A study was conducted to determine if adult corn rootworm (Diabroticaspp.) population estimates were influenced by training and experience of the sampler and(or) if they were affected by inherent personal differences between individuals of equal training and experience. Two levels each of plant counts, ear-tip collections, and timed collections were used in replicated studies in 2 Iowa cornfields. One field was typical of cornfields grown for grain production. The other field was late planted and late maturing, simulating those fields that develop extreme corn rootworm problems because of their attractiveness to migrating beetles.The plant counts and ear-tip collections were not significantly influenced by the maturity of the field or the investigators' inherent abilities or level of experience. Corn rootworm population estimates produced by timed collections were influenced by both field maturity and investigator variability.