A host other than the target host for parasitoids, one that biocontrol practitioners may more readily rear than the target host in a laboratory, thus implying that the biocontrol agent is not absolute [..]

When you force a biological control agent to feed on an insect or mite that it would not feed on it in nature. This can allows for higher production levels.

An insect that is not the preferred host but is used as a host for the production of parasitoids. such as hosts are usually used because they are easier to rear in large numbers than the preferred host.