Sterile, diploid males occur in many Hymenoptera and result from homozygosity at the sex locus. Multiple alleles exist at this locus so that diploid male production is inversely proportional to the number of alleles in a population. Allelic diversity can be maintained by a single, large population or via multiple, inbred lines. Simple calculations show that small numbers of inbred lines can maintain surprisingly high allelic diversity. Two-allele lines with ≥10 diploids per generation are unlikely to go extinct and may reduce culture effort, as well as being less affected than a large population by population crashes. However, the choice between a single, large population and multiple lines is affected by the biological attributes of a given host-parasitoid system. If resources permit a combination of both methods, this may be the best solution.