SUSCEPTIBILITY OF SOFTWOOD BLOCKS TO DAMAGE BY SUBTERRANEAN TERMITES (ISOPTERA, RHINOTERMITIDAE, MASTOTERMITIDAE)

Three field bioassays were conducted to evaluate responses of the Aust ralian subterranean termites Coptotermes acinaciformis (Froggatt) and the giant northern termite Mastotermes darwiniensis Froggatt to untrea ted softwood timbers. In the first bioassay, containers with a test bl ock of each of southern yellow pine (SYP, Pinus spp.), hoop pine Arauc aria cunninghamii Ait ex D. Don and slash pine Pinus elliottii Engelm. were prepared. These and other containers with blocks of termite-susc eptible timber (feeder blocks) were exposed to termites by connecting to infested trees for 10 weeks. Hoop pine sapwood was significantly mo re susceptible to termite damage than either SYP or slash pine sapwood . SYP is a generic name for 5 different species of pine, which are dif ficult to separate reliably. Therefore, caution should be exercised wh en using ''SYP'' for field bioassays against termites to ensure that s amples are at least from the same species of pine and preferably from the same length of timber. The rate of mass loss per block appeared in dependent of the number of blocks exposed to termites within a contain er. Variation in mass loss of hoop pine feeder blocks was significant. In a second field bioassay, termite responses to varying masses of ho op and slash pines during several exposure periods were determined. So ftwood blocks were placed in plastic containers and attached to termit e mounds. Significant inter-colony variability was demonstrated. Preli minary screening to determine vigour of termites should minimise this variation. The rate of mass loss per block was independent of the numb er of blocks in a container and appeared linear. Numbers of termites i n a container appeared to be correlated with the mass of susceptible t imber available. Implications for combining block mass and exposure ti me to achieve a standard mass loss in untreated blocks are discussed. Responses of C. acinaciformis and M. darwiniensis to untreated sapwood and heartwood of hoop and slash pines and white cypress Callitris gla ucophylla Thompson and Johnson were examined in a third experiment. Ho op pine sapwood and slash pine sapwood are susceptible to damage by bo th species of termites, slash pine heartwood appears resistant. Hoop p ine heartwood was susceptible to damage by M. darwiniensis, but resist ant to C. acinaciformis. White cypress heartwood was resistant to both species of termites, with little damage to the sapwood. To minimise t he considerable intra- and inter-species variations in susceptibility of softwoods to subterranean termites, the species and the proportions of sapwood and heartwood of test material should be known. The releva nce of these data to wooden bait stakes used in in-ground termite bait ing stations and to synthetic baits used in above-ground termite baiti ng stations is discussed.