Postharvest fumigation of California table grapes with ozone to control Western black widow spider (Araneae: Theridiidae)

•Fumigation with ≥14gm−3 ozone for 1h at 3°C controls Latrodectus hesperus.•Elevated levels of carbon dioxide did not increase treatment efficacy.•This treatment could be used to export table grapes from California. Ozone fumigations were evaluated for postharvest control of Western black widow spider (BWS), Latrodectus hesperus (Chamberlin and Ivie), in fresh table grapes destined for export from California USA. Mature adult female black widow spiders were contained in separate gas-permeable cages within a flow-through vacuum chamber and exposed for 1h at 3±1°C (x¯±s) and 67.5kPa to gaseous ozone at eight steady-state concentrations (i.e, [O3]ss) over the range 0.71±0.04–16.91±0.28gm−3 (x¯±s) (i.e., 500±25–12,000±200ppmv (μLL−1)) with or without supplementation of atmospheric carbon dioxide levels, respectively 129.3 or ca. 0.8gm−3 [CO2]ss (i.e., 100,000 or ca. 600ppmv). Regression models of the concentration-mortality response predict 98% mortality of adult female BWS populations following ozone fumigation for 1h at 3±1°C when headspace [O3]ss is maintained at ∼14gm−3 (i.e., 10,000ppmv) with ambient atmospheric CO2 levels ([CO2]ss=0.8gm−3). Providing evidence to support the use of these treatment parameters for control of BWS in packed table grapes, 0 survivors were observed from 268 total specimens treated in a series of confirmatory fumigations conducted for 1h at 3±1°C and 67.5kPa with headspace [O3]ss and [CO2]ss maintained ≥14 and ca. 0.8gm−3, respectively.