Methoxyfenozide resistance of the housefly,Musca domesticaL. (Diptera: Muscidae): cross-resistance patterns, stability and associated fitness costs

BACKGROUND The housefly, Musca domestica L. (Diptera: Muscidae), is an insect pest of public health and veterinary importance with the ability to develop resistance to insecticides. Methoxyfenozide, an ecdysone agonist, is a biorational insecticide used for the management of various insect pests, including houseflies. To design an effective resistance management strategy, life history traits based on laboratory observations were established for methoxyfenozide-resistant (MXY-SEL), unselected counterpart (UNSEL) and reciprocal cross-strains of housefly. RESULTS The MXY-SEL strain developed a resistance ratio of 160.99 after 30 generations of selection with methoxyfenozide by compared with the UNSEL strain. The MXY-SEL strain showed very low cross-resistance to cyromazine, fipronil and chlorpyrifos and no cross-resistance to spinosad and bifenthrin when compared with the Methoxy-Field population. Resistance to methoxyfenozide, cyromazine, fipronil, spinosad, chlorpyrifos and bifenthrin was unstable in the MXY-SEL strain. The MXY-SEL strain had a reduced relative fitness (0.31), with lower hatchability, a lower number of next-generation larvae, a lower intrinsic rate of natural increase and a lower biotic potential compared with the UNSEL strain. CONCLUSIONS The disadvantageous life history traits of the MXY-SEL strain suggest that development of resistance to methoxyfenozide has considerable fitness costs for this strain. Moreover, the unstable resistance to the tested chemicals provides useful information for preserving the efficacy of these chemicals. © 2016 Society of Chemical Industry