Evaluation of the larval migration inhibition assay for detecting macrocyclic lactone resistance in Dirofilaria immitis.

•We measured drug susceptibility in Dirofilaria immitis using an in vitro assay.•High control migration rates (>90%) were observed.•No differences between resistant and susceptible larvae were observed.•IC50 and IC95 values were better defined with eprinomectin than ivermectin.•Motility might not be an appropriate measure of drug susceptibility for D. immitis.