Black Twig Borer
​Black twig borer (BTB), Xylosandrus compactus, belongs to the family Scolytidae and tribe Xyleborini. All species of Xyleborini are ambrosia beetles with the ambrosia fungus serving as the primary food for their development. BTB was first discovered on Oahu in 1961 and can also be found throughout Hawaii and all over the world.  

BTB is a serious pest of shrubs and trees and can cause extensive economic damage to coffee. It attacks the live twigs and branches, especially if the host has suffered some setback such as transplanting or drought. Most other species of the tribe Xyleborini attack only unhealthy or newly felled trees. Seedlings and twigs are readily killed
after a single gallery formation by an adult female. The list of host plants attacked in Hawaii is over 100 species of shrubs and trees in 44 families. There is a seasonal effect and plant stress effect on BTB population fluctuations. BTB populations show seasonal fluctuations throughout the year; however, populations are higher during the dry season. BTB population levels are directly related to plant stress, including harvesting and dry season. There were significantly more BTB at lower elevations than higher elevation farms.

Adult female BTB are about 1.7 mm long, 0.73 mm wide, and dark blackish-brown in color. Adult BTB males start off light brown and then turn reddish brown a few days later. Males are smaller than the female, 0.90 - 1.3 mm in length and about 0.44 mm in width. Male BTBs are incapable of flying.

​After initial boring, mother BTBs remain in the entry tunnels of their brood galleries throughout the period of brood development, and emerge from entry tunnels after about 26 days following initial boring. Their female progeny left the galleries after about 29 days following initial boring. On the other hand, unmated BTB females produce only male progeny. In the field, the ratio of female to male is about 9:1.

Symptoms of BTB Damage:
  • Premature yellowing and flagging (leaf tip points toward the ground) of the coffee tree leaves.
    • ​Flagging of branches occurs 5 to 7 days after initial tunneling and gallery formation. 
  • Small hole(s), about 1.0 mm in diameter, typically found on the underside of the lateral. 
    • Holes may also be found on coffee verticals, and particularly on younger verticals.
  • Necrosis (death) of leaves and stem extending from the entry hole distally (towards the branch tip) to the terminal of the branch.
  • Premature ripening and necrosis of berries distal of the entry hole.
  • Galleries within the stem and hollowing of the branch pith. 
    • ​Adults, eggs, larvae and pupae may be found in these galleries.
  • ​Adult female BTB can bore into the flower-end of coffee berries. 
    • ​Seed damage is infrequent but can occur. BTB eggs and larvae have not been found in the berry.

Methods of control:
  • Prompt removal of infested branches, which may also be destroyed by composting, burying or burning (ag burn permit may be required).
    • ​Don't allow BTB to escape and return to the field.
  • Maintain healthy plants by providing coffee trees with consistent and adequate fertilizers and irrigation.
  • Replace unhealthy seedling coffee trees with grafted coffee trees for tolerance to coffee root-knot nematode (CRKN) when planting and farming in locations infested with nematode.
    • Trees grafted onto Coffea liberica var. dewevrei rootstock, such as 'Fukunaga', may provide tolerance to CRKN. 
  • HDOA and coffee-approved Imidacloprid products may be used for chemical control.
    • Imidacloprid's mode of action is similar on target and non-target beneficial insects including honeybees, predatory ground beetles and parasitoid wasps. Imidacloprid is ineffective against spider mites and nematodes.
    • Repeated use of imidacloprid products have also been observed to increase mite damage on coffee trees, thereby reducing tree health.

Additional reading about Black Twig Borer:
Contact website management if you require any assistance with the site or information provided.