Wood from one hundred and fifteen species of trees has been exposed to marine borers in three different tropical waters for periods up to 90 months. Underwater sites were in the Panama Canal Zone and included two oceans and a brackish water lake. Over 30 species of marine boring organisms were identified from these waters; their extreme activity in the warm tropical environments provided a very thorough screening test for the woods. Samples have been evaluated separately for resistance to the three principal classes of borers: teredo, pholad, and limnoria. Several of the woods were resistant to one or more of the borer types. Some of these resistant species are relatively unknown as marine construction timbers, and in some instances they proved to be more durable than greenheart, teak, and other commercially used marine woods. The species most resistant to all borers was Dalbergia retusa (cocobolo), whose oily extract may provide leads to the development of a satisfactory wood preservative for marine use. The woods most resistant to each of the different classes of borers are tabulated, with their respective silica content and density included. Silica was shown to be significant only in relation to teredine borers, while wood density was important only with pholads. Woods considered to be of special interest because of findings in the study are discussed individually. As MAN EXTENDS his activities into the sea, a knowledge of the biological, chemical, and physical effects of the marine environment on the materials of his equipment and structures becomes increasingly important. Of the structural materials, wood, one of the oldest, is still and foreseeably will continue to be of great usefulness. This position is maintained because of a unique combination of properties inherent in wood: high strength-to-weight ratio, resiliency, flexural strength, and economy of use. In the absence of marine boring organisms, the durability of wood under water is high. When exposed to marine borers, however, wooden structures are subject to severe damage, particularly in warm temperate and tropical waters. It has been estimated that damage caused by these organisms in the United States of America alone may average 200 to 250 million dollars annually (Galler 1969). Many procedures have been tried in an effort to deter marine borers, but most have failed because of the divergent methods of attack and wide tolerance range of different classes of borers. The most frequently used method of borer protection is pressure treatment with whole creosote. But as pointed out by several investigators (Menzies and Turner 1956, Vind and Hochman 1961, Colley 1969), in waters infested with Limnoria tripunctata,' the treatment is much less effective, and in tropical waters where limnoria is continuously active, creosoted timbers are often destroyed in a few years. Examples of attack on creosoted pilings in the tropical waters of the Panama Canal Zone are shown in figure 1 for Coco Solo harbor on the Caribbean coast and in figure 2 for Balboa harbor on the Pacific coast. Replacement of creosoted timbers at the latter site, alone, costs 100 to 200 thousand dollars annually. Another protective measure sometimes used is sheathing of pilings with borer-proof material, such as plastic, concrete, or metal. This sheathing procedure is effective as long as the cover is intact. Any small opening, however, will afford access to teredine borers (Teredo, Bankia), and intensive internal damage to the pilings can occur. Such damage usually goes undetected for some time while the large area of unaffected sheathing gives a false appearance of soundness. The use of naturally resistant kinds of wood is still another approach to borer control. Some woods are reputed to have a high natural resistance to certain borers. A few of these, such as Ocotea rodiei2 (greenheart) and Dicorynia paraensis (angelique), have been marketed worldwide on this basis. These naturally resistant woods have been very successful in some installations while giving poor results in others, indicating that here, as in the case of creosote, environmental variability probably exercises a telling influence. On the Isthmus of Panama, the flora from North and South America and from the Pacific and Atlantic watersheds all meet and mingle, and a great variety of timber species is found. Hence, among the most abundant natural products of Panama are large stands of these tropical trees. In accordance with a treaty between the Republic of Panama and 1 Authorities for all borer binomials are cited in table 2A. 2 Authorities for all tree binomials are cited in table 1.
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May 1, 1974
Massoud A H Saad 
Open Access