PARENT SESSION
Oral Session #78: Insect Population and Community Ecology. Presiding: R. Denno.
Friday, August 10, 2001. 8:00 AM to 11:45 AM. Hall of Ideas I.
Density, natality, and mortality of Atta cephalotes colonies in relation to soil type and vegetation at La Selva Biological Station, Costa Rica.
Wells-Sweeney, Heather1, Rathbun, Stephen1, Haines, Bruce1, 1
ABSTRACT- Of the fifteen species of leaf-cutting ants in the genus Atta, five are important agricultural pests at low elevations between Argentina and southern USA. Insecticides commonly are used for pest control but have negative environmental impacts. Our goal was to search for biological or biophysical controls of A. cephalotes by tracking colony natality, growth, and mortality in a mosaic of soil types and land uses at La Selva Biological Station, Costa Rica (10° 26' N, 83° 59' W) in 1988, 1990, 1993, 1994, 1996, and 1997. Vegetation and soil type were determined by comparing colony locations to soil and vegetation coverages in Geographic Information Systems (GIS) using ArcView. Estimated colony densities were compared among soil types and among vegetation types using the Wald test. Estimated colony densities of A. cephalotes in the surveyed region differed among soil types (p<0.001) and among vegetation classes (p=0.0275), with the greatest estimated density in abandoned Theobroma cacao plantations (3.29 colonies/ha) and the lowest estimated density in abandoned cattle pasture (0.56 colonies/ha) and old-growth forest (0.65 colonies/ha). Total colony natality did not differ among soil types (p=0.463) or vegetation classes (p=0.403). Soil type had no effect on total colony mortality (p=0.1175) but vegetation had a marginal effect (p=0.069), with the greatest mortality rate found in selectively-logged forest. Discovery of biological or biophysical controls of A. cephalotes remains elusive.
KEY WORDS: Atta cephalotes, population density, mortality, natality