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Evolutionary affiliations of eighteen families of Hemiptera (s.l.) are inferred using molecular phylogenetic analysis of nucleotide (nt) sequences of 18S rDNAs. Exemplar taxa include: Archaeorrhyncha (=Fulgoromorpha): flatid, issid, dictyopharid, cixiid and delphacid; Prosorrhyncha (=Heteropterodea): Peloridiomorpha (=Coleorhyncha) ‐peloridiid, Heteroptera gerrid, lygaeid and mirid; Clypeorrhyncha [=extant (monophyletic) cicadomorphs]: cicadid, cercopoids (cercopid, aphrophorid), membracid and cicadellids (deltocephaline and cicadelline); and Sternorrhyncha: psyllid, aleyrodid, diaspidid and aphid. Analysed sequences encompass a region beginning ≅550 nucleotides (nts) from the 5'‐end to ≅200 nts upstream from the 3'‐end of the gene [≅1150 base pairs (bp) in euhemipteran to >1400 bp in sternorrhynchan taxa]. Maximum parsimony and bootstrap analyses (PAUP) identify four principal hemipteran clades, Stenorrhyncha, Clypeorrhyncha, Archaeorrhyncha and Prosorrhyncha. These lineages are identified by synapomorphies distributed throughout the gene. Sternorrhyncha is a sister group to all other Hemiptera (i.e. Euhemiptera sensu Zrzavy), rendering Homoptera paraphyletic. Within Euhemiptera, clades Clypeorrhyncha, Archaeorrhyncha, Prosorrhyncha and Heteroptera are supported by one, three, two and three synapomorphic sites, respectively. There is equitable parsimonious inference for Archaeorrhyncha as the sister group to Prosorrhyncha (Neoherriiptera sensu Sorensen et al.) or Clypeorrhyncha, in either case rendering Auchenorrhyncha paraphyletic. Neohemiptera is supported by one synapomorphy. Within Clypeorrhyncha, clade cicada + cercopoids is the sister group of the clade cicadellids + membracid (Membracoidea sensu Dietrich & Deitz). Among archaeorrhynchans, clade delphacid + cixiid is the sister group of the clade dictyopharid + flatid + issid. Within Prosorrhyncha, the peloridiid is sister to the Heteroptera. Within Heteroptera, gerrid is the sister group of the clade mirid + lygaeid (Panheteroptera sensu Schuh). Based on secondary structure of synonymous 18S rRNA, two synapomorphies each of Sternorrhyncha, Prosorrhyncha and Heteroptera are compensatory substitutions on stem substructures. All other synapomorphies identifying major lineages of Hemiptera are noncompensatory substitutions on either bulges or stems. Short basal internodal distances suggest radiation of hemipteran lineages at the suborder level occurred rapidly. Morphological, palaeoentomological and eco‐evolutionary factors supporting the 18S rDNA‐based phylogenetic tree are discussed.

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Phylogenetic analysis of 18S rDNA nucleotide sequences of hemipteran exemplars shows Sternorrhyncha (psyllids, whiteflies, aphids and scales) is monophyletic and forms a sister group to all other hemipterans (Euhemiptera). Whiteflies form a sister group to all other Sternorrhyncha. Primary structures of 18S rDNAs of all sternorrhynchans are exceptionally long (approximately 2200 to approximately 2500 bp) due to internal expansions. These expansions are a synapomorphy of Sternorrhyncha; other hemipterans possess shorter 18S rDNAs (approximately 1900 to approximately 1925 bp). The 18S rDNA of whiteflies is the longest recorded to date and has a base substitution rate of approximately 3 times greater than Euhemiptera taxa examined. The relevance of these findings to the fossil record, feeding strategies, reproductive biologies, and geoclimatic distribution is discussed.

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Host‐finding by the parasitic wasp Orgilus lepidus, a braconid parasite, is mediated by two kairomones present in the frass of the host insect, the potato tuberworm. A volatile substance identified as heptanoic acid elicits heightened searching behavior, resulting in the parasite contacting the frass. A contact chemical stimulus in the frass induces the parasite to probe the substrate with the ovipositor, culminating in contact with the host. Zusammenfassung DURCH KAIROMONE VERMITTELTES WIRTSFINDUNGSVERHALTEN IN DER PARASITISCHEN WESPE, ORGILUS LEPIDUS Das Auffinden des Wirts durch die parasitische Wespe Orgilus lepidus wird durch zwei Kairomone vermittelt, die im Bohrmehl des Wirtsinsekts, der Kartoffelmotte (Phthorimaea operculella) vorliegen. Eine flüchtige Substanz, identifiziert als Heptansäure, löst erhöltes Suchverhalten aus, das zur Kontaktnahme des Parasiten mit dem Bohrmehl führt. Ein chemischer Kontaktreiz im Bohrmehl veranlasst den Parasiten, das Substrat mit dem Legestachel solange zu sondieren, bis er mit dem Wirt in Berührung kommt.

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