Quantity limits: Included in, not in addition to, the quantity limits for other medicinal and toiletry articles: The total aggregate quantity per person cannot exceed 2 kg (70 ounces) or 2 L (68 fluid ounces). The capacity of each container must not exceed 0.5 kg (18 ounces) or 500 ml (17 fluid ounces).*
This exception is for repellents that are sprayed/applied directly on a person's skin and clothing and as such are included in the exception for medicinal and toiletry articles. Insect repellents or insecticides designed to be sprayed in the air or at the insect are not included in this exception.
See the regulation: 49 CFR 175.10(a)(1)
Tip: Most insect repellents in non-aerosol liquid pump sprays and other forms (liquids, lotions, wipes, etc.) are not restricted as hazardous materials – and therefore not subject to size or quantity limits. Some liquid repellents, including some containing Picaridin, are flammable liquids--these are still allowed but must stay within the size and quantity limits mentioned above.
*Liquids, gels, and aerosols in carry-on baggage are further limited to 100-ml (3.4 oz) containers at the TSA security checkpoint.