Floating emergence traps were used in 15 road gullies to determine the effectiveness and longevity of S-methoprene briquets over 124 days. Samples were taken monthly from October 2014 to March 2015. Two treatment methods were assessed: application of briquet using a float, and application without a float. These methods were compared with untreated control gullies. Mosquito emergence peaked in early November, and decreased by February. Effectiveness of the briquet was not impacted significantly by the presence or absence of a float (P = 0.329). Gullies yielded a mean of 108 mosquitoes per day per gully over the season. Culex quinquefasciatus and Aedes notoscriptus were the most abundant species. The maximum number of Cx. quinquefasciatus emerging could exceed 1,600 per day per gully. Aedes notoscriptus numbers could exceed 70 adults per day per gully. Treatment with S-methoprene was highly effective against both species for at least 70 days and partially effective for up to 120 days. Treatment provided no control by day 124. S-methoprene provided 90% control over 124 days. Road gullies have been confirmed as a significant larval habitat and are likely to be increasing the potential for Ross River virus transmission in the area.