Previous research on the Coastal brown ant (Pheidole megacephala Fabricius) in the Brisbane area (Queensland) has indicated that this species may have an adverse effect on some native ants. The work reported on here is an investigation of morphological, physiological and behavioural traits which could enable the Coastal brown ant to physically eliminate other ant species.
The venom apparatus is formally described. The furcula is reduced in this species, and the sting was found to be unsuitable as a piercing weapon. Gas chromatographs of the poison and Dufour's glands of the minor worker and the mandibular glands of the major worker were uninformative, as the material was insufficiently concentrated in the solvent. A run with a scanning time of 43 minutes was done with concentrated Dufour's gland/solvent. Twelve constituents were identified. Most of these were long chain hydrocarbons in the range C15-25. Two small peaks belonged to volatiles. These have not been certainly identified, but may have ethological importance. Further work in this area would be desirable. The construction of artificial colonies of the species used in the behavioural studies is described.
Behavioural studies of interactions between P. megacephala and the native formicid species Rhytidoponera metallica, Camponotus aeneopilosus and Iridomyrmex sp. 1 are described. The native species showed no significant decrease in activity in the presence of P. megacephala volatiles (from crushed corpses of the ant). The same conclusion was reached in tests involving the effect of native species volatiles on P. megacephala. Agonistic interactions between the Coastal brown ant and individuals of the above species did not show significant differences in the casualty figures. Interactions between a native ant species and multiple Coastal brown minors (one trial series of five and one of ten workers) and one major, resulted in an increased casualty rate for Iridomyrmex sp.1 only. It was found that all ant species had behaviours that enabled them to avoid conflict. These included 'freezing', evasion, and threat displays.
It is concluded that if the Coastal brown does have an adverse effect on other ants, it may be for reasons other than simply having superior weaponry at its disposal or its greater aggressiveness.