Curing Raisins with Sulfur Dioxide Suppresses Population Growth of Indian Meal Moth, Plodia Interpunctella (hubner) (lepidoptera: Pyralidae)

A sulfur dioxide treatment is often used to preserve the color and flavor of raisins. We used a life table approach to examine the effects of residual sulfites on Plodia interpunctella (Hubner) when larvae fed on raisins under controlled laboratory conditions. Raisins were fumigated with 66 g/m3 or 133 g/m3 SO2 for either three or six hours, or received no SO2 exposure (control). A two sex life table was constructed for insects in each treatment (n = 70 per treatment). Total immature mortality exceeded 90% in 66 g/m3 SO2 treatments, and 80% in 133 g/m3 SO2 treatments, compared to 28.6% in controls. Sulfur dioxide treatments significantly extended developmental time relative to controls, again more so in the 66 g/m3 SO2 treatments than in the 133 g/m3 treatments, but did not affect the adult longevity of survivors. All SO2 treatments reduced the fecundity of surviving female moths to a small fraction of controls, without significant differences among them. These effects combined to result in significantly diminished life table parameters in all treatments relative to controls, although generation times were increased more in the 66 g/m3 SO2 treatments than in the 133 g/m3 treatments. These inverse dosage-dependent effects may reflect increased feeding avoidance of sulfite residues in the higher dose treatments that resulted in reduced consumption. We conclude that residual sulfur and sulfites deposited on fruit surfaces during SO2 treatment provide substantial control of P. interpunctella, and should effectively suppress the proliferation of moths within bulk stores of dried raisins.