The current application of low persistence pesticides is unreliable for protecting wooden structures from termite attack. These applications may also pose an environmental and public health risk. Consequently, there is a need for the development of alternative systems to protect wooden structures from termites. Investigated here is the interaction between Australian termites, Coptotermes acinaciformis Froggatt, and to a lesser extent, Mastotermes darwiniensis Froggatt and Schedorhinotermes seclusus Hill, and a barrier system for protection of wooden structures. The aim was to develop an improved barrier for the protection of wooden structures that maximizes protection and minimizes environmental and health risks. Specifically, the performance of a barrier to protect wood against termite attack that incorporates a synthetic pyrethroid into polyurethane formulations is investigated. This research was conducted in parallel with other project contributors focusing on material science aspects of the research goals. A fundamental problem in assessing the value of termite barrier strategies lies in developing and interpreting laboratory assays that can deliver reasonable predictions of performance in the field. This is particularly the case with respect to the behaviour of termites over much longer periods in the field than can be undertaken in the laboratory. The approach to laboratory trials presented here is to define individual termite capabilities and, in combination with behavioural studies, to develop an understanding of factors which affect termite performance. The key experimental approach involved various laboratory based assays to evaluate termite foraging behaviour and performance against a range of barrier materials, progressing to field trials with the best performing material. Various species of termites; M. darwiniensis (Mastotermitidae), Cryptotermes primus (Hill) (Kalotermitidae), C. acinaciformis , Coptotermes frenchi Hill and S. seclusus (Rhinotermitidae), Microcerotermes serratus (Froggatt), Microcerotermes turneri (Froggatt) and Nasutitermes walkeri (Hill) (Termitidae) and Porotermes adamsoni (Froggatt) (Termopsidae); were investigated to determine the force that they can develop at their mandible tips. Larger termites can generate higher pressures on their mandible tips than smaller termites. By quantifying the mandible strength of a termite it was possible to contrast the capabilities of various economic termite species. Damage caused by an individual termite biting on synthetic materials was measured using electron microscope generated three dimensional models of indentations caused to the material. This was successful in quantifying the immediate capabilities of individual termites of different species. Most species were found to inflict a similar amount of damage to high density polyethylene. However M. darwiniensis caused much more damage than other species examined. Micro hardness testing was utilized to determine the relative hardness of pest termite mandibles. Termites were found to have mandibles much harder than any tested synthetic material. It was therefore found to be unrealistic to aim to develop barrier technology based on “harder than termite mandible material”. Trials using groups of termites in the laboratory demonstrated large differences in the performance of termites against various synthetic materials. There was a tendency for harder materials to suffer less damage. Mechanical properties of the barrier alone were found to be insufficient to stop termite damage. The resistance of polyurethane formulations incorporating insecticides to termite attack in the laboratory demonstrated a potential suitability for termite barrier technology. In behaviour trials, persistence of termite attack at the barrier face was found to be due not only to deterrent chemicals, but also to physical characteristics. Softer materials are not only easier for termites to remove but termites attack softer materials with greater tenacity, more termites spend more time attacking softer materials. Laboratory toxicity trials confirmed the bioavailability of Bifenthrin when incorporated within the barrier material and enabled the establishment of expected concentrations for effective protection. Termites were found to require direct contact with the barrier for mortality to occur. Trials designed to quantify repellence of the Bifenthrin in the barrier found that termites did not escape mortality by avoiding contact with the barrier material. As such pure Bifenthrin is shown to protect the barrier material directly by causing mortality rather than by repelling live termites away from the barrier. Field trials were conducted in northern Queensland where colonies of economic termites could be directly targeted. Wooden blocks were coated in polyurethane containing a range of Bifenthrin concentrations and trialed over an eight month period. Combination of the pyrethroid Bifenthrin in a polyurethane barrier at concentrations as low as 0.07% proved successful in preventing damage by the economically important termites M. darwiniensis and C. acinaciformis under high pressure field conditions. Only very small amounts of Bifenthrin migrated into adjacent soil, concentrations reached were in the order of 100 µg/kg of soil. For comparison the MLR for Bifenthrin in bananas for human consumption is 100 µg/kg. Bifenthrin in a polyurethane barrier could be used for the protection of houses and other wooden structures in the same manner as existing barrier film technology in order to minimise environmental and health risks associated with direct pesticide application techniques.
| Identifer | oai:union.ndltd.org:ADTP/279274 |
| Creators | Aaron Stewart |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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