Values of LC50, LC90 and LC99,9 of phosphine generated from PHOSTOXINRpellets for
third instar larvae and pupae of Sitotroga cerealella at 20 and 28°C for fixed exposure periods
of 2, 4, 8, 24, 48 and 72 h were determined and presented.
It was found that the values of the lethal concentrations of phosphine considerably
decreased with increasing exposure periods. The gas was less effective at short exposure
periods (2—8 h) than at long exposure ones (24—72 h).
The CT-product required at a given exposure time for 50 or 90 % kill of the insect stages
was greater at 20 than at 28°C. Pupae of S. cerealella were more tolerant to phosphine than
larvae.
Various carbon dioxide concentrations (20, 50, 78 %) applied alone showed a negligible
effect on larval and a slight effect on pupal mortalities at short exposure periods, but the
mortalities resulting at longer exposure times (24-72 h) were found between 4—60 % at the two
test temperatures.
Larval mortalities obtained from mixtures of the LC50 of PH3 + CO2 were significantly
higher than those of each gas alone, whereby a synergistic action was proved for all exposure
periods at 20°C and 28°C.
An increase in pupal mortalities was achieved at all exposure periods with exception of 8 h at
20°C, and an independent joint action was found at short and long exposures at 28°C.