Evaluating control methods for red imported fire ant and their effects on hibiscus mealybug in citrus

The red imported fire ant (Solenopsis invicta) may disrupt biological control of hibiscus mealybug (Nipaecoccus viridis) in Florida citrus. Controlling S. invicta may therefore be necessary for effective management of hibiscus mealybug. We evaluated four different methods to control S. invicta (ground applications of insecticide, two different insecticidal ant baits and spot-treating ant colonies with hot water) to determine how these different treatments affected ants tending to hibiscus mealybug colonies, natural enemy abundance within hibiscus mealybug colonies and hibiscus mealybug colony abundance. While all treatments reduced the number of S. invicta colonies in treated areas compared to an untreated control, only ground applications of insecticide and the two ant baits significantly reduced the abundance of S. invicta found tending hibiscus mealybug colonies. Additionally, significantly more Brachymyrmex obscurior ants were found tending mealybug colonies in plots treated with either of the two ant baits. There was no significant effect of treatment on the abundance of natural enemies in hibiscus mealybug colonies, but significantly fewer natural enemies were found in mealybug colonies tended by S. invicta, and significantly more natural enemies were found in mealybug colonies tended by B. obscurior. Ground applications of insecticide, the abamectin ant bait Clinch and hot water treatments all reduced the overall number of hibiscus mealybug colonies compared with control areas, while the S-methoprene ant bait Extinguish did not. Our results suggest that reducing the number of S. invicta tending hibiscus mealybug colonies can lead to higher natural enemy abundance and lower hibiscus mealybug abundance. However, methods used to control S. invicta may have different impacts on ant species like B. obscurior, leading to different outcomes with natural enemies.