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Exploration of Argentine ant (Linepithema humile) Biology for Pest Management

Abstract

The invasive Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), has successfully established itself in many urban, agriculture and natural habitats worldwide, causing economic damage and disruption of ecosystem processes. Current management strategies for the Argentine ant often rely on insecticidal sprays that contribute to environmental contamination. The overall goal of this dissertation was to develop novel pest control techniques that utilize the Argentine ants’ chemistry and unique genetic makeup to help eliminate or reduce pesticide applications for their control, and to explore their chemical defense system as a possible cause of their ecological dominance over native ants worldwide.

A novel baiting technique, “pheromone-assisted baiting technique”, was developed and tested against Argentine ant populations in the laboratory and residential sites. The technique relies on commercially available bait that has been treated with the Argentine ants’ trail pheromone, (Z)-9-hexadecenal. Laboratory results indicate an increase in foraging activity and final morality of Argentine ants with the incorporation of (Z)-9-hexadecenal into a commercially available bait. Field results demonstrate that the pheromone-baiting technique achieves a 74% reduction in Argentine ant activity by the end of 4 weeks. The pheromone-assisted baiting technique demonstrates effective ant control while reducing the amount of insecticides applied in the environment.

RNA interference (RNAi) has the potential to become an effective alternative to conventional pest control baiting techniques. RNAi is a post-transcriptional gene-silencing technique which is triggered by the presence of double-stranded RNA (dsRNA). Laboratory experiments indicate 52% mortality after 7 days when the RNAi bait was consumed by Argentine ants. The study provides proof-of-concept of an RNAi baiting technique for Argentine ant pest management.

Argentine ants utilize pygidial gland secretions for inter- and intra-specific communication during aggressive interactions with a heterospecific competitor, the California harvester ant (Pogonomyrmex californicus). Chemical analyses indicated that Argentine ants deploy two iridoids, dolichodial and iridomyrmecin, during aggressive interactions. The compounds cause high levels of irritation to the harvester ants and elicit alarm and attraction of Argentine ant nestmates. The results demonstrate semiochemical parsimony in Argentine ants for various colony-level tasks and help us to understand the mechanisms underlying their successful establishment among various competitors outside their native ranges.

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