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Insect growth regulators: modes of action and mode of action-dependent peculiarities in the evaluation of the efficacy for their use in wood preservation
1997 - IRG/WP 97-30155
Up to now, the insecticides used in wood preservation are either of more or less non-specific mode of action - like boron - or of neurotoxic mode of action - like chlorinated hydrocarbons, carbamates and pyrethroids. The active ingredients actually used are primarily mirroring the progress in active ingredient research in plant protection. The methods of testing of the insecticidal efficacy of wood preservatives are developed in the seventies when oil-borne preservatives with chlorinated hydrocarbon-insecticides of high penetration capabilities are dominating. So, the complete testing inventory was neurotoxintailored during this time and consequently topranking unconsciously this group of insecticides in the past. This type of topranking was decisive for the selection of the pyrethroids as replacement for the chlorinated hydrocarbon-insecticides and the rejection of the competing JHA's (WÄLCHLI & TSCHOLL 1975, TSCHOLL 1977) and molt inhibitors (DOPPELREITER 1980, CYMOREK & POSPISCHIL 1982) in the early eighties. The testing problems arising from the introduction of the molt inhibitors in wood preservation were not severe (PALLASKE et al. 1993, VALCKE & PALLASKE 1995), but it could be pointed out, that not the full bandwith of insecticidal properties is taken into account (GRAF 1995, PALLASKE 1995). This gap in test methodology gains more importance in the evaluation of the efficacy of hormon-analoga for their use in wood preservation and requires the modification of some standard test methods (GRAF 1996). A brief review of the modes of action of the "modern" insecticides like chitin synthesis inhibitors, juvenil hormone analoga and ecdysone mimics is given for highlighting the modifications required in testing repertoire and for pointing out the changes in valuation criteria requested for a correct and reliable valuation of preservatives with ovicidal mode of action.
M Pallaske


The Use of Insect Hormones as Non-Neurotoxic Insecticides in Wood Preservatives
2002 - IRG/WP 02-30277
The ecdyson and juvenile hormone analogues show a clear difference in their effect on the house borer, Hylotrupes bajulus. In the tested dosages, the ecdyson analogues have only a slight ovicidal effect but a very clear effect on old larvae. With a dosage of 1250 mg/m², Halofenozid achieved 100% mortality after 27 weeks and Tebufenozid after 40 weeks. The two juvenile hormone analogues, Fenoxycarb and Pyriproxyfen, behave differently. They show a clearly recognisable to high ovicidal effect if the treated wood surface has not been aged, however, their eradicant effect is not anywhere near sufficient. In the case of Fenoxycarb at a dosage of 1250 mg/m², 100% mortality was only achieved after 94 weeks. Pyriproxyfen in the same dosage of 1250 mg/m² took 124 weeks to achieve 96% mortality. Fenoxycarb and Pyriproxyfen did not prove to be very weather resistant in the aging experiments. This means that treated wood in hazard class 3 must always be protected against the influence of weather with a top coat. Two months of outdoor or adequate artificial weathering showed that without a top coat the concentration of the active substance would have to be increased by at least two to three powers of ten to achieve sufficient biological effect on eggs and egg larvae required by EN 399.1 (field testing).
E Graf, M Barkhoff, R Hamberg, H Büttner, M Pallaske