Phosphine Susceptibility of Adult Megaselia scalaris (Loew) (Diptera: Phoridae)

Summary Megaselia scalaris (Loew) (Diptera: Phoridae) is a synanthropic fly that lives in a wide range of warmer regions globally. Although it is listed as a quarantine pest in the Eurasian Economic Union, phytosanitary protocols have not been established. The larva feeds on moist food material and cannot grow on dry matter, including cured tobacco. However, adults of this species have been detected in containers containing tobacco in Russian ports. In this study, difference in susceptibility to phosphine between developmental stages and the lethal effect of phosphine on adults was evaluated. Fortunately, the adult which is the potential contaminable stage in tobacco was demonstrated to be the least tolerant. The phosphine concentrations to achieve probit 9 mortality (≈LC99.9968) for adult flies were calculated to be 636.2 ppm at 15 °C, 565.9 ppm at 20 °C, and 280.1 ppm at 25 °C with 6 h of exposure. The concentration × time products (Ct, ppm·d), the cumulative exposure to the fumigant, at respective temperatures were calculated as 159.1 ppm·d at 15 °C, 141.5 ppm·d at 20 °C, and 70.0 ppm·d at 25 °C, which are much lower than those recommended for the control of insect pests of cured tobacco leaves by CORESTA (Cooperation Centre for Scientific Research Relative to Tobacco). These are 1800 ppm·d (300 ppm × 6 d) at 16–20 °C and 800 ppm·d (200 ppm × 4 d) at temperatures higher than 20 °C. The results suggest that the standard fumigation protocol for stored tobacco will be adequate to control adult M. scalaris. The probit 9 values obtained in this study can be further utilized for the development of phosphine-based quarantine and preshipment treatments for this species.