Postharvest Fumigation of Fresh Citrus with Cylinderized Phosphine to Control Bean Thrips (Thysanoptera: Thripidae)

Bean thrips (BT), <i>Caliothrips fasciatus</i> (Pergande), is a pest of concern to certain countries that import fresh citrus fruit from California, USA. A series of laboratory-scale exploratory fumigations with phosphine at 4.9 ± 0.3 °C (mean ± 2 SD; <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mi>x</mi><mo>¯</mo></mover><mo>±</mo><mn>2</mn><mi>s</mi></mrow></semantics></math></inline-formula>) were conducted to evaluate the postharvest control of adult BT. Models of the duration–mortality response predicted ca. 99% mortality of BT populations when headspace concentrations of phosphine, [PH₃], are maintained at levels ≥0.4 g m⁻³ (250 ppmv (µL L⁻¹)) and ≤1.5 g m⁻³ (1000 ppmv (µL L⁻¹)) for 12 h, with the duration representing the lower bound of the 95% confidence level (CL). Confirmatory fumigations, each lasting 12 h, were then conducted using BT-infested sweet oranges, <i>Citrus sinensis</i> (L.), at pulp temperature (<i>T</i>) ≤ 5 °C to corroborate the exploratory results. Three formulations of cylinderized phosphine were used: 1.6% phosphine by volume in nitrogen, VAPORPH3OS^®, and ECOFUME^®, all applied at two levels, ca. 1.5 g m⁻³ (1000 ppmv (µL L⁻¹)), as well as 0.5 g m⁻³ (300 ppmv (µL L⁻¹)). Collectively, across the formulations, an applied dose of ca. 1.5 g m⁻³ (1000 ppmv (µL L⁻¹)) resulted in 0 survivors from 38,993 (probit 8.60, 95% CL; probit 9, 72% CL) treated BT, while an applied dose of 0.5 g m⁻³ (300 ppmv (µL L⁻¹)) resulted in 0 survivors from 31,204 (probit 8.56, 95% CL; probit 9, 70% CL) treated BT. Results were discussed in the context of commercial and operational features of quarantine and pre-shipment (QPS) uses of phosphine to treat fresh fruit and, specifically, the control of BT in fresh citrus exported from California, USA, to Australia.