Mass-production of parasites and predators is
often necessary or desirable in connexion with many
biological control projects, particularly where attempts
are made to increase parasitism or predation
by mass releases of entomophages over a wide area
at a time in the season when these natural enemies
are few or absent. However, the term "massproduction"
is vague and individuals differ in their
concepts of large numbers. Moreover, the actual
numbers needed in connexion with different biological
control problems vary considerably. Some
successful parasite introductions have been made
with only a dozen or so individuals; others have
required very large numbers before establishment
has been obtained