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Simple Summary Stink bugs (Pentatomidae) are one of the most diverse insect groups in suborder Heteroptera (Hemiptera). They are either plant feeders or predators, comprising series of invasive agricultural pests and natural enemies with great economic importance. Species of stink bugs possess various antennal and mouthpart traits apparently related with feeding habits, but key morphological traits associated with feeding habit shift remain largely unexploited. In this study, we compare the ultrastructures of antennae, labia, and mandibular and maxillary stylets of 17 pentatomid species, representing both phytophagous and predatory species chosen from four subfamilies. We identify a set of key ultrastructural characteristics closely associated with feeding habit transition in stink bugs and discuss their adaptative implications in an evolutionary aspect. Abstract The family Pentatomidae (stink bugs) is one of the largest groups in Heteroptera, containing many important pests and natural enemies. They exhibit highly diversified feeding habits and related structural modifications, but the key morphological characteristics associated with feeding habit radiation remain unclear. In the current study, we address this question by analyzing morphological variations of feeding related organs. We compare the ultrastructures of antennae and mouthparts across the chosen 17 species in Pentatomidae, representing both plant feeders and predators from four subfamilies. A strong association between ultrastructural adaptation and feeding habit transition has been revealed. The long, sharp, and hook-like mandibular teeth and maxillary barbs are exclusively present in predatory Pentatomidae, suggesting their tight association with the shift of feeding habit from phytophagy to predation. Significant differences between phytophagous and predatory species are also found in antennal and labial sensilla types and arrangements, implying their important function in food selection. Our data identify a series of key morphological structures associated with feeding habit variations among stink bugs, which will facilitate future studies on adaptive evolution of feeding habits, utilization, and population control of economic species in Pentatomidae as well as in other heteropteran lineages.

Simple Summary The assassin bugs (Heteroptera: Reduviidae) are one of the largest and morphologically most diverse families of true bug, having essential impacts on forest ecosystems as predators. The spinous reduviid genus Sclomina exhibits shape mimicry and protective coloration adapted to the spinous Rubus plant that they inhabit. The genus Sclomina shows gradual morphological variability, so its morphological classification is still unresolved, and its biology is almost unknown. In this study, DNA barcodes and morphological evidence were combined to accurately divide the species of a comprehensive collection sampled in South China and North Vietnam. We found three cryptic species. The biological information and mimicry behavior uncover their successive evolutionary survival strategies. Abstract Sclomina Stål, 1861 (Heteroptera: Reduviidae: Harpactorinae) is endemic to China and Vietnam, with only two species, Sclomina erinacea Stål, 1861 and Sclomina guangxiensis Ren, 2001, characterized by spinous body and dentate abdominal connexivum. However, due to variable morphological characteristics, Sclomina erinacea, which is widely distributed in South China, is possibly a complex of cryptic species, and Sclomina guangxiensis was suspected to be an extreme group of the S. erinacea cline. In the present study, we conducted species delimitation and phylogenetic analyses based on the mitochondrial cytochrome c oxidase subunit I (COI) gene sequences of 307 Sclomina specimens collected from 30 sampling localities combined with morphological evidence. The result showed that all samples used in this study were identified as five species: Sclomina guangxiensis is a valid species, and Sclomina erinacea actually includes three cryptic species: Sclomina xingrensis P. Zhao and Cai sp. nov., Sclomina pallens P. Zhao and Cai sp. nov., and Sclomina parva P. Zhao and Cai sp. nov. In this paper, the genus Sclomina is systematically revised, and the morphological characteristics of the five species are compared, described, and photographed in detail. We elucidate the evolutionary history of Sclomina based on results of estimated divergence time. The body shape and coloration (green in nymph and brown in adult) of Sclomina match their environment and mimic the Rubus plants on which they live. The symbiotic relationship between Sclomina and spinous Rubus plants is presented and discussed.

Most assassin bugs are predators that act as important natural enemies of insect pests. Mitochondrial (mt) genomes of these insects are double-strand circular DNAs that encode 37 genes. In the present study, we explore the duplication and rearrangement of tRNA genes in the mt genome of Reduvius tenebrosus, the first mt genome from the subfamily Reduviinae. The gene order rearranges from CR (control region)-trnI-trnQ-trnM-ND2 to CR-trnQ-trnI2-trnI1-trnM-ND2. We identified 23 tRNA genes, including 22 tRNAs commonly found in insects and an additional trnI (trnI2), which has high sequence similarity to trnM. We found several pseudo genes, such as pseudo-trnI, pseudo-CR, and pseudo-ND2, in the hotspot region of gene rearrangement (between the control region and ND2). These features provided evidence that this novel gene order could be explained by the tandem duplication/random loss (TDRL) model. The tRNA duplication/anticodon mutation mechanism further explains the presence of trnI2, which is remolded from a duplicated trnM in the TDRL process (through an anticodon mutation of CAT to GAT). Our study also raises new questions as to whether the two events proceed simultaneously and if the remolded tRNA gene is fully functional. Significantly, the duplicated tRNA gene in the mitochondrial genome has evolved independently at least two times within assassin bugs.