Further experiments on olfactory conditioning in a parasitic insect. The nature of the conditioning process

In the course of a recent paper (Thorpe and Jones 1937) it was shown by means of experiments with an olfactometer of the Mclndoo type, that the parasitic ichneumonid, Nemeritis canescens (Grav.). is strongly attracted by the odour of the larva of its normal host, the Mediterranean flour moth, Ephestia kühniella (Zell). This response is an inherent one, and is manifested throughout the life of the adult parasite. The insect can also be reared on the larvae of the closely allied genera of wax moths, Meliphora and Galleria. Whereas the larvae of Meliphora exert no attraction whatever on parasites reared from Ephestia, they exert a quite definite attraction on individuals which have been reared from Meliphora or which have been exposed to contact with Meliphora larvae for a period shortly after emergence from the cocoon. Insects which have been treated in this way, wrhen given the choice in the olfactometer between Meliphora and Ephestia, whilst still preferring the latter, show significant attraction to the former, such that the proportion choosing Ephestia is reduced from 85 to 65-8%. It was concluded from these experiments that Nemeritis has an oviposition response to Ephestia larvae, but that an additional oviposition response to the odour of Meliphora, a response which is entirely lacking in the normal animal, can be conditioned by contact with the new host. Such conditioning can take place either in the pre-imaginal stage when the larva is feeding inside its host caterpillar, or in the adult stage immediately after emergence.