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Effect of Solenopsis invicta (Hymenoptera: Formicidae) on Flower-Visiting Behavior of Insects on Brassica napus (Brassicales: Brassicaceae)

Abstract This study used field trials to investigate how the fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) affects the flower-visiting behavior of insects on rapeseed Brassica napus L. (Brassicales: Brassicaceae). Chemicals from fire ants were identified, and their electrophysiological effects on the cabbage white butterfly Pieris rapae (L.) (Lepidoptera: Pieridae) were analyzed by gas chromatography—electroantennogram detection (GC-EAD) bioassays. The results showed that S. invicta significantly reduced the abundance of pollinators. The number of striped flea beetles (Phyllotreta striolata [F.]; Coleoptera: Chrysomelidae) and hover flies (Eristalinus quinquestriatus [F.] and E. quinquelineatus [F.]; Diptera: Syrphidae) in fire ant—included and fire-ant-and-aphid-included plots was 43.5 and 39.4% lower, respectively, than in control plots. The visiting duration at a single flower for P. rapae in the plots that had fire ants and aphids excluded was significantly longer than in the fire ant—included (1.42 fold) and fire-ant-and-aphid-included plots (1.29 fold). However, the visiting frequency of P. rapae and of the Chinese honey bee Apis cerana F. (Hymenoptera: Apidae) and the duration of each visit of A. cerana were not significantly changed. Antennae of P. rapae showed obvious electrophysiological reactions to the volatiles of S. invicta, and n-heptacosane elicited the largest EAD response. Our results suggest a negative effect and its chemical mechanism of S. invicta on the behavior of several flower-visiting insects.