Pulsating stars have become important tools for studying the interior structure. Known instability strips for early-type main sequence stars comprise the delta Scu stars, beta Cep stars, and the slowly pulsating B stars (SPB). This article presents results of a seven-year photometric monitoring of the open cluster NGC 3766. Several new variables belonging to the known classes are found. Most significantly, detection is reported of 36 main sequence stars between the red edge of the SPB stars and the blue edge of the delta Scu stars. These variables appear to be members of a new class for which the authors propose the designation "low amplitude periodic A and late-B variables.