The action of phosphine against the eggs of phosphine-resistant and -susceptible strains of Rhyzopertha dominica F

The 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)degreesC, 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 observ ed in treated batches with progressive increase of phosphine dose in the fi rst 2-3 days. On subsequent days the numbers hatching were often similar to those in controls, and sometimes exceeded control hatch, especially follow ing a 5-day exposure. A critical change in the order of susceptibility of e gg 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. (C) 2001 Society of Chemical Ind ustry.