Abstract
The species belonging to Sclerodermus (Hymenoptera: Bethylidae) are currently the most important insect natural enemies of wood borer pests, mainly buprestid and cerambycid beetles, in China. However, some sibling species of this genus are very difficult to distinguish because of their similar morphological features. To address this issue, we conducted phylogenetic and genetic analyses of cytochrome oxidase subunit I (COI) and 28S RNA gene sequences from eight species of Sclerodermus reared from different wood borer pests. The eight sibling species were as follows: S. guani Xiao et Wu, S. sichuanensis Xiao, S. pupariae Yang et Yao, and Sclerodermus spp. (Nos. 1–5). A 594-bp fragment of COI and 750-bp fragment of 28S were subsequently sequenced. For COI, the G-C content was found to be low in all the species, averaging to about 30.0%. Sequence divergences (Kimura-2-parameter distances) between congeneric species averaged to 4.5%, and intraspecific divergences averaged to about 0.09%. Further, the maximum sequence divergences between congeneric species and Sclerodermus sp. (No. 5) averaged to about 16.5%. All 136 samples analyzed were included in six reciprocally monophyletic clades in the COI neighbor-joining (NJ) tree. The NJ tree inferred from the 28S rRNA sequence yielded almost identical results, but the samples from S. guani, S. sichuanensis, S. pupariae, and Sclerodermus spp. (Nos. 1–4) clustered together and only Sclerodermus sp. (No. 5) clustered separately. Our findings indicate that the standard barcode region of COI can be efficiently used to distinguish morphologically similar Sclerodermus species. Further, we speculate that Sclerodermus sp. (No. 5) might be a new species of Sclerodermus.
Highlights
Monochamus alternatus Hope (Coleoptera: Cerambycidae), a longhorned pine sawyer beetle, is considered the major pest of pine trees and an important vector of the pinewood nematode, the causal agent of pine wilt disease [1,2,3]
The highest parasitism of 32.51% was noted when the ratio of pest and Bethylidae species was 1: 8–10 [8]. These findings suggest that S. guani is an important parasitic enemy that can be effectively used to prevent M. alternatus larvae; the parasitism was more than 20% in Fujian, China [9]
cytochrome oxidase subunit I (COI) barcode sequences were used for the identification of several Sclerodermus species for the first time, to our knowledge
Summary
Monochamus alternatus Hope (Coleoptera: Cerambycidae), a longhorned pine sawyer beetle, is considered the major pest of pine trees and an important vector of the pinewood nematode, the causal agent of pine wilt disease [1,2,3]. In the last 20 years, pine wilt disease was reported in 10 provinces of China [5]. Between 1996 and 2001, the stand volume loss caused by the pine wilt disease was more than 1 million m3, and the direct economic loss was estimated to be approximately above 400 billion Yuan RMB [6]. A biological control program was initiated in 2000 to control the longhorned beetle [4]. That program surveyed the natural enemies of M. alternatus [4]
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