Abstract
The oriental fruit fly Bactrocera dorsalis (Hendel) causes devastating losses to agricultural crops world-wide and is considered to be an economically important pest. Little is known about the digestive enzymes such as serine proteases (SPs) in B. dorsalis, which are important both for energy supply and mitigation of fitness cost associated with insecticide tolerance. In this study, we identified five SP genes in the midgut of B. dorsalis, and the alignments of their deduced amino acid sequences revealed the presence of motifs conserved in the SP superfamily. Phylogenetic analyses with known SPs from other insect species suggested that three of them were trypsin-like proteases. Analyses of the expression profiles among the different developmental stages showed that all five genes were most abundant in larvae than in other stages. When larvae were continuously fed on diet containing 0.33 μg/g β-Cypermethrin, expression of all five genes were upregulated in the midgut but the larval development was delayed. Biochemical assays were consistent with the increased protease activity exhibited by SPs in the midgut after treatment with β-Cypermethrin. Taken together, these findings provide evidence for the hypothesis that enhanced SP activity may play an indirect role in relieving the toxicity stress of insecticide in B. dorsalis.
Highlights
The oriental fruit fly, Bactrocera dorsalis (Hendel), is one of the most destructive pests in the world and causes huge financial losses worldwide [1]
The transcriptional changes of all five serine proteases (SPs) genes transcripts in larvae exposed to β-Cypermethrin determined by quantitative real-time-PCR (qRT-PCR) which showed significant upregulation of BdSP3, BdSP5, BdSP1, BdSP2, and BdSP4 in larvae following the treatment with β-Cypermethrin, especially for BdSP3
We found the overexpression of SPs and the enhanced SPs activity in B. dorsalis upon the exposure of β-Cypermethrin, which may probably be explained in this way: the detoxification process is known to draw energy allocated to normal development and absence of energy supplement may impair the normal development and reproduction in insects [31,32]
Summary
The oriental fruit fly, Bactrocera dorsalis (Hendel), is one of the most destructive pests in the world and causes huge financial losses worldwide [1]. SPs are known to dominate in the larval gut environment and contribute to about 95% of the total digestive activity [7] They are dominant proteolytic enzymes in the midgut of Drosophila [8]. Most pyrethroids contain cyclopropane carboxylic acid (or a moiety equivalent group) linked to aromatic alcohols through a central ester (or ether) bond Modifications to this basic structure are designed to increase insecticidal potency or photostability [12]. We hypothesized that exposure to insecticides may enhance protein digestion in insects resulting in additional energy, and increased availability of amino acids for protein synthesis This in turn will supply the materials to produce the detoxification apparatus without costing energy for other physiological processes. The results might provide some evidence for the indirect role of SPs in insecticide tolerance
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