A liquid insecticidal composition for use with a electrically powered heated emanation device is described wherein the composition comprises a microemulsion of: 0.01 2.0 wt% pyrethroid insecticide selected from at least one of: cyphenothrin, prallathrin, allethrin, esbiothrin, transfluthrin and/or metofluthrin； 0 1.0 wt% natural oil； 0 2.0 wt% fragrance； 1.0 5.0 wt% surfactant； 0.1 3.0 wt % fatty acid ester； 0.0 40.0 wt% semi polar or polar organic solvent (derived from petrochemicals)； 0.0 30.0 wt% polar organic solvent (not derived from petrochemicals)； 0 8.0 wt% additive(s)； and water to 100 wt% of the total wt% of the composition wherein water comprises at least 30.0 wt% of the total composition. A replaceable refill containing the insecticidal composition and a system for emanating the composition from the refill is also described. The exemplified fatty acid ester is isopropyl myristate. The natural oil is preferably d-limonene or cintronella oil. An esbiothrin based example includes diethylene glycol mono butyl ether as the solubilizer instead of a fatty acid ester.
