We previously demonstrated that six genes involved in ecdysteroid signaling are expressed preferentially in Kenyon-cell subtypes in the mushroom bodies of the honeybee (Apis mellifera L.). To further examine the possible involvement of ecdysteroid signaling in honeybee brain function, we isolated a cDNA for the A isoform of the ecdysone receptor gene homolog AmEcR-A and analyzed its expression in the brain. In situ hybridization revealed that AmEcR-A is expressed selectively in the small-type Kenyon cells of the mushroom bodies in the worker and queen brain, like AmE74 and AmHR38, suggesting a possible association of these gene products. Analysis of AmEcR-A expression in queen and worker abdomens demonstrated that AmEcR-A is strongly expressed in nurse cells of the queen ovary, suggesting that ecdysteroid and ecdysteroid signaling have roles in oogenesis. Our present results further support the possible involvement of ecdysteroid signaling in brain function, as well as in regulating queen reproductive physiology in the adult honeybee.