A mixed function oxidase factor contributing to permethrin and dichlorvos resistance in Lycoriella mali (fitch) (diptera: Sciaridae)

Several observations suggested that enhanced mixed function oxidase (MFO) activity was one of several factors contributing to permethrin and dichlorvos resistance in the mushroom pest, Lycoriella mali (Fitch) (Diptera: Sciaridae). This was investigated using the mixed function oxidase inhibitor, piperonyl butoxide (PBO), in topical application bioassays with reference and field‐selected resistant strains. At the LD50, strains of resistant colonies (AV1, AV2, TK1) used in this study were 41‐(AV1), 34‐(AV2), and 62‐fold (TK1) resistant to permethrin, relative to the reference strain (ONT9). Permethrin in the reference strain was only synergized 2‐ (ONT9) and 4‐ (ONT13) at the LD50. Synergist ratios for resistant strains were 12 (AV1), 34 (AV2) and 94 (TK1) at the LD50. Moderate dichlorvos resistance was twice documented in the AV strain. Resistance ratios of 37 (AV4) and 52 (AV9) were observed at the LD50, relative to the reference strain (ONT10). Dichlorvos was synergized only 2‐fold at the LD50 in the reference strain (ONT10). However, PBO abolished dichlorvos resistance in the AV9 strain. The effectiveness of PBO in these studies indicated that enhanced MFO activity was present in resistant L. mali from southeastern Pennsylvania. Resistance to DDT (54‐fold at the LD50) was also documented. Other factors, such as an altered target site (kdr), may also have contributed to control failures with permethrin.