The tolerance of developmental stages of four stored product moths to phosphine

The tolerance to phosphine of different stages of Ephestia elutella, E. kuehniella, E. cautella and Plodia interpunctella was followed closely at 10–30°C. Eggs of all species were highly tolerant for the first 30–45% of the developmental period, but all other stages were much more susceptible. Maximum exposure periods permitting some survival over a practical range of concentrations were 1 day at 30°C, 2 days at 25°C, 3–4 days at 20°C, and 5–8 days at 15°C. Some eggs of E. elutella survived the very high CT products of 142 mg h/l. in a 2-day exposure at 25°C, and 288 mg h/l. in an 8-day exposure at 15°C. In a 3-day exposure at 25°C, and a 9-day exposure at 15°C, CT products of about 4 and 20 mg h/l. respectively were sufficient for complete control of all species. Eggs of P. interpunctella were susceptible to low temperature and survived exposures to phosphine at 15°C less well than other species. Survivors from fumigated eggs were of normal fertility.Although much less tolerant than eggs, younger pupae, especially those of E. kuehniella, were more tolerant than larvae or older pupae. The fertility of adults of normal weight emerging from surviving pupae was markedly depressed.In most fumigation experiments, differences in tolerance between laboratory and wild stocks were small. However, wild stocks tended to be more tolerant of cold than laboratory stocks, and survived fumigation better in long exposures at lower temperatures.