificially inoculated into mandarin fruit, significantly greater EF doses were necessary to control B. dorsalis inside fruit, with the LCt99 values for eggs increased to 1,606.0 and 1,761.0 at 20 and 4 °C, respectively. Although these calculated EF doses were effective against B. dorsalis, they caused significant damage to quality of mandarins, including reduced sugar content and increased fruit decay. These findings indicate that EF fumigation alone is not a feasible stand-alone treatment for disinfesting B. dorsalis in mandarins. We discuss future research directions aimed at maintaining treatment efficacy while minimizing fruit damage by combining EF fumigation with other phytosanitary treatments.