Response to and transport of brood by workers of Tapinoma erraticum (Formicidae; Dolichoderinae) during nest disturbance.

An attempt was made to describe the principle signals involved in the recognition of nymphs by Tapinoma workers. A behavioural measure, the way and extent to which workers transported different objects presented to them, was used to quantify this relationship. These objects were homo- or heterospecific nymphs, or different baits. Two types of test were generally used in such studies: retrieval - bringing back objects to the nest, and removal - transport of objects during displacement of the nest. The second type of test was used in this study. The results, in decreasing order of recognition were as follows. Tapinoma workers transport homospecific and Tetramorium nymphs at 100%. The smaller nymphs of Solenopsis impregnated with Tapinoma extract were transported at 77%. The nymphs of Solenopsis with their own odour were transported at 21%, paper impregnated. with Tapinoma extract at 12%, while 'odourless' Tapinoma nymphs and neutral paper were not transported at all. These results imply an intervention of both physical and chemical factors, the threshold significance of signals and their global implication depending on the test situation and its disturbing effect. They also depend on the nature of the different objects presented in combination; Tapinoma workers transport heterospecific brood much less readily in the presence of their own brood. The attractiveness of nymphs is not an all or none phenomenon. In a study of the adoption of homospecific nymphs from another nest, this gradation was apparent in the distribution of nymphs in the nest and their order of transport during removal tests; certain nymphs were left aside in the first 3 days of presentation, were amongst the last to be transported during removal, and then by the most active workers. The perception of the brood by the workers may thus occur at different levels: (1) Perception of a factor that may be vaguely defined as 'transportable object' in a removal test - with objects of type 'nymph' for example; (2) perception of the species; (3) perception of the colony. The worker ant during its life acquires a certain 'knowledge' of its own brood through familiarization, which expresses itself in terms of specific patterns of care for the brood, but this attention, although given preferentially to the brood, is not exclusive under stress.