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Background: Much has been learned about basic biology from studies of insect model systems. The pre-eminent insect model system, Drosophila melanogaster , is a holometabolous insect with a derived mode of segment formation. While additional insect models have been pioneered in recent years, most of these fall within holometabolous lineages. In contrast, hemimetabolous insects have garnered less attention, although they include agricultural pests, vectors of human disease, and present numerous evolutionary novelties in form and function. The milkweed bug, Oncopeltus fasciatus (order: Hemiptera)-close outgroup to holometabolous insects-is an emerging model system. However, comparative studies within this order are limited as many phytophagous hemipterans are difficult to stably maintain in the lab due to their reliance on fresh plants, deposition of eggs within plant material, and long development time from embryo to adult., Results: Here we present the harlequin bug, Murgantia histrionica , as a new hemipteran model species. Murgantia -a member of the stink bug family Pentatomidae which shares a common ancestor with Oncopeltus  ~ 200 mya-is easy to rear in the lab, produces a large number of eggs, and is amenable to molecular genetic techniques. We use Murgantia to ask whether Pair-Rule Genes (PRGs) are deployed in ways similar to holometabolous insects or to Oncopeltus . Specifically, PRGs even - skipped, odd - skipped, paired and sloppy - paired are initially expressed in PR-stripes in Drosophila and a number of holometabolous insects but in segmental-stripes in Oncopeltus . We found that these genes are likewise expressed in segmental-stripes in Murgantia, while runt displays partial PR-character in both species. Also like Oncopeltus , E75A is expressed in a clear PR-pattern in blastoderm- and germband-stage Murgantia embryos, although it plays no role in segmentation in Drosophila . Thus, genes diagnostic of the split between holometabolous insects and Oncopeltus are expressed in an Oncopeltus -like fashion during Murgantia development., Conclusions: The similarity in gene expression between Murgantia and Oncopeltus suggests that Oncopeltus is not a sole outlier species in failing to utilize orthologs of Drosophila PRGs for PR-patterning. Rather, strategies deployed for PR-patterning, including the use of E75A in the PRG-network, are likely conserved within Hemiptera, and possibly more broadly among hemimetabolous insects., Competing Interests: Competing interestsThe authors declare that they have no competing interests., (© The Author(s) 2020.)

Hemiptera is a large clade of insects understudied in terms of developmental biology. Halyomorpha halys , the Brown Marmorated Stink Bug (BMSB, referred to throughout as H. halys ), is an invasive hemipteran pest of the mid-Atlantic region of the USA that has rapidly spread to other regions in recent years, devastating a wide range of crops using a piercing and sucking mechanism. Its phylogenetic position, polyphagous habits, and rapid spread in the USA suggested that H. halys would be an ideal system to broaden our knowledge of developmental mechanisms in insects. We and others previously generated transcriptome sequences from different life stages of this insect. Here, we describe tools to examine gene expression patterns in whole-mount H. halys embryos and to test the response of H. halys to RNA interference (RNAi). We show that spatial and temporal patterns of gene expression in H. halys can be effectively monitored by both immunostaining and in situ hybridization. We also show that delivery of dsRNA to adult females knocks down gene function in offspring, using the homeotic gene Sex combs reduced ( Scr ). Knockdown of Hh - Scr resulted in dramatic malformations of the mouthparts, demonstrating for the first time that RNAi is effective in this species. Our results suggest that, despite difficulties with long-term laboratory culture of H. halys , this species shows promise as a developmental system.