Toxicological studies of phosphine against the lesser grain borer, Rhyzopertha dominica (Fabr.) (Coleoptera Bostrychidae)

Abstract

The toxicity of phosphine (hydrogen phosphide, PH3) has been determined on the adults of R. dominica (Fabr.) at different temperatures (10, 20 and 30°C) over a wide range of concentrations at different periods of exposure (4-96 hours). The efficiency of phosphine against the adult beetles was less toxic as the temperature was decreased from 30 to 10°C. The rate of decrease in concentration with an increase in exposure period to achieve a fixed level of mortality (50% and 95%), was much more rapid between 4 to 48 h than between 48 to 96 h exposures. The rate of increase in both Lc.t. 50 and 95 values (Lethal concentration-time product) with increasing the period of exposure varied at the tested temperature, especially at shorter periods of exposure. This indicates that the relationship between the c.t.~product and mortality varied with these factors acting either single or in double and triple interactions.