When oviposition is observed on a test plant, further tests are required. In particular, it is necessary to measure the viability of the eggs, the ability of the plant to support larval development, the mortality of the pupal stage, and the size and fecundity of the resulting adults. These tests determine the physiological host range, that is, the range of plants on which larval development can occur. Larval development tests may be the only viable test for insects which do not show normal oviposition behaviour in cages.
The eggs may be placed on the plant material by the ovipositing adult or they may be manually transferred to the point of feeding. Manual transfer is
necessary for some Lepidoptera that randomly lay eggs. The development of the eggs into adults is then monitored.
Normally the larvae are placed on the test plant without previously feeding on any other plant. This is to avoid induced food preference, that is, the phenomenon where larvae that have fed on one plant species will often reject other acceptable host species. Occasionally, however, older larvae are tested. These larvae are partly reared on the normal host and are then transferred to the test species. This tests for the situation where a similar transfer is possible in nature.
