Host specificity in the slave-making ant Harpagoxenus canadensis M. R. Smith

Abstract

The slave-making ant Harpagoxenus canadensis frequently parasitizes two host species in the genus Leptothorax (subgenus Leptothorax s.str.) which are part of the L. "muscorum" complex and are currently referred to as Leptothorax sp. A and Leptothorax sp. B. A sympatric member of this subgenus, L. retractus, is rarely enslaved. Of 48 complete slave-maker colonies from various sites, 26 contained only Leptothorax sp. A slaves (54.2%), 11 contained only Leptothorax sp. B slaves (22.9%), and 11 contained slaves of both species (22.9%). Of 65 partial slave-maker colonies from one site, 10 contained only Leptothorax sp. A slaves (15.4%), 55 contained only Leptothorax sp. B slaves (84.6%), and none contained slaves of both species. Leptothorax retractus was common at some sites but was never found as a slave in this study. Differences in host-utilization patterns within and between populations might reflect differing host densities but could be influenced by genetic or learned predispositions of the parasites or differential interspecific compatibilities among the various species. Possible collector bias must also be considered. Female reproductives of the host species (n = 13) were occasionally found in slave-maker nests. Most of these were Leptothorax sp. A intermorphs (workerlike females; n = 11) and were inseminated but not egg laying. The only Leptothorax sp. A gynomorph (a primarily winged female) was uninseminated and not egg laying, and the only Leptothorax sp. B gynomorph could not be dissected.