Novel and effective baits are needed to manage pest housefly populations and avoid the development of insecticide resistance. In this study, we bioassayed the efficacy of Zyrox®, a novel fly bait containing a novel 0.5 % cyantraniliprole insecticide, to kill adult houseflies under laboratory conditions. We found that Zyrox® killed a significantly greater proportion of flies than the current competing fly bait, QuickBayt®, after a 24-h exposure. The cumulative mortalities of houseflies were up to 96.36 % and 92.57 % for Zyrox® and 78.88 % and 68.76 % for QuickBayt® in no-choice and choice tests, respectively. Our results suggested that there was negligible behavioral resistance to both fly baits but revealed that Zyrox® appeared to work slower than QuickBayt® (at a 3-h exposure, proportionally fewer flies were killed by Zyrox® than by QuickBayt®). Importantly, we found that the efficacy of Zyrox® did not diminish with the age of the bait (up to 90 days old). In actual knockdown time (KDT) feeding bioassay, the results showed that Zyrox® knocked down flies significantly slower (11.97 min for females; 12.30 min for males) than QuickBayt® (1.89 min for females; 2.24 min for males). These results reveal the high efficacy of Zyrox® bait to kill adult flies and suggest that it is a promising slow-action bait for management of houseflies.