Sublethal effects of the chitin synthesis inhibitor, hexaflumuron, in the cotton mirid bug, Apolygus lucorum (Meyer-Dür)

• We determined the median lethal concentration (LC50) of hexaflumuron in first instar nymphs of A. lucorum.
• We investigated the sublethal effects of hexaflumuron including the development and weight of immature stages.
• We investigated the trehalose and glucose contents when treated with sublethal hexaflumuron concentrations.
• We examined two trehalases activities when treated with sublethal hexaflumuron concentrations.
• We measured the transcript levels of two corresponding genes when treated with sublethal hexaflumuron concentrations.

Hexaflumuron is a type of benzoylphenylurea insecticide which is highly toxic for many insects. Sublethal doses of hexaflumuron have been shown to significantly affect insect growth and development. However, the action mechanism of hexaflumuron is not well understood. In the present study, first instar Apolygus lucorum nymphs were exposed to sublethal doses of hexaflumuron based on the estimated 120 h acute LC50 valve of 20.53 mg/ml. We found that exposure to sublethal hexaflumuron doses resulted in a significant increase in development time and reduced the weights of fifth instar A. lucorum nymphs. We also measured trehalose, which is a primary blood sugar in insects, and the enzyme trehalase that is involved in energy metabolism. Trehalose content in first instar nymphs significantly increased following hexaflumuron treatment while the glucose content, soluble trehalase activity and expression levels of ALTre-1 mRNA decreased significantly. However, no significant changes in membrane-bound trehalase activity and ALTre-2 mRNA expression were observed. In addition, these decreases or increases could be correlated to increases in treatment time or concentration of hexaflumuron, respectively. The present findings indicated that sublethal doses of hexaflumuron could interfere the normal carbohydrate metabolism by depressing the expression of ALTre-1 in A. lucorum, which provide valuable information on the physiology and molecular mechanisms for the toxicity of hexaflumuron.

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