Novaluron is a chitin synthesis inhibitor (a benzoylphenyl urea) that kills larval stages and causes reversible cessation of laying viable eggs in adults of the Colorado potato beetle, Leptinotarsa decemlineata (Say). Previous studies also suggest that it has ovicidal properties, but not on all tested egg masses. We investigated if egg maturity at the time of exposure affects its susceptibility to novaluron. Novaluron application significantly reduced the hatch of eggs that were 0-24 h old at the moment of treatment, but had no effect on the eggs that were 96?120 h old. Novaluron also interfered with the development of the hatched larvae regardless of the egg age at the time of treatment, probably due to chorion feeding by neonates. Ovicidal properties of novaluron may contribute to Colorado potato beetle control, but their effect will be limited to newly laid eggs. If that window of susceptibility is missed, hatching larvae will be exposed to a fairly old novaluron residue that might be weathered down to sublethal levels. This supports the current recommendations to apply novaluron as a larvicide.