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Behavioral ecology of the leaf-cutting ant, Acromyrmex octospinosus (Reich), in Guadeloupe, F.W.I.

University of British Columbia

The foraging behavior of the leaf-cutting ant, Acromyrmex oct ospinosus (Reich), was studied between September 1983 and August 1984 in 2 areas of Guadeloupe, F.W.I. At Lemesle, the ants usually foraged primarily during the day, but occasionally were most active at night. At Bois de Lomard, a drier area, all the colonies foraged mostly at night, but colonies with part of their territory in the shade sometimes exhibited low levels of activity during the day. Efficiency of food gathering (% incoming ants laden) varied during the day, but usually followed the above patterns of activity. Monthly correlations between trail surface temperature or vapor density deficit and total activity/min or efficiency were extremely variable, except for colonies that did not shift the timing of their peak activity; for these, 75% of the correlations were significant. Peak activity and efficiency occurred during the dry season for 5 colonies, 2 or 3 mo before the nuptial flight during the first half of May. The average efficiency level of colonies was not correlated with the average size of their foraging force. The ants visited 83% of the plant species in their territory, but actively cut only 44% and 31% of them at Bois de Lomard and Lemesle, respectively. A small number of plant species constituted most of the diet of the ants, and the dominance-diversity curves for the proportion of each plant species in the diet revealed a log normal distribution. The colony preference for a set of plant species was determined by the combined choices of all foragers, although some individuals had a preference different from the overall colony choice. The ants preferred flowers, fruits, or young leaves. More of the first 2 plant parts were cut at Lemesle than at Bois de Lomard. The proportions of the different plant parts collected varied each month, as ants responded to the appearance of the preferred plant parts by concentrating their foraging on them or on other portions of the plant species harboring them. The ants collected an average of 364 kg fresh material/ha/year. The compass distribution of the primary foraging trails around colonies was not significantly different from random for 3 of 4 colonies at Bois de Lomard, and 4 of 5 colonies at Lemesle. Temporary trails were created to transitory resources, while "permanent" trails (lifespan >120 days) led to less transient resources. Colonies near fruit bearing trees usually had more trails than colonies farther away. The size of foragers caught at the ends of 0.15, 5.25, and 13 m trails increased exponentially with the length of the trails. The pheromone trail established to particular resources persisted about 40 h in the field. Attenuation occurred in stepwise fashion, with the highest rate during the day. Pheromone trails exposed to UV light (253.7 nm) in the laboratory disappeared twice as fast as control trails. Weather affects the timing of foraging activity of Acromyrmex octospinosus. The insect has developped an opportunistic system of foraging. The amount of biomass cut by colonies is relatively low, and the insect would not be a problem if it did not sometimes concentrate its cutting in subsistance gardens.

Text

2010-08-08

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http://hdl.handle.net/2429/27208

Plant Science

University of British Columbia

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