Conoderinae: the Brazilian weevil that thinks it’s a fly!
Widespread among Curculionidae Beetles, also called weevils, mimicry offers in these species amazing study patterns.
Two Brazilian entomologists, Sergio A. Vanin (Department of Zoology – University of Sao Paulo) and Tadeu J. Guerra (Department of Biology – Federal University of Minas Gerais), described in 2012 a remarkable new species of weevil that mimics flies of the Sarcophagidae family, hence its name Timorus sarcophagoides (read interview of Tadeu J. Guerra at the end of article). It belongs to the subfamily Conoderinae which includes more than 200 genera and nearly 1500 species worldwide, most of which were described during the 19th and early 20th centuries.
The weevils of this subfamily are mainly known for their mimicking coloration of ants, bees or other beetles. In Panama and Costa Rica, nearly 20% of the species are mimetic of Tachinidae, Muscidae and Tabanidae flies. In the 1990s, the work of American entomologist Henry Hespenheide (University of California, UCLA) identified 75 species (9 genera) of Conoderinae weevils miming flies.
Broader, this type of mimicry is found in 6 other families and 21 genera of Neotropical Beetles (Central American tropical forests). Among these taxa, many species are not mimetic, which shows that the resemblance with flies is a convergent adaptation that appeared several times during evolution (homoplastic type adaptation : similar morphological or physiological traits between species that do not have a common phylogenetic origin).
Many collection specimens from museums whose biology is strongly deficient remain undescribed. The only key for determining this subfamily available was made by the Austrian entomologist Karl Maria Heller (1864-1945) in 1894. The characterization of Conoderinae genera is complicated by the absence of phylogenetic data and the discovery of many undescribed species that integrate into several genera and do not meet current criteria.
The discovery of T. sarcophagoides was made by entomologist T. J. Guerra during botanical observations in the heritage reserve of Vellozia, a private area of “Campos Rupestres” between 1100 m and 1400 m above sea level, located in the vicinity of the Serra do Cipo National Park, in Santana do Riacho (Minas Gerais) in southeast Brazil ( see map).
The vegetation, typical of the mountains of the region, consists of mosaics of open fields and rocky outcrops where herbaceous strata and scattered trees develop. These ecosystems shelter a diversified flora associated with these poor high altitude environments with a mesothermic climate: a cold season between May and September and warm between October and April. Collections were conducted from October to March 2009.
Morphological description of Timorus sarcophagoides
Sergio A. Vanin and Tadeu J. Guerra give a complete description of Timorus sarcophagoides, accompanied by biological and ecological observations.
The species has been positioned as belonging to the Zygopini tribe due to morphological characteristics such as the presence of a rostral canal formed solely by the prosternum. The search in the Curculionidae collections of the Zoology Museum of the University of Sao Paulo (MZUSP) allowed to find specimens with similar patterns, two of which, unidentified, seem to belong to the same species, one coming from the state of Minas Gerais (Lagao Santa) and the second from the state of Rio de Janeiro (Rio de Janeiro). Their examination showed, using Heller’s key, that the new species belonged to the genus Timorus (Schoenherr, 1838).
Morphological characters of Timorus sarcophagoides :
The Zygopini tribe consists of 33 genera of which 31 are found in the neotropical forests of America and 2 in Africa (Cameroon and Tanzania). The two genera already present in Brazil are Lissoderes (Champion, 1906) and Copturomorpha (Champion, 1906): Timorus differs morphologically at the level of metasternum and coxa. Furthermore, Timorus cannot be related to the other 8 genera of neotropical Zygopini (Arachnomorpha, Microzygops, Philenis, Helleriella, Larides, Phileas and Zygopsella) due in particular to prominent postocular lobes and posterior femurs that are longer than those of the anterior and medial legs.
While 5 species of the genus Timorus have been described in Brazil and 2 in French Guiana, none of them show a sexual dimorphism and a mimetic coloration similar to T. sarcophagoides : larger rostrum size in females, presence in males of thoracic spines used in intra-sexual selection (struggle to access females agonistic behaviour). However, the adaptive meaning of sexual dimorphism in weevils remains controversial because the history of these Beetles remains poorly understood.
This species is therefore the first of this type to be identified in South America and in a savannah environment.
Biology of T. sarcophagoides
Two consecutive years of observation in natura de Timorus sarcophagoides suggest that larvae and imagos feed exclusively on a single host plant species, mistletoe Psittacanthus robustus (Loranthaceae). Tadeu J. Guerra showed that adults are present only between November and February, the flowering period of the host plant, when they consume pollen grains, stamens and ovaries after piercing the tissues, but also the buds. The eggs, laid in February, are deposited in the root system of the host plant where the larvae, rhizophagi (feeding on roots), develop from March to September.
The pupae were exclusively found inside the roots in October, suggesting that the metamorphosis ends just before the start of the rainy season in October. Adults have a stereoptypical rubbing behaviour of the legs when they move imitating that of flies. When images are disturbed, they gain the underside of leaves or young shoots and leak away from the stimulus. During a capture, the images drop to the ground while remaining motionless: thanatos (“do the dead”).
The species is diurnal: individuals spend the night motionless on the leaves. When they feed, the rostrum of the imagos penetrates the inside of the plant tissues. It is then difficult for them to flee quickly from a possible predator.
Timorus sarcophagoides has a colouring and behaviour strongly similar to those of Sarcophagidae flies. Moreover, this species is very similar to another species from Panama: Euzurus ornativentris (Lechriopini) (Champion, 1906) (see photos at the end of the article – Paul Betner).
Sarcophagidae flies are commonly found in rocky touch environments throughout the year, but very abundantly between November and March. They are frequently placed on vegetation, flowers and leaves of P. robustus for example.
caption id=”attachment_3921″ align=”alignleft” width=”319″] T. sarcophagoides feeding on a floral receptacle and detail on a floral bud pierced with P. robustus (Source : Vanin & Guerra, 2012)[/caption]
The pattern of Torimus sarcophagoides does not converge towards a specific species of Sarcophagidae fly but more generally towards species of the genera Ravinia and Peckia (Euboettcheria) and Oxysarcodexia.
According to Hespenheide (1995), mimicry of weevils towards flies is a tropical phenomenon that more frequently survive in 4 to 8 mm phytophagous species using branches and trunks as micro-habitats. Sarcophagidae flies are not chemically armed against predators, but are perceived by predators as fast and agile, and therefore difficult to catch, which can provide a selective and adaptive advantage to similar species. A strong pressure of selection is thus exerted on the coloration by the visual predators that are the birds for example. This mimicry is called Mülllerian.
The author, T. J. Guerra, disagrees with this hypothesis. For him, the fact that only Timorus sarcophagoides takes advantage of the situation would make it a mimicry of type Batesian (read framed to discover the explanations of Tadeu J. Guerra – Read his interview below). The ecological origin and evolution of this type of mimicry remains difficult to demonstrate: Timorus sarcophagoides could constitute a preliminary model for future studies on this theme.
What does Tadeu J. Guerra say about it ?
Müllerian mimicry is characterized by the phenotypic convergence (coloration and/or behavior) of several harmful species (toxic for example) and emitting a warning signal (so-called aposematic species) in order to increase their protection potential against predators who learn to recognize them Lepidoptera du genus Heliconius). When a vulnerable species mimics one or more harmful aposematic species to fool the predator, mimicry is referred to as Batesian.
In the case of Timorus sarcophagoides and model flies, only the weevil takes advantage of the situation on the sole criterion of morphological similarity. As the model flies are not harmful, the system is based solely on the escape behaviour which is totally different between the two species. Mimicking Sarcophagidae flies sends a signal to potential predators: “I’m a fly, don’t try to capture me, I’m too fast and agile”. By broadening the definition of Batesian mimicry to behaviour (escape capacity), the author qualifies this mimicry as Batesian.
For him, Hespenheide’s proposal would be feasible if weevils and model flies exhibited the same leakage behaviour.
Interview of Tadeu J. Guerra
Can you explain us how you discovered the first specimen of Timorus sarcophagoides ?
I accidentally discovered the species. During my doctoral thesis at L’UNICAMP in Brazil, I studied the natural history and ecology of a mistletoe Psittacanthus robustus (Loranthaceae) in the grasslands of the Espinhaço region. The objective was to understand the mechanisms of infection of host trees by mistletoe and its reproductive ecology: pollination and dispersal by birds.
One of the experiments state to follow the reproductive phenology of mistletoe. One day in 2007 while collecting data on flowers of this species, I saw something that completely surprised me: a weevil feeding on a flower bud and behaving like a fly! In the days that followed, I did some Google research and after reading several available articles I thought, maybe, it might be a good idea to collect some specimens and send them to a specialist. So I contacted Dr. Sergio A. Vanin and sent him the specimens.
After their examination, he was delighted to be able to announce to me that it was probably a new species and that we could begin a collaboration to describe it. He did the taxonomic work and I gathered the available information on the biology of the species.
What are the evolutionary mechanisms behind the mimicry of Timorus sarcophagoides with flies of the Sarcophagidae family ?
The hypotheses on the evolutionary mechanisms of this mimicry were mainly proposed by Henry Hespenheide. He proposes that the adaptive advantage should be linked to flight behaviour in the face of predation, as many mimetic insect species do, in particular phytophagous insects. However, this mimetic complex in the subfamily Zygopinae (Coleoptera, Curculionidae) is very interesting because model flies are not supposed to be repugnant or harmful but on the contrary fast and elusive. Thus, the main hypothesis is that these mimetic weevils deceive predators orienting themselves by vision, recognizing in them prey types with high predation costs and therefore to avoid.
Experimental studies demonstrating this “escape mimicry” in nature are still lacking, and as a result, these theories remain speculative. Hespenheide’s idea is that this type of mimicry would be Mülllerian: it assumes that weevils can be as fast and sharp as flies. On this point, I totally disagree. I have seen these insects in nature many times and I am sure they are neither fast nor lively like flies. In fact, all specimens were easy to collect by hand. This is virtually impossible with model flies. For that, at least for T. sarcophagoides, I am totally convinced that mimicry is Batesian type, the weevil benefits from looking like something it is not, fast and sharp.
It is difficult to conclude on the origin of this mimicry because there is currently no phylogenetic visibility on the group. We can suggest that the mimicry between these species reflects an evolutionary convergence since the mimetic characteristics are found in several species from different families.
Where are your searches on this species ?
I am finishing a manuscript where we tested the adaptive potential of these weevils using modeling paste replicas placed in the habitat during the T occurrence period. sarcophagoides. We have recorded numerous attempts of attacks by birds showing that they could exert strong selection pressure on these insects. Furthermore, the results of our field experience were very clear regarding the adaptive potential of this mimicry: red-eyed weevil replicas were much less attacked by avian predators than brown-eyed or eyeless control replicas.
Do you still study this species ?
No, actually I started my career as an ornithologist. Then I became interested in mistletoes mainly in their relationships with birds that pollinate them and scatter their seeds. During my PhD, I found a plethora of insects associated with this plant and started to conduct several studies including the ecological aspect of weevils (see publications).
What interests you about insects ?
I have been fascinated by insects since childhood, especially their behaviour. I consider myself a naturalist: being in nature makes me happy. I really enjoy going out into the wild and exploring insect behaviour with my two children: insects are easy to turn. Observing phenomena like mimicry, bees and butterflies visiting flowers, predators like ants or wasps attacking their prey really makes my day.
I can’t explain it with words, I just like it. It’s a lot more fun than watching television or reading a book. I hope to do this for a long time to come.
What are you currently working on and what are your next scientific projects ?
I am currently studying the seed dispersal system of a plant species of the genus Miconia (Melastomataceae). I am interested in understanding how birds, lizards and ants contribute to the seed dispersal of this endemic plant from the Brazilian highlands.
caption id=”attachment_3929″ align=”alignleft” width=”281″] Mnemynurus sp. Conoderinae – Reserve La Fortuna – Panama (Source : Paul Berner – 2016)[/caption]
For more information :
– Vanin S.A. & ; Guerra T. J. (2012) : Une nouvelle espèce remarquable de charançon imitant la mouche à chair (Coleoptera : Curculionidae : Conoderinae) du sud-est du Brésil. Zootaxa 3413:55-63 (liena>)
strong>Recommandations d’ouvrages sur cette thématique :
>”text-decoration : underline ;”>Recommandations d’ouvrages sur cette thématique
– Coléoptères du monde : une encyclopédie em>(Patrice Bouchard, Yves Bousquet & ; Christopher Carlton – Editions …..) Delachaux & ; Niestlé – 656 pages – 7 avril 2016) (Retrouvez l’interview de l’auteur icia>)
– Evolution of the Insectsimg style=”border : none !important ; marge : 0px !important ;” src=”http://ir-fr.amazon-adsystem.com/e/ir ?” src=”http://ir-fr.amazon-adsystem.com/e/ir ?t=passioentomo-21&l=as2&o=8&a=0521821495″ alt=”” width=”1″ height=”1″ height=”1″ border=”0″ /> (David Grimaldi & ; Michael S. Engel – Edition : Cambridge University Press – 772 pages – 16 mai 2005)
– Evolution of Plant-Pollinator Relationships (Sébastien Patiny – Edition : Cambridge University Press – 514 pages – 8 décembre 2011)/p>>>(Sébastien Patiny – Edition : Cambridge University Press – 514 pages – 8 décembre 2011)
– Insect-Plant Biologyimg style=”border : none !important ; marge : 0px !!important ;” src=”http://ir-fr.amazon-adsystem.com/e/ir ?t=passioentomo-21&l=as2&o=8&a=0198525958″ alt=”” width=”1″ height=”1″ height=”1″ border=”0″ /> (Louis M. Schoonhoven, Joop J.A. van Loon & ; Marcel Dick – édition : OUP Oxford – 448 pages – 1 décembre 2005)
– Mimicry, and Other Protective Resemblances Among Animalsimg style=”border : none !important ; margin : 0px !important ;” src=”http://ir-fr.amazon-adsystem.com/e/ir ?” src=”http://ir-fr.amazon-adsystem.com/e/ir ?t=passioentomo-21&l=as2&o=8&a=B01G5QW7US” alt=”” width=”1″ height=”1″ height=”1″ border=”0″ /> (Alfred Russel Wallace – Edition : White Press – 98 pages – 28 juillet 2016)