Inhibition properties of three acetylcholinesterases of the pinewood nematode Bursaphelenchus xylophilus by organophosphates and carbamates

The pinewood nematode, Bursaphelenchus xylophilus, causes severe damage to pine species by transmitting the pine wilt disease, and the injection of nematicides, such as emamectin benzonate and milbemectin, is the most common practice to control this pest. However, despite their high efficacy, these macrocyclic lactone nematicides are expensive, limiting their practicability. In an attempt to screen affordable alternative nematicidal agents, we expressed three recombinant acetylcholinesterases (ACES, EC 3.1.1.7) of B. xylophilus using an in vitro baculovirus expression system and evaluated the effects of 11 organophosphates (OPs) and three carbamates (CBs) on the toxicological properties of the enzymes. Of the three recombinant B. xylophilus ACEs (BxACEs; BxACE-1, BxACE-2 and BxACE-3), BxACE-1 and BxACE-2 were highly inhibited by OPs and CBs, including paraoxon, dichlorvos, chlorpyrifos-oxon, chlorpyrifos-methyl-oxon, mevinphos and carbofuran, as demonstrated by an inhibition assay. In contrast, BxACE-3 was insensitive to most of the pesticides tested, with the exception of mevinphos. BxACE-2 was more sensitive than BxACE-1 and BxACE-3 to most of the OPs, whereas BxACE-1 was more sensitive to the CBs than BxACE-2 and BxACE-3. An in vivo toxicity assay revealed that some compounds that were rarely employed as nematicides exhibited higher toxicities than those chemicals commonly used as nematicides. The inhibition kinetic data and in vivo toxicity assay obtained in this study should provide essential information for the development of OP- and CB-based nematicides against B. xylophilus. The availability of recombinant ACEs will also facilitate the development of an in vitro screening system to develop potential OP- and CB-based nematicides. (C) 2012 Elsevier Inc. All rights reserved.