Environmental Mutagenesis 9:343-348 (1987) zy Brief Communication zyx Lack of Mutagenicity of the Organophosphorus Insecticide Malathion in z Drosophila melanogaster A. Velazquez, A. Creus, N. Xamena, and R. Marcos Divisio de Genetica, Departament de Genetica i Microbiologia, UniversitatAutonoma de Barcelona, 08193 Bellaterra, Spain Key words: zyxwvutsrq Drosophila melanogaster, malathion, sex-linkedrecessivelethals, sex-chromosome loss, nondisjunction INTRODUCTION zyxwvut Malathion is one of the most frequently used insecticides, and like other organophosphorus compounds, it exhibits alkylating properties [Bedford and Robin- son, 19721. Because of the relatively low toxicity of malathion, probably resulting from its metabolism [wild, 19751, the genetic risk from this insecticide may be higher than that of other more toxic pesticides. Most experiments carried out to detect the mutagenicity of malathion in micro- organisms show no detectable effects [wildemauwe et al, 19831. However, with reference to the chromosomal damage caused by malathion in eukaryotes, the results are more contradictory. In Drosophila melanogaster, Valencia zyxw [ 19811 reported that malathiori shows no mutagenicity either in the sex-linked recessive lethal (SLRL) test zyx OT the sex-chromo- some loss (SCL) test after adult feeding; due to the very low concentrations used (0.25 and 0.50 ppm) we agree with Valencia in considering that malathion may not have been adequately tested. In view of this, we tested this compound in the SLRL assay using a strain previously selected for resistance to malathion and also tested its ability to induce SCL and nondisjunction (ND). MATERIALS AND METHODS Strains The following strains of D melanogaster were used: Received June 3, 1986; revised and accepted December 5, 1986. Address reprint requests to Dr. R. Marcos, Departament de Genttica i Microbiologia, Facultat de Citncies, Universitat Autbnoma de Barcelona, 08193 Bellaterra, Spain. zyxw 0 1987 Alan R. Liss, Inc.