Resumo. The solenopsis mealybug, Phenacoccus solenopsis Tinsley, 1898 (Hemiptera: Pseudococcidae), is widely distributed globally and is a significant polyphagous pest affecting a variety of plants of agricultural, medicinal, and ornamental value, including certain weeds. In this study, we present, for the first time, the occurrence and damage caused by P. solenopsis on false lemon balm, Lippia alba (Mill.). N.E. Br. ex Britton & P. Wilson (Verbenaceae) in Brazil. Specimens of the solenopsis mealybug were collected and examined on L. alba in a residential area of Floriano city, Piauí state, Brazil, from July to November 2025. The damage caused by the mealybug primarily manifests on the branches of false lemon balm, resulting in yellowing and desiccation, with a comparatively lesser impact on the host’s leaves. Throughout our observations, the solenopsis mealybug population on the host declined by November 2025. This represents the first documented instance of P. solenopsis in Piauí, thereby increasing the total number of Brazilian states reporting occurrences of this pest to 11. Additionally, we noted the mutualistic relationship between P. solenopsis and Dorymyrmex sp. (Hymenoptera: Formicidae: Dolichoderinae). This study also updates information regarding the distribution and host plants of P. solenopsis in Brazil.