Biological invasions pose threats to native flora and fauna in ecosystems worldwide, and can be particularly devastating to the specialized ecosystems of oceanic islands. The Argentine ant (Linepithema humile) has been established in the high-elevation shrubland of Haleakala National Park, Maui HI, since at least 1967. An ant-exclusion experiment, surveys of herbivorous insects on the endemic shrub Dubautia menziesii, surveys of local ant density, and behavioral experiments involving L. humile and representative herbivorous insects were conducted to determine effects of L. humile on the makeup of the local herbivorous insect community.
Ants determine the species composition of the herbivore community on D. menziesii, according to the level of aggression shown by the ants towards the insects during the behavioral experiments. The normally abundant native herbivorous species Orthotylus iolani (Heteroptera: Miridae) was completely absent within the ants' range, and was vigorously attacked by the ants during the behavioral experiment. Additionally, large populations of at least two species of plant-damaging scale insects that are tended by the ants as trophobionts were found almost exclusively within the ants' range and not outside their range, and were shown no aggression during the behavior experiment. The exclusion experiment was only partially successful, with no significant changes evident in the insect communities as a result of short-term ant exclusion from D. menziesii.
These results indicate that L. humile is contributing to significant changes in the Haleakala arthropod fauna and may pose a threat to endemic plants such as D. menziesii and the closely related and endangered Hawaiian silversword (Argyroxiphium sandwicense subsp. macrocephalum).
Species 1: Hymenoptera Formicidae Linepithema humile (Argentine Ant)
Species 2: Heteroptera Miridae Orthotylus iolani
Species 3: Heteroptera Lygaeidae Nysius coenosulus
Keywords: invasive species, community ecology
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