After collection from an apple orchard sprayed nine consecutive years with carbaryl and when evaluated by a slide-dip or leaf-dip residue treatment, anAmblyseius fallacis(Garman) population exhibited a 25- to 77-fold resistance level to carbaryl. Following both independent and simultaneous selections with azinphosmethyl and carbaryl in the laboratory and hybridization with a similarly treated organophosphorus-resistant strain, a strain resistant to both chemicals was obtained and maintained for 10–25 generations in the laboratory. Possibilities for establishing this population in the field and its useful role in providing for biological control of spider mites in an integrated pest management program are suggested. Also, additional chemical selection trials withA. tallacisare reported.