Colony size,density and distribution of the leaf-cutting ant,Acromyrmex octospinosus (Reich) in cultivated fields

• 1 Fields of citrus, cacao and rubber in Trinidad were surveyed to measure the number and density of nests of Acromyrmex octospinosus. The greatest density (=153 nests/ha) was in an undisturbed field of young cacao; in established crops density ranged from 3–36 nests/ha.
• 2 Mounds of new nests appeared throughout the year, but most often 4–10 months after the main nuptial flights. Nests reached maximum size, with up to 17 holes, about three years after foundation.
• 3 The ratio of workers to brood was between 5 and 9: 1 for most of the year but it increased to 27: 1 as the sexuals developed. A medium-large colony produced 200–300 queens and males/year; the largest single nest contained about 14,000 individuals.
• 4 The average intake of leaf fragments into laboratory nests was 1 fragment/6.5 individuals. It increased to 1 fragment/2.1 individuals when sexuals were present. Foragers collecting from fields of established cacao preferred flowers to leaves.
• 5 In fields with crops planted on cambered beds, nests were concentrated on the dry edges of drains in the dry season, but they were moved to drier ground in the wet season. Nests were aggregated in 13 of the 16 fields examined, the remaining three fields were exceptionally well drained.
• 6 In newly planted cacao an estimated 6—17% of plants were defoliated and destroyed. In established cacao ants collected about 3000 flowers/ha each day. Laboratory data suggest that ants could defoliate about 25 three-year old citrus trees in a year.