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Abstract: The pyrethrum esters have been used for centuries as insecticides (O'Brien, 1967) and are registered and recommended in Canada for use in mushroom production (Ingratta, 1980). The natural pyrethrins are unsuitable for general agronomic utilization because they are unstable in air and light (Elliot et al., 1973a). This characteristic results in low residual activity in mushroom houses but the extremely low mammalian toxicity of the pyrethroid group makes them a desirable chemical for use on food products. The low mammalian toxicity is a result of ester cleavage and oxidation of the acid and alcohol produced (Chamber, 1980). During the early 1970s a new group of modified cyclopropane acids were tested for insecticidal activity and found to be about one hundred times as potent as natural pyrethrins for controlling houseflies (Elliot et al., 1973a). Unfortunately these materials were also photounstable but the discovery of permethrin (Elliot et al., 1973b) was the basis for the development of a wide variety of synthetic pyrethroids which have significant residual properties under light. Since that time many research projects have demonstrated the effectiveness of the synthetic pyrethroids in controlling Diptera (Spillberger et al., 1979), Lepidoptera (Hoyt et al., 1978; Harris et al., 1978a, b; Crowder et al., 1979), Acarla (Rock, 1979) and Homoptera (Hoyt et al., 1978). This project was initiated to determine the activity of permethrin (3-(phenoxyphenyl) methyl (±)-cis, trans-3-(2,2-dichloroethenyl)- 2,2-dimethyl cycloprane carboxylate), cypermethrin(cC-cyano -3-phenoxybenzl 2,2-dimethyl-3-(2,2 dichlorovinyl) cyclopropane carboxylate), and fenvalerate (cyanol (3-phenoxyphenyl) methyl 4-choloro-alpha -(1-methyethyl) benzeneacetate) in the control of the mushroom infesting Diptera (Lycoriella and Megaselia). Studies on phytotoxioity of the pesticides to mushrooms were conducted on mushroom mycelium in pure culture and on mushroom crops grown in a controlled environment. Mushroom sporophores were analysed for pesticide residues to determine whether the levels recommended for insect control had resulted in excessive levels of chemical in the marketed product.
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