A continuous sieving apparatus is described. The continuous sieving apparatus includes an inclined sieve surface attached to a wall. The inclined sieve surface is inclined with respect to a horizontal axis for pupae to continuously flow across down the incline. A set of openings is formed in the sieve surface so as to define a set of pathways extending through the sieve surface. The set of opening are defined by a length dimension that is greater than a width dimension. When the inclined sieve surface is submerged in a liquid, a first pupa having a first cephalothorax width that is less than the width dimension is free to move through any one of the set of openings, and a second pupa having a second cephalothorax width that is greater than the width dimension is prevented from moving through the set of openings.