Quality control

While the main objective of mass rearing is to produce as many insects as possible for release, the insects produced should be of high quality and their natural attributes should be preserved. The mass-reared insects should be as fit genetically, physically and behaviourally as a natural population. Selection of biological and behavioural characteristics under laboratory rearing conditions may reduce the ability of populations to establish after release into the field. These effects may be minimised by the periodic re-introduction of field collected insects into the laboratory culture once the agents have established in the field. Care should be taken to ensure that the field collected insects are free of parasitoids, ectoparasites and diseases acquired in the field.

Quality control issues such as maintenance of genetic and behavioural fitness are discussed by Boller (1972), Heuttel (1976), Chambers (1977), Mackauer (1972, 1976, 1980), Bigler (1989) and Leppla and Fisher (1989).

General hygiene

Insect populations in mass rearing insectaries can be rapidly depleted by outbreaks of disease. Lepidopterous larvae are particularly susceptible to bacterial and viral infections. Entomophagous fungi can affect many insects particularly those which spend part of their life cycle on or in the soil. Allen (1980) discussed insect diseases and their elimination in laboratory and insectary rearing.

Care must be taken to ensure that only healthy insects are used to start colonies. It is prudent to maintain susceptible colonies in as many cages as is practical so that if part of a colony is affected by a disease outbreak, those cages can be isolated. Colonies should be checked regularly for signs of infection. Insects, host material and soil in infected colonies should be disposed of hygienically and the cages sterilised. Strong bleach is a suitable sterilant.

Insects of many Orders are susceptible to microsporidian parasites such as Nosema. An apparently healthy colony may be infected by these parasites at sub-lethal levels. The disease only becomes apparent when otherwise unexplained mortality occurs and insect squashes are microscopically examined by an insect pathologist. Microsporidians are transmitted transovarially so normal hygiene techniques are ineffective in preventing outbreaks, but they are extremely important in preventing spread. Specialised procedures are necessary to ensure colonies are free of microsporidian infection. Dunn and Andres (1980) and Etzel et al. (1981) describe techniques used to eliminate Nosema from colonies of insects prior to their use as control agents.

Pest control in food plant material

High quality host plant material to be used as food for the insects has to be available in sufficient quantity to sustain continued production at the desired rate. Plants grown intensively as hosts often become infested by pests such as lepidopterous larvae, aphids, whiteflies, scales, mealy-bugs and two-spotted mites. Where possible, predatory biological control agents such as neuropterans, coccinellids and mites should be used to control these pests. If it becomes necessary to use chemicals, only non-residual chemicals with very short withholding periods should be used.

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