Defensive chemicals of tawny crazy ants, Nylanderia fulva (Hymenoptera: Formicidae) and their toxicity to red imported fire ants, Solenopsis invicta (Hymenoptera: Formicidae).

Nylanderia fulva (Mayr) has been reported as being able to displace Solenopsis invicta Buren, one of the most aggressive invasive ants in the world. Like S. invicta, N. fulva use chemical secretions in their defense/offense, which may contribute to their observed superior competition ability. In this study, the defensive chemicals of N. fulva workers and their toxicity against S. invicta workers were investigated. Like other formicine ants, N. fulva workers produce formic acid in their poison glands and 2-ketones and alkanes in Dufour glands. Of these, undecane and 2-tridecanone are two principal compounds in the Dufour gland. Topical LD50 values of 2-tridecanone and undecane against S. invicta workers ranged from 18.51 to 24.67 μg/ant and 40.39 to 84.82 μg/ant, respectively. Undecane and 2-tridecanone had significantly higher contact toxicity than formic acid, whereas formic acid had significantly higher fumigation toxicity than undecane and 2-tridecanone. The combination of 2-tridecanone as a contact toxin and formic acid as a fumigant significantly decreased KT50 values when compared to those of individual compounds. N. fulva does not seem unique in terms of the chemistry of its defensive secretion as compared to other formicine ants. However, this ant contained more than two orders of magnitude of formic acid (wt/wt) than other formicine ants and one order of magnitude of 2-tridecanone than the common crazy ant, Paratrechina longicornis (Latreille). The quantity, rather than quality, of the chemical secretion may contribute to the superior competition ability of N. fulva.