Laboratory bioassays were conducted to detect possible alteration in
susceptibility of two field Tribolium castaneum (Herbst) populations (sampled
in a warehouse in Nikinci and a silo in Jakovo) to dichlorvos, malathion,
chlorpyrifos-methyl, pirimiphos-methyl, deltamethrin and bifenthrin after
previous selection with the LD80 of pirimiphos-methyl and deltamethrin. Data
from the topical application bioassays show that chlorpyrifos-methyl was the
most toxic insecticide to T. castaneum adults of the Nikinci population
selected with pirimiphosmethyl and deltamethrin, while malathion was the
weakest, and both selection procedures changed/reduced significantly only the
toxicity of deltamethrin and bifenthrin, increasing their resistance ratios
(RR) at the LD50 from 1.1 to 1.8 (bifenthrin) and from 0.9 to 2.2
(deltamethrin). Deltamethrin was the most toxic insecticide for Jakovo adults
selected with the LD80 of pirimiphosmethyl, while malathion was again the
least toxic. Selection of that population had no effect on insecticide
toxicity, except of malathion, which had a rise in RR at the LD50 from 26.0
to 29.8.