DEVELOPMENT OF AGGREGATION BEHAVIOR IN THE GERMAN-COCKROACH, BLATTELLA-GERMANICA (DICTYOPTERA, BLATTELLIDAE)

Larvae and imagines of the German cockroach, Blattella germanica Von Linne 1767, are known to aggregate in hiding places during their resting phases. A biological assay was used to determine the aggregation behaviour of the larvae, as a function of age and experience. Filter paper, which was impregnated with a methanol extract of the faeces, was presented in a 2 choice test from which an ''aggregation index'' [AI] was calculated to indicate the degree of aggregation on either side. First instar larvae [L1] reared from an isolated ootheca aggregate after eclosion as soon as the cuticula has hardened. During the L1 period, aggregation remains on a high level until the first moult at 10 - 14 days. L1 individuals allowed continuous contact with filter paper impregnated with faeces extract, reach higher aggregation values than the controls which had no access to adult faeces or faeces extract before the test. This is thought to be due to some kind of learning effect (sensitization, imprinting).