Thermophilia in a tropical Australian ant of the Melophorus aeneovirens (Lowne) species-group (Hymenoptera: Formicidae)

Observations were made on the activity of three colonies of a Melophorus species of the aeneovirens species-group in woodland at Black Jungle, near Darwin in the monsoonal tropics of the Northern Territory. Melophorus aeneovirens displays thermophilic behaviour typical of the genus. Colony activity rates and duration varied between colonies in relation to the microclimatic conditions of the nests. The lowest nest mound temperature at which activity was initiated was 35.2 degrees C; the highest was 45.3 degrees C. Foraging (leaving the nest) did not occur below a threshold of 38 degrees C. Activity levels peaked at around midday. Cessation of activity in the afternoon corresponded with temperatures between 38.3 degrees C and 42.8 degrees C. Activity levels differed between minor and major workers, with the latter most active prior to 10.00h and the miners most active during the remaining hours of the day. The activity of a single colony of M. aeneovirens was strongly negatively correlated to the activity of the behaviourally dominant ant Iridomyrmex sanguineus. The average foraging time of M. aeneovirens workers was 11 min, the mean furthest displacement from the colony was 9 m and the furthest, 25 m. Melophorus aeneovirens differed from arid and semi-arid congeners in having year-round activity, lower initial activity levels, less random and slower foraging, and in not exploiting thermal refugia.