Ant–scale mutualism increases scale infestation, decreases folivory, and disrupts biological control in restored tropical forests

Ant–hemipteran mutualisms can have positive and negative effects on host plants depending on the level of hemipteran infestation and plant protection conferred by ants against folivory. Differential effects of such mutualisms on plant survival are well documented in undisturbed and ant‐invaded systems, but few have explored how anthropogenic disturbance affects interactions between hemipterans and native ant species and what the consequences may be for recovering ecosystems. Within a fragmented landscape in Costa Rica, restored tropical forests harbor a mutualism between the native ant Wasmannia auropunctata and the scale insect Alecanochiton marquesi on the abundant, early‐successional tree Conostegia xalapensis. I added A. marquesi scales to C. xalapensis seedlings and either allowed or excluded W. auropunctata to investigate if this mutualism leads to increased scale infestation, decreased scale mortality, and decreased folivory. I also examined whether these effects are mediated by the percentage of remnant forest cover in the landscape. I found that seedlings with ants excluded had fewer scale insects and higher herbivory than plants with ants present. I also found evidence that scale mortality due to fungal attack and parasitism was higher on ant‐excluded versus ant‐allowed seedlings but only at sites with high surrounding landscape forest cover. Together, these results suggest that mutualisms between scale insects and native ants can promote scale infestation, reduce folivory on native plant species, and potentially disrupt biological control of scale insects in recovering tropical forests. Further, my experiment underscores the importance of remnant tropical forests as sources of biological control in anthropogenically disturbed landscapes. in Spanish is available with online material. Resumen Los mutualismos entre hormigas y hemípteros pueden tener efectos positivos y negativos en las plantas hospedadoras, dependiendo del nivel de infestación de hemípteros y la protección de las plantas que confieren las hormigas en contra la folivoría. Los efectos diferenciales de estos mutualismos en la supervivencia de las plantas están bien documentados en sistemas no perturbados e invadidos por hormigas, pero pocos han explorado cómo la degradación del hábitat afecta las interacciones entre hemípteros y especies de hormigas nativas y cuáles son las consecuencias para la recuperación de los ecosistemas. Dentro de un paisaje fragmentado en Costa Rica, los bosqu