The Propagation of insect Parasites on unnatural Hosts

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Abstract
When an insect parasite successfully attacks a host in the natural environment, the criterion of success being the development of the parasite progeny to maturity, the species attacked is described as a “natural host.” Parasites are used in biological control work with respect to their natural hosts. However, when the mass breeding of parasites for field distribution has to be carried out, the provision of natural hosts in sufficient quantity is in many cases difficult or impossible, unless they can be easily obtained in large numbers from the field. But some of these hosts have only a single generation a year. Others live in the larval stage in parts of growing plants which cannot be satisfactorily handled so as to produce mass infestations; on the other hand, attempts to rear such insects on detached fragments of plant tissue often result in heavy mortality. Other hosts which are very satisfactory for parasite propagation in some respects, become very susceptible to epidemics of disease when kept in large numbers in confinement. Even without these difficulties, the propagation in the laboratory of large numbers of natural hosts is often tedious and expensive.