Dillapiol, the main constituent in dill Anethum sowa Roxb. ex Fleming (Apiaceae) oil and wild pepper, Piper aduncum L. (Piperaceae), is an effective cytochrome P450 inhibitor similar to piperonyl butoxide (PBO). Laboratory and field trials with pyrethrum Chrysanthemum cinerariifolium (Trevir.) vis. extracts combined with dillapiol (1:5 and 1:16 ratio) were effective against both insecticide-susceptible and -resistant Colorado potato beetle Leptinotarsa decemlineata (Say). In the laboratory, pyrethrum efficacy was increased 2.2-fold with the SS strain and 9.1-fold with the RS strains by using pyrethrum dillapiol. Two field trials with the pyrethrum dillapiol formulation demonstrated efficacy ≥10 times than that of pyrethrum alone. The residual activity (half-life) of the combination exposed to direct sunlight was 3 h but it increased to 10.7 h by adding 2% of the sunscreen octylmethoxycinnamate.