Field exposure of borate-treated softwood to subterranean termites (Isoptera: Rhinotermitidae, Mastotermitidae)

Abstract

Four field bioassays were conducted with 2 Australian subterranean termites , Coptotermes acinaciformis (Froggatt) and the giant northern termite Masto termes darwiniensis Froggatt, to determine responses to berate-treated slas h pine Pinus elliottii Engelm, sapwood. Softwood blocks were placed in plas tic lunch-boxes and attached to infested trees. Termite responses were dete rmined by mass losses of borate-treated and water-treated test blocks over a period of 5 or 10 weeks. In 2 other bioassays, berate-treated softwood bl ocks and frames were placed on concrete brick assemblies, in an above-groun d, weather-protected situation in an area of high termite hazard. Termite r esponses were determined by mass losses over a period up to 125 or 25 weeks . The work was conducted at Beerburrum and near Ingham, in Queensland, Aust ralia. Termite responses to berate-treated slash pine sapwood varied in the 4 field bioassays. Apparent differences in feeding behaviour be tween the 2 termite species are mentioned. Total prevention of damage by field popula tions of termites was not achieved. Berate retentions in excess of 1.2% and 1.4% mass/mass boric acid equivalent appear necessary to prevent significa nt damage of softwood by C. acinaciformis and M. darwiniensis, respectively . The data were used to derive 5% protection/toxic thresholds (PT5%) and va lues for a different term (PTa5%), defined as In(5%)/slope. The relationshi p between these terms is discussed and used to explain apparent anomalies i n efficacy data from various test methodologies. PTa5% appears to be useful because it is essentially independent of the intercept, but dependent upon the slope of the line for each data set. Further work, to examine the vari ation of slope with exposure time, season, timber species, termite species and the presence of untreated material, is needed. In the interim, the impo rtance of adequate bioassay duration and the need to use termites selected for strong vigour at foraging sites are emphasised.