Abstract
The invasive Argentine ant (Linepithema humile) has become established worldwide in regions with Mediterranean or subtropical climates. The species typically disrupts the balance of natural ecosystems by competitively displacing some native ant species via strong exploitation and interference competition. Here we report that Argentine ants utilize glandular secretions for inter and intra-specific communications during aggressive interactions with a heterospecific competitor, California harvester ant (Pogonomyrmex californicus). Chemical analyses indicated that Argentine ants deploy glandular secretions containing two major volatile iridoids, dolichodial and iridomyrmecin, on the competitor’s cuticular surface during aggressive interactions. Bioassays indicated that the glandular secretions function as a defensive allomone, causing high levels of irritation in the heterospecific. Furthermore, the same glandular secretions elicited alarm and attraction of conspecific nestmates, potentially enabling more rapid/coordinated defense by the Argentine ants. Two major volatile constituents of the glandular secretion, dolichodial and iridomyrmecin, were sufficient to elicit these responses in conspecifics (as a mixture or individual compounds). The current study suggests that invasive Argentine ants’ superior exploitation and interference competition may rely on the species’ effective semiochemical parsimony.
Highlights
From its native range in South America, the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae) has become a global invader, in areas with Mediterranean climates[1]
Headspace volatile samples were analyzed from the following samples using solid phase microextraction (SPME) and gas chromatography – mass spectrometry (GC-MS): vials with Argentine ants and single harvester ant (Aggression), vials with Argentine ants only (Argentine ant control), and vials with single harvester ant only (Harvester ant control)
The headspace volatile analyses indicated that two iridoids, dolichodial and iridomyrmecin, were consistently present in relatively large quantities in the vials where there were aggressive interactions between Argentine ants and harvester ants (Fig. 2, Aggression, 10 of 10)
Summary
From its native range in South America, the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae) has become a global invader, in areas with Mediterranean climates[1]. Exploitation competition (i.e., depleting resources that would otherwise be used by other species) and interference competition (i.e., prohibiting access to resources by other species via direct interactions) have been studied to understand their roles in the Argentine ant’s successful establishment in non-native habitats, especially against other native ant species[2,12,13]. Coastal environments with fresh water from natural springs or ephemeral waterways may provide suitable environmental conditions for Argentine ant establishment[39] This habitat overlap between harvester ants and the Argentine ants results in competitive interactions between the two species[38,40]. In California, invasive Argentine ant populations have been observed to exploit the brood of Pogonomyrmex subnitidus (Emery) colonies, resulting in the eventual decline of harvester ant populations[41]
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