AbstractThe effect of phosphine at exposure periods of 24, 48 and 120 h on hatching and mortality of 0‐ to 1‐day‐old eggs of susceptible (TN6) and resistant (FC10) strains of Rhyzopertha dominica of field origin was investigated. The fumigant affected hatching in both the strains. In a 48‐h exposure at 27 (± 2) °C, the LD99 doses for the eggs of TN6 and FC10 were 0.56 and 3.25 mg litre−1, respectively. Significant reduction in hatching was observed in treated batches with progressive increase of phosphine dose in the first 2–3 days. On subsequent days the numbers hatching were often similar to those in controls, and sometimes exceeded control hatch, especially following a 5‐day exposure. A critical change in the order of susceptibility of egg and adult stages of the two strains was noticed. In 48‐h exposures, eggs of the susceptible strain were more tolerant than their adults, whilst the reverse was true in the resistant strain.© 2001 Society of Chemical Industry