In laboratory tests on the spruce budworm, Choristoneura fumiferana (Clemens), EL-494®, a new moult-inhibiting insect growth regulator, was found to be more active than Dimilin. The EC so determined by diet tests was 0.205 ppm for the 3rd, 0.249 for the 4th, 0.287 for the 5th, and 0.486 for the 6th instars. Stadia! sensitivity was not detected. In greenhouse tests this compound was found to be resistant to leaching and UV-degradation; the compound remained active on spruce foliage for at least 15 days. In preliminary field tests EL-494 showed good potential as a control agent. © 1979, Entomological Society of Canada. All rights reserved.