species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
ambrosia beetle
Ambrosia beetles are beetles of the weevil subfamilies Scolytinae and Platypodinae (Coleoptera, Curculionidae), which live in nutritional symbiosis with ambrosia fungi. The beetles excavate tunnels in dead or stressed trees into which they introduc ...
. Common names for this beetle include black twig borer, black coffee borer, black coffee twig borer and tea stem borer. The adult beetle is dark brown or black and inconspicuous; it bores into a twig of a host plant and lays its eggs, and the larvae create further tunnels through the plant tissues. These beetles are agricultural pests that damage the shoots of such crops as
coffee
Coffee is a beverage brewed from roasted, ground coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content, but decaffeinated coffee is also commercially a ...
,
tea
Tea is an aromatic beverage prepared by pouring hot or boiling water over cured or fresh leaves of '' Camellia sinensis'', an evergreen shrub native to East Asia which probably originated in the borderlands of south-western China and nor ...
avocado
The avocado, alligator pear or avocado pear (''Persea americana'') is an evergreen tree in the laurel family (Lauraceae). It is native to Americas, the Americas and was first domesticated in Mesoamerica more than 5,000 years ago. It was priz ...
.
Description
This beetle is dark brown or black. The adult female is up to long and about half as wide. The head is convex at the front with an indistinct transverse groove above the mouthparts. Each antenna consists of a funicle (base) with five segments and an obliquely truncated club slightly longer than it is wide. 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 e ...
is rounded with six or eight serrations on the front edge. The
elytra
An elytron (; ; : elytra, ) 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 (sometime ...
are convex and grooved and have fine perforations, and there are bristles between the grooves. The adult male is a smaller insect, has an unserrated pronotum and no wings.
The eggs are smooth, white and ovoid, about long. The
larva
A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...
e are creamy white with brownish heads and have no legs. The
pupa
A pupa (; : pupae) is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages th ...
e are cream-coloured and exarate (with free appendages).
Distribution
''Xylosandrus compactus'' has a wide distribution in the tropics. Its range extends from Madagascar and much of tropical Africa, through Sri Lanka and southern India, Thailand, Vietnam, Malaysia, China and Japan to Indonesia, New Guinea and various islands in the Pacific. It was introduced into the continental United States in 1941 and has also spread to Brazil and Cuba. It arrived in Hawaii in 1961, and here it infests over one hundred species of timber trees, fruit trees, ornamental trees and fruit bushes. Its presence in Hawaii is putting some rare and threatened endemic trees such as ''
Alectryon macrococcus
''Alectryon macrococcus'', known as ''Alaalahua'' or ''Māhoe'' in Hawaiian, is a slow-growing flowering tree in the soapberry family, Sapindaceae, that is endemic but manifests rarely in mesic forests of Kauai, Oahu, Molokai, and Maui Hawaii. ...
'', '' Colubrina oppositifolia'', '' Caesalpinia kavaiensis'', and '' Flueggea neowawraea'', at risk.
In 2011, ''Xylosandrus compactus'' was first detected in Europe in Portici and Naples, likely introduced through the international trade of nursery plants. Since then, within a few years, it has spread along the Tyrrhenian coast (2012 in Tuscany and Liguria, 2016 in Lazio and Sicily), subsequently reaching the northern inland areas (2015 in Lombardy), and finally the Adriatic coast (2018 in Emilia-Romagna, 2019 in Veneto). In 2015, the species expanded from Liguria to France (French Riviera), and in 2019 it was recorded in Spain (Mallorca, Balearic Islands) on a carob tree, which was promptly treated in an attempt to eradicate the beetle. In July of the same year, ''X. compactus'' was also found in southern Greece infesting carob, laurel, olive, Judas tree, and shrubs of the genus ''Rhamnus,'' thereby becoming a concern at the European level.
Hosts
Some 225 species of plants in 62 families have been recorded as acting as hosts for this beetle. In a natural broad-leafed forest it does not normally cause much damage, but when it infects plantations of susceptible host plants it may become a pest. Major crops where it does serious damage are coffee, tea, avocado and cocoa. In India it attacks ''
Khaya grandifoliola
''Khaya grandifoliola'', also called African mahogany, Benin mahogany, large-leaved mahogany, or Senegal mahogany, is a species of plant in the family Meliaceae. It is found in Benin, the Democratic Republic of the Congo, Ivory Coast, Ghana, Guin ...
'' and ''
Khaya senegalensis
''Khaya senegalensis'' is a species of tree in the Meliaceae family that is native to Africa. Common names include African mahogany, dry zone mahogany, Gambia mahogany, khaya wood, Senegal mahogany, ''cailcedrat'', ''acajou'', ''djalla'', and '' ...
'', which are grown as shade trees in plantations, and similarly in Africa it attacks ''
Erythrina
''Erythrina'' is a genus of plants in the pea family, Fabaceae. It contains about 130 species, which are distributed in tropical and subtropical regions worldwide. They are trees, with the larger species growing up to in height. These species ...
'' sp. and ''
Melia azedarach
''Melia azedarach'', commonly known as the chinaberry tree, pride of India, bead-tree, Cape lilac, syringa berrytree, Persian lilac, Indian lilac, or white cedar, is a species of deciduous tree in the mahogany family (biology), family, Meliace ...
''. It is particularly damaging in tree nurseries, killing seedlings and young saplings. A study in Uganda's shaded
robusta coffee
''Coffea canephora'' (especially ''C. canephora var. robusta'', so predominantly cultivated that it is often simply termed ''Coffea robusta'', or commonly robusta coffee) is a species of coffee plant that has its origins in central and west ...
systems, tree species suppressing ''X. compactus'' infestation characteristically exuded copious sap regardless of any stress. Therefore, the presence or absence of copious sap exuding from trees upon injury likely differentiates ''X. compactus'' hosts from non-hosts.
Ecology
In Florida, where ''X. compactus'' has been introduced, the life cycle is completed in about twenty-eight days. Like other ambrosia beetles, the adult female carries fungal
symbionts
Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term
Fusarium
''Fusarium'' (; ) is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants. Most species are harmless saprobes, and are relatively abundant members of the s ...
'' species. These fungi colonize the
xylem
Xylem is one of the two types of transport tissue (biology), tissue in vascular plants, the other being phloem; both of these are part of the vascular bundle. The basic function of the xylem is to transport water upward from the roots to parts o ...
tissue of the plant host, and are consumed by the adult beetles and larvae. Male larvae are produced from unfertilised eggs and are few in number; they remain in the gallery and eventually mate with their sisters. After pupation, the newly emerged female beetles remain in the tunnels for about eight days, and mating takes place here. They then crawl out of the tunnels and fly to another host tree, carrying some of the fungus with them. Here they tunnel into sound wood on the underside of the branch, introduce the fungus and start laying eggs. The females live for about forty days; symptoms of the infestation of a twig include the death of the stem and leaves beyond the tunnel entrance.