Knocking and scraping as alarm signals in Dolichoderinae ants from the Malay Peninsula (Hymenoptera : Formicidae : Dolichoderinae)

The defence signaling and behaviour in Dolichoderinae ant species from the Malay Peninsula are observed in the field and brought home to the lab for m easurements. The results are discussed in comparison with the corresponding behaviour in the European ants Camponotus ligniperda (Latreille 1802) and C herculeanus (Linnaeus 1758). 6 out of the 7 investigated tropical ant spe cies from the Malay Peninsula were found to produce vibration signals with the exception of Dolichoderus tuberifer Emery 1887. The vibrations were gen erated in 2 different manners, namely by knocking and scraping. A high spee d camera (500 pictures / s) was employed to scrutinise the production of th e signals. To achieve the generation of vibrations 5 species (Dolichoderus thoracicus (Smith 1860), D burmanicus Bingham 1903, D sulcaticeps (Mayr 1870) and 2 no n-described species) scratch over the ground using their mandibels whilst s tanding. The signals reveal a distinct pattern of three clearly distinguish able sequences and are characterised by a repetivity of 3-5 times in genera l However, the signals can occur up to 15 times. One element of the signal lasts 0.04-0.14 s (depending on temperature). The time between the elements lasts 0.22-0.36 s The frequency domain reveals a range from 1-19.5 kHz. In contrast, the sixth species (Dolichoderus patens (Mayr 1870)) uses its g aster to generate the signals. It hits the ground. It can move slowly durin g vibration production. The signal only lasts 0.012-0.019 s with breaks of 0.058-0.162 s accordingly. The signal is repeated up to 30 times and even m ore frequently in a few cases, with frequencies detected between 0.5-22 kHz . In general, only the workers of the various species seem to generate vibr ation signals, never the sexuals. Behavioural patterns were examined in D thoracicus and D patens. Workers of D thoracicus reacted in different ways depending on their level of excitem ent while perceiving the vibration signal. If excitement was low they froze , motionless. When more excited they also produced signals or increased the ir running speed manifoldly and showed a lower threshold of aggression towa rds visually perceivable moving objects. Threatening behaviour (i.e. stradd ling of the mandibles) was observed when objects were obscured. The behavio ur takes place outside the nest. In contrast, the workers of D patens did n either move vivdly nor reacted aggressively, but gravitated slowly towards the nest instead. At low excitement levels a waving of their gaster was rec orded, whereas a knocking motion onto the ground could be observed when the ants were stimulated excessively. On perception of these signals the sexua ls of either species were prompted swiftly to move into the nest.