Effect of salithion enantiomers on the trehalase system and on the digestive protease, amylase, and invertase of Tribolium castaneum

(R)(+)-Salithion was a more potent inhibitor than (S)(-)-enatiomer on the larval growth, pupation, and emergence of Tribolium castaneum. According to concentration needed for 50% larval weight gain inhibition (IC₅₀), (R)(+)-enantiomer was ∼17-fold more potent than the (S)(-)-enantiomer. Larvae fed for 2 days on dietary concentration of 2 and 4 ppm (R)(+)-salithion resulted in larval weight gain inhibition of ∼10 and ∼55%, correlating well with the inhibition of the activity of the soluble larval gut trehalase. Similar correlation was obtained with 20 and 40 ppm of (S)(-)-salithion. At a concentration of 10^-4 M, salithion enantiomers had no effect on the trehalase activity in vitro. Hence, the compound affects the biological process, leading to a reduced activity of trehalase in vivo. Both enantiomers had no effect in in vivo assays on the digestive protease and amylase activity. Invertase, which plays a minor role in carbohydrate digestion in Tribolium larvae, as compared to amylase, was inhibited to some extent by salithion enantiomers. Hence, the reduced activity of the trehalase system appears to be an important factor for the growth suppression observed after salithion application.