Wood Deterioration and Preservation - American Chemical Society

Chapter 15

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Marine Wood Boring Arthropods: Ecology, Functional Anatomy, and Control Measures Simon M. Cragg Institute of Marine Science, School of Biological Sciences, University of Portsmouth, Ferry Road, Portsmouth P O 4 9 L Y , United Kingdom

Wood boring arthropods cause damage of major economic significance to coastal structures. The curculionid Pselactus is restricted to the upper intertidal in decayed wood. Limnoriids occur in full salinity subpolar to tropical waters, from the intertidal zone to over 1000m. Sphaeromatid borers are euryhaline temperate and tropical, intertidal species. These isopods have low fecundity, iteroparity and extended parental care, and thus compete effectively once established in a substrate. They migrate to new substrata as young adults. Limnoriids usually lack a resident microbial flora, but ingest wood particles containing wood-degrading microorganisms. Cellulose is degraded during gut passage, but the source and functioning of a full suite of lignocellulose degrading enzymes remains to be demonstrated. Sphaeromatids may not ingest wood. Neither creosote nor C C A treatments provide complete protection from these organisms. Protocols for evaluating antiborer measures that take account of migratory and substrate seeking behaviour are needed.

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© 2003 American Chemical Society Goodell et al.; Wood Deterioration and Preservation ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

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Introduction In temperate waters, wood boring isopod crustaceans from the family Limnoriidae limit the service life of timber structures. In tropical waters, members of the Sphaeromatidae are also a serious threat to such structures (Figure 1.). The relative importance of damage caused by these crustaceans and by the wood boring bivalves (shipworms and Martesia) depends on environmental conditions. Unlike the shipworms, attack by these crustaceans is readily detectable even at the early stages. Species from the two crustacean families are capable of attacking timber treated to control shipworms. Other isopods and the amphipod crustacean Chelura also burrow into wood. Insects can cause damage in the high intertidal zone. Reviews of the biology of wood boring crustaceans (1,2,3) will be updated herein, focusing on unresolved questions about their functioning and ecology.

Identification and Systematics of Wood Boring Arthropods The type of borer can usually be determined from features of the tunnels that they excavate. Recognition to family level may not be sufficient to enable appropriate decisions about anti-borer measures: some species of the Limnoriidae have greater resistance to chemical treatments than others (3). The main wood-boring Crustacea and their diagnostic features are illustrated by Kuhne (4). Studies of comparative anatomy of limnoriids (5,6,7) and of sphaeromatids (8) have facilitated identification by providing keys to species and genera, detailed line drawings and S E M images (Figs. 2 and 3). Intensive collection in tropical and subtropical waters of Central and North America (5) and of Australasia (6) has increased the number of known limnoriid species considerably. Collections from deeper waters have also added to the list of species (9,10). More additions to the species list can be expected when other waters are examined more closely (11). The genera Phycolimnoria and Limnoria were separated on the basis of having clearly distinct mandible types (5), but it is now known that there is a gradation in mandible anatomy so the genera have been merged into Limnoria, which can be distinguished from Paralimnoria on the basis of uropod anatomy (6). There are two wood-boring species of Paralimnoria and forty nine species of Limnoria, encompassing algal burrowers, seagrass borers and many wood borers. Hadromastax, is no longer considered a member of the Limnoriidae, but Lynseia, a seagrass borer, has been placed within the family and a revised key to the limnoriid genera is available (7).

Goodell et al.; Wood Deterioration and Preservation ACS Symposium Series; American Chemical Society: Washington, DC, 2003.


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Figure 1. Port Moresby, Papua New Guinea: CCA-treated hoop pine pilings destroyed by infestation in the intertidal zone by Sphaeroma triste (Reproduced with permission from an unpublished source. Copyright IRG Secretariat, Stockholm.)



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Figure 2. S E M image of ventral view partially curled specimen of Limnoria cristata from Singapore. Features of the dished pleotelson (to right) are used to identify the species. Note partially folded peraeopods (walking limbs) with dactyls (distal claw-shaped articles) extending away from body. (Reproduced with permission from an unpublished source. Copyright IRG Secretariat, Stockholm.) Goodell et al.; Wood Deterioration and Preservation ACS Symposium Series; American Chemical Society: Washington, DC, 2003.


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Figure 3. S E M image of posterior view of Sphaeroma triste showing its characteristic broad, toothed exopods of the uropods (limbs attached to the final body component - the telson). (Reproduced with permission from an unpublished source. Copyright IRG Secretariat, Stockholm.)



277 Some members of the genus Sphaeroma have been separated, on the basis of mouth part anatomy, into a new genus, Lekanesphaera (12). The borers S. annandalei, S. quoyanum and S. terebrans remain within Sphaeroma. Other isopods have been reported from tunnels in wood in tropical intertidal sites: the cirolanids, Ceratolana, a borer of decayed mangrove wood, and Anopsilana willeyi, probably a predator (13,14), and a number of species of Corallana (Corallanidae), some from CCA-treated piling (15). The amphipod borer family Cheluridae has not had any revisions or additions since the appearance of Kiihne's key (4), which describes three species within the genus Chelura, though previously Barnard allocated each of the three species to a separate genus (16). The curculionid Pselactus is included in a key of the Cossoninae (17).

Ecology of Arthropod Borers

Biogeography Wood boring insects are generally assumed to be terrestrial organisms. However, wood-boring weevils occur in decayed wood in the intertidal zone around the coast of southern Great Britain (18). Attack by subterranean termites has also been observed in the intertidal zone on wood attached to a concrete wharf in Papua New Guinea. The earth runways of the termites extended about 100m under the concrete deck (unpub. obs.). Some wood boring members of the Limnoriidae are only known from single sites. Others are distributed in waters around the globe within a certain latitudinal range: L. borealis - boreal; L. lignorum - boreal and temperate northern; L. quadripunctata - temperate and warm temperate North and South of the equator; L. tripunctata - temperate and tropical; Paralimnoria andrewsi subtropical and tropical (4,5,6). Wood boring sphaeromatids are restricted to warmer waters: S. quoyanum occurs in New Zealand, warm temperate Australia and, probably as an introduced species, in California, S. triste has been reported from India, northern Australia and Papua New Guinea while S. terebrans may be circumtropical (8). Chelura terebrans occurs in temperate and subtropical waters North and South of the Equator, while C. insulae has only been reported from islands in the Caribbean and the tropical Pacific, and C. brevicaudafromJapan (19).


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Environmental Factors Determining Distribution The geographical ranges of crustacean borers are principally determined by water temperature (1). Studies of fluctuations in populations of three sympatric species of Limnoriafromthe temperate waters off southern Great Britain support this notion (20), with L. lignorum being most tolerant of unusually low temperatures, L. quadripunctata being stenothermal and L. tripunctata, eurythermal. Local variations in temperature regime due to a warm water plume from a power station affected species dominance. Temperature probably determines the latitudinal range of Sphaeroma quoyanum on either side of the equator and the circumtropical distribution of & terebrans. Local distribution is strongly influenced by salinity. Sphaeroma spp. in Australasia and India are markedly euryhaline (14, 21). Laboratory studies indicate that the Limnoria species studied to date are much more stenohaline (1), which probably accounts for their otherwise surprisingly low profile in major intertidal wood resources - mangrove ecosystems, as these are most profuse where there is a freshwater input. Limnoriids have, however, been reported as root borers in mangroves in full salinity seawater (22). Pselactus ranges from the high intertidal into the splash zone above (23). Sphaeroma burrowing is virtually restricted to the intertidal zone (24). In the first case the distribution may be reflect the range of conditions tolerated by basidiomycete decay fungi; in the second, it may reflect adaptation to their natural habitat - the less heavily corticated, intertidal prop roots of the mangrove Rhizophora (22). Limnoriids occur in the intertidal zone, but have also have been found in waterlogged wood at depths of over 1000m and over 400km from the nearest forest (10).

Population Dynamics and Dispersal

Adult Limnoria occur as pairs in burrows and may remain paired for over 10 months. Broods of up to 30 are produced by the boreal L. lignorum, but no more than 6 in tropical P. andrewsi (25). Eggs are released into a ventral brood pouch and are retained there throughout embryonic development. Juveniles are released into the adult burrow and frequently form side burrows from the parental burrow. Parental care is also reported for Sphaeroma, sometimes with juveniles of one species being found with the brood of another (26,27). Mean brood size varies with female size between 20 and 48 in S. terebrans and 19 and 101 in S. annandalei (28).



279 The life cycle strategy of wood boring isopods - low fecundity, iteroparity, extended parental care - is characteristic of AT-selected species. As such, they would be expected to be strong competitors capable of maximising resource share once established. On the other hand, there are many typical r-selected species among the wood boring molluscs (teredinids and pholads), which produce hundreds of thousands of minute planktotrophic larvae with no period of parental care. These are well adapted to colonising new environments due to high fecundity and high dispersal potential due to transport on ocean currents during the planktonic larval phase. Other wood boring bivalves brood their larvae during some or all of larval development, so that they display more Kselected characteristics (29), but even in brooding species, fecundity is much higher than in crustacean borers. Juvenile Sphaeroma establish new tunnels close to the parental tunnels, though young adults have been reported to migrate in the water column (30). Late juveniles and young adults of Limnoria have also been reported to disperse during specific periods of the year (1,31), perhaps triggered to move by overcrowding (5). The dispersal potential of crustacean borers is likely to be less than that of bivalve borers, due to much smaller numbers of offspring and the inability to feed, unlike the planktotrophic bivalve veligers, when dispersing, which limits in the dispersal period. Nonetheless, the colonisation of wood in the deep sea argues for an effective mechanism for locating such a patchily distributed food resource as wood. Evidence for contact chemical cues has been provided by laboratory experiments (32), but distance chemical reception, of value during migration, is harder to demonstrate (33). Wood boring species of Sphaeroma are not necessarily dependent on wood as a substrate. Large colonies occur in inert intertidal substrates (34,35).

Interactions with other Organisms Competition may occur between Sphaeroma and molluscan borers (36). Crustacean borers may also either be outcompeted or removed by predators (37). They play host to a range of epizooites (1) and bacteria (38). No resident gut microflora has been found in either Limnoria or Chelura (39), except when living on creosote treated wood (40), but there is a commensal relationship between the non-borer S. serratum and a hindgut-resident trychomycete fungus (41). The lignolitic ascomycete fungus Lulworthia readily colonises wood with hyphae, but appears to only form peritheca after Limnoria forms tunnels (42). A range of cellulose-degrading microorganisms has been reported to be associated with wood-boring isopods (43).


280 The co-occurrence of Limnoria and Chelura has been interpreted as a loose form of symbiosis. Chelura is reported to consume the faecal pellets of Limnoria (1, 19), but may not depend on this, as it is capable of forming its own tunnels and produces faecal pellets consisting of particles of wood (44 and Fig.4).


Functional Anatomy

Appendages and Feeding Mechanisms of Isopods Wood boring isopods have a sequence of paired, jointed appendages: antennae, mouth parts, thoracic limbs (peraeopods), abdominal limbs (pleopods) and uropods. A clearer idea of complex inter-appendage interactions is provided in illustrations of mouth parts in situ and with the attached muscles (6). The innermost mouth parts, the mandibles, have heavily scleratosed cutting processes responsible, together with head movements, for tunnel forming. The outermost mouthparts, the maxillipeds, can reach back to clean the peraeopods during grooming. The peraeopods are walking limbs and pleopods serve as fans for creating respiratory, locomotory and feeding currents. S. quoyanumfilterfeeds within its burrow, by beating its pleopods to draw seawater between the long setae on its peraeopods (45). In S. terebrans, these setae have fine side branches that form an effective fine net (46 and Fig. 5).

Gut Structure and Function The gut of the wood boring isopods consists of a simple oesophagus leading into a complex midgut region of filters and spines, which directs particles into the cuticle lined hindgut. Opening off the midgut are elongated glandular side pockets which form the hepatopancreas. Liquid in the hindgut can be exchanged with the midgut and hepatopancreas following contraction of muscles surrounding the hepatopancreas pockets or the hindgut. The hepatopancreas has been a focus for the search for endogenous cellulase production (47), but though gut resident microorganisms may not be involved in the production of enzymes (38), ingested wood degrading microorganisms could be an enzyme source (48). Cellulase activity has been detected in hepatopancreas extracts from Sphaeroma terebrans (49). The lignin-to-cellulose ratio in faecal pellets of Limnoria is markedly higher than that of the source wood (50,51), indicating cellulose breakdown during gut passage. However, the presence and source(s) of the full suite of enzymes


Goodell et al.; Wood Deterioration and Preservation ACS Symposium Series; American Chemical Society: Washington, DC, 2003. terebrans

reared separate

(Reproduced with permission from an unpublished source. Copyright IRG Secretariat, Stockholm.)

Figure 4. SEM image of faecal pelletfromChelura from Limnoria on balsa wood (Ochroma lagopus).


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Figure 5. S E M image of detail of the plumose setae on peraeopod of Sphaeroma terebrans (source: reference n o 46) (Reproduced with permissionfroman unpublished source. Copyright IRG Secreta Stockholm.)



283 required to break down crystalline cellulose within the lignocellulose complex remains to be demonstrated by critical experimentation. Wood alone is a poor source of dietary nitrogen. Extra nitrogen may be gleaned during the grooming process (38), during which bacteria are removed from the exoskeleton and may be transferred via the setae of the peraeopods (Fig. 6) and maxillipeds to the mouth. Bacteria and fungi colonising the surfaces of tunnels may also be a source of additional nitrogen (48). Within the hepatopancreas cells of Limnoria and Sphaeroma are granules containing copper. These are more numerous and have a more varied morphology in animals burrowing into CCA-treated wood, but no evidence of chromium or arsenic accumulation has been detected (46,52). Such granules occur in other isopods living in contaminated environments and appear to enable the organisms to tolerate high environmental levels of metals. Tolerance to creosote appears to be achieved in a different manner. Individuals of L. tripunctata growing on creosote treated wood have larger numbers of bacteria within the food mass in the gut, but also bacteria associated with the hind gut cuticle. It is suggested that these bacteria may break down the toxic components of the creosote and may provide a supplementary source of nitrogen when they are lysed in the gut (39). The report of crystals of hydrated protein complexed with iron in Limnoria hepatopancreas cells (50) deserves further investigation in the light of findings regarding other metals.

Protection of Wooden Structures Against Arthropod Borers Tropical hardwoods with heartwood containing bioactive extractives are used in maritime construction because of their ability to resist borer attack. Field and lab observations have identified timbers resistant to limnoriid attack, though resistance may vary with latitude and species of limnoriid (3, 53). Furthermore, microbial degradation may reduce the protective value of these extractives (3,54). Laboratory tests could provide more precision in identifying specifically arthropod-resistant species. Choice-type or force feeding tests may yield different findings (55), with the former approach being relevant to initial settlement while the latter may evaluate the capacity to minimise subsequent colony growth. Standard timber treatments offer good protection against teredinids, but species of Limnoria and Sphaeroma are capable of attacking timber treated with C C A or creosote and many novel treatments have been tested without identifying one that provides demonstrable efficacy against all types of arthropod (3). Even physical barriers are vulnerable to Sphaeroma (56). However, at least in the case of wood ingesters like limnoriids, modification of wood chemistry to reduce access for cellulases may prove effective (57). Biological control, using



(Reproduced with permission from an unpublished source. Copyright IRG Secretariat, Stockholm.)

Figure 6. SEM image of distal articles of peraeopods 1 (left of image) and 7 (right) of Limnoria cristata showing comb setae used in grooming.


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285 competing or predatory organisms has not yet been explored (36). The need for innovation is becoming more pressing as environmental concerns call into question the use of existing treatments. Field trials, even adjacent to natural populations, suffer from unpredictable recruitment and are difficult to interpret as the intensity of attack is due to success of initial settlement and to subsequent colony formation. In the laboratory, testing relies on animals changing many of their sensory responses from their burrow-dwelling mode to migration mode. Laboratory assays tailored to borer behaviour promise to assist the development of new approaches to the problem of arthropod attack on wood below the high tide mark.

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286 21. Cragg, S.M., 1988. In Biodeterioration 7 Houghton, D.; Smith, R.W.; Eggins, H.O.W., Eds, Elsevier, London. 22. Ellison, A . M . ; Farnsworth, E. J. Exp. Mar. Biol. Ecol. 1990 142, 91-104. 23. Sawyer, G. S.; Cragg, S. M. Mat. Org. 1995, 29, 67-79. 24. Cragg, S.M.; Levy, C.R., Int. J. Wood Pres. 1979 1, 161-168. 25. Menzies, R. J. Bull. Mus. Comp.Zool.,Harvard 1954 112, 363-388. 26. Messana, G.; Bartolucci, V . ; Mwaluma, J.; Osore, M . Ethology Ecology & Evolution 1994 Spec. Issue 3, 125-129. 27. Thiel, M. J. Nat. Hist. 2000 34, 737-745. 28. Krishnan, R. V.; Nair, N. B. Zool. Anz. 1973 191, 119-122. 29. Hoagland, K . E.; Turner, R. D. Malacologia 1981 21, 111-148 30. Cheriyan, P.V. Forma et Functio 1973 6, 1-68. 31. Eltringham, S. K.; Hockley, A . R. Limnol. Oceanogr. 1961 6, 467-482. 32. Geyer, H . Int. J. Wood Pres. 1981 2, 77-89. 33. Henderson, S. M.; Cragg, S. M.; Pitman, A . J. Int. Res. Grp. Wood Pres. 1995 96-10157, 18pp. 34. Krishnan, R. V.; Nair, N. B. Zool. Anz. 1973 191, 119-122. 35. Talley, T.; Crooks, J. A.; Levin, L. A . Marine Biology 2001 138, 561-573. 36. Si, A.;Alexander, C. G.; Bellwood, O. J. Mar. Biol. Ass. UK 2000 80, 1131 1132. 37. Kirkegaard, J. B.; Santhakumaran, L . N. Vid. Med.Dansk Nat.Foren. 1967, 130, 213-216. 38. Boyle, P.J. & Mitchell, R. Appl. Environ.Microbiol.1981 42, 720-729. 39. Boyle, P.J. & Mitchell, R. Science, 1978 200, 1157-1158. 40. Zachary, A.; Parrish, K.K.; Bultman, J.D. Mar. Biol. 1983 75, 1-8. 41. Charmantier, G.; Manier, J.-F. Vie Milieu 1981 31, 101-111. 42. Corte, A . M. Giorn. Bot. Ital. 1975 109, 227-237. 43. E l Shanshoury, A.R.; Mona, M.A.; Shoukr, F.A.; E l Bossery, A.M. Mar. Biol.1994 119, 321-326. 44. Cragg, S.M.; Daniel, G., Int. Res. Grp. Wood Pres. 1992 4180-92, 1-10. 45. Rotramel, G. Crustaceana 1975 28, 7-10. 46. Cragg, S.M.; Icely, J.D. Int. Res. Grp. Wood Pres. 1982 491, 1-26. 47. Ray, D. L . In Marine Wood Boring and Fouling Organisms Ray D. L . Ed. Washington University Press, 1959, pp 46-59. 48. Daniel, G.; Nilsson, T.; Cragg, S. Holz Roh- Werkstoff 1991 49, 488-490. 49. Benson, L.; Rice, S.; Johnson, B . Florida Scientist 1999, 62, 128-144. 50. Fahrenbach, W.H. In Marine Wood Boring and Fouling Organisms Ray D. L. Ed. Washington University Press, 1959. 51. Seifert, K . Holz Roh- und Werkstoff 1964, 6, 209-215. 52. Tupper, C.; Pitman, A. J.; Cragg, S. M. Holzforschung 2000 54, 570-576. 53. Kalnins, M. Proc. Amer. Wood Pres. Assoc. 1976 250-262. 54. Pitman, A . J.; Cragg, S. M.; Daniel, G. Mat. Org. 1997 31, 281-291. 55. Kuhne, H. Mat. Org. 1964 3, 107-118. 56. Eaton, R. A . Int. Res. Grp. Wood Pres. 1996 Doc. No. IRG/WP/96-10170. 57. Johnson, B.R.; Rowell, R . M . Mat. Org 1988 23, 147-156.


Wood Deterioration and Preservation - American Chemical Society

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