Mitochondrial introgression and mito-nuclear discordance obscured the closely related species boundaries in Cletus Stål from China (Heteroptera: Coreidae).

Accurate taxonomy and delimitation are of great importance for pest control strategies and management programs. Here, we focus on Cletus (Insecta: Hemiptera: Coreidae), which includes many crop pests. The species boundaries still conflict and only cytochrome c oxidase subunit I (COI) barcoding has been previously used for molecular studies. We generated new mitochondrial genome and nuclear genome-wide SNPs to explore the species boundaries of 46 Cletus samples from China using multiple species delimitation approaches. All results recovered a monophyly with high support, except for two closely related species in clade I - C. punctiger and C. graminis. Mitochondrial data demonstrated admixture in clade I, while genome-wide SNPs unambiguously identified two separate species, which were confirmed by morphological classification. Inconsistent nuclear and mitochondrial data indicated mito-nuclear discordance. Mitochondrial introgression is the most likely explanation, and more extensive sampling and more comprehensive data are needed to ascertain a pattern. Accurate species delimitation will shed light on species status; thus, an accurate taxonomy is of particular concern, as there is a pressing need to implement precise control of agricultural pests and to perform further research on diversification.

Insecticide resistance governed by gut symbiosis in a rice pest, Cletus punctiger, under laboratory conditions.

Resistance to toxins in insects is generally thought of as their own genetic trait, but recent studies have revealed that gut microorganisms could mediate resistance by detoxifying phytotoxins and man-made insecticides. By laboratory experiments, we here discovered a striking example of gut symbiont-mediated insecticide resistance in a serious rice pest, Cletus punctiger. The rice bug horizontally acquired fenitrothion-degrading Burkholderia through oral infection and housed it in midgut crypts. Fenitrothion-degradation test revealed that the gut-colonizing Burkholderia retains a high degrading activity of the organophosphate compound in the insect gut. This gut symbiosis remarkably increased resistance against fenitrothion treatment in the host rice bug. Considering that many stinkbug pests are associated with soil-derived Burkholderia, our finding strongly supports that a number of stinkbug species could gain resistance against insecticide simply by acquiring insecticide-degrading gut bacteria.

The role of Oryza sativa L. 'Milyang 44' husks on the resistance to two rice stink bugs.

To elucidate the resistance mechanisms of the rice (Oryza sativa L.) cultivar 'Milyang 44' against rice stink bugs, we compared the number of stylet sheaths, husk perforations, and feeding marks on the surface of the grains caused by Leptocorisa chinensis and Cletus punctiger on Milyang 44 and the control cultivar, i.e., 'Aichinokaori SBL'. We also examined the cross-sectional structure of the rice husks. We found that the number of stylet sheaths per panicle was higher in Milyang 44 than in Aichinokaori SBL for both rice stink bug species, except in one test involving C. punctiger. However, Milyang 44 had significantly less damage per number of stylet sheaths than Aichinokaori SBL, resulting in a lower percentage rates of pecky rice grains in Milyang 44. Interestingly, there was no difference in the percentage rates of pecky rice between the two cultivars after removing one third of the husks. Histological analysis showed that the sclerenchymatous cell wall containing lignin of husk was thicker in Milyang 44 than in Aichinokaori SBL, suggesting that the husk of Milyang 44 plays an important role in its resistance to these two rice stink bug species.

The complete mitochondrial genome sequence of Cletus rubidiventris (Heteroptera: Coreidae).

Cletus rubidiventris is a crop pest, especially for rice. This study first reported the complete mitochondrial genome of this species. The total length of mitochondrial genome is 15,590 bp and including 13 PCGs, 22 tRNA genes, and 2 rRNA genes, with 31.8% T, 15.8% C, 41.6% A, and 10.8% G. The overall GC content of the genome is 27%. The mitochondrial genome order, nucleotide composition, and codon usage pattern is similar to C. punctiger. The phylogenetic tree shows that C. rubidiventris belong to the Coreidae.

The complete mitochondrial genome sequence of Cletus punctiger (Heteroptera: Coreidae).

Cletus punctiger is a famous economic crop pest in China, especially for rice. Here, we first reported the complete mitochondrial genome sequence of this pest. The mitochondrial genome is 16,166 bp in length, including 13 protein-coding genes (PCGs), 22 tRNA genes, 2 rRNA genes, and 1 control region (D-Loop). The maximum likelihood (ML) phylogenetic tree confirmed that C. punctiger belonged to the Coreidae subfamily.

Species diversity can be overestimated by a fixed empirical threshold: insights from DNA barcoding of the genus Cletus (Hemiptera: Coreidae) and the meta-analysis of COI data from previous phylogeographical studies.

The use of genetic distances to identify species within the framework of DNA barcoding has to some extent improved the development of biodiversity studies. However, using a fixed empirical threshold to delimit species may lead to overestimating species diversity. In this study, we use a new data set of COI sequences for 366 specimens within the genus of Cletus as well as conduct an analysis on the same genetic data for collected morphologically defined species from previous phylogeographical studies, to test whether high intraspecific genetic divergences are common with the premises of comprehensive sampling. The results indicate C. graminis Hsiao & Cheng , is the same species with C. punctiger (Dallas, 1852) and should be synonymized and that the distributional record of C. pugnator (Fabricius, 1787) in China is correct. High intraspecific genetic differentiations (0%-4.35%) were found in C. punctiger. Furthermore, as to the mined data, the maximum intraspecific K2P distances of 186 species (48.44% of 384) exceed 3%, and 101 species (26.30%) can be divided into two or more clusters with a threshold of 3% in cluster analysis. If genetic distance is used to delimit species boundaries, the minimum interspecific K2P distance of the congeneric species should be considered rather than only using the fixed empirical value; otherwise, the species richness may be overestimated in some cases.