Prolonged efficacy of IR3535 repellents against mosquitoes and blacklegged ticks in North America.

Here I report the first findings of consistently high, long-duration efficacy of IR3535 (ethyl butyl acetyl aminopropionate) formulations in the United States. I tested novel, controlled-release formulations of IR3535, at 10% in lotion and at 20% in pump spray and aerosol, against mosquitoes in the field and blacklegged ticks in the laboratory. These were also the first studies to be conducted under the authority of the U.S. Environmental Protection Agency's Human Studies Rule of 2006, and the protocols underwent science and ethics reviews by five entities. IR3535 is better known in Europe than in North America, having been marketed in the United States only more recently, and there are comparatively few publications on its efficacy. I began with pretrial studies of dosing behavior to compute formula-specific mean dosing rates for the subsequent efficacy trials. Dosing rates were lower than the 1 ml/600 cm rate commonly used to quantify efficacy. Complete protection times ranged from 7.1 to 10.3 h for mosquitoes and from 9.1 to 12.2 h for blacklegged ticks. Long protection duration resulted in many cases being truncated by darkness or eventual subject withdrawal, which suggests that actual protection times were probably greater.