The seed beetle Stator limbatus adjusts egg size in response to the quality of the oviposition host, laying small eggs on the high quality host, Acacia greggii seeds, and larger eggs on the poor quality host, Cercidium floridum seeds. We examined various proximate mechanisms of this egg-size plasticity. Once exposed to a new host, it takes 24 to 48 h for females to change the size eggs they lay. Beetles that came into direct contact with seeds adjusted egg size to a much greater extent than beetles that only came in contact with the fruits or were physically separated from the seeds. Egg size was not affected by size of the seed. Both the host seed in which the larvae were reared as well as the host to which adults were subsequently exposed influenced egg size. The default egg size in the absence of a suitable host is slightly larger than the size egg laid on A. greggii. Thus, beetles increase egg size in response to C. floridum seeds and slightly decrease egg size in response to A. greggii seeds.