Realized Heritability and Fitness Costs of Diflubenzuron Resistance in Musca domestica L. (Diptera: Muscidae)

The house fly, Musca domestica L., is a medically important cosmopolitan pest distributed worldwide. Diflubenzuron, a chitin synthesis-inhibiting insect growth regulator, is widely used for the control of medically important insect pests. In this study, the biological and population characteristics of diflubenzuron-unselected (Diflu-Unsel) and diflubenzuron-selected (Diflu-Sel) M. domestica were evaluated using the age–stage, two-sex life-table theory to support resistance management efforts. The results showed that the Diflu-Sel (G46) strain developed 319.935-fold resistance to diflubenzuron after 42 generations of selection compared with the Diflu-Unsel (G46) strain. Using the LC50 of diflubenzuron in the Diflu-Unsel (G5) as the parental generation before selection, the realized heritability (h2) of diflubenzuron resistance was estimated as 0.054. Larval and pupal development durations and the total preoviposition period were significantly prolonged, whereas adult duration, total longevity from egg to adult, oviposition period, and fecundity were significantly reduced in the Diflu-Sel (G46) strain compared with the Diflu-Unsel (G46) strain, resulting in a relative fitness value of 0.39. Population parameters, including the intrinsic rate of increase, finite rate of increase, generation time, doubling time, gross reproductive rate, and net reproductive rate, were significantly lower in the Diflu-Sel (G46) strain than in the Diflu-Unsel (G46) strain. These results demonstrate that resistance to diflubenzuron can evolve in M. domestica but may be accompanied by substantial fitness costs, which may facilitate resistance management. The findings provide valuable insights for designing sustainable diflubenzuron resistance management strategies for M. domestica.