Local shifts in the foraging range of Azteca instabilis induced by an entomopathogenic fungus infecting its mutualistic partner, Coccus viridis

The emergence of spatial structure through endogenous, biotic processes is an active area of research, and has been demonstrated in a variety of ecosystems, e.g., forest gaps, mussel beds, and arid vegetation patterns. The spatial distribution of Azteca instabilis (Hymenoptera: Formicidae) ant colonies in a shade coffee agroecosystem has been shown to emerge through a self-organization process involving local expansion and density-dependent control. Local expansion of colonies occurs when a queen from a polygynous nest establishes a satellite nest in a neighboring shade tree. However, the cause of density-dependent control is not known. A potential causal agent is an entomopathogenic fungus, Lecanicillium lecanii (Zimmermann), which attacks the ants’ mutualistic partner, the green coffee scale Coccus viridis (Hemiptera: Coccidae). Although recent results provide support for the hypothesis that an L. lecanii epizootic may cause an A. instabilis colony to die or migrate, much is still unknown about the effects of a local epizootic on an ant colony. Through a combination of repeated spatial surveys of L. lecanii infection and A. instabilis foraging 1) throughout the normal seasonal spread of L. lecanii and 2) following experimental infection of A. instabilis-tended scale populations, we show that A. instabilis may partially adapt to a local epizootic by expanding its foraging range to uninfected, neighboring scale populations previously tended by other ant species, but that these appropriated scale populations likely provide only a small fraction of the carbohydrate resources available to the colony prior to the epizootic.