Native herbivores affected more by invasive ants than by foliar quality or competition.
Altfeld, Laura*,1, Stiling, Peter1, 1 University of South Florida, Tampa
ABSTRACT- In Florida, Baccharis halimifolia is host to the myrmecophile Aphis coreopsidis, the monophagous beetle, Trirhabda bacharidis, two leaf mining dipterans, Amauromyza maculosa and Liriomyza trifolii, the gall fly Neolasioptera lathami, and the stem borer Oidaematophorus balanotes. Prior work has revealed that the singular effects of (1) early season folivory by larval T. bacharidis and (2) ant attending by Argentine ants are significant for many herbivores of this host plant. Here we present the results from factorial experiments which combine the effects of (1) ant attendance, (2) larval herbivory by T. bacharidis and (3) nitrogen enrichment. The presence of Argentine ants had a greater impact on more species of herbivores than either early season folivory or nitrogen enrichment. Aphids were significantly more abundant in the presence of ant attendants (P = 0.005), particularly on trees that had not experienced herbivory by T. bacharidis larvae (P = 0.03). The two leaf miners were significantly less abundant in the presence of ants (P = 0.003 and P = 0.034), likely due a significantly higher number of ant-damaged leaf mines (P < 0.001) in the presence of the ants. The stem borer was also significantly less abundant when ants were present (P < 0.001). Aphid predators were affected by the interaction of larval herbivory by T. bacharidis and ant presence, reflecting the same pattern as their prey, predators were more abundant on ant attended host plants that had not experienced larval herbivory (P = 0.042). Nitrogen effects were positive for the gall fly (P = 0.04) and T. bacharidis larvae (P = 0.049). Adult T. bacharidis were marginally more abundant on fertilized host plants (P = 0.1). Our results indicate that ant tending by Argentine ants has important consequences for insects on B. halimifolia, more so than herbivory by an exploitative competitor such as T. bacharidis or nitrogen limitation.
Key words: Argentine ants, ant-aphid interactions, invasive species, Baccharis halimifolia
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