Kingdom Animalia Class Insecta Family Curculionidae Rank Species | Phylum Arthropoda Order Coleoptera Genus Platypus | |
Similar Platypus, Platypus australis, Platypus cylindrus, Hylastes ater, Platypodinae | ||
Platypus apicalis, known by its common name the New Zealand pinhole boring beetle, is a wood boring beetle endemic to New Zealand and found throughout the North and South Island in a range of environments.
Contents
Description
The colour of Platypus apicalis is mainly dark-brown, with yellow basal joint of antennae, metathorax and femora. The body is cylindrical in cross section and greatly elongated from front to rear. It is less than 2 mmm wide and about 5.8 mm long. The mandibles of adults are oriented downward. The terminal segment of the antennae is dorso-ventrally flattened and larger than the other antennal segments. A narrow longitudinal groove is present on the middle of the pronotum. The elytra bear parallel longitudinal grooves, are mainly smooth but pubescent at their rear end and sides, and are slopping downward at their posterior end.
Platypus apicalis exhibits sexual dimorphism. The elytrae of males bear tooth like projections at their posterior end. The body of females is more pubescent than this of males, lack elytral teeth, and have a more rounded shape. Adult males release a strong and distinguishable odor when emerging from the tree they developed in. Females have not been found to release this scent.
Eggs are round, less than 1 mm in diameter, and have a creamy appearance. Young larvae are flat and have fleshy projections on sides. In contrast, fully grown larvae are white, cylindrical and legless with yellow coloured heads. At this stage the mandibles begin to orient downward and ridges start to appear on the top of the prothorax.
Natural range
Platypus apicalis only occurs in New Zealand. More specifically, it occurs on the West coast of the South Island and the centre of the North Island in natural beech wood forests and in certain exotic plantations, such as these of eucalyptus.
Habitat preferences
The habitat preference of this species is predominantly dead beech wood forest, including Red Beech, Silver Beech and Black beech. The beetle has no preference for hard or soft wood as it resides inside the Beech trees and some Eucalyptus species. The Platypus resides in the dead wood of the tree but when numbers grow due to sufficient breeding material, healthy trees are threatened by their invasion. They are considered pests at times to native forests but only when they threaten healthy trees. Their main pest area is the forestry plantations where they colonise and render some high quality timber useless due to imperfections and colour change in the timber.
Economic significance
Platypus apicalis can be a pest in high quality timber plantations. It vetors fungi that develop into the wood, altering its colour. In addition, their tunnels, which go deep into the wood, create imperfections in the finished timber, which also weakens it.
Life cycle/Phenology
The life cycle begins with a male adult boring a tunnel into a host tree and releasing fungal spores along the way. Fungal species, particularly ambrosia fungi, serve as the primary food for the beetle. This tunneling process usually occurs within the early summer months of November and December. Once the tunnel is several centimetres long, the insect will release an odour that acts as an attractant to female insects. If enough male beetles do this at once, it leads to so called "mass attacks" on trees where swarms of beetles attack a single host specimen. Copulation occurs at the tunnel entrance and afterward the female goes into the tunnel and begins the process of making a nest. The male continues to enlarge the tunnel and remove excess frass (excreta). The tunnel is initially radial but eventually has a sharp right angle and moves towards the heartwood of a tree. Meanwhile the female lays the first batch of egg containing four to seven eggs. Following this, another branch of the tunnel is then started by the male and eventually a second egg batch is laid. At this point 8–10 months have passed since copulation.
While the exact time of larval hatching is not yet certain, it is known that there is a period of two years from the time the nest is laid to the time that fully grown beetles emerge from hosts. During this time the larvae go through several stages. Initially the larva simply extend the tunnels of the parents. These extensions differ from the parents in that the tunnels are concave rather than flat. During this time, the larvae grow bigger in size and begin to take on some adult features. After a period of several months, the larva excavate pupal chambers within the tree. The larvae then enter the chambers and become pupas, intermediate insect form. Finally, when two years have passed since the egg laying, adult beetles emerge from the chambers and exit the tree. This occurs during the summer months of January to March. The average number of beetles per tree is 115. The adult beetles then go out into the forest and look for a new host tree. The lifecycle is then repeated. The average lifespan of an adult pinhole beetle is estimated to be 3–4 years.
Diet and foraging
Platypus apicalis is classified as an ambrosia wood boring beetle. Beetles in the category survive by boring tunnels into the xylem (water transport tissue) and phloem (food transport tissue) of a host tree species. Ambrosia beetles have a symbiotic relationship with a category of fungus known as Ambrosia. Fungal spores are contained within the gut of Ambrosia beetles and as beetles bore into a tree, they release the spores. The fungus is then cultivated within the tree and used by the beetles as a food sources. The xylem and phloem tissue of the tree is merely a medium for the fungus, it is not a source of food for the beetle.
Predators, parasites, and diseases
Along with the Ambrosia fungi, pathogenic fungi is associated with the fully grown beetles. This fungi has been known to infect and kill the host tree when it is attacked by the adult beetles. Populations of the insect are currently controlled by agricultural cultural practices, there are no effective predators of the insect, there is a species of parasitic nematode known to situate with the insect but its effectiveness in population control is unknown. Scientists have tested strains of B. bassiana, B. brongniartii and Metarhizium anisopliae which are found in southern beech forests or in places where no Platypus are found. They were tested on both the adult and larvae stages of the insect, a total of 10 isolates where tested and scientists found that all killed the adult stage of the insect. This provides a natural and common control method that could be used in the future to help control the population of the Platypus apicali.
Other information
Platypus apicalis has both biodiversity and economic impacts. From a biodiversity perspective, the beetles are a threat to beech trees. While some trees have been known to survive, in most cases the combination of the tunnels through the xylem and phloem and the subsequent fungal infection prove lethal. This and the fact that it has no known predators and few parasites makes it a potential threat to beech tree population numbers. There is also the threat of the species escaping New Zealand via exports of lumber. Beech species exist throughout much of the world and it is conceivable that the insect could survive quite well elsewhere. From an economic standpoint, the tree reduces the amount of native timber available. Even if a tree is not killed outright, the invasion often causes defects such as concealed rot pockets and irregular wood cores. Damaged trees are also easy targets for other species of fungi. This not only affects logging companies, but also associated industries.