Encouraging ants to defend food against competitors: Transitioning from competitive exclusion to coexistence

Biological invasions significantly impact agricultural economies and public health, surpassing mere ecological disruptions between native and non-native species. This extends to interactions within the invasive community, especially competition and symbiosis, which may dictate the survival or coexistence of different invasive species. This study examined the complex ecological interactions between two invasive pests, <i>Planococcus lilacinus</i> and <i>Bactrocera dorsalis</i>, and their coexistence facilitated by another invader, the ant <i>Solenopsis invicta</i>. Empirical field studies and detailed laboratory experiments, enhanced by chemical ecology, revealed that <i>S. invicta</i> affected the competitive dynamics of <i>P. lilacinus</i> and <i>B. dorsalis</i> on trees. The increase of <i>S. invicta</i> correlated with reduced <i>B. dorsalis</i> damage but had a converse effect on <i>P. lilacinus</i>. Laboratory tests showed <i>B. dorsalis</i> outcompeted <i>P. lilacinus</i> only in the absence of <i>S. invicta</i>. Interactions suggest that the honeydew of <i>P. lilacinus</i> attracted <i>S. invicta</i>, which then deterred <i>B. dorsalis</i> oviposition through chemical signals, thus enabling the two pests' coexistence. The study identified two key honeydew components, ethyl lactate and cis-linalooloxide, that attracted both <i>S. invicta</i> and <i>B. dorsalis</i> at a 10 % v/v concentration. However, <i>S. invicta</i>-specific semiochemicals, d-limonene and dodecanoic acid repelled <i>B. dorsalis</i>. The research outcomes not only deepen understanding of invasive species dynamics but also herald new ways to minimize crop damage from <i>P. lilacinus</i> or <i>B. dorsalis</i>, contributing significantly to economic and agricultural sustainability.