Xyleborus perforans (island pinhole borer)

X. perforans should be considered a high-risk quarantine pest; most of the species in Xyleborus and related genera should be considered potential quarantine pests. This is because members of the tribe Xyleborini (Xyleborus plus related genera) are all inbreeding, with the males generally mating with their sisters within the parental gallery system before dispersal. Thus the introduction of only a few mated females may lead to the establishment of an active population if suitable host plants can be found and environmental conditions are satisfactory. A very wide range of host plants have been recorded for many species of Xyleborus and related genera. Any woody material of suitable moisture content and density may be all that is required. The direct risk of establishment of populations of species of Xyleborus perforans outside its present range should be considered serious, although the species is not currently known to attack healthy trees.

This species is doubtfully distinct from Xyleborus volvulus (F.), with which it appears to intergrade in some areas (Wood and Bright, 1992; Bright and Skidmore, 2002). Molecular studies are needed on populations from different areas to determine intraspecific and interspecific relationships. Many references to the species are given by Wood and Bright (1992), and by Bright and Skidmore (1997, 2002). The synonymy given follows these authors.

The following diagnostic notes refer to females only and include only the minimum characters required to differentiate this species from other pest species.Adult FemaleLength 2.1-2.5 mm. Frons convex, entire surface minutely reticulate, with faint, shallow punctures. Antennal club solid on posterior face. Pronotum 1.2 times longer than wide; sides moderately arcuate; anterior margin broadly rounded, without serrations. Elytra 1.7 times longer than wide; apex narrowly rounded. Elytral declivity steep, convex, commencing on posterior third of elytra; face of each elytron with a row of 4 to 5 small, acute granules in interspaces 1 and 3; several smaller granules are present in interspaces 4, 5 and 6; interspace 7 rounded, with small, acute granules.Immature StagesThe immature stages have not been described.

It should be noted that Wood and Bright (1992) refer all records of the species from Central and South America which appear in CIE (1973) to the closely related species Xyleborus. Within Africa, both species are believed to occur (Wood and Bright, 1992), sometimes within the same country. Schedl (1963) refers nearly all the African records to Xyleborus volvulus (as its synonym X. torquatus). Because the two species may intergrade (Wood and Bright, 1992), and biological and other information in this datasheet is equally valid to both species, the African records in CIE (1973) have been retained here.

As with a number of other widespread species of Xyleborus and related genera, it is difficult to be certain of the extent of the native distribution. This species appears to be native in the Oriental region through to Australia. It was probably introduced into Africa hundreds of years ago through commerce, and has undoubtedly been introduced to many of the Pacific islands through human agency many years ago. The species has frequently been intercepted in timber imported to Japan from countries in the region from Cambodia, the Philippines and Indonesia to the Solomon Islands (Ohno et al., 1987, 1988, 1989; Ohno, 1990), but has not become established on the main islands of Japan. It has also been intercepted in imported timber in Australia and India (where it also native) (Schedl, 1964; Krishnasamy et al., 1991), New Zealand (Bain, 1974, 1977; Brockerhoff et al., 2003), and in Germany, Italy and Poland (Cola, 1971, 1973; Bright and Skidmore, 1997), but is not established in New Zealand or in Europe.

Several other species of Xyleborus with similar habits to X. perforans have been imported to tropical and subtropical areas around the world. A few have become important pests, either because they may attack living or stressed trees, or because of their abundance in disturbed forest areas, and their very wide host range. X. perforans is a secondary borer, but it can attack injured trees, and is often very abundant in recently felled timber. Kühnholz et al. (2003) note that a number of secondary borers have started to attack living trees, and discuss the possible reasons for this change of habit. The risk of introduction outside its present geographic range must be considered high. X. perforans is not specifically listed as a quarantine pest, but Xyleborus spp. are included in the APHIS Regulated Pest List in the USA, and as quarantine pests in New Zealand.

Adult females fly readily and flight is one the main means of movement and dispersal to previously uninfected areas. Of more importance however, is the movement of infested woody material in timber, dunnage and crating. Numerous species of Xyleborus and related genera have been taken in port cities from raw logs destined for saw mills, from discarded ship dunnage, and in similar circumstances.Both adults and larvae of X. perforans are dependent on the growth of the fungus on the walls of the gallery system in the wood for their food. The fungus is transmitted by the female in a mycangium. In X. perforans, this most probably consists of mandibular pouches, as in related species, including X. volvulus (Francke-Grosmann, 1966; Beaver, 1989). 'Contamination ' of the mycangia by the spores of pathogenic fungi is possible. Spores of pathogenic fungi can also be transported on the cuticle of the beetle, although their chance of survival there is much less than in the mycangial pouch. No specific studies have been made on fungi associated with X. perforans.

Members of Xyleborus and the related genera Ambrosiodmus, Euwallacea, Xyleborinus and Xylosandrus are all ambrosia beetles that feed and breed in a variety of forest trees and shrubs. Depending on the species, they may be found in small branches and seedlings to large logs. All are potentially damaging to agriculture and/or forestry under suitable conditions. Many species, previously considered of only minor importance, may become important pests in agriculture and forestry as a result of the continuing destruction of natural forests and the expansion of forest and tree crop plantations, agroforestry and agriculture. X. perforans is widely distributed and very common. It attacks hundreds of host plant species in many plant families in forests and plantations(Browne, 1961; Schedl, 1963; Gray and Wylie, 1974), and has been intercepted in Japan and elsewhere from imported timber of many species and families (e.g. Ohno et al., 1987, 1988, 1989; Ohno, 1990). Its wide host range, coupled with its tolerance of a considerable range of climatic conditions, makes it a potential pest in forest plantations. It is normally found in dying, dead and newly-felled trees, and usually infests material of a moderate to large size. Given the great range of host trees attacked, and the differences between geographical areas, it is not possible to distinguish 'main host' trees from 'other host' trees. It may be expected that almost any crop, plantation or ornamental tree in a particular area can be attacked. The list that is given here is a small selection of hosts only.

Attacked plants may show signs of wilting, branch die-back, shoot breakage, chronic debilitation, sun-scorch or a general decline in vigour.

The important pest species in the genus Xyleborus and the related genera Ambrosiodmus, Euwallacea, Xyleborinus and Xylosandrus, are all ambrosia beetles in the Xyleborini, a tribe with a social organization of extreme polygamy. The sexual dimorphism is strongly developed, and the ratio of females to males is high. The biology of X. perforans has been studied by Beeson (1930), Browne (1961), Schedl (1963) and Kalshoven (1964). The species is particularly common in disturbed areas. It flies mainly around dusk, and may be attracted to light in large numbers. It normally attacks stressed or recently felled trees, but also readily attacks newly sawn timber (Browne, 1961). It also attacks fire-damaged trees, and salvaged logs (Wylie and Shanahan, 1976; Wylie et al., 1999). Living trees are normally only attacked through injuries or diseased areas (Browne, 1961). It is not very size-selective, and attacks stems from about 5 cm diameter to the largest logs, but is not found in small shoots and twigs (Browne, 1961). The gallery system consists of branching tunnels, without enlargements, and penetrate deeply into the wood. When there are dense attacks, the tunnels from different broods may intersect (Beeson, 1930). The tunnels are usually in one transverse plane, but Kalshoven (1964) notes that some galleries have more than one transverse level, the levels connected by vertical galleries, and that side branches may connect to the outside, forming additional openings to the exterior. Sometimes there may be a surface gallery, at the cambial level, before the beetle penetrates the wood (Browne, 1961). The first eggs appear when the tunnel length is from 3-8 cm (Kalshoven, 1964), and the larvae develop and pupate within the gallery system. The parent female and the larvae feed on the ambrosia fungus growing on the walls of the galleries. Kalshoven (1964, quoting Zehnter, 1900) gives the duration of the egg stage as 4 days, the larval stage as 7-9 days, and the pupal stage as 4 days, giving a total of only 16-18 days from egg to teneral adult. These are likely to be optimal figures, and in most conditions a generation would be expected to take 4-6 weeks. The total brood size is difficult to estimate because of the intricacies of the tunnel system. Kalshoven (1964) gives figures of 56 to 112 for advanced gallery systems, and total broods may be even higher in favourable conditions. After mating with their brother(s), the new generation of females emerges through the original entrance hole (or presumably also through any additional openings from the gallery system to the exterior). Kalshoven (1964, quoting Zehnter, 1900) suggests that the first females of the new generation extend the gallery system, and begin to lay eggs before the parental female has died, so that there may be overlapping generations within a single cane stem. In most countries where it occurs, breeding is continuous throughout the year (Browne, 1968), although Beeson (1930) notes that there may be marked seasonal fluctuations in populations.

The immature stages of xyleborines have few natural enemies. The female parent normally remains in the gallery entrance whilst the immature stages are developing, preventing the entry of potential predators and parasitoids. Provided that the female remains alive and the growth of the ambrosia fungus on which the larvae feed is satisfactory, mortality of the immature stages is likely to be very low. Most mortality is probably during the dispersal of the adults, and during gallery establishment. Adult ambrosia beetles are predated by lizards, clerid beetles and ants as they attempt to bore into the host tree. Adults will also fail to oviposit if the ambrosia fungus fails to establish in the gallery. One species of hymenopteran parasitoid (Eulophidae) has been bred from adults of X. perforans attacking macadamia trees in Hawaii (LaSalle, 1995). It oviposits in the adult, and the immature stages of X. perforans are not attacked.

X. perforans has been recorded as a minor pest of sugarcane and coconut trees in Indonesia (Kalshoven, 1964; Browne, 1968), and in the days of wooden beer, wine and rum barrels, was known to bore into casks and cause leakage (Blandford, 1893; Schedl, 1963). It has been known to cause minor damage by its attacks on the tapped panels of rubber trees in Guyana and Sri Lanka (Browne, 1968), and on coffee and coffee shade trees in Suriname (LePelley, 1968). However, it is more important in many areas because of its heavy attacks on newly felled trees and recently sawn, unseasoned timber. The attacks result in numerous pinholes in the wood and fungal staining around them (Browne, 1961), and can render the timber unusable for furniture or veneer.

Some success has been obtained by using traps baited with ethanol placed in and around port facilities where infested material may be stored. Simple types of trap are described by Bambara et al. (2002) and Gregoire et al. (2003). Visual inspection of suspected infested material is required to detect the presence of ambrosia beetles. Infestations are most easily detected by the presence of entry holes made by the attacking beetles, and the presence of frass produced during gallery construction.

When Xyleborus species are detected in plant material in areas outside the present range of the species, it is necessary to immediately destroy all of the infested material. When they are detected in traps, plant material in the vicinity of the trap should be actively inspected, with special attention directed towards imported woody products such as crating, dunnage and lumber milling scraps. If an active infestation is detected, control using insecticides is possible but is of limited effectiveness. Chemical control is not generally effective because the adult beetles bore deep into the host material. However, Jose and Thankamony (2005) found that a mixture of carbaryl and quinalphos was highly effective (99%) against infestation of rubber trees by Xyleborus perforans and X. similis, when swabbed weekly on the beetle-infested region of the bark. Jagginavar and Naik (2005) also report on the management of X. perforans in pomegranate orchards using insecticide mixtures. The following insecticides were used against the ambrosia beetle, Euwallacea fornicatus, which is destructive to tea: fenvalerate, deltamethrin, quinalphos and cypermethrin (Muraleedhaan, 1995). Selvasundaram et al. (2001) found that lambda-cyhalothrin 2.5 EC was more effective in reducing E. fornicatus populations than fenvalerate. Jose et al. (1989) suggest the use of solutions of boric acid and borax, which have both fungicidal and some insecticidal action, to protect stored wood. These insecticides may also be effective against other ambrosia beetles, but the concealed habitats in which these species feed and reproduce, the difficulties and high costs of insecticide application, and environmental concerns all limit the effectiveness of chemical control. The use of the parasitoid, Phymastichus xylebori, which attacks the adult beetle, has been suggested by LaSalle (1995). However, it seems unlikely that this would be practical or effective. In logging areas, prompt removal of the felled timber from the area will reduce attacks, and rapid conversion to seasoned, sawn timber will reduce the depth of such attacks as have occurred (Roberts, 1987). It should be noted that debarking may increase the susceptibility to attack (Supriana et al., 1978). X. perforans normally forms part of a complex of bark and ambrosia beetle species attacking felled trees, and control measures need to be directed against all species at the same time (Beaver, 2000).