Xylosandrus compactus

Xylosandrus compactus

The black twig borer or black coffee borer, black coffee twig borer, tea stem borer (Xylosandrus compactus Eichhoff, 1875) is an insect belonging to the Curculionidae family.

Systematic –
From a systematic point of view it belongs to:
Eukaryota domain,
Kingdom Animalia,
Subkingdom Eumetazoa,
Bilateria branch,
Phylum Arthropoda,
Subphylum Tracheata,
Superclass Hexapoda,
Class Insecta,
Subclass Pterygota,
Endopterygota cohort,
Superorder Oligoneoptera,
Coleopteroidea section,
Order Coleoptera,
Suborder Polyphaga,
Infraorder Cucujiformia,
Superfamily Curculionoidea,
Curculionidae family,
Subfamily Scolytinae,
Xyleborini Tribe,
Genus Xylosandrus,
X. Compactus species.
The terms are synonymous:
– Xyleborus compactus Eichhoff, 1875;
– Xyleborus morstatti Hag. 1954.

Geographic Distribution and Habitat –
Xylosandrus compactus is a beetle of Asian origin, now present in all tropical countries and in the south-east of the United States of America where it damages many types of agricultural plants.
It is an insect with a wide distribution in tropical areas. 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 of the Pacific. It was introduced to the continental United States in 1941 and has also spread to Brazil and Cuba. It arrived in Hawaii in 1961, and here infests over one hundred species of trunk trees, fruit trees, ornamental trees and fruit shrubs. Its presence in Hawaii is putting at risk some rare and threatened endemic trees such as Alectryon macrococcus, Colubrina oppositifolia, Caesalpinia kavaiensis and Flueggea neowawraea.
Its presence was also reported in Italy for the first time in Campania. Now it is also present in other areas, such as Tuscany.

Morphology –
Xylosandrus compactus is a beetle with a dark brown or black color.
The adult female is up to 2 mm long and about half that wide. The head is convex anteriorly with an indistinct transverse groove over the mouthparts.
Each antenna consists of a cord (base) with five segments and an obliquely truncated club that is slightly longer than it is wide.
The pronotum is rounded with six or eight serrations on the anterior edge. The elytra are convex and grooved and have fine perforations and bristles are present between the grooves.
The adult male is a smaller insect, has a non-serrated pronotum and has no wings.
The eggs are smooth, white and ovoid, about 0.5 mm long.
The larvae are creamy white with brownish heads and have no legs.
The pupae are cream-colored and exarate (with free appendages).

Aptitude and biological cycle –
Xylosandrus compactus is a xylophagous insect which, in the presence of high populations, can damage host plants.
It is the adult females that are responsible for the infestation of a new host plant where they dig the characteristic tunnels; like all lignicolous bark beetles, X. compactus also obtains the necessary nourishment for the development of the larvae from the proliferation of particular fungi, called “ambrosia”, which the females carry on their body and introduce into the host plant at the time of the formation of the galleries.
During the formation of the tunnels, and in particular in the first few days, the female pushes the rosura outwards which often, remaining pressed, forms a long, clear and fragile cylinder protruding from the entrance hole. It then widens to form an elongated breeding chamber where the eggs are laid and larval development begins.
The female then digs one to three new short tunnels (2–3 cm) where the development of the larvae can continue. All the internal walls of the breeding chamber and the secondary galleries are soon covered by the fungi introduced by the female, essential for the larval development and the subsequent maturation of the new adults.
Wintering is generally supported by the adults at the base of the trees attacked during the previous summer. Except for delays due to unfavorable climatic conditions, spring emergence begins around mid-May, and the adults move about one meter above the ground in flight in search of a suitable host for colonization.
As soon as she arrives on the bark, the female begins digging the system of tunnels where the eggs will be laid after mating.
Approximately 28 days are needed at a temperature of 25°C for development from egg to adult to occur.
Due to the attacks, typical flag-like wilting of the young branches or suckers is evident, due to the spread of the symbiotic fungus in the host’s xylem and at the same time to the tunnels dug by the adult female.

Ecological Role –
Xylosandrus compactus is a xylophagous insect that tends to damage, in the presence of high populations, the shoots of crops such as coffee, tea, cocoa and avocado or other potential plants in newly introduced countries.
About 225 plant species in 62 families have been recorded as hosts for this beetle. In a natural deciduous forest it does not normally cause much damage, but when it infects plantations of susceptible host plants it can become a dangerous pest. The main crops where it causes serious damage are coffee, tea, avocado and cocoa. In India it attacks Khaya grandifoliola and Khaya senegalensis, which are grown as shade trees in plantations, and similarly in Africa it attacks Erythrina sp. and Melia azedarach. It is particularly harmful in nurseries, killing seedlings and young saplings. A study of Ugandan robusta coffee systems found that tree species that suppress X. compactus infestation typically exude copious sap regardless of any stress. Therefore, the presence or absence of abundant sap exuding from trees following injury likely differentiates X. compactus hosts from nonhosts.
Like other beetles, the adult female carries fungal symbionts, particularly Ambrosiella xylebori and Fusarium species. These fungi colonize the xylem tissue of the host plant and are consumed by adult beetles and larvae.
In the event of significant infestations, or the risk of them, it is advisable to cut and eliminate the infected parts and carry out good cultural care of the plants to increase their vegetative growth.
Furthermore, it is advisable not to specialize the cultivation of plants susceptible to attack, by intercropping, even with alternate rows, of other non-susceptible plants and other measures typical of agroecological techniques.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Russo G., 1976. Agricultural Entomology. Special Part. Liguori Editore, Naples.
– Pollini A., 2002. Manual of applied entomology. Edagricole, Bologna.
– Tremblay E., 1997. Applied entomology. Liguori Editore, Naples.

Photo source:
– https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium.57234