Neste trabalho procurou-se mostrar a ação de diversas formulações de defensivos sobre o Bacillus thuringiensis var. Kurstacki (Berliner, 1915), Metarrhizium anisopliae (Metch.) Sorokin e Aspergillus sp. Foram estudados 15 inseticidas e um fungicida. Os experimentos foram executados no laboratório de Patologia de Insetos do Departamento de Entomologia da ESALQ-USP. O estudo foi realizado, adicionando-se os defensivos na dose de 10, 100 e 1000 ppm, nos meios de culturas onde eram cultivados os microrganismos. Observou-se que os microrganismos se comportaram de modo diferente em relação aos defensivos e doses. Quanto ao B. thuringiensis verificou-se que o methomyl foi o produto menos tóxico, enquanto que o parathion ethyl e endosulfan destacaram-se como produtos altamente tóxicos ao patógeno. Determinou-se que a ação bactericida dos defensivos foi a que inibiu o crescimento bacteriano. Quanto ao M. anisopliae verificou-se que o oxicloreto de cobre, vamidothion, monocrothophos, dimethoate e omethoate não afetaram o crescimento do fungo na dose de 10 ppm e que o oxicloreto de cobre, monocrotophos e omethoate favoreceram o crescimento do patógeno. Na dose de 100 ppm o oxicloreto de cobre, dimethoate, vamidothion e omethoate não afetaram o crescimento do fungo, havendo um efeito favorável do oxicloreto de cobre. Para a dose de 1000 ppm o oxicloreto de cobre e methomyl não apresentaram efeito negativo sobre o M. anisopliae, sendo que o omethoate favoreceu o desenvolvimento do patógeno. Determinou-se, também, que o triazophos, permethrin, pirimiphos methyl, phenthoate, monocrotophos, methomyl, dichlorvos, malathion, fenitrothion, parathion ethyl, endonsulfan e chlorpyrifos ethyl inibiram o desenvolvimento do M. anisopliae em todas as doses. Quanto ao Aspergillus sp., os produtos permethrin e phenthoate não afetaram o seu desenvolvimento na dose de 10 ppm. O omethoate foi o único inseticida que não inibiu o crescimento do Aspergillus sp. na dose de 1000 ppm. Determinou-se, também, que o oxicloreto de cobre, triazophos, dimethoate, pirimiphos methyl, vamidothion, methomyl, dichlorvos, malathion, fenitrothion, parathion ethyl, endosulfan e chlorpyrifos ethyl inibiram o desenvolvimento do Aspergillus sp. em todas as doses. Concluiu-se, finalmente, que todos os defensivos, exceto o parathion ethyl a 1000 ppm, apresentaram ação fungistática sobre o M. anisopliae e Aspergillus sp.

This work was carried out in order to study the action of 15 insecticides and 1 fungicide on Bacillus thuringiensis var. kurstacki (Berliner, 1915), Metarrhizium anisopliae (Metch.) Sorokin and Aspergillus sp. The experiments were set in the laboratory of Insect Pathology, Department of Entomology at “Escola Superior de Agricultura Luiz de Queiroz”, University of São Paulo. The action of such materials was studied by adding the concentrations of 10, 100 and 1,000 ppm of chemical in the culture medium of the microrganisms. There were different reactions the microrganisms in relation to the chemicals as well as to the different concentrations. Concerning B. thuringiensis it was observed that methomyl was the least toxic chemical, while parathion ethyl and endosulfan were highly toxic to the pathogen. The growth of the bacterium was inhibited by the bactericide action of the chemicals. As for M. anisapliae, copper oxichloride, vamidothion, monocrotophos, dimetlioate and omethoate did not affect the fungus growing in the concentration of 10 ppm. On the other hand, copper oxichloride, monocrotophos and omethoate favored the growth of the pathogen. When the concentration of 100 ppm was used, copper oxichloride, dimethoate and omethoate did not affect fungus growing, while a favourable effect of copper oxichloride was observed. When the concentration of 1,000 ppm was employed, copper oxychloride and methomyl did not show a negative effect on M. anisopliae, while omethoate favored the development of the pathogen. It was also observed that triazophos, permethrin, pirimiphos methyl, phenthoate, monocrotophos, methomyl, dichlorvos, malathion, fenitrothion, parathion ethyl, endosulfan, and chlorpyrifos ethyl inhibited the development of M. anisopliae in all the concentrations. Concerning Aspergillus sp., permethrin and phentlioate did not affect its development in the concentration of 10 ppm. Omethoate was the only insecticide that did not inhibit the growing of Aspergillus sp. in the concentration of 1,000 ppm. The following chemicals: copper oxichloride, triazophos, dimethoate, pirimiphos methyl, vamidothion, methomyl, dichlorvos, malathion, fenitrothion, parathion ethyl, endosulfan, and chlorpyrifos ethyl inhibited the development of Aspergillus sp. in all the concentrations. The results indicated that all the chemicals but parathion ethyl in the concentration of 1,000 ppm, showed a fungistatic action on M. anisopliae and Aspergillus sp.