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      Black twig borer attack causing flagging (Photo: Andrew J. Boone, South Carolina Forestry Commission) - Click for full size   Black twig borer galleries in magnolia twig (Photo: Forrest L. Oliveria, USDA Forest Service) - Click for full size
    Taxonomic name: Xylosandrus compactus (Eichhoff, 1875)
    Synonyms:
    Common names: ambrosia beetle (English), black twig borer (English), Dunkler-Holzbohrer (German)
    Organism type: insect
    Originally from Asia, Xylosandrus compactus has spread to many coffee growing areas throughout the world where it causes damage not only to agricultural crops, but also to native forest trees. Beetles (Coleoptera) in the family Scolytidae, to which Xylosandrus compactus belongs, are among the most damaging insects worldwide. Because most scolytids breed under bark or inside wood, it has long been recognised that scolytids can easily be moved through international trade.
    Description
    "The black twig borer is a very small (1/16 inch), shiny, black, cylindrical beetle. Twig entrance holes are about 1/32 inch in diameter and usually found on the lower surface of the twig. Eggs are extremely small, oval, white and translucent. Black twig borer grubs are white and legless. The body of young grubs is pointed at the rear. Older grubs have a brownish heads and round tails. The pupa is about the size of the adult and clearly shows the legs,wings and head." (Baker, 1994). Xylosandrus compactus belongs to the Xyleborini tribe, all of which feed on ambrosia fungus and are called ambrosia beetles.
    Occurs in:
    agricultural areas, natural forests, planted forests
    Habitat description
    There are more than 200 recorded hosts of the black twig borer, some of them are the orchids Cattleya, Dendrobium, Epidendrum, Vanda; other hosts include anthurium, avocado, citrus, coffee, cacao, brushbox (Tristania conferta), turpentine tree (Syncarpia glomulifers), paper-bark (Melaleuca leucadendron), red-ironbark eucalyptus (Eucalyptus sideroxylon), blackbutt eucalyptus (E. pilularis), robust eucalyptus (E. robusta), Koa haole (Leucaena glauca), guava, vervain (Stachytarpheta jamaicensis), Christmasberry (Schinus terebinthifolius) floral red ginger, litchi, macadamia, mango, mahogany, hibiscus, kukui, star jasmine, pikake, periwinkle, Surinam cherry (Hara & Tenbrink, 1994) etc.
    General impacts
    At least one of the fungi in the ambrosia is Fusarium solani. Infested twigs usually dieback to a point below the brood chamber. Although the ambrosia usually does not kill the whole plant, the dieback of twigs can have considerable impact on the appearance of infested trees and shrubs.
    Female black twig borers tunnel into woody twigs, leaving pin-sized entry holes. Once inside they excavate galleries and lay eggs. This excavation, along with the introduction of pathogens, is the cause of damage to the host. Ambrosia beetles are serious pests of forest trees and, to a lesser extent, shade and fruit trees. Most ambrosia beetles attack primarily weak or unhealthy plants; however, the black twig borer is known to attack healthy plants as well, which makes it a potentially very serious pest to native forest trees as well as other plants. Damage is not caused by feeding, since the beetle larvae feed on ambrosia introduced by the female. Infestation by one to three females is sufficient to kill the twig or branch. Infestation becomes apparent when die-back of twigs and branches occurs. A severe infestation can kill host plants, including large trees (Hara & Tenbrink, 1994).
    Ambrosia beetles can be important pests of nursery production. Beetles sometimes introduce pathogenic fungi or bacteria. Fungi growing in trees can block water and sugar conducting tissues, producing tree wilting, dieback,or death.
    Geographical range
    Native range: The black twig borer is native to Asia.
    Known introduced range: The black twig borer has spread to coffee growing areas of the world. Considered a serious coffee pest in French Guinea, it is also widely distributed the tropical areas of West Africa, coffee growing areas of East Africa, Madagascar, Mauritius, Seychelles, India, Malaysia, Java, Sumatra, and Fiji. In Japan it attacks tea. New World locations include Brazil and Cuba. In the U. S. it is established in Hawai‘i and the Southeastern states. It was discovered at Kailua, Oahu in November of 1961 and is now widespread in the Islands. A ban on shipment of woody plants to Hawai‘i Island failed to prevent its introduction into the coffee growing areas of that island (Hara and Tenbrink, 1994).
    Introduction pathways to new locations
    Nursery trade:
    Solid wood packing material: Scolytids, such as the black twig borer, are among the most commonly intercepted families of insects on solid wood packing materials at U.S. ports of entry, representing 93–94% of all reported insects. Similarly, scolytids were the most commonly intercepted group of insects found in association with solid wood packing materials in Chile and New Zealand (Haack, 2003).
    Transportation of habitat material: Scolytids, such as the black twig borer, are commonly intercepted in food products such as seeds and nuts.
    Management information
    Preventative measures: In 2002, United Nation FAO's (Food and Agriculture Organization) Interim Commission on Phytosanitary Measures imposed a global standard for treating wood packaging International Standard for Phytosanitary Measures No. 15 to stop the spread of invasives.

    Maintaining healthy trees and shrubs is the first line of defence against the ambrosia beetles attacking weak hosts. This includes proper fertility, maintaining proper soil pH, and adequate soil moisture. Pruning and destruction of beetle-infested plant material is essential. Good tree care to promote tree vigor and health will help in resisting infestation or recovering from infestation.

    Chemical: Chemical control is not the best option for these beetles since the host is already very weak or dying.However studies show that Chlorpyrifos provided 83% mortality of all stages of the black twig borer infesting flowering dogwood in Florida (Mangold et al., 1977). Hata & Hara (1989) reported 100% mortality of adult females with chlorpyrifos. Marsden in 1972 recommended malathion (not to be applied to blooming orchids).

    Biological: "Literature on natural enemies indicates that the black twig borer is parasitized by at least one species of eulophid wasps of the genus Tetrastichus. Nine species of this genus, all accidentally or purposely introduced, are in Hawai‘i; whether any are parasitizing black twig borer is not recorded" (Nishida, 1992).

    Nutrition
    Adult beetles bore into trees to lay eggs and introduce a mutualistic fungus “ambrosia” that serves as food for adult and larval beetles.
    Reproduction
    Black twig borers spend the majority of their lives inside the host plant. The exception is the adult female, which leaves the gallery by way of the parent's entrance hole and establishes a new gallery elsewhere. Each year sees several generations.
    Lifecycle stages
    The black twig borer, Xylosandrus compactus, is one of the few ambrosia beetles that attacks healthy plants! This beetle is very small, dark and more or less oval in top view. The largest specimens are just over one-sixteenth inches long.
    The life cycle of the black twig borer is completed in about a month. Female beetles attack twigs or branches and bore in to the pith (or if the twig is large, they bore into the wood about half to one and one half inches). Black twig borers are capable of laying eggs without mating (parthenogenesis). After the females bore into a twig, they form a small chamber in which the mostly female eggs are laid. The tiny eggs (less than 1mm long) are smooth, white ovals laid over a period of several weeks. They hatch three to five days after being laid. Larvae are grubs, white and legless. The tiny grubs feed on the fungi that grow on the walls of the brood chamber.The grubs pupate and then (if males happen to have developed) the new beetles mate before leaving the twig to infest new twigs. The pupae are initially white, changing to light brown with black wings (female) near maturity. This process takes at least 6 days. Female adults, initially light brown, turn shiny black in 3 to 4 days; females are 1.6-1.8mm long (about 1/16 in). Males are about half as long and incapable of flight. After emerging from the pupal stage they turn from light brown to reddish brown in 3 to 4 days.If the twig is small, only one female will attack it. If the twig is more robust, up to 20 females will attack it. In the summer it takes about a month from egg to adult beetles. In the winter, development is much slower. The adults overwinter inside the damaged twigs.
    Over 224 plant species in 62 families are susceptible to the black twig borer.
    Reviewed by: Dr Anthony Cognato Department of Entomology Texas A&M University USA
    Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Friday, 24 June 2005


ISSG Landcare Research NBII IUCN University of Auckland