Abstract: 【Aim】 There is a facultative mutualistic interaction between the red imported fire ant, Solenopsis invicta and the cotton aphid, Aphis gossypii. Fire ants may utilize cotton aphid-induced cotton volatiles to locate mutualistic partners. This study aims to test the olfactory and behavioral responses of S. invicta workers to cotton volatiles induced by cotton aphid. 【Methods】 The behavioral response of S. invicta workers to cotton odor was tested by Y-tube. The electroantennogram (EAG) responses of the fire ant workers to nine volatile compounds including (1S)-(-)-α-pinene, (1S)-(-)-β-pinene, β-caryophyllene, (E, E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT), (E)-4,8-dimethyl 1,3,7-nonatriene (DMNT), octanal, 6-methyl-5-hepten-2-one, (Z)-(3)-hexenyl acetate, and methyl salicylate at different dosages (100, 10, 1 and 0.1 μg) were tested using fire ant alarm pheromone 2-ethyl-3,5(6)-dimethylpyrazine as the positive control, and the influence of the volatile compounds on the behavior choice of the fire ant workers was tested by Y-tube olfactometer. 【Results】 The results showed that fire ant workers were significantly attracted to the cotton plants damaged by cotton aphids over undamaged ones. The EAG responses of fire ant workers to the nine volatile compounds were dose-dependent. These compounds triggered the highest EAG response in fire ant workers at the dose of 100 μg, and methyl salicylate and 6-methyl-5-hepten-2-one caused the greatest EAG responses. In behavioral selection experiments, fire ant workers were significantly attracted to methyl salicylate, 6-methyl-5-hepten-2-one and DMNT. 【Conclusion】 Among cotton aphid-induced volatile compounds, methyl salicylate and 6-methyl-5-hepten-2-one significantly attract fire ants, and they may play a key role in locating cotton aphids by fire ants for establishment of mutualistic interaction.

Key words: Solenopsis invicta, aphid-ant mutualism, plant volatiles, electroantennogram, behavioral response