Characterization of cuticular compounds of the cerambycid beetles Monochamus galloprovincialis, Arhopalus syriacus, and Pogonocherus perroudi, potential vectors of pinewood nematode

In Portugal, dozens of bark and wood-boring beetle species have been recorded colonizing Pinus pinaster Aiton (Pinaceae), the main conifer species affected by pine wilt disease (PWD). However, its causal agent, the pinewood nematode (PWN), Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle (Parasitaphelenchidae), has been recovered only from the black pine sawyer, Monochamus galloprovincialis (Olivier) (Coleoptera: Cerambycidae). To understand the mechanisms underlying this specific relationship, our goal was to characterize the cuticular compounds (CCs) of three of the most abundant wood-boring cerambycids, M. galloprovincialis, Arhopalus syriacus (Reiter), and Pogonocherus perroudi (Mulsant) Villiers, colonizing infested P. pinaster. Three methods of extracting CCs were assessed: (1) headspace solid phase microextraction (SPME), (2) extraction with organic solvent (pentane or ethanol), and (3) hydrodistillation. Pentane extraction was most effective, using pooled samples of each of the insects’ developmental stages. Extracts were analysed by gas chromatography-mass spectrometry (GC-MS) to identify compounds, and by GC for quantification. The pentane extracts contained predominantly straight-chain (n-C) and methyl-branched hydrocarbons (meC). Cluster analysis defined two main clusters, with cluster A comprising A. syriacus samples dominated by n-C23 (7-39%), n-C25 (9-31%), and n-C27 (5-11%). Pogonocherus perroudi and the larvae from M. galloprovincialis grouped in sub-cluster B1, characterized by high proportions of n-C27 (20-52%), n-C29 (4-18%), and 3-meC27 (8-18%). Sub-cluster B2 included the remaining M. galloprovincialis samples, dominated by n-C27 (10-14%), n-C25 (8-10%), 5-meC25 (9-16%), 2-meC26 (6-12%), and 3-meC27 (6-10%). The CC profiles of the various species may play a key role in triggering the movement of PWN from the tree to callow adults of the specific insect vector, among all insects colonizing infested host trees. Identification of key components would potentially allow the development of valuable tools to manage PWD, for example, in a lure to quickly detect PWN in a tree, or conversely, by treatment of felled wood with PWN repellents to disrupt PWN transfer to its insect vector, breaking the transmission cycle.