Xylosandrus crassiusculus (Motschulsky)

Kirkendall, Lawrence R. & Ødegaard, Frode, 2007, Ongoing invasions of old-growth tropical forests: establishment of three incestuous beetle species in southern Central America (Curculionidae: Scolytinae), Zootaxa 1588, pp. 53-62 : 54-57

Xylosandrus crassiusculus (Motschulsky)

( Fig. 1 a–c)

Records. New to Neotropics, recently established in North America. COSTA RICA, Heredia, Cariari, Pocosí, Finca Prima Vera, 0–100 m, Mar. 1996, trunk of standing Tectona grandis (teak, Verbenaceae ), M. Arguedas (2 beetles), 29 July 1997, 15– 20 cm dbh 6 years-old standing teak killed by Nectria nauriticola fungus, L. R. Kirkendall (1); Heredia, La Selva Biological Station 10o 26’ N, 84o 01’ W, 50–150 m elevation, 26 July 1996, trunk of felled Vochysia ferruginea (Vochysiaceae) L. R. Kirkendall (1); La Selva, ground-level UV light traps in second growth forest, 4 Aug. (1) and 24 Sept. (2), 11 Nov. (1), 1998, and 8 Feb. and 29 Mar. 1999 (1 each); La Selva, canopy UV light trap in old-growth forest, 2 Feb. 1999, ALAS project (1); La Selva, Malaise traps near treefalls not far from a forest edge, Nov. 1998 and Aug. 1999, ALAS project (1 each date); La Selva, 7 July 1999, 8 cm dia. broken branch of Pourouma bicolor (Urticaceae) (1) and 1 cm dia. broken branch of Protium pittieri (Burseraceae) , L. R. Kirkendall (1); La Selva, 8, 17 & 19 Dec. 2003, 8 Mar. 2004, woody petiole of fallen leaf of Cecropia insignis ( Urticaceae ; not breeding), old growth forest, Justin Calabrese (1 each date); La Selva, 26–27 Mar. 2004, canopy UV light 30 m up Lecythis ampla (Lecythidaceae) tree at CCL 350 in old-growth forest ca. 300 m from secondary forest (abandoned plantation), Gunther Brehm (1); La Selva, 27–28 Mar. 2004, ground-level UV light at SUR 900 in old-growth forest near border with secondary-growth forest, Gunther Brehm (1); La Selva, 27 Mar. 2004, 1.5 cm branch with green leaves of cut-up, fallen Topobea maurofernandeziana (Melastomataceae) at CEN 565, L. R. Kirkendall (2); La Selva ( ALAS project), 16 Feb.–18 April 2004, 5 combined Malaise/flight intercept traps, secondary forest (402); same place and period, 5 combined Malaise/flight intercept traps, primary forest (134); La Selva, 24 June–11 July 2006, secondary forest and forest edges, 21 collections from 13 thin, fallen Castilla elastica (Moraceae) branches, 1 from fallen Cecropia leaf, Hanne Andersen; Prov. Alajeula, Canõ Negro, 49 m, 1–5 Sept. 2005, J. Azofeifa, Y. Cárdenas, M. Moraga, ecotono, INBio collection #84533 (1); Prov. Limón, La Suerte Biological Station, 10o 26’ 30” N, 83 o 46’ 15” W, pitfall traps in secondary forest and a grove of exotic bamboo, 14 May 2005 (22) and 16 Sept. 2006 (10), light trap in secondary forest 12 April 2006 (1), Erica McAlister.

PANAMA, Colon Prov. San Lorenzo Protected Area, 917’N 79º58’W 130 m elevation, old-growth forest, 22 Sept. 2003 to 30 Oct. 2004, ground level UV light traps, R. Kitching (149), ground level flight intercept traps, A. Tishechkin (76), flight intercept traps at different heights, R. K. Didham, L. L. Fagan & M. Rapp, 0 m (136), 1.3 m (61), 7 m (119), 14 m (27), 21 m (3), 28 m (1), pit fall traps, E. Medianero (7), Malaise traps, S. Pinzon & N. D. Springate (2); same site, beating 2 cm dia. recently dead branches of Calliandra sp. ( Fabaceae ) 15 Oct. 2003, F. Ødegaard (1), beating 3 cm dia. recently dead branches of Poulsenia armata (Moraceae) 28 May 2004, F. Ødegaard (1).

Diagnosis. Among xyleborine ambrosia beetles, Xylosandrus crassiusculus is easily recognizable by the combination of shape ( Fig. 1 a,b), separated procoxae (placing it in Xylosandrus ), size (2.2–2.5 mm), and characteristic declivity with its dull surface and dense, scattered fine granules ( Fig. 1 c; see also Rabaglia et al., 2006).

Comments. Like many other xyleborines, this stout, medium-sized Oriental species has been transported through commerce to many parts of the world (CAB International, 2005b). First detected in North America in 1974, it has rapidly spread throughout the southeastern U. S., westwards as far as Texas and northwards as far as Maryland ( Atkinson et al., 1988; Bright & Skidmore, 2002; Rabaglia, 2003; Rabaglia et al., 2006; Wood & Bright, 1992). Small populations have recently become established in Oregon as well, introduced via hardwood railroad ties (CAB International, 2005b; LaBonte et al., 2005). This aggressive species is considered a high-risk quarantine pest, and is recorded as killing otherwise healthy nursery stock and saplings (especially transplants) where it has been introduced in Africa and the U.S. ( Atkinson et al., 1988; Browne, 1963; CAB International, 2005b; Roberts, 1969; Schedl, 1962). For example, X. crassiusculus has caused considerable mortality to Cinchona planted in Java ( Kalshoven, 1924), to Aucoumea kleiniana and Khaya ivoriensis plantations in Ghana ( Browne, 1963), to peach orchards in South Carolina ( Kovach & Gorsuch, 1985), and to potted Quercus shumardii and Ulmus parviflora in a nursery in Florida ( Atkinson et al., 2005). It is not known if the species can kill healthy plants or branches in natural forests. Local populations are known to have spread successfully into native tropical forests on Hawaii ( Samuelson, 1981) and in peninsular Malaysia ( Maeto et al., 1999). The species normally breeds in smaller diameter stems or branches of a wide variety of host plant families; in Costa Rica it has been also collected several times from the woody petioles of fallen Cecropia leaves, though no breeding activity has been observed in them. Although common in small diameter breeding material, X. crassiusculus has also been collected from larger trunks and from timber ( Atkinson et al., 1988). The stratification data from flight intercept traps in the Panama study, suggest that this species normally flies at heights under 10 m above the ground.

The earliest neotropical records are from a teak plantation and from La Selva Biological Research Station, both near the Caribbean port of Limón, northeast Costa Rica. The specimens from teak were taken from one of several trees which had apparently been initially weakened or killed by a lightning strike. The ambrosia beetles attacking the affected trees were primarily Euplatypus parallelus (Fabricius) and Xyleborus affinis Eichhoff , and included X. ferrugineus (Fabricius) , X. volvulus (Fabricius) and the platypodines Megaplatypus latreillei (Chapuis) and M. liratus (Blandford) .

La Suerte Biological Station is located 22 km E of La Selva, and less than 10 km NW of the teak plantations. The pitfall traps were baited with feces (monkey, human, cow, or chicken) and contained ethanol as a preservative. (Many scolytine beetles were found in the traps, presumably attracted by the ethanol.)

If X. crassiusculus had been established much earlier in northeast Costa Rica, specimens would certainly have been collected. Before 1996, no X. crassiusculus were collected by J. Saunders in the 1960s during thesis research on a cacao farm only about 40 km SE of La Selva; at La Selva in Malaise traps run by P. E. Hanson and helpers (1991–1993, as part of a country-wide Malaise trap network); or during extensive trapping and hand-sampling associated with the ALAS arthropod survey in the early and mid-1990s.

Some of the above records are from old-growth (primary) forest, though all of these are from sites less than 1 km from secondary-growth forest and almost all were sampled along or very close to established trails.This species is now the second most frequently collected scolytine breeding in small branches at La Selva Biological Station, after Xylosandrus morigerus— another well-established Asian exotic. Curiously, the two native central American congeners [ X. curtulus (Eichhoff) , X. zimmermanni (Hopkins) ] are rarely collected by hand or in traps in Costa Rica – Panama, and native genera of ambrosia beetles specialized to small branches, such as Coptoborus and Theoborus , are infrequently encountered and uncommon in traps.

Many hundreds of individuals of X. crassiusculus have been collected from La Selva Biological Station since 1996. The single specimen found by the nation-wide insect inventory being conducted by INBio is from Caño Negro Wildlife Refuge, located approximately 90 km NW of La Selva and ca 15 km S of Lake Nicaragua. Taken together, these finds suggest that the species is now well established and widespread in the north and east of Costa Rica; it is also likely that it has spread into southern Nicaragua as well.

The large numbers of this species collected in the old growth forest in the Colón region of Panama indicate a well-established population there as well, but lack of earlier research in the region means that the age of the population is unknown. Since there has not been any other intensive collecting of wood-breeding insects along the Caribbean coast of southern Central America, we cannot say whether the collections from Heredia and Colón represent separate introductions or two samples from one continuous population. However, there are no specimens from southeastern Costa Rica in the country-wide general insect collections of the national biodiversity institute INBio. Nor has the species been found in flight intercept trap, Malaise, or UV light collections from Belize or Nicaragua conducted in the 1990s (Kirkendall, unpublished data). The species is not yet known from South America ( Wood, 2007).

Figures

FIGURE 1. Invasive Asian xyleborine ambrosia beetles in Central American forests. (a – c) Xylosandrus crassiusculus: the shape (a), size (2.2 – 2.5 mm), and dull declivity with dense long setae and dense, scattered granules (c) are characteristic. (d) Xyleborinus exiguus: note the plain, convex declivity with a distinctive border of large teeth at the apex. (e – h) Euwallacea fornicatus: arrow (g) indicates suture on the posterior face of the antennal club (upper antenna in figure shows anterior face).