Do fatty acids in vegetable oil attract red imported fire ants?

Vegetable oil in ant bait is highly attractive to the red imported fire ant (Solenopsis invicta). Previous research showed that S. invicta transported significantly more bait containing corn oil than coconut oil, though the mechanism underlying this phenomenon remains unclear. It is known that corn oil primarily consists of unsaturated fatty acids including linoleic acid and oleic acid, whereas coconut oil is mainly composed of saturated fatty acids including lauric acid and myristic acid. Therefore, we hypothesized that the attractiveness of corn oil bait is due to its unsaturated fatty acid components. This study compared the foraging behavior of fire ants in response to baits containing corn oil, coconut oil, and their principal fatty acid components (linoleic acid, oleic acid, lauric acid and myristic acid). Under field conditions, S. invicta transported significantly more corn oil bait than coconut oil bait, but little baits containing fatty acids were transported. Under laboratory conditions, search time for the different baits was not significantly different; however, corn oil bait was transported significantly earlier than the four fatty acid baits. Moreover, the transport speed of corn oil bait was significantly faster than that of the other five baits. Furthermore, toxicity tests indicated that neither corn oil, coconut oil, nor the four fatty acids were toxic against S. invicta, average fire ant mortality remained below 30% with no significant differences. This study showed that the main fatty acid components of corn oil and coconut oil were not attractive for S. invicta, indicating that the attraction mechanism of vegetable oils was far more complex than expected. Future research should focus on the minor components of vegetable oils and the synergistic effects of multiple compounds, which would provide an important theoretical basis for developing precise and environmentally friendly control methods for S. invicta.