Resource availability as a key driver of Argentine ant, Linepithema humile, invasion success
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Resource availability has frequently been identified as a key driver for the successful invasion of non-native ants. Essential macronutrients for ant colony survival include protein and carbohydrates. Long term studies have shown that along an ant invasion front, resource use shifts from a protein-rich diet during the establishment phase of the invasion to a carbohydrate dominated diet once colonies have become established. This implies that protein is a key resource for propagule establishment. In contrast, more recently carbohydrate resources obtained from mutualistic associations have been shown to be more effective in facilitating colony establishment. It is important to assess which of the macronutrients propagules prefer and which is possibly important for establishment and how these macronutrients are partitioned between the larvae and the worker and queen castes. Experimental laboratory trials assessed resource preference within the invasive Argentine ant, Linepithema humile, and the degree of resource partitioning between developing larvae and the two female castes using protein marking techniques. Colony survival was also assessed when ants had access to a single macronutrient, namely carbohydrate or protein. Argentine ant propagules showed a preference for carbohydrate resources with high numbers of ants recruited to carbohydrates in comparison to protein resources. Resource partitioning analyses showed a high degree of carbohydrate sharing through trophallaxis whilst protein resources were poorly spread throughout the colony, except for queens which were positive for the uptake of both protein and carbohydrates, suggesting greater consumption of both the macronutrients as compared to developing larvae and workers. Colony mortality did not differ between those maintained on protein or carbohydrate diets. This study provides a strong case for carbohydrate preference within the Argentine ant, suggesting that propagules, during initial establishment, only use protein due to their inability to maintain mutualistic associations with plants or trophobionts until sufficient numeric abundance has been reached.