''Platypus quercivorus'', the oak ambrosia beetle, is a species of

weevil Weevils are beetles belonging to the Taxonomic rank, superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and Herbivore, herbivorous. Approximately 97,000 species of weevils are known. They b ...

and pest of

broad-leaved tree A broad-leaved, broad-leaf, or broadleaf tree is any tree within the diverse botanical group of angiosperms that has flat leaves and produces seeds inside of fruits. It is one of two general types of trees, the other being a conifer, a tree with ne ...

s.Sone, K., Mori, T., Ide, M. (1998). Life history of the oak borer, ''Platypus quercivorus'' (Murayama) (Coleoptera : Platypodidae). ''Applied Entomology and Zoology 33'': 67-75. This species is most commonly known for vectoring the

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

responsible for excessive oak dieback in Japan since the 1980s.Kamata, N., Esaki, K., Kato, K., Igeta, Y., Wada, K. (2002). Potential impact of global warming on deciduous oak dieback caused by ambrosia fungus ''Raffaelea sp'' carried by ambrosia beetle ''Platypus quercivorus'' (Coleoptera : Platypodidae) in Japan. ''Bulletin of Entomological Research 92'': 119-126. It is found in Japan, India, Indonesia, New Guinea, and Taiwan.

Description

Since ''P. quercivorus'' belongs to the

Platypodinae Platypodinae is a weevil subfamily in the family Curculionidae. They are important early decomposers of dead woody plant material in wet tropics; all but two species are ambrosia beetles that cultivate fungi in tunnels excavated in dead wood as t ...

, it has distinct clubs on the end of its stout antennae with three solid segments.Benzel, J. (2015). Screening aid: Ambrosia beetles, ''Platypus quercivorus'' (Murayama), ''Megaplatypus mutatus'' (Chapuis). Identification Technology Program (ITP), USDA-APHIS-PPQ-S&T, Fort Collins, CO. 7 pp. Usually, the beetle is between 4 and 5 mm long, reddish-brown in colour, and is elongate and roughly cylindrical. The

prothorax The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites (exoskeletal plates) are the pronotum (dorsal), the prosternum (ventral), and the propleuron (lateral) on ea ...

is as wide as the head. Males have a shallow, unarmed plate on the underside of 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 ...

and a convex and downward slope of their

elytra An elytron (; ; , ) is a modified, hardened forewing of beetles (Coleoptera), though a few of the true bugs (Hemiptera) such as the family Schizopteridae are extremely similar; in true bugs, the forewings are called hemelytra (sometimes alterna ...

. The elytra have a broad square end and spines at the top. Females have a

mycangium The term mycangium (pl., mycangia) is used in biology for special structures on the body of an animal that are adapted for the transport of symbiotic fungi (usually in spore form). This is seen in many xylophagous insects (e.g. horntails and bark b ...

on the

pronotum The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites (exoskeletal plates) are the pronotum (dorsal), the prosternum (ventral), and the propleuron (lateral) on ea ...

for carrying

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

fungi spores.Esaki, K., Kato, K., Kamata, N. (2004). Stand-level distribution and movement of ''Platypus quercivorus'' adults and patterns of incidence of new infestation. ''Agricultural and Forest Entomology 6'': 71-82. Although this trait may be in both females and males, it is always in females and rarely in males.

Habitat

Although well known in Japan, this species also lives in India, Indonesia, New Guinea and Taiwan.Kobayashi, M., Ueda, A. (2002). Preliminary study of

mate choice Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior.Bateson, Paul Patrick Gordon. "Mate Choice." Mate Choic ...

in ''Platypus quercivorus'' (Murayama) (Coleoptera : Platypodidae). ''Applied Entomology and Zoology 37'': 451-457. Trees to inhabit are often selected for based on

olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...

and visual cues.Yamasaki, M., Futai, K. (2012). Discrimination among host tree species by the ambrosia beetle ''Platypus quercivorus''. ''Journal of Forest Research 17'': 149-155. Infestation of these habitats occurs in stages beginning with males flying to and landing on a tree and then boring into the bark through the stems. Typically, this species aggregates in areas with clusters of similar, suitable trees to increase infestation efficiency. This may be due to

coevolution In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well ...

ary factors with tree species ''

Quercus crispula ''Quercus crispula'', commonly known as mizunara from the Japanese, is a deciduous broad-leaved tree of the genus ''Quercus''. As ''Quercus mongolica'' var. ''crispula'', it is considered a variety of ''Mongolian oak'' by some authorities, ...

'' as it is most suitable for gallery formation and is distributed in a clumped pattern.Yamasaki, M., Sakimoto, M. (2009). Predicting oak tree mortality caused by the ambrosia beetle ''Platypus quercivorus'' in a cool-temperate forest''. Journal of Applied Entomology 133'': 673-681. This allows for an increased chance of more abundant, successful galleries. Trees are also selected for more often with increasing

diameter at breast height Diameter at breast height, or DBH, is a standard method of expressing the diameter of the trunk or bole of a standing tree. DBH is one of the most common dendrometric measurements. Tree trunks are measured at the height of an adult's breast, ...

(DBH). This allows for more room for gallery formation, which are often located in lower trunks of oak trees.Kuroda, K. (2001). Responses of ''Quercus'' sapwood to infection with the pathogenic fungus of new wilt disease vectored by the ambrosia beetle ''Platypus quercivorus''. ''Journal of Wood Science 47'': 425-429. Males of this species are attracted to soaked logs over dry logs.Kitajima, H., Goto, H. (2004). Rearing technique for the oak platypodid beetle, ''Platypus quercivorus'' (Murayama) (Coleoptera : Platypodidae), on soaked logs of deciduous oak tree, ''Quercus serrata'' Thunb. Ex Murray. ''Applied Entomology and Zoology 39'': 7-13. The

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...

conditions of the submerged logs increases the likelihood of a male choosing those logs to create a gallery. This may occur because those conditions favour the growth of the beetle's fungi

symbionts Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

. There is a preference for edge habitats over deep forest interiors.Igeta, Y., Esaki, K., Kato, K., Kamata, K. (2003). Influence of light condition on the stand-level distribution and movement of the ambrosia beetle ''Platypus quercivorus'' (Coleoptera : Platypodidae)''. Applied entomology and Zoology 38'': 167-175. Roadsides and other edges act as attractions for the beetle. This attraction may be due to an increased light presence as the species is positively

phototactic Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive li ...

. This beetle prefers habitats with the highest light intensity when offered varying intensities. It has been suggested that the 0.4˚C increase in average temperature compared to the last 100 years in Japan is responsible for the increased range of the beetle and oak dieback. The warmer climate has allowed the beetle to move north, encountering its best suited host, ''Q. crispula''. It is proposed that as the climate increases, more overlap between the beetle and the best suited host will occur, resulting in an even stronger oak dieback

epidemic An epidemic (from Ancient Greek, Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of patients among a given population within an area in a short period of time. Epidemics ...

Reproduction

Mate choice

Due to the

monogamous Monogamy ( ) is a form of Dyad (sociology), dyadic Intimate relationship, relationship in which an individual has only one Significant other, partner during their lifetime. Alternately, only one partner at any one time (Monogamy#Serial monogamy, ...

nature of the oak ambrosia beetle, mate selection is vital for both females and males. It is in the male's best interest to select a mate capable of excavating the gallery, planting nourishing fungi for larvae,

oviposition The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...

, and bringing frass to the male for removal. For females, selecting a male that has bored into a tree with sufficient resources is important to increase

fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...

. Mating is male-initiated. Males will bore a cylindrical entrance tunnel during late spring to early summer, meet the female there, and mate at the entrance hole. The male will enter the gallery first, followed by the female. Then, both back out of the gallery, changing positions so that the female will enter first for the second entrance, and enter again. They will then both back out until the female's

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

is exposed and

copulation Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetrat ...

will begin. It is suggested that female mate choice occurs between the first and second entrance because she is then able to view the gallery whereas male mate choice occurs at the beginning of the process when he decides whether or not to let the female enter the tunnel he bored. Once both the male and female have chosen to proceed with reproduction, males make signals to prevent other females from entering the gallery.

Parental Care

Each pairing will create one gallery with vertical and lateral branches and die in it together.Kinuura, H., Kobayashi, M. (2006). Death of ''Quercus crispula'' by inoculation with adult ''Platypus quercivorus'' (Coleoptera : Platypodidae). ''Applied Entomology and Zoology 41'': 123-12. The female will deposit eggs at the tunnel's ends two to three weeks following gallery completion. This must be done in trees that have not been previously infested by other ''P. quercivorus''. The male will then create a barricade at the gallery's entrance with his body. Here, he waits for the female to bring frass and bored dust which the male will then discard outside. This species has a high reproduction rate, which in addition to low brood

mortality Mortality is the state of being mortal, or susceptible to death; the opposite of immortality. Mortality may also refer to: * Fish mortality, a parameter used in fisheries population dynamics to account for the loss of fish in a fish stock throug ...

resulting from cooperative parental care, may contribute to the high reproductive success of this species. Reproductive success is shown to be higher in logs than in living trees. Galleries in living trees lowers reproductive success of the oak ambrosia beetle because the tree's defensive mechanism of sap secretion enters galleries and kills individuals. Tree species ''Q. crispula'' is the most suitable host species for reproducing and rearing offspring.

Growth and development

Eggs hatch in about a week. The

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e then graze on the symbiotic fungi covering the gallery walls and pass through five

instar An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...

s. Adults emerge from their mother galleries 2–4 hours following dawn due to their diurnal tendencies. Approximately 40% of

broods Broods is a New Zealand musical duo from Nelson, composed of Georgia Josiena Nott on lead vocals, with older brother and multi-instrumentalist Caleb Allan Joseph Nott on production and backing vocals. They released the single "Bridges", which w ...

reach adulthood by late summer to early fall. After reaching adulthood, individuals usually leave their galleries but some remain in their maternal galleries. The remaining 60% of broods will reach the fifth larval stage by mid fall and overwinter in pupal chambers. These individuals emerge as adults in late spring to early summer. This brooding technique is partially

bivoltine Voltinism is a term used in biology to indicate the number of broods or generations of an organism in a year. The term is most often applied to insects, and is particularly in use in sericulture, where silkworm varieties vary in their voltinism. ...

because approximately 40% of each population takes one year to complete a life cycles whereas the other 60% may have two generations in a year. Individuals that remain in maternal galleries are often shown to not reproduce but rather, clean the galleries, which presents the possibility that this species may have

eusocial Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generat ...

tendencies. It is assumed that parents die either before or during winter.

Interspecific relationships

''P. quercivorus'' has symbiotic relationships with fungi and oak trees.Endoh, R., Suzuki, M., Okada, G., Takeuchi, Y., Futai, K. (2011). Fungus Symbionts Colonizing the Galleries of the Ambrosia Beetle ''Platypus quercivorus''. ''Microbial Ecology 62'': 106-120.

Symbiotic relationship with fungi

''P. quercivorus'' acts as the primary vector for the

parthenogenic 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 development ...

fungus ''

Raffaelea quercivora ''Raffaelea quercivora'' is a species of fungus in the family Ophiostomataceae The Ophiostomataceae are a family of fungi in the Ascomycota, class Sordariomycetes. The family was circumscribed by J.A. Nannfeldt in 1932. Species in the f ...

,'' which causes

Japanese Oak Wilt Japanese oak wilt (also called mortality of oak trees in Japan) is a fungal disease caused by ''Raffaelea quercivora'' fungus affecting by oak trees. In 1998, Japanese plant pathologists group was isolation, inoculation and reisolation the dead tre ...

disease. The oak ambrosia beetle bores into sapwood and heartwood of host oaks commonly including ''Q. crispula'' and ''Quercus serrata''. Once infected, these trees wilt and die, paralleling the effects of

Dutch elm disease Dutch elm disease (DED) is caused by a member of the sac fungi (Ascomycota) affecting elm trees, and is spread by elm bark beetles. Although believed to be originally native to Asia, the disease was accidentally introduced into Americas, America ...

. The oak ambrosia beetle carries not only the pathogen itself, but also dietary fungus symbionts in mycangia. Once galleries are constructed by the beetle in the sapwood of a host tree, the released fungi disseminate in yeast-like

microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

and grow on the gallery walls. ''P. quercivorus'' larvae then hatch and feed on the growing fungi. In addition to ''R. quercivora'', ''P. quercivorus'' has at least one other main symbiont, ''Candida kashinagacola,'' as these two fungi species are found in all tree host types selected for by the beetle. The latter fungus species, however, has not been linked to any parasitic tree diseases. In both relationships, the beetle receives a food source and the fungus receives transport into its final host.

Predatory relationships with oak trees

By acting as a vector for ''R. quercivora'', the oak ambrosia beetle has killed trees since the 1980s. This species attacks all trees and logs but prefers debilitated trees and fresh logs for rearing offspring. Typically, infestation rates are high, possibly to efficiently utilize sparse resources. Working together with the fungi they vector, the ambrosia beetle galleries disrupt the flow of water within trees, leading to

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

within 2–3 months of the attack. Mass attacks of the beetle are necessary to overcome defense mechanisms of trees. Often, ''P. quercivorus'' attacks trees from the family

Fagaceae The Fagaceae are a family of flowering plants that includes beeches, chestnuts and oaks, and comprises eight genera with about 927 species. Fagaceae in temperate regions are mostly deciduous, whereas in the tropics, many species occur as evergre ...

but is known to attack 45 different woody plant species from 27 genera in 17 families. Infestation occurs in stages. First, trees surrounding previously infested trees are infested early in the season. Then, major infestation occurs from the epicentre formed at the upper forest margin or at a forest edge, which then spreads downward into the remaining forest.

Dispersal

These individuals spread through long-distance dispersal and diffusion. Endemic populations are limited to weakened, old, and highly stressed tree populations but will attack healthy trees once local ''P. quercivorus'' populations reach an overcrowded threshold. Infestation happens quickly and parallels

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

with no regulating factors. This species may grow in population size and numbers in sudden outbreaks. These sudden outbreaks may be due to climatic and biological factors that cause host trees to reduce the amount of sap they secrete through parasite-induced necrosis, which is their main defense mechanism to control ''P. quercivorus'' populations. Additionally, habitats with an abundance of suitable host plants may encourage population outbreaks. Populations form through the use of

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

s released by members of the species in order to attract more individuals to overcome the tree's defenses. From analyzing interception trap results, oak ambrosia beetles are known to move upwards along slopes. Typically, adult movement is influenced by environmental factors such as light, wind, and gravity. It is thought that upward movement of wind majorly influences ''P. quercivorus'' movement. Additionally, oak ambrosia beetles have positive phototaxis and fly more near forest edges. Adults tend to concentrate near upper edges of forests and have a gradient population along slopes. This species is labelled as an edge species due to its preference for edge habitat.

Control techniques

Although not yet implemented, researchers suggest that protecting frequently attacked trees is important. One way to do this is by binding the trunks with vinyl sheets which will prevent the beetle from boring into trees and transmitting the fungus. Researchers understand that not all trees should be protected but those with a high probability of being attacked should be. Trees from the family Fagaceae that have a larger DBH, are in clumps, and are on edges near excess light should be included in the protection plan.

References

External links

The Invasive Species Compendium webpage for ''P. quercivorus''
{{Taxonbar, from=Q7712360 Platypodinae Beetles described in 1925