Molecular phylogeny of the assassin bugs (Hemiptera: Reduviidae), based on mitochondrial and nuclear ribosomal genes

The first comprehensive cladistic analysis of Reduviidae, the assassin bugs, based on molecular data is presented and discussed in the context of a recently-published morphological analysis. Assassin bugs are essential components of ecosystems, but also important in agriculture and medicine. Sampling included 94 taxa (89 Reduviidae, 5 outgroups) in 15 subfamilies and 24 tribes of Reduviidae and is based on 3300 base pairs of mitochondrial (16S) and nuclear (18S, 28SD2, 28SD3-5) ribosomal DNA. Partitions of the dataset were aligned using different algorithms implemented in MAFFT and the combined dataset was analyzed using parsimony, partitioned maximum likelihood and partitioned Bayesian criteria. Clades recovered in all analyses, independent of alignment and analytical method, comprise: Cimicomorpha and Reduviidae; Hammacerinae; Harpactorinae; Apiomerini; Peiratinae; Phymatinae; Salyavatinae; Triatominae; Phymatinae + Holoptilinae; the higher Reduviidae (Reduviidae excluding Hammacerinae and the Phymatine Complex); Ectrichodiinae + Tribelocephalinae; (Triatominae + Zelurus) + Stenopodainae. Hammacerinae are rejected as sister group to all remaining Reduviidae in all analyses, as is the monophyly of Reduviinae, Emesinae and Harpactorini. High support values for Triatominae imply that blood-feeding has evolved only once within Reduviidae. Stenopodainae and part of Reduviinae are discussed as close relatives to Triatominae.     

Molecular phylogeny of Harpactorinae and Bactrodinae uncovers complex evolution of sticky trap predation in assassin bugs (Heteroptera: Reduviidae)

Sticky trap predation, the use of adhesive substances to trap and capture prey, is an intriguing yet poorly studied predatory strategy. Unique among known sticky trap predators, assassin bugs (Reduviidae) have evolved both exogenous and endogenous sticky trap predatory mechanisms: some trap their prey with sticky plant resins, some scavenge insects entrapped by sticky plant trichomes and others self‐produce sticky secretions. The evolution of these different strategies in assassin bugs is poorly understood due to the lack of comprehensive phylogenies. We reconstruct a phylogeny of Reduviidae (141 taxa; > 5000 bp) focusing on the Harpactorinae and Bactrodinae that engage in sticky trap predation. Ancestral state reconstruction, and temporal and geographical divergence analyses show that sticky trap predation techniques in assassin bugs evolved at least seven times independently since the late Cretaceous: use of sticky plant trichomes evolved as many as four times, resin‐use twice independently and once as a transition from trichome use, and ‘self‐stickiness’ once. Exogenous and endogenous sticky traps first appeared in the Neotropics, with the two exogenous mechanisms (resin and trichome use) subsequently evolving independently in the Old World. This study illustrates, for the first time, the complex evolutionary pattern of sticky trap predation within assassin bugs.     

Cladistic analysis of Reduviidae (Heteroptera: Cimicomorpha) based on morphological characters

Abstract.  With more than 6600 species worldwide, Reduviidae (Insecta: Heteroptera), or assassin bugs, form the second largest and one of the most diverse groups of true bugs. The poor condition of the higher-level classification of Reduviidae is reflected by the facts that different authors recognize between 21 and 32 subfamily-level names and that Reduviidae were never subjected to a rigorous cladistic analysis using an exemplar approach. In the present study, a cladistic analysis of higher-level taxa of Reduviidae based on 162 morphological characters and 75 ingroup and outgroup species is presented. Twenty-one subfamily-level taxa of Reduviidae were examined, accounting for 28 tribes. In addition to characters previously used for diagnosis in Reduviidae, information on recently published character complexes is used in the present analysis, supplemented with new character information gathered specifically for this project. Reduviidae are supported as a monophyletic group with Pachynomidae as their sister taxon. The major results of this study are the support of a sistergroup relationship of Hammacerinae with the remaining Reduviidae, the monophyly of the Phymatine Complex, the relatively basal position of Harpactorinae within Reduviidae as well as a novel hypothesis on the relationships within this group, and the sistergroup relationship of Ectrichodiinae + Tribelocephalinae and their placement in a clade that also contains Emesinae, Saicinae, and Visayanocorinae. The analysis further supports a clade formed by paraphyletic Salyavatinae + Sphaeridopinae, renders Vesciinae non-monophyletic, and demonstrates the polyphyly of Reduviinae. Pseudocetherinae are shown to group with some Reduviinae. Triatominae are supported as a monophyletic group and are nested among additional Reduviinae and Stenopodainae.     

Geological Changes of the Americas and their Influence on the Diversification of the Neotropical Kissing Bugs (Hemiptera: Reduviidae: Triatominae)

Background

The family Reduviidae (Hemiptera: Heteroptera), or assassin bugs, is among the most diverse families of the true bugs, with more than 6,000 species. The subfamily Triatominae (kissing bugs) is noteworthy not simply because it is the only subfamily of the Reduviidae whose members feed on vertebrate blood but particularly because all 147 known members of the subfamily are potential Chagas disease vectors. Due to the epidemiological relevance of these species and the lack of an efficient treatment and vaccine for Chagas disease, it is more common to find evolutionary studies focusing on the most relevant vectors than it is to find studies aiming to understand the evolution of the group as a whole. We present the first comprehensive phylogenetic study aiming to understand the events that led to the diversification of the Triatominae.

Methodology/Principal Findings

We gathered the most diverse samples of Reduviidae and Triatominae (a total of 229 Reduviidae samples, including 70 Triatominae species) and reconstructed a robust dated phylogeny with several fossil (Reduviidae and Triatominae) calibrations. Based on this information, the possible role of geological events in several of the major cladogenetic events within Triatominae was tested for the first time. We were able to not only correlate the geological changes in the Neotropics with Triatominae evolution but also add to an old discussion: Triatominae monophyly vs. paraphyly.

Conclusions/Significance

We found that most of the diversification events observed within the Rhodniini and Triatomini tribes are closely linked to the climatic and geological changes caused by the Andean uplift in South America and that variations in sea levels in North America also played a role in the diversification of the species of Triatoma in that region.     

Untangling the assassin's web: Phylogeny and classification of the spider-associated Emesine complex (Hemiptera: Reduviidae)

Web-building spiders are formidable predators, yet assassin bugs in the Emesine Complex (Hemiptera: Reduviidae: Emesinae, Saicinae, and Visayanocorinae) prey on spiders. The Emesine Complex comprises >1000 species and these web-associated predatory strategies may have driven their diversification. However, lack of natural history data and a robust phylogenetic framework currently preclude tests of this hypothesis. We combine Sanger (207 taxa, 3865 bp) and high-throughput sequencing data (15 taxa, 381 loci) to generate the first taxon- and data-rich phylogeny for this group. We discover rampant paraphyly among subfamilies and tribes, necessitating revisions to the classification. We use ancestral character state reconstructions for 40 morphological characters to identify diagnostic features for a revised classification. Our new classification treats Saicinae Stål and Visayanocorinae Miller as junior synonyms of Emesinae Amyot and Serville, synonymizes the emesine tribes Ploiariolini Van Duzee and Metapterini Stål with Emesini Amyot and Serville, and recognises six tribes within Emesinae (Collartidini Wygodzinsky, Emesini, Leistarchini Stål, Oncerotrachelini trib.n. , Saicini Stål stat.n. , and Visayanocorini Miller stat.n. ). We show that a pretarsal structure putatively involved in web-associated behaviours evolved in the last common ancestor of Emesini, the most species-rich clade within Emesinae, suggesting that web-associations could be widespread in Emesinae.     

Molecular phylogeny of Harpactorini (Insecta: Reduviidae): correlation of novel predation strategy with accelerated evolution of predatory leg morphology

Much research and discussion have focused on the effects of key innovations on lineage diversification, whereas little has been done to investigate their role in morphological evolution using phylogenetic approaches. Here we present the first comprehensive molecular phylogeny of the Harpactorini (Insecta: Reduviidae), the largest assassin bug tribe, sampling 229 terminal taxa and using five gene segments (28S D2, D3–D5, 16S, COI, and Deformed). Employing comparative phylogenetic methods, we demonstrate the correlation of a putative key innovation, the sticky trap predation strategy, with accelerated rates of morphological evolution of the predatory fore leg in assassin bugs. We show that bugs exhibiting sticky trap predation have evolved more slender and longer fore femora than non‐sticky bugs. Using phylogenetically independent contrast analyses, we document correlated evolution between femoral thickness and length. We argue that the novel sticky trap predation strategy may allow sticky bugs to alleviate functional constraints on the fore femur and thus to attain a higher rate of evolution than other Harpactorini or Reduviidae. We discuss the possibility that sticky bugs represent a case of adaptive radiation. We also test historical supra‐generic groups within the Harpactorini, and show that most of them are not monophyletic. We confirm the paraphyly of Harpactorini with respect to Rhaphidosomini.     

Systematics and biogeography of Rhodniini (Heteroptera: Reduviidae: Triatominae) based on 16S mitochondrial rDNA sequences

Aim The tribe Rhodniini is one of six comprising the subfamily Triatominae (Heteroptera: Reduviidae), notorious as blood‐sucking household pests and vectors of Trypanosoma cruzi throughout Latin America. The human and economic cost of this disease in the American tropics is considerable, and these bugs are unquestionably of great importance to man. Studies of the evolution, phylogeny, biogeography, ecology, physiology and behaviour of the Rhodniini are needed to help improve existing Chagas’ disease control programmes. The objective of the study reported here was to propose biogeographical hypotheses to explain the modern geographical distribution of the species of Rhodniini. Location Neotropical region. Methods We employed mitochondrial rDNA sequences (16S) currently available in GenBank to align sequences of Rhodniini species using ClustalX. The analyses included 16S sequences from predatory reduviid subfamilies (Stenopodainae, Ectrichodiinae, Harpactorinae, Reduviinae and Salyavatinae) present in GenBank as an outgroup. Cladistic analysis used the program PAUP to derive trees based on maximum parsimony (MP) and maximum likelihood (ML). Known distribution data for Rhodniini species were obtained from reviews and plotted on maps of South and Central America using the program iMap. An area cladogram was derived from the cladistic result to show the historical connections among the studied taxa and the endemic areas. The program TreeMap (Jungle Edition) was used to deduce taxon–area associations where the optimal solutions to explain the biogeographical hypothesis of the Rhodniini in the Neotropics were those with lowest total cost. Results Parsimony and maximum‐likelihood analysis of 16S rDNA sequences included 14 species of Rhodniini, as well as five species of predatory Reduviidae representing five of the predatory subfamilies. Tanglegrams were used to show the relationship between the Neotropical areas of endemism and Rhodniini species. When TreeMap with codivergence (vicariance) events were weighted as 0 and duplication (sympatry), lineage losses (extinction) and host switching (dispersal) were all weighted as 1, 20 scenarios were found to explain the biogeographical history of Rhodniini in the Neotropical region. Twelve of the optimal solutions with the lowest total cost were used to explain the biogeography of the Rhodniini in the Neotropics. These optimal reconstructions require six vicariance events, 20 duplications (sympatry), at least three dispersals, and at least one extinction event. Main conclusions The Rhodniini have a complex biogeographical history that has involved vicariance, duplications (sympatry), dispersal and extinction events. The main geological events affecting the origin and diversification of the Rhodniini in the Neotropics were (1) uplift of the Central Andes in the Miocene or later, (2) break‐up of the Andes into three separate cordilleras (Eastern, Central and Western) in the Plio‐Pleistocene, (3) formation of a land corridor connecting South and North America in the Pliocene, and (4) uplift of the Serra do Mar and Serra da Mantiqueira mountain systems between the Oligocene and Pleistocene. The relationships and biogeographical history of the species of Rhodniini in the Neotropical region probably arose from the areas of endemism shown in our work.     

Millipede assassins and allies (Heteroptera: Reduviidae: Ectrichodiinae,Tribelocephalinae): total evidence phylogeny,revised classification and evolution of sexual dimorphism

Evolution of sexual dimorphism in animals has long been of interest to scientists, but relatively few studies have reconstructed evolutionary patterns of extreme sexual dimorphism at a phylogenetic scale, especially in insects. Millipede assassin bugs (Heteroptera: Reduviidae: Ectrichodiinae; 736 spp.) and their sister taxon, Tribelocephalinae (150 spp.), exhibit sexual dimorphism that ranges from limited to extreme, a phenomenon apparently modulated by female morphology. Here, we reconstruct the first phylogeny for the subfamilies Ectrichodiinae and Tribelocephalinae with comprehensive generic representation (152 taxa in 72 genera) using morphological and molecular data (six gene regions). The combined phylogenetic results indicate that Tribelocephalinae are paraphyletic with respect to Ectrichodiinae, and that Ectrichodiinae themselves are polyphyletic. Based on these results, we synonymize Tribelocephalinae with Ectrichodiinae syn.n. , describe three new tribes (Ectrichodiini trib.n. , Tribelocodiini trib.n. , and Abelocephalini trib.n. ) and two new subtribes (Opistoplatyina subtrib.n. and Tribelocephalina subtrib.n. ), and revise Tribelocephalini sensu n. Ancestral state reconstruction of sexual dimorphism reconstructed limited sexual dimorphism in the ancestor of Ectrichodiinae sensu n. with at least seven evolutionary transitions to extreme sexual dimorphism within the clade. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:C810E20F‐D66A‐461F‐A0E6‐AB1073EA3E3C .     

Araneophagic behavior of Gardena brevicollis Stål (Heteroptera: Reduviidae): Foraging on pre‐dispersal spiderlings in the spider's web

Araneophagic behavior of an Emesinae assassin bug, Gardena brevicollis Stål (Hemiptera: Reduviidae) was observed in the field. The bug invaded a web of Acusilas coccineus Simon (Araneae: Araneidae) spiderlings and hunted five juvenile spiders. The bug showed stalking tactics to prey on spiders, whereas luring tactics, which have been reported in other Emesinae bugs, were not observed. To the best of my knowledge, the present study is the first report of araneophagy in the genus Gardena and the first report of araneophagic behavior in East Asian assassin bugs.     

Chemical ecology of triatomine bugs: vectors of Chagas disease

Knowledge of chemical ecology of haematophagous triatomine bugs (Hemiptera: Heteroptera: Reduviidae) could be of practical value because this polyphyletic subfamily includes species of medical importance, such as vectors of Trypanosoma cruzi Chagas (Kinetoplastida: Trypanosomatidae), the aetiological agent of Chagas disease. For particular species of Dipetalogaster, Panstrongylus, Rhodnius and Triatoma, therefore, we review information on exocrine glands and products, interpreting their apparent roles as semiochemicals in the aggregation, alarm, defence, host-finding and sexual behaviour of these Triatominae.     

Functional diversity and trade‐offs in divergent antipredator morphologies in herbivorous insects

Predator–prey interactions may be responsible for enormous morphological diversity in prey species. We performed predation experiments with morphological manipulations (ablation) to investigate the defensive function of dorsal spines and explanate margins in Cassidinae leaf beetles against three types of predators: assassin bugs (stinger), crab spiders (biter), and tree frogs (swallower). There was mixed support for the importance of primary defense mechanisms (i.e., preventing detection or identification). Intact spined prey possessing dorsal spines were more likely to be attacked by assassin bugs and tree frogs, while intact armored prey possessing explanate margins were likely to avoid attack by assassin bugs. In support of the secondary defense mechanisms (i.e., preventing subjugation), dorsal spines had a significant physical defensive function against tree frogs, and explanate margins protected against assassin bugs and crab spiders. Our results suggest a trade‐off between primary and secondary defenses. Dorsal spines improved the secondary defense but weakened the primary defense against tree frogs. We also detected a trade‐off in which dorsal spines and explanate margins improved secondary defenses against mutually exclusive predator types. Adaptation to different predatory regimes and functional trade‐offs may mediate the diversification of external morphological defenses in Cassidinae leaf beetles.     

Phylogenetic comparative analysis supports aposematic colouration–body size association in millipede assassins (Hemiptera: Reduviidae: Ectrichodiinae)

The diversity of colour patterns and its importance in interactions with the environment make colouration in animals an intriguing research focus. Aposematic colouration is positively correlated with body size in certain groups of animals, suggesting that warning colours are more effective or that crypsis is harder to achieve in larger animals. Surprisingly, this relationship has not been recovered in studies investigating insects, which may have been confounded by a focus on aposematic taxa that are also gregarious. Millipede assassin bugs (Hemiptera: Reduviidae: Ectrichodiinae) comprise species with cryptic and aposematic colour patterns across a range of body sizes, are typically solitary as adults and are thus an excellent model for investigating a possible association between colouration and body size. Here, we use a comprehensive phylogeny for Ectrichodiinae, ancestral state reconstruction of colouration, and phylogenetic comparative methods to test for a colouration–body size association. The ancestor of Ectrichodiinae is reconstructed as cryptically coloured, with multiple subsequent transitions between aposematic and cryptic colouration. Aposematic colouration is positively associated with male body length and supports the hypothesis that selection on Ectrichodiinae body size may influence evolutionary transitions between aposematic and cryptic colouration or alternatively that selection for aposematic colouration influences body size evolution.     

Predatory behaviour of an araneophagic assassin bug

Assassin bugs from the genus Stenolemus (Heteroptera, Reduviidae) are predators of web-building spiders. However, despite their fascinating lifestyle, little is known about how these insects hunt and catch their dangerous prey. Here we characterise in detail the behaviour adopted by Stenolemus bituberus (Stål) during encounters with web-building spiders, this being an important step toward understanding this species’ predatory strategy. These bugs employed two distinct predatory tactics, “stalking” and “luring”. When stalking their prey, bugs slowly approached the prey spider until within striking range, severing and stretching threads of silk that were in the way. When luring their prey, bugs attracted the resident spider by plucking and stretching the silk with their legs, generating vibrations in the web. Spiders approached the luring bug and were attacked when within range. The luring tactic of S. bituberus appears to exploit the tendency of spiders to approach the source of vibrations in the web, such as might be generated by struggling prey.     

Bugs with backpacks deter vision-guided predation by jumping spiders

As a case study of how insects use masks as a defence against vision-guided predators, an experimental study was carried out using Acanthaspis petax , a reduviid bug ('ant bug') that covers itself with a 'mask', or 'backpack', made from carcasses of its preferred prey (ants), and three salticid spider species, Hyllus sp., Plexippus sp. and Thyene sp., salticids being predators with exceptionally acute vision. The ant bugs and the salticids were from the Lake Victoria region of East Africa. In each test, a salticid was presented with a live bug or a lure made from a dead bug, with the mask removed ('naked') or intact ('masked'). Salticids made predatory responses to naked bugs significantly more often than to masked bugs. These findings suggest that salticids readily identify naked bugs as prey, but fail to identify masked bugs as prey.     

Sticky predators: a comparative study of sticky glands in harpactorine assassin bugs (Insecta: Hemiptera: Reduviidae)

Zhang, G. and Weirauch, C. 2011. Sticky predators: a comparative study of sticky glands in harpactorine assassin bugs (Insecta: Hemiptera: Reduviidae). —Acta Zoologica (Stockholm) 00 : 1–10. For more than 50 years, specialized dermal glands that secrete sticky substances and specialized setae have been known from the legs of New World assassin bugs in the genus Zelus Fabricius (Reduviidae: Harpactorinae). The gland secretions and specialized ‘sundew setae’ are involved in enhancing predation success. We here refer to this predation strategy as ‘sticky trap predation’ and the specialized dermal glands as ‘sticky glands’. To determine how widespread sticky trap predation is among Reduviidae, we investigated taxonomic distribution of sticky glands and sundew setae using compound light microscopical and scanning electron microscopical techniques and sampling 67 species of Reduviidae that represent 50 genera of Harpactorini. We found sticky glands in 12 genera of Harpactorini and thus show that sticky trap predation is much more widespread than previously suspected. The sticky glands vary in shape, size and density, but are always located in a dorsolateral position on the fore tibia. Sundew setae are present in all taxa with sticky glands with the exception of Heza that instead possesses unique lamellate setae. The sticky trap predation taxa are restricted to the New World, suggesting a New World origin of this unique predation strategy.     

On the myrmecomorph Coquillettia insignis Uhler (Hemiptera: Miridae): arthropod predators as operators in an ant-mimetic system

The nature of female-limited mimicry in the myrmecomorphic plant bug Coquillettia insignis Uhler is described, including aspects of its relation to possible ant models and to co-occurring visual arthropod predators. Twelve species of ants were collected with C. insignis on its host plant Lupinus caudatus Kell., of which six species were common: third instar to adult female mimics closely resemble four of these six species, in both morphology and behaviour. The mimetic significance of these close correspondences is indicated by the results of over 500 feeding trials, using the three most common species of co-occurring visual arthropod predators as operators. Two of these three species (Sussacus papenhoei Gertsch: Salticidae; and Sinea diadema (Fabricius): Reduviidae), classified C. insignis with corresponding models and not with closely related, non-mimetic plant bugs. Furthermore, after having had a single 'unpleasant' experience with the ant Formica fusca assassin bugs that had previously accepted C. insignis as prey rejected them in 19 out of 23 trials. These findings indicate that C. insignis is a Batesian mimic, with visual arthropod predators functioning as one class of potential operator. Implications for future research on perception and learning in arthropod predators is briefly discussed.     

Defining phyla: evolutionary pathways to metazoan body plans

SUMMARY Phyla are defined by two sets of criteria, one morphological and the other historical. Molecular evidence permits the grouping of animals into clades and suggests that some groups widely recognized as phyla are paraphyletic, while some may be polyphyletic; the phyletic status of crown phyla is tabulated. Four recent evolutionary scenarios for the origins of metazoan phyla and of supraphyletic clades are assessed in the light of a molecular phylogeny: the trochaea hypothesis of Nielsen; the clonal hypothesis of Dewel; the set-aside cell hypothesis of Davidson et al.; and a benthic hypothesis suggested by the fossil record. It is concluded that a benthic radiation of animals could have supplied the ancestral lineages of all but a few phyla, is consistent with molecular evidence, accords well with fossil evidence, and accounts for some of the difficulties in phylogenetic analyses of phyla based on morphological criteria.     

Alternative predatory tactics of an araneophagic assassin bug (Stenolemus bituberus)

Predators of dangerous prey risk being injured or killed in counter-attacks and hence may use risk-reducing predatory tactics. Spiders are often dangerous predators to insects, but for a few, including Stenolemus bituberus assassin bugs, web-building spiders are prey. Despite the dangers of counter-attack when hunting spiders, there has been surprisingly little investigation of the predatory tactics used by araneophagic (spider-eating) insects. Here, we compare the pursuit tendency, outcome and predatory tactics of S. bituberus against five species of web-building spider. We found that S. bituberus were most likely to hunt and capture spiders from the genus Achaearanea, a particularly common prey in nature. Capture of Achaearanea sp. was more likely if the prey spider was relatively small, or if S. bituberus was in poor condition. S. bituberus used two distinct predatory tactics, ‘stalking’, in which they slowly approached the prey, and ‘luring’, in which they attracted spiders by manipulating the web to generate vibrations. Tactics were tailored to the prey species, with luring used more often against spiders from the genus Achaearanea, and stalking used more often against Pholcus phalangioides. The choice of hunting tactic used by S. bituberus may reduce the risk posed by the prey spider.     

Biology and predatory ability of the reduviid Sycanus falleni Stal (Heteroptera: Reduviidae: Harpactorinae) fed on four different preys in laboratory conditions

The reduviid Sycanus falleni Stal (Heteroptera: Reduviidae) is an important predatory insect in biological control pests in vegetable, soybean, corn and rice plants. It is omnivorous species and has a wide range of prey. The influence of fed on four different preys as Pieris rapae (Linnaeus), Spodoptera litura (Fabricius), Plutela xylostella (Linnaeus) and Corcyra cephalonica (Stainton) on biological parameters, ability to eat prey and body weight of the nymph and adult of S. falleni were evaluated in laboratory conditions (26 ± 2 °C, 75 ± 5% RH and light:dark 14:10 h) in Vietnam. The biological parameters of reduviid S. falleni reared on the laboratory were determined by observing the development stage of egg, development stage of nymph, pre-oviposition period, life cycle, longevity of adult, number of eggs laid, sex ratio. The nymph and adults of reduviid S. falleni consumption the number of P. xylostella, P. rapae, S. litura and C. cephalonica larvae were different, and an adult female consumed more than an adult male while the body weight of the I and V nymphal instars, male and female adults of reduviid S. falleni wasn't significantly different (P < 0.01).