Samples of hypogeal mealybugs were collected on the roots of potted plants of Thimus vulgaris (Lamiaceae), in a greenhouse located at the Universidad Militar Nueva Granada in the city of Cajicá, in the department of Cundinamarca. The mealybugs were found in high populations causing dieback of the plants. Slide-mounted specimens were prepared according to Williams & Granara de Willink’s (1992) protocol with author’s modifications. The mealybugs were identified as Rhizoecus cyperalis (Hambleton) using the morphological description of Hambleton (1946) and the keys by Kozár & Konczné Benedicty (2007) and Williams & Granara de Willink (1992). The diagnostic features that identify R. cyperalis are: cephalic plate absent; tritubular pores on dorsum closely surrounded by 1–4 (usually 3) body setae.