Toxicity of phosphine on the developmental stages of rust-red flour beetle, Tribolium castaneum Herbst over a range of concentrations and exposures

The susceptibility of the developmental stages of
rust-red flour beetle, Tribolium castaneum to a range of concentrations
of phosphine over varying durations from 24 to
168 h was reconnoitered in the laboratory at 25±2 °C.
Responses of the life stages exposed to phosphine were compared
with those of un-treated controls over 24, 48, 72, 96,
120, 144 and 168 h exposures and mortality was assessed after
14 days. Among the life stages tested, pupae were more tolerant
to phosphine followed by the egg and the larval instars. At
24 h, the maximum LC50 value was observed in case of egg;
1.571 mgL−1; followed by the pupae, 6th instar, 4th instar and
2nd instar larvae with LC50 values of 1.184, 0.336, 0.212 and
0.081 mgL−1 respectively. However, continued exposure of
the developmental stages to phosphine, recorded maximum
LC values in the pupae followed by egg and the larval instars.
A linear increase in the mortality responsewas witnessed in all
the insect stages when the exposure periods were extended
from 24 to 168 h with increasing concentrations of phosphine,
conversely significant increase in mortality was greatly apparent
during the initial treatment periods.