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Identification and Characterization of Trail Pheromones and Queen Pheromones in the Argentine Ant, Linepithema humile (Mayr)

  • Author(s): Neff, Richard Ryan
  • Advisor(s): Rust, Michael K
  • et al.

Pheromones are integral to the communicative feedback loops that govern colony cohesion in social insects. These pheromones may be glandular in origin, as with trail pheromones, or may be deposited on the cuticle, like cuticular hydrocarbons. Whether glandular or cuticular, pheromones are often complex mixtures that include multiple glandular products. The first part of this dissertation identifies the volatile and cuticular chemicals found in the different castes and developmental stages of the Argentine ant, Linepithema humile (Mayr). Volatile headspace collections were made for live and macerated samples of queens, virgin female reproductives (gynes), males, workers, gyne larvae, and worker larvae. Queens and workers differed significantly in their relative proportions of dolichodial and iridomyrmecin, and also qualitatively in their saturated hydrocarbons (SHCs) and unsaturated hydrocarbons (UHCs). Queens were characterized by an abundance of 5-Me and 5,11-dimethylalkanes and a homologous series of long-chain UHCs. In Chapter 3, I explored the relative contributions of three worker-derived compounds to worker trail-following response and determined the absolute configuration of ant-derived (natural) iridomyrmecin. Of the three compounds only Z9-16:Ald induced trail-following in worker. Natural iridomyrmecin was 94.5% (+)-iridomyrmecin, with small amounts of (+)- and (-)-isoiridomyrmecin. In Chapter 4 I showed that both saturated and unsaturated CHCs are required to inhibit workers from rearing new queens in queenless colonies, although the active queen pheromone components could not be delineated further. Finally, using four different diets ranging from nutrient-poor to highly-enriched, it was discovered that enriched and highly-enriched diets actually suppressed queen production. Queens from these colonies had significantly higher juvenile hormone levels than did queens fed standard diets.

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