Strawberry fruit, western flower thrips and two-spotted spider mites were exposed to a range of ethyl formate (EF) concentrations from 0.8 to 2.4%. Ethyl formate treatments included both single and multiple applications of EF, the multiple applications having a venting period between each application. Additionally, target pests were exposed to EF and elevated levels of CO 2 from 5 to 95 kPa, balance air to total 101 kPa. Exposure to EF resulted in significant mortality for western flower thrips; however, complete control was achieved only in the treatments with the highest cumulative exposures, multiple applications of 0.8% or 2.4% EF. Two-spotted spider mites were less susceptible to EF with the most effective treatment, 2.4% EF, resulting in 66% mortality. Low levels of CO 2 (5 kPa or 10 kPa) combined with 1.3% EF significantly increased two-spotted spider mite mortality, however, levels of CO 2 ≥20 kPa significantly decreased mite mortality compared to treatments with EF in air. There was no significant difference in mortality for western flower thrips exposed to 0.8% EF in the presence of CO 2 at 5, 10, 20, and 40 kPa when compared to 0.8% EF in air. Treatment with 0.3% EF with ≥40 kPa CO 2 resulted in significantly decreased western flower thrips mortality compared with that of 0.3% EF in air. However, for 0.8% EF, western flower thrips mortality only declined in an atmosphere of ≥80 kPa CO 2 . There was no significant difference in strawberry condition between treated and untreated fruit, however increased levels of acetaldehyde, ethanol, ethyl acetate and EF were detected in fruit exposed to EF. In two separate experiments, strawberry fruit showed calyx damage in fruit exposed to concentrations of 0.8% or 1.6% EF, respectively.
The postharvest control of arthropod pests is a challenge that the California citrus industry must overcome when exporting fruit overseas. Currently, methyl bromide fumigation is used to control postharvest pests on exported citrus, but it may soon be unavailable because of use restrictions and cost of this health-hazard ozone-depleting chemical. Ethyl formate is a natural plant volatile and possible alternative to methyl bromide in postharvest insect control. The objectives of this study were 1) to evaluate the mortality of third instar California red scale [Aonidiella aurantii (Maskell)] (Hemiptera: Diaspididae) and adult western flower thrips [Frankliniella occidentalis (Pergande)] (Thysanoptera: Thripidae) under a wide range of ethyl formate concentrations, 2) to determine the ethyl formate concentration required to reach a Probit 9 level of control for both pests, and 3) to test the effects of ethyl formate fumigation on the quality of navel oranges [Citrus sinensis (L.) Osbeck] and lemons [Citrus limon (L.) Burman f.] at 24 h after fumigation, and at different time periods to simulate shipping plus storage (5 wk at 5 degrees C), and shipping, storage, handling, and shelf-life (5 wk at 5 degrees C, plus 5 d at 15 degrees C, and 2 d at 20 degrees C). The results indicate that ethyl formate is a promising alternative to methyl bromide for the California citrus industry, because of successful control of adult western flower thips and third instar California red scale and no deleterious effect on fruit quality at any of the evaluated periods and quality parameters.
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