The toxicity of phosphine with an emphasis on the relative importance of concentration and exposure time was studied by exposing 4th instar larvae of Trogoderma granarium to a constant dose (Ct product) of phosphine with changing in its variables i.e. concentration and exposure period. The dose was determined on the basis of preliminary bioassay test and the dose which caused about 50% mortality was selected. The data from toxicological study revealed that the mortality was the lowest at the minimum exposure time (6 hrs) with the highest concentration (1.536 mg/l). The mortality was significantly increased with an increase in exposure time up to 36 hrs and found non-significant above the same. Thus, it could be concluded that exposure time is more important in the toxicity of phosphine against T. granarium and a minimum of 36 hrs of exposure period is needed to achieve a specified level of response with the same dose.
Bioassay, Exposure period, Phosphine, Trogoderma granarium.
