The telephone-pole beetle (''Micromalthus debilis'') is a
beetle
Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
native to the eastern United States, and the only living representative of the otherwise extinct
family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Micromalthidae. They have an unusual lifecycle involving asexually reproducing (
parthenogenetic
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...
) female larvae, as well as non-functional "ghost adults".
Taxonomy
Classification of ''M. debilis'' was historically controversial and unsettled. The species, first reported by
John Lawrence LeConte
John Lawrence LeConte (May 13, 1825 – November 15, 1883) was an American entomologist of the 19th century, responsible for naming and describing approximately half of the insect taxa known in the United States during his lifetime, in 1878, was long considered one of the
Polyphaga, and placed in the
Lymexylidae or
Telegeusidae, or as a family within the
Cantharoidea. However, characteristics of larvae, wings, and male genitalia show that it is in the suborder
Archostemata, where it has been placed since 1999.
Morphology and life cycle
![Micromalthus life cycle](https://upload.wikimedia.org/wikipedia/commons/e/e8/Micromalthus_life_cycle.webp)
The adult beetle is elongated, ranging from in length, and a dark brown to blackish color, with brownish-yellow legs and
antennae. The head is larger than the
thorax
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
, with large eyes protruding from either side.
The
larvae are wood-borers that feed on moist and decaying
chestnut and
oak
An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...
logs. They have also been reported as causing damage to buildings and poles (hence the name).
The life cycle is unusual in that the
cerambycoid stage of the larva gives birth via
parthenogenesis
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...
to
caraboid larvae, or more rarely, develops into an adult female. Adult males also rarely develop, consuming their mother from the inside. Development into adults is triggered by high temperatures, but this also results in high mortality of larvae. The adult females have a lifespan of six days, while males only live for around 12 hours, with a strongly biased
sex ratio
The sex ratio (or gender ratio) is usually defined as the ratio of males to females in a population. As explained by Fisher's principle, for evolutionary reasons this is typically about 1:1 in species which reproduce sexually. Many species d ...
towards females. The adults of both sexes are sterile, and are
vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
remnants of a time when the lifecycle involved sexual reproduction. The loss of sexual reproduction is likely associated with its infection by ''
Wolbachia
''Wolbachia'' is a genus of intracellular bacteria that infects mainly arthropod species, including a high proportion of insects, and also some nematodes. It is one of the most common parasitic microbes, and is possibly the most common reproducti ...
'' bacteria.
In an experimental study, heating was used to generate substantial numbers of adults to simulate the now non-functional adult life cycle. This species showed sex-role reversal. Females preferred to mate with males that originated from a different log than the one from which they originated, with a "dance" motion involving shaking of their abdomens and beating of their wings likely used to reject males. Females also competed for and initiated interactions with males, grasping the males' genitalia with their own.
Evolutionary history
Genetic studies have placed ''Micromalthus'' as more closely related to
Ommatidae than to
Cupedidae
The Cupedidae are a small family of beetles, notable for the square pattern of "windows" on their elytra (hard forewings), which give the family their common name of reticulated beetles.
The family consists of about 30 species in 9 genera, with ...
within Archostemata. A close relationship between Ommatidae and Micromalthidae is supported by several morphological characters, including those of the mandibles and male genitalia. The oldest record of Micromalthidae is ''
Archaeomalthus'' from the
Upper Permian
The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...
of Russia around 252 million years old, which is morphologically similar in many respects to ''Micromalthus'' including an only weakly sclerotised body. Several other fossil genera of the family are known including ''
Cretomalthus,'' known from a larva found in Early Cretaceous (
Barremian
The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is precede ...
) Lebanese amber. As well as ''
Protomalthus'' from the mid-Cretaceous (
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...
-
Cenomanian)
Burmese amber
Burmese amber, also known as Burmite or Kachin amber, is amber from the Hukawng Valley in northern Myanmar. The amber is dated to around 100 million years ago, during the latest Albian to earliest Cenomanian ages of the mid-Cretaceous period. The ...
of Myanmar.
Fossils of ''Micromalthus'' are known from the Miocene aged
Dominican amber
Dominican amber is amber from the Dominican Republic derived from resin of the extinct tree '' Hymenaea protera''.
Dominican amber differentiates itself from Baltic amber by being nearly always transparent, and it has a higher number of fossil inc ...
(adults and larvae, which were found to not be distinguishable from the living species
[ ]) and
Mexican amber (larvae), the upper Eocene
Rovno amber
Rivne amber, occasionally called Ukrainian amber, is amber found in the Rivne Oblast and surrounding regions of Ukraine and Belarus. The amber is dated between Late Eocene and Early Miocene, and suggested to be contemporaneous to Baltic amber. ...
of Ukraine (''Micromalthus priabonicus''), the early
Eocene
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
(
Ypresian
In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian ...
) aged
Oise amber
Oise ( ; ; pcd, Oése) is a department in the north of France. It is named after the river Oise. Inhabitants of the department are called ''Oisiens'' () or ''Isariens'', after the Latin name for the river, Isara. It had a population of 829,419 ...
of France (''Micromalthus eocenicus'') A possible specimen of ''Micromalthus'' is known from Burmese amber, but the poor preservation of the specimen makes the assignment tentantive.
Status
Reports of the species are infrequent and it is unknown whether they are rare, or common and unrecognized. A recent study by Bertone ''et al.'' (2016) found telephone-pole beetles in a survey of the indoor arthropod fauna in 50 houses located in and around
Raleigh, North Carolina
Raleigh (; ) is the capital city of the state of North Carolina and the seat of Wake County in the United States. It is the second-most populous city in North Carolina, after Charlotte. Raleigh is the tenth-most populous city in the Southe ...
.
A recent survey found that the species had spread to every continent except Australia. With finds in South Africa, Hong Kong, Belize, Cuba, Brazil, Japan, Hawaii, Italy and Austria, the dispersal is likely connected to the timber trade.
References
External links
*
*
Tree of Life page, with pictures and videoThe life cycle of Micromalthus debilis
{{Authority control
Archostemata
Beetles of North America
Beetles described in 1878