The role of ant biodiversity, temporal, and spatial foraging dynamics in maintaining a system of biological control in an organic coffee agroecosystem in Chiapas, Mexico

Factors that shape interspecific competition, such as differential competitive strategies, and niche and resource partitioning, play major roles in the formation of ecological communities. Such interspecific interactions and resultant community structure can facilitate ecosystem functioning. Such is the case in an organic coffee agroecosystem in Chiapas, Mexico where the dominant ant, Azteca instabilis (Hymenoptera: Formicidae) and associated insect community facilitate biological control of several coffee pests. One important mechanism limiting the distribution of A. instabilis, may be severely reduced availability of its hemipteran mutualist, the green coffee scale (Coccus viridis, Hemiptera: Coccidae) due to infection by the fungus Lecanicillium lecanii (Hypocreales: Cordycipitaceae). L. lecanii primarily infects dense populations of the scales that build up during the wet season in bushes protected by Azteca ants. We hypothesized that Azteca is maintained in the system despite the decimation of high density scale populations, by taking over low density populations tended by non-dominant ants that exist on the periphery of Azteca nest clusters. Foraging activity of all scale-tending ant species found, and scale and L. lecanii density were surveyed at multiple time steps at two natural sites and seven experimental sites at which L. lecanii infection was induced. The foraging patterns of Azteca were found to follow through time those of the other scale-tending ants as resource availability shifted due to L. lecanii infection. We conclude that the interactions among Azteca, the non-dominant scale-tending ants, the scale and the fungus maintain Azteca persistence through cyclical variability in spatial distribution of viable scale populations.