The lesser mealworm beetle, Alphitobius diaperinus (Panzer), is a widespread serious pest in poultry production facilities and is difficult to control by conventional means. Although pheromone-based tools have become useful in the management of other beetle pests, no pheromone was known for A. diaperinus, and this study sought to develop basic pheromone information. Volatiles were collected in the laboratory from groups of male and female A. diaperinus maintained on poultry food (chick starter mash). Gas chromatographic-mass spectrometric analysis of volatiles collected from feeding males and females revealed five male-specific compounds that were identified as (R)-(+)-limonene, (E)-beta-ocimene, (S)-(+)-linalool, (R)-(+)-daucene, and 2-nonanone. Emission of these began 1-2 weeks after adult emergence and could continue for at least 1 year, ceasing and resuming in response to changes in food availability and quality and other factors. No female-specific compounds were discovered. A synthetic blend of the five male compounds was attractive to both sexes in poultry production facilities in Illinois and Arkansas, indicating that the blend functions as an aggregation pheromone, but it is not yet known whether all five compounds are required for activity. A new pitfall trap is described for field use.